ENGINEERING 'LIBRARY Practical Marine Engineering FOR MARINE ENGINEERS AND STUDENTS WITH Aids for Applicants for Marine Engineers' Licenses By WILLIAM F. DURAND PROFESSOR OF MARINE ENGINEERING, CORNELL UNIVERSITY. New York Marine Engineering, Inc. 309 Broadway 1901 o ENGINEERING Copyright, 1901 By MARINE ENGINEERING, Inc. Preface. A I \HE purpose of the author in the preparation of this work has been to provide help for the operative or practical marine engineer, either for the man who has already en- tered the profession, but who may wish to perfect himself more fully in many branches of the subject, or for the applicant for the lowest round of the ladder, or for the young man whose atten- tion is first turning to this field, and who may wish some simple and fairly complete presentation of the subject from the prac- tical standpoint. The treatment of the subject throughout has thus been with a view to simplicity, but without undue sacrifice of generality or exactness of statement. It has been the desire of the author to bring the subject, so far as treated in the present work, within the grasp of those who have not had the advantages of higher mathematical and engineering education, but who may wish, nevertheless, to fit themselves for positions of honor and respon- sibility in the field of operative marine engineering. With this end in view only such parts of the general field of engineering have been included as are of special interest to the practical marine engineer. On these topics, however, the attempt has been made to give the largest amount of useful in- formation in the simplest and most compact form. In the ma- rine field itself likewise, selection has been necessary, and many interesting parts of the subject have been omitted or briefly referred to in order to give more room for the practical side of the subject. Thus the book does not treat of the de- signing of marine machinery except in an incidental way. For the operative engineer the topics of greater importance are con- struction, operation, management and care. The simpler parts of the subject of design are, however, represented by the U. S. Hi. 836454 PREFACE. rules regarding the design and construction of marine boilers, and by many hints regarding proportions and relations scat- tered throughout the work. In the chapters dealing descriptively with engines, .boilers and auxiliaries, it has been impossible of course, to describe ex- haustively every form of design or appliance to be met with in marine practice. The purpose has been rather to describe typical or standard forms, and to give the general conditions which the various parts must fulfil. The illustrations have been specially chosen with a view to supplement the text in these various particulars, and it is hoped that they will form not the least instructive and acceptable feature of the work. The subject of operation, management and repair has been given special attention, and it is hoped that this part of the work will be of value, especially to the young engineer lacking in practical experience. In Chapter VIII is gathered a collection of miscellaneous problems and discussions, many of which, it is hoped, will be of value to the professional engineer in connection with the vari- ous questions likely to arise in his experience. The chapters on valve gears and on indicator cards while necessarily brief are intended to present the fundamental features of the subject in such manner as to aid the novice and instruct and stimulate the professional engineer to a better understanding of these im- portant branches of the subject. The chapter on propulsion and powering is necessarily brief, but the fundamental principles are given, with a few simple rules and the discussion of most of the problems commonly arising in practical engineering work. The chapters on refrigeration and on electricity on shipboard are added in order to give the marine engineer some notion of the fundamental principles controlling the operation of refrig- erating and electric machinery, these two important auxiliaries of modern marine engineering practice. They are of necessity quite incomplete, especially Chapter XII, but it is hoped that nevertheless they may be of aid to the marine engineer in un- derstanding the mode of operation of such machinery, and in giving to it the proper care. In Part II is given an elementary discussion of computa- tions for engineers, or rather of the mathematics upon \vhich such computations depend. A general knowledge of the sub- ject is pre-supposed, but the more essential features of the ele- iv PREFACE. mentary mathematics usually required are given and illustrated with many problems. It is hoped that this feature of the work may be of aid to those who wish to drill themselves in such com- putations as the marine engineer is commonly called upon to make. Attention may also be called to the appendix containing a list of questions, each with page reference to the part of the book where the answer may be found. The answer, of course, will not usually be found in the direct form suggested by the ques- tion, but a discussion of the subject will be found giving the in- formation needed for the answer, which may be put into form by the reader for himself. It is believed that such an exercise will be of far greater value than the perusal of a series of ques- tions and answers in the usual catechism form. Throughout the work numerous problems have been scat- tered, accompanied usually by illustrative examples, showing the method of working. Numerous cross references have also been given, to aid in the more complete explanation of any given topic, and in finding these use should be made of the table of contents, giving the page location of each section and bracket subdivision. A collection of miscellaneous problems is also added at the end of the book, as well as a set of steam tables for use in the so- lution of the various problems requiring a knowledge of its vari- ous mechanical and physical properties. CONTENTS. Contents CHAPTER I. Principal Materials of Engineering Construction. 5ECTION. PAGE. 1. Aluminum I 2. Antimony I 3. Bismuth 2 4. Copper 2 5. Iron and Steel 3 i ] Cast Iron 4 2] Malleable Iron 9 3 Wrought Iron 10 4 Blisters and Laminations u 5 Steel 12 6. Lead 23 7. Tin 24 8. Zinc 24 9. Alloys 24 10. The Testing of Metals ' 26 i ] Different Kinds of Tests 26 2] Explanation of Terms Used 26 3] Test Pieces for Iron 28 4 Test Pieces for Steel and Other Materials 28 5] Bending, Quenching and Hammer Tests 29 CHAPTER II. Fuels. 11. Coa! 3i i] Composition and General Properties 3 1 2] Combustion 3 2 3] Impurities in Coal. Clinker Formation 35 4] Weathering of Coal 36 5] Spontaneous Combustion 37 6] Corrosion 4 7! Transportation and Stowage \ 40 8] General Comparison Between Bituminous and Anthracite Coal 4i 12. Briquettes and Artificial Fuel 41 13. Liquid Fuel 4 2 i ] Composition 42 2] Combustion 43 "3! Danger of Explosion : 44 4] Evaporative Power 44 "5l Stowage and Handling 45 6] Use of Oil and Coal Combined 46 7] Cost 46 vii. CONTENTS. CHAPTER III. Boilers. ON. PAGE. 14. Types of Boilers 47 i ] The Scotch Boiler 50 2] Direct Tubular Boiler, Gunboat Type 50 Direct Tubular Boiler, Locomotive Type 51 The Flue and Return Tubular or Leg Boiler 51 5J The Flue Boiler 52 : 6 n Water-Tube Boilers 53 7] Relative Advantages of Different Types of Boilers 56 15. Riveted Joints 67 16. Materials and Construction 86 i ] Materials 86 2] Joints 86 3] Construction of Fire-Tube Boilers 87 4] Construction of Water-Tube Boilers . 108 5] Common Sizes and Dimensions of Scotch Boilers 112 '6] Common Proportions for Scotch Boilers 112 7] Weights of Boilers 112 8 Western River Boat or Flue Boilers 113 17. Boiler Mountings and Fire Room Fittings 115 i] Safety Valves IIS 2] Muffler 118 3] Stop Valve n8 4] Dry-Pipe, or Internal Steam Pipe 120 '5 Feed Check Valve and Internal Feed Pipe 121 Surface and Bottom Blows 122 7 Steam Gauges 124 Water Gauge and Cocks 125 [9] Hydrokineter 127 [10] Hydrometer 127 [III Boiler Saddles 128 [12 Boiler Lagging 129 18. Draft 129 19. Boiler Design in Accordance with the Rules of the U. S. Board of Supervising Inspectors of Steam Vessels , 138 CHAPTER IV. Marine Engines. 20. Types of Engines and Arrangement of Parts 154 21. Description of Principal Parts of a Marine Engine 165 [i] Cylinders 165 "2] Columns 168 3 1 Bed-Plates 172 '4! Engine Seating 174 5] Pistons 175 6] Piston-Rods 179 7] Crossheads 180 8] Connecting-Rods 184 9] Crank Shafts 185 [10] Line Thrust and Propeller Shafts 188 [nl Bearings 190 22. Western River Practice 199 23. The Steam Turbine 207 24. Engine Fittings 209 f i ] Throttle Valve 209 \2\ Main Stop Valve 212 [3] Cylinder Drain Gear and Relief Valves 215 viii. CONTENTS. 4 Starting Valves 216 5] Reversing Gear 217 6] Turning Gear 220 7] Joints and Packing 220 Reheaters 225 9J Governors 225 [ 10] Counter Gear 227 fii] Lagging 228 [12] Lubrication and Oiling Gear 228 25. Piping 237 [i] Systems and Materials 237 \2\ Expansion Joint 239 [3] Globe Angle and Straightway Valves 240 CHAPTER V. Auxiliaries. 26. Circulating Pumps '. 241 27. Condensers 243 28. Air Pumps 245 29. Feed Pumps and Injectors 251 30. Feed Heaters 255 31. Filters 260 32. Evaporators 261 33. Direct Acting Pumps 263 34. Blowers or Fans 267 35. Separators 267 36. Ash Ejectors 269 37. General Arrangement of Machinery 271 CHAPTER VI. Operation, Management and Repair. 38. Boiler* Room Routine 273 [i] Starting Fires and Getting Under Way 273 [2] Fire Room Routine 277 [3] Emergencies and Casualties 287 39. Engine-Room Routine and Management 298 [i] Getting Under Way 298 [2] Routine Operation 301 [3] Minor Emergencies and Troubles 304 40. Boiler Corrosion 308 41. Boiler Scale 319 42. Boiler Overhauling and Repairs 328 i ] Inspection and Test 328 2] Leakage from the Joints of Boiler Mountings 333 '3] Leakage About Shell Joints 333 4] Leakage at Internal Joints 334 5] Patches 336 61 Cracks and Holes 336 7 Blisters and Laminations 337 8] Tubes 338 [9! Leakage About Stays and Braces 339 [10] Bulging or Partial Collapse of Furnace or Combustion Chamber Plates 339 FIT] Split in Feed-Pipe 341 43. Engine Overhauling, Adjustment and Repairs 341 i] Cylinders 342 2] Pin Joints and Bearings 343 3] Crosshead Guides 345 4] Crosshead Marks 346 [12 CONTENTS. PAGE. Lining Up 347 Valve Gear 352 Thrust Bearings 353 Circulating Pump 353 Condensers 353 Air Pumps 355 Pumps in General 355 Piping 355 44. Spare Parts 356 45. Laying Up Marine Machinery 356 CHAPTER VII. Valves and Valve Gears. 46. Slide Valves 358 i] Simple Slide Valve 358 2] Double Ported Slide Valve 360 3J Piston Valve 361 4] Equilibrium Piston 365 5] Jy' s Assistant Cylinder 366 6] Equilibrium Rings 367 _7] Outside and Inside Valves 368 47. Motion Due to Simple Excentric and Its Representation by Valve Diagram 369 [I] \2 Simple Excentric 369 Oval Valve Diagram 372 Bilgram Valve Diagram 377 Zeuner Valve Diagram 379 48. Stephenson Link Valve Gear 380 49. Braemme-Marshall Gear 386 50. Joy Valve Gear 391 51. Walschaert Valve Gear 391 52. Crank Valve Gear 393 53. Details of Stephenson Link Valve Gear * 397 fi] Excentric and Strap and Excentric Rod 397 [2] Link 400 [3] Link Block and Valve Stem 402 54. Valve Setting 405 i] Putting an Engine on the Center 405 [2] Setting the Valve 406 [3] Valve Setting from the Indicator Card 408 f: CHAPTER VIII. Steam Bngine Indicators and Indicator Cards. 55. Indicator Cards 410 [i] Descriptive 410 [2] The Indicator Card and the Operation of the Valve Gear. . 413 [3] Working up Indicator Cards for Power . 417 [4] Combined Indicator Cards 425 56. Steam Engine Indicators 429 [i] Descriptive 429 [2] Reducing Motions 431 [3] Taking an Indicator Card 434 CHAPTER IX. Special Topics and Problems. 57. Heat and the Formation of Steam 438 [i] Constitution of Matter 438 [2] Heat 439 x. CONTENTS. SECTION*. PAGE. [3] Steam ; 444 [4] Total Heat in a Substance 450 [5] Latent Heat in Passing from Ice to Water 452 58. Steam Boiler Economy 453 T ] General Principles 453 [2] Evaporation Per Pound of Coal 455 13] Evaporation Per Pound of Combustible 459 59. Steam Engine Economy 460 [i] General Principles 460 [2] Relation of Expansion to Economy 469 [3] Economy of the Actual Engine 471 60. Coal Consumption and Related Problems 472 61. The Lever Safety Valve and the Safety Valve Problem 476 62. The Boiler Brace Problem 480 63. Strength of Boilers 485 64. Loss by Blow Off 489 65. Gain by Feed Water Heating 491 66. The Proportions of Cylinders for Multiple Expansion Engines. . 492 67. Clearance and Its Determination 494 68. The Iiffect of Clearance in Modifying the Apparent Expansion Ratio as Given by the Point of Cut-Off 496 69. Engine Constant 497 70. Indicated Thrust 498 71. Reduced Mean Effective Pressure 499 72. Pressure on Main Guides 502 73. Force Required to Move a Slide Valve 503 74. Amount of Condensing Water Required 504 75. Work Done by Pumos 505 76. Discharge of Steam Through an Orifice 507 77. Computing Weights of Parts of Machinery 508 FT] Units to be Used ". 508 [2] Approximations and Short Cuts 509 CHAPTER X. Propulsion and Poweringf. 78. Measure of Speed 514 79. Propulsion 514 80. Screw Propeller 517 [i] Definitions 517 [2] Varieties of Propellers 523 [3! Materials 526 f4l Measurement of Pitch 526 81. Paddle Wheels 531 82. Powering Ships 534 83. Reduction of Power When Towing or When Vessel is Fast to a Dock 537 84. Trial Trios 539 85. Special Conditions for Speed Trials 544 CHAPTER XI. Refrigeration. 86. General Principles 545 87. Refrigeration by Freezing Mixtures 546 88. Refrigeration by Vaporization and Expansion 547 89. Principal Features of Ammonia Refrigerating Apparatus 549 90. Refrigeration by the Expansion of a Compressed Gas 553 91. Principal Features of Compressed Air Refrigerating Apparatus 554 92. Operation and Care of Refrigerating Machinery 556 xi. CONTENTS. CHAPTER XII. Electricity on Shipboard. SECTION. PAGE. 93. Introductory 559 94. The Dynamo 565 95. Wiring and The Distribution of Light and Power 571 96. Lamps 575 97. Operation and Care of Electrical Machinery 577 i ] Routine Care 577 '2] Faults 578 Part II. COMPUTATIONS FOR ENGINEERS. SECTION. PAGE. 1. Common Fractions 581 i] Units of Measurement and Definitions 581 2] Reduction of a Mixed Number to an Improper Fraction.. 583 3] Reduction of an Improper Fraction to a Mixed Number 584 4] Reduction of Fractions Without Change of Value 584 5] Addition of Common Fractions 586 6] Subtraction of Fractions 587 7] Multiplication of Fractions 588 8] Divisions of Fractions 588 9] Multiplication and Division of Fractions 589 [10] Complex Fractions 591 2. Decimal Fractions 592 i ] Introductory 592 2] To Reduce Decimals to Lower Terms 593 3 To Raise Decimals to Higher Terms 593 4] To Reduce a Decimal Fraction to a Common Fraction. .. . 593 51 To Reduce a Common Fraction, Proper or Improper, to a Decimal 593 6] To Add Decimals 594 7] To Subtract Decimals 594 8] To Multiply Together Two Numbers Expressed Decimally 595 9] To Find the .Quotient of Two Quantities, Expressed Deci- mally 595 3. Percentage - 596 4. Compound Numbers 599 [ 1 1 Long or Linear Measure 599 '2] AvoirdtiDois Weight or Measure 599 "3] Square Measure 599 4] Cubic or Volume Measure 600 "5] Liquid Measure 600 6] Dry Measure 600 7l Shipping Measure 600 8] The Metric System of Weights and Measures 600 [9! Conversion Tables 601 [iol Reduction of Compound Numbers 602 fill Addition of Compound Numbers 603 [12] Subtraction of Compound Numbers 603 [13] Multiplication of Compound Numbers 604 [14] Division of Compound Numbers 604 5- Duodecimals 605 6. Ratio and Proportion 607 [i] Simple Proportion 607 CONTENTS. SECTION*. PAGE. [2] Compound Proportion 610 7. K\ oiution and Involution 612 f i ] Introductory 612 [2] ' To Extract the Square Root 613 [3] To Extract the Cube Root 615 8. Mathematical Signs, Symbols and Operations 616 9. Geometry and Mensuration 621 i ] Square 621 2] Rectangle 622 3] Parallelogram 622 4] Trapezoid 623 5] Triangle 623 6 Right-Angled Triangle 624 7 j Trapezium 625 81 Regular Polygons 625 9] Irregular Figures 626 10] Circle 626 1 1 Circular Ring or Annulus 628 12] Sector of Circle 628 13] Segment of Circle 629 14] Ellipse 629 15] Figures With an Irregular Contour 630 16] Prism 633 17] Cylinder 634 [18] Any Solid with a Constant Section Parallel to the Base, Either Right or Oblique 635 [19] Wedge 635 [20] Right Pyramid * 635 \2i General Pyramid 636 [22 Right Circular Cone 637 [23 General Cone 637 [24] Frustum of Right Pyramid '. . 638 [25] Frustum of General Pyramid 639 T26] Frustum of Right Cone 639 [27] Frustum of General Cone 640 [28] Sphere 640 [29! Volume of Irregular Shape 640 [30 Volume Generated by Any Area Revolving About an Axis 641 10. Problems in Geometry 642 [i] At Any Point in a Straight Line to Erect a Perpendicular 642 [2] To Bisect the Distance Between Two Points 643 [3] To Find the Center from which to Pass an Arc of Given Radius Through Two Given Points 643 [4] To Divide a Given Line into a Given Number of Equal Parts 643 [5] To Construct a Triangle, Having Given the Three Sides. .. 643 [6] To Bisect a Given Arc or Angle 644 [7] To Construct a Mean Proportional 644 "[8] To Construct a Fourth Proportional 644 [9] To Construct a Square Equivalent in Area to a Given Rectangle 645 [10] To Construct a Square Equivalent in Area to a Given Triangle 645 TII] With One Given Side, to Construct a Rectangle Equivalent to a Square 64; [12! To find the Length of an Arc of a Curve 645 [13] To Construct an Ellipse 646 [14] To Construct any Regular Polygon 647 [15] To Develop the Surface of a Cylinder 648 CONTENTS. 'ION. PAGE. [16] To Develop the Surface of a Cylinder which is Intersected by Another Cylinder, the Two Axes being in the same Plane 648 ~i?] To Develop the Surface of a Cone t . . . . 649 18] To Develop the Surface of the Frustum of a Cone 649 [19] To Develop the Segments of an Elbow 649 11. Physics , 650 i] Acceleration Due to Gravity 650 2] Specific Gravity 650 3], Heat Unit 651 4] Specific Heat 651 5] Expansion of Metals 651 12. Mechanics 652 1 Introductory 652 2 Force 652 3 Specification of a Force 652 4 Moment of a Force 653 5] Resultant 653 6] Work 653 7] Power 653 8] Energy 655 [9] Conservation of Energy 656 loj Statics 656 1 1 ] Dynamics 656 12] Propositions in Statics 656 13] Mechanical Powers 659 14] Examples in Mechanics 665 \iv. Practical Marine Engineering CHAPTER I. PRINCIPAL MATERIALS OF ENGINEERING CONSTRUCTION. Sec. i. ALUMINUM. The commercially pure metal, i. e., with less than i per cent impurity, is white in color, soft, ductile and malleable. It melts at about 1,160 F., has a tensile strength of about 15,000 Ib. per square inch of section, but lacks in stiffness and resilience, or the power to withstand shocks. Aluminum does not oxidize readily under the influence of ordinary air, but when in contact with sea water, or in air charged with sea water, the corrosion is often serious in extent. Aluminum cannot be welded except electrically, is not suitable for forging or rolling when hot, and cannot be tempered or hard- ened. It is, however, suitable for casting, and when cold can be rolled into sheets and drawn into wire, and in thin sheets or small pieces may be spun or flanged, or worked under the hammer in various ways. Aluminum unalloyed is of comparatively small value to the engineer, but it enters into several valuable alloys, as described in Section 9, and its use in this way has increased to a consider- able extent within the past few years. Sec. 2. ANTIMONY. The pure metal is whitish in color, quite brittle and crystal- line or laminated in structure, and has a melting point of about 840 F. It is useless in the pure state for ordinary engineering purposes, but is a valuable ingredient of various alloys used for bearing metals, etc., as described in Section 9. 2 PRACTICAL MARINE ENGINEERING. Sec. 3. BISMUTH. The pure metal is light red in color, very brittle and highly crystalline in structure, with a melting point of about 510 F. It is useless in the pure state for engineering purposes, but forms a part of various alloys used for bearing metals, etc., as described in Section 9. Sec. 4. COPPER. In the pure state the metal is red in color, soft, ductile and malleable, with a melting point of about 2,000 F., and a tensile strength of from 20,000 to 30,000 Ib. per square inch of section. Copper is not readily welded except electrically, but, on the other hand, is readily joined by the operation of brazing. At- tempts have been made to temper or harden it, but the operation has not been made a practical success. It is readily forged and cast, and when cold may be rolled into sheets or drawn into wire, and in sheets or small pieces may be spun or flanged or worked under the hammer in various ways. The tensile strength of copper, rapidly falls off as the tem- perature rises above about 400 F., so that at from 800 to 900 the strength is only about one-half what it is at ordinary tempera- tures. This peculiarity of copper should be borne in mind when it is used in places where the temperature is liable to rise to these figures. Again, if copper is raised nearly to its melting point in contact with the air it readily unites with oxygen and loses its strength in large degree, becoming, when cool, crumbly and brit- tle. Copper in this condition is said to have been burned. The possibility of thus injuring the tenacity of copper is of the highest importance in connection with the use of brazed joints in steam pipes. In the operation of brazing a joint, the surfaces to be joined are cleaned, bound together with wire or otherwise, then sup- plied with brazing solder in small bits, mixed with borax as a flux, and placed in a clear fire until the solder melts and forms the joint. The brazing solder, or hard solder, as it is often called, is usually a brass or alloy of copper and zinc. The melting point of all such alloys is below that of copper, and when copper is joined to brass, or two pieces of brass are joined together, the solder used must have a melting point lower than either of these metals. In the operation of brazing a copper joint, therefore, the greatest care must be taken in the selection of a solder and in attention to the fire, so that there may be no danger of burning MATERIALS. 3 the copper, and thus endangering the quality of the metal in the joint. Copper unalloyed is used chiefly for pipes and fittings, espe- cially for junctions, elbows, bends, etc. For large sizes the ma- terial is made in sheets, bent and formed to the desired shape and brazed at the seams. Small sizes are either made by the same general process or from solid drawn pipe, which may be bent as desired after drawing. Copper is also largely used as the chief ingredient of the various brasses and bronzes, as described in Section 9. Sec. 5. IRON AND STEEI,. Classification. It will be convenient to give here a general classification of iron and steel products based on the methods of manufacture. The following is the classification used by Prof. J. B. Johnson in his text book on the Materials of Construction. MALLEABLE. Wrought Iron. Rolled or forged from a puddle ball ; it con- tains slag and other impurities and cannot be hardened by sud- den cooling. Steel. Rolled or forged from a cast ingot and free from slag and similar matter. Soft Steel. Will weld (with care), and cannot be hardened by sudden cooling. It is sometimes called ingot iron, and has the same uses as wrought iron. Medium Steel. Welds imperfectly except by electricity. Will not harden by sudden cooling. Hard Steel. Will not weld. Hardens by sudden cooling. Tool steel, etc. SEMI-MALLEABLE. Steel Castings. Malleable metal cast into forms. Malleable Cast Iron. Non-malleable metal cast into forms and then brought to a semi-malleable condition. NON-MALLEABLE. Cast Iron ; Hard Cast Steel. Non-malleable metal cast into forms. In describing these products at length we shall find it con- venient to begin with cast iron. 4 PRACTICAL MARINE ENGINEERING. [i] Cast Iron. This material consists of a mixture and combination of iron and carbon, with other substances in varying proportions. (i) Influence of Carbon. In the molten condition the car- bon is dissolved by the iron and held in solution just as ordin- ary salt is dissolved by water. The mixture or combination of the two elements is thus entirely uniform. The proportion of carbon which pure melted iron can thus dissolve and hold in solution is about 3^ per cent. If chromium or manganese is present also, the capacity for carbon is much increased, while with silicon, on the other hand, the capacity for carbon is de- creased. In the various grades of cast iron the proportion of carbon is usually found between 2 per cent and 4.5 per cent. Now, when such a molten mixture cools and becomes solid, there is a tendency for a part of the carbon to be separated out and no longer remain in intimate combination with the iron. The carbon thus separated or precipitated out from the iron takes that form known as graphite, and collects together in very small flakes or scales. The carbon which remains in intimate combination with the iron is said to be combined, while that which is separated out is usually called graphitic. The qualities of cast iron depend chiefly on the proportion of total carbon and on the relative proportions of combined and graphitic carbon. With a high proportion of graphitic carbon the iron is soft and tough, with low tensile strength, and breaks with a coarse grained dark or grayish colored fracture. In fact the substance in this condition may be considered as nearly pure iron with fine flakes of graphite entangled and distributed through it, thus giv- ing to the iron a spongy structure. The iron thus forms a kind of continuous mesh about the graphite, which decreases the strength by reason of the decrease of cross-sectional area actually occupied by the iron itself. Such irons are termed gray. As the relative proportion of graphitic carbon decreases and that of combined carbon increases, the iron takes on new properties, becoming harder and more brittle. Its tensile strength also increases to a certain extent, and the fracture be- comes fine grained or smooth and whiter in color. When these characteristics are pronounced the iron is said to be white. When about half the carbon is combined and half separates out as graphite, the effect is to produce a distribution of dark spots MATERIALS. 5 or points scattered over a whitish field. Such irons are said to be mottled. In a general way with a large proportion of total carbon there is likely to be formed a considerable amount of graphitic carbon, and hence such irons are usually gray and soft. With a large proportion of carbon also the iron melts more readily and its fluidity is more pronounced. As the proportion of total car- bon decreases the cast iron approaches gradually the condition of steel, whose properties will be discussed in a later paragraph. Of the special ingredients in cast iron the. combined carbon is one of greatest importance. It is that chiefly which by uniting with the iron gives it new qualities, and the principal influence of other substances lies in the effect which they may have on the proportion of this ingredient. As between graphitic and com- bined carbon, the former does not affect the quality of the iron itself, but acts physically by affecting the structure of the cast- ing; while the latter, by entering into combination with the iron, acts chemically and produces a new substance with different qualities. The following percentages of combined carbon are recommended for qualities of iron as indicated: PROPORTION OF COMBINED CARBON. Soft cast iron 10 to . 15 of one per cent. Greatest tensile strength about .45 of one per cent. Greatest transverse strength about . 70 of one per cent. Greatest crushing strength one per cent or over. The proportions of combined and graphitic carbon are in- fluenced by the rate of cooling, and by the presence or absence of various other ingredients. Slow cooling allows time for the separation of the carbon and thus tends to form graphitic car- bon and soft gray irons. Quick cooling, or chilling in the ex- treme case, prevents the formation of graphitic carbon and thus tends to form hard, white irons. In addition to carbon, small quantities of silicon, sulphur, phosphorus, manganese and chromium may be found in cast iron. (2) Influence of Silicon. The fundamental influences of silicon are two. (a) It tends to expel the carbon from the com- bined state and thus to decrease the relative proportion of com- bined carbon and increase that of graphitic carbon. (b) Of itself silicon tends to harden cast iron and to make it brittle. These two influences are opposite in character, since an in- crease in graphitic carbon softens the iron. In usual cases the 6 PRACTICAL MARINE ENGINEERING. net result is a softening of the iron, an increase in fluidity, and a general change toward those qualities possessed by iron with a high proportion of graphitic carbon. This applies with a pro- portion of silicon from 2 per cent to 4 per cent. With more than this the influence on the carbon is but slight and the result on the iron is to decrease the strength and toughness, giving a hard but brittle and weak grade of iron. A chilled cast iron is an iron which if cooled slowly would be gray and soft, but, as explained in (i), by sudden cooling, from contact with a metal mould or other means, becomes white and hard, especially at and near the surface. Certain grades of cast iron tend to chill when cast in sand moulds. This prop- erty is usually undesirable. In such cases the tendency can be prevented by the addition of silicon, which, by forcing the car- bon into the graphitic state on cooling, prevents the formation of the hard, chilled surface. In all cases the actual effect of adding silicon will depend much on the character of the iron used as a base, and only a statement of the general tendencies can here be given. To sum up, a white iron which would give hard, brittle and porous castings can be made solid, softer and tougher by the ad- dition of silicon to the extent of perhaps 2 or 3 per cent. As the silicon is increased the iron will become softer and grayer and the tensile strength will decrease. At the same time the shrink- age will decrease, at least for a time, though it may increase again with large excess of silicon. The softening and toughen- ing influence, however, will only continue so long as additional graphite is formed, and when most of the carbon is brought into this state the maximum effect, has been produced, and any fur- ther addition of silicon will decrease both strength and tough- ness. (3) Influence of Sulphur. Authorities are not in entire agreement as to the influence of sulphur on cast iron, some be- lieving that it tends to increase the proportion of combined car- bon, while others maintain that it tends to decrease both the combined carbon and silicon. It is generally agreed, however, that in proportions greater than about .15 to .20 of I per cent it increases the shrinkage and the tendency to chill, and decreases the strength. Sulphur does not, however, readily enter cast iron under ordinary conditions, and its influence is not especially feared. An increase in the proportion of sulphur in cast iron MATERIALS. 7 is most likely to result from an absorption of sulphur in the coke during the operation of melting in the cupola. (4) Influence of Manganese. This element by itself de- creases fluidity, increases shrinkage, and makes the iron harder and more brittle. It combines with iron in all proportions. With manganese less than one-half, the combination is usually called spicgcleifcn. With manganese more than one-half it is called ferro-manganese. One of the most important properties of manganese in combination with iron is that it increases the capacity of the iron for carbon. Pure iron will only take about 3*X per cent of carbon, while with the addition of manganese the proportion may rise to 6 per cent or 7 per cent. Manganese is also believed to decrease the capacity of iron for sulphur, and to this extent may be a desirable ingredient in proportions not exceeding I per cent to i l /2 per cent. (5) Influence of Chromium. This substance is rarely found in cast iron, but it has the property, when present in large proportion, of raising the capacity of the iron for carbon from about $y 2 per cent up to about 12 per cent. (6) Shrinkage of Cast Iron. At the moment of hardening, cast iron expands and takes a good impression of the mould. In the gradual cooling after setting, however, the metal con- tracts, so that on the whole there is a shrinkage of about % in. per foot in all directions, though this amount varies somewhat with the quality of the iron and with the form and dimensions of the pattern. In a general way hardness and shrinkage in- crease and decrease together. (7) Strength and Hardness of Cast Iron. The hardness of cast iron is chiefly dependent 'on the amount of combined car- bon, as noted above in (i). The strength is also chiefly dependent on the same ingre- dient. As shown in (i), the greatest crushing strength is ob- tained with sufficient combined carbon to make a rather hard, white iron, while for the maximum transverse or bending strength the combined carbon is somewhat less and the iron only moderately hard, and for the greatest tensile strength the combined carbon is still less and the iron rather soft. Metal still softer than this grade works with the greatest facility, but is deficient in strength. Numerical values for the strength will be given at a later point. 8 PRACTICAL MARINE ENGINEERING. (8) Uses of Cast Iron in Marine Engineering. Cast iron is used for cylinders, cylinder heads, liners, slide valves, valve chests and connections, and generally for all parts having con- siderable complexity of form. It is also used for columns, bed plates, bearing pedestals, caps, etc., though cast and forged steel are to some extent displacing cast iron for some of these items. It is also used for grate bars, furnace door frames, and minor boiler fittings, and for a great variety of special purposes usually connected with the stationary or supporting parts of machines. (9) Inspection of Castings. In the inspection of castings care must be had to note the texture of the surface, and to this end the outer scale and burnt sand should be carefully removed by the use of brushes or chipping hammer, or, if necessary, by pickling in dilute muriatic acid. The* flaws most liable to occur are blow holes and shrinkage cracks. The latter, however, are not often met with when the moulding and casting are properly carried out. The parts of the casting most liable to be affected by blow holes are those on the upper side or near the top. On this account a sinking head or extra piece is often cast on top, into which the gases and impurities may collect. This is afterward cut off, leaving the sounder metal below. The presence of blow holes, if large in size or in great number and near the surface, may often be determined by tap- ping with a hand hammer. The sound given out will serve to indicate to an experienced ear the probable character of the metal underneath. (10) Special Operations on Cast Iron. Cast iron may be softened and toughened by the process of malleablizing, as de- scribed in (2). It may be somewhat hardened on the surface by arresting the usual process of malleablizing at a suitable point and then hardening as for steel. This operation arrested before completion results in the formation of a surface layer of material having essentially the properties of steel. Cast iron may be brazed to itself or to most of the com- mon structural metals by the use of a brazing solder of suitable melting point, and with proper care in the operation. Cast iron may also be united to itself or to wrought iron or steel by the operation of burning. This consists in placing in position the two pieces to be united, and then allowing a stream of melted cast iron to flow over the surfaces to be joined, the adjacent MATERIALS. 9 parts being protected by fire clay or other suitable material. The result is to soften or partially melt the surfaces of the pieces, and by arresting the operation at the right moment they may be securely joined together. [a] Malleable Iron. (i) Composition and Manufacture. If a casting of hard, white iron, or one with a large proportion of combined carbon, be packed in some material which will not fuse at a red heat, which will exclude the air, support the piece and prevent defor- mation when hot, and if it be then subjected to continuous red heat for some days, the combined carbon will be separated from the iron, but will not be able to collect together in flakes or scales or to form the same structure as in soft, gray cast iron. In consequence the iron crystals remain in more intimate con- tact, much as in steel, and the tensile strength and toughness are greatly increased. It has long been supposed that this operation involved an actual withdrawal of the carbon from the iron, and to this end the substances usually employed are either the common red oxide of iron in the form of hematite iron ore, or the black oxide in the form of mill scale, or the corresponding oxide of manganese. These have a decarbonizing effect ; that is, under the conditions existing they will to some extent withdraw the carbon from the surface layer of iron. Analyses of malleable iron show, how- ever, that only to a slight extent is Ihe carbon actually with- drawn as a whole, and that the principal change is in the condi- tion of the carbon, as above explained. The surface effect, however, extending in, as it does, for perhaps 1-16 in., is un- doubtedly a valuable feature, and while a good quality of malle- able iron has been made by the use of river sand as a packing medium, the use of the substances mentioned above is rather to be preferred. In order that the process may be successful, the iron must have nearly all the carbon in the combined state, and must be low in sulphur, as the latter substance is found to greatly in- crease the time necessary. It has been customary to use only good charcoal-melted iron in which the sulphur is very low, though a coke-melted iron is quite as suitable, provided the pro- portion of sulphur is correspondingly small. The process can rarely be applied to very large castings, because such, cooling io PRACTICAL MARINE ENGINEERING. slowly, usually show a considerable proportion of graphitic carbon. To carry out the process the castings are embedded in the material selected. The whole is then inclosed in a cast-iron box or pot and is subjected to a full red heat for from two or three days to as many weeks, depending on the size of the piece. (2) Physical and Mechanical Properties. Outside of the numerical information, to be given later, attention may be called to the ductility of malleable iron, which is from four to six times that of cast iron, though only about one-tenth that of wrought iron. Nevertheless good malleable iron can be bent and twisted to a very considerable extent before' breaking, and its ability to withstand blows or shocks is very much greater than cast iron. Malleable iron may with care be forged and welded, and it may be case hardened much as with wrought iron. (3) Uses in Marine Engineering. Malleable iron is used for junction boxes and for pipe fittings in certain varieties of water-tube boilers, and to some extent for general pipe fittings on board ship. It would seem that the use of this material might with advantage be extended to many parts in which more strength and toughness are required than can be provided by cast iron of the ordinary type. [3] Wrought Iron. (i) Composition and Manufacture. Wrought iron is nearly pure iron mixed with more or less slag. Nearly all the wrought iron used in modern times is made by the puddling process. For the details of this process reference may be had to text-books on metallurgy. We can only note here that in a furnace some- what similar to the open-hearth referred to in [5] (4) most of the carbon, silicon and other special ingredients of cast iron are re- moved by the combined action of the flame and of a molten bath of slag or fluxing material consisting chiefly of black oxide of iron. As this process approaches completion small bits of near- ly pure iron begin to separate out from the bath of melted slag and unite together. This is helped along by the puddling bar, and after the iron has thus become separated from the liquid slag it is taken out, hammered or squeezed, and rolled down into bars or plates. Some of the slag is necessarily retained in the iron and by the process of manufacture is drawn out into fine threads, MATERIALS. 11 giving to the iron a stringy or fibrous appearance when nicked and bent over or when pulled apart. The proportion of carbon in wrought iron is very small, ranging from .02 to .20 of one per cent. In addition, small amounts of sulphur, phosphorus, silicon and manganese are usually present. The proportion of sulphur should not exceed .01 of one per cent. Excess of sulphur makes the iron red-short, that is, brittle when red hot. ' The proportion of phosphorus may vary from .05 to .25 of one per cent. Excess of phosphorus makes the metal cold- short, that is, brittle when cold. The proportion of silicon may vary from .05 to .30 of one per cent. The proportion of manganese may vary from .005 to .05 of one per cent. The influence of the silicon and manganese is usually slight and unimportant. (2) Special Properties. Wrought iron is malleable and ductile, and may be rolled, forged, flanged and welded. It can- not be hardened as steel, though by the process- of case-harden- ing a surface layer of steel is formed and may be hardened. Wrought iron may be welded, because for a considerable range of temperature below melting (which takes place only at a very high temperature indeed) the iron becomes soft and plastic, and two pieces pressed together in this condition unite and form on cooling a junction nearly as strong as the solid metal. In order to be thus successful, however, the iron must be heated sufficient- lytobringit to the plastic condition, yet not overheated, and there must be employed a flux (usually borax) which will unite with the iron oxide and other impurities at the joint, and form a thin liquid slag, which may be readily pressed out in the operation, thus allowing the clean metal faces of the iron to effect a union as desired. (3) Uses in Marine Engineering. In modern practice the place of wrought iron in marine engineering has been almost en- tirely taken by steel. Its former office was for all moving parts requiring strength and toughness. It is still used to some ex- tent for the stay bolts and braces of boilers, and for boiler tubes. [4] Blisters and I/aminations. With modern boiler material these defects are happily rare. 12 PRACTICAL MARINE ENGINEERING. In older practice, however, when wrought iron was the material employed for boiler plates, such defects were quite frequently met with. A lamination consisted in the separation of the ma- terial of the plate into layers not welded together and therefore lacking the strength and solidity of the plate proper. The for- mation of such places was usually due to the presence of slag in the iron which in the operation of rolling the plates would be- come thinned out into a sheet or layer .separating the two gaits of the iron and preventing them from becoming welded together and thus forming a solid homogeneous plate. Such places may vary in size from a trifling amount up to patches of several square feet in area. Now when a plate with such laminations is worked into the structure of a boiler with the continual fluctua- tions of temperature and the consequent expansions and con- tractions, it very frequently happens that the two parts of the laminations become separated from each other, and in particular the thinner of the two will become raised often to a considerable extent, thus forming a so-called blister. The chief danger from such a blister on the heating surface arises from the non-con- ductivity of the plate for heat at this point, and the consequent danger of its overheating and giving rise to a serious rupture. Further reference to this point will be found in Sec. 38 [3]. In examining a plate for laminations or small blisters not plainly shown to the eye, the hammer test is usually considered the most reliable. The plate is tapped over its surface, and judging by the sound an experienced ear can usually detect the locality and approximate extent of trouble of this character. [5] Steel. (i) General Composition. The properties of steel depend partly on the proportions of carbon and other ingredients which it may contain, and partly on the process of manufacture. The proportion of carbon is intermediate between that for wrought iron and for cast iron. In the so-called mild or structural steel the carbon is usually from i-io to 1-4 or 1-3 of one per cent. In spring steel the carbon proportion is somewhat greater, and in high carbon grades such as are used for tool steel, etc., the carbon is from .6 to 1.2 per cent. In addition to the carbon there may be sulphur, phosphorus, silicon and manganese in varying but very small amounts. From the proportion of carbon it follows that steel may be MATERIALS. 13 made either by increasing the proportion in wrought iron or decreasing the proportion in cast iron. The earlier processes followed the first method, and high-grade steels are still made in this way by the crucible process. (2) Crucible Steel. In this process a pure grade of wrought iron is rolled out into flat bars. These are then cut and piled and packed with intermediate layers of charcoal and subjected to a high temperature for several days. This recar- bonizes or adds carbon to the w r rought iron, and thus makes what is then called cement or blister steel. These bars, are then broken into pieces of convenient size, placed in small crucibles, melted, and cast into bars or into such forms as are desired. NOTE. Mild or structural steel is made wholly by the second general method the reduction of the proportion of carbon in cast iron. There are two general processes, known as the Bessemer and the Siemens Martin or Open-hearth. (3) Bessemer Process. In this process the carbon and sili- con are burned almost entirely out of the cast iron by forcing an air blast through the molten iron in a vessel known as a con- verter. A small amount of Spiegel eisen or iron rich in carbon and manganese is then added in such weight as to make the propor- tion of carbon and manganese suitable for the charge as a whole. The steel thus formed is then cast into ingots or into such forms as may be. desired. In this process no sulphur or phosphorus is removed, so that it is necessary to use a cast iron very nearly free from these ingredients in order that the steel may have the properties de- sired. A modification by means of which the phosphorus is re- moved, and known as the basic Bessemer process, is used to some extent. In this, calcined or burnt lime is added to the charge just before pouring. This unites with the phosphorus, removes it from the steel, and brings it into the slag. In the basic process the lining of the converter is made of gannister or a calcined magnesia limestone, in order that it may not also be attacked by the added limestone and the resulting slag. In that form of Bessemer process first noted, and often known as the acid process in distinction from the latter or basic process, the lining of the converter is of ordinary fire clay or like material. The removal of the phosphorus by the basic process makes possible the use of an inferior grade of cast iron. At the same i 4 PRACTICAL MARINE ENGINEERING. time, engineers are not altogether agreed as to the relative values of the two products, and many prefer steel made by the acid process from an iron nearly free from phosphorus at the start. (4) The Open-hearth Process. In this process a charge of material consisting of wrought iron, cast iron, steel scrap, and sometimes certain ores, is melted on the hearth of a reverbera- tory furnace heated by gas fuel on the Siemens Martin or re- generative system. The carbon is thus partially burned out in much the same manner as for wrought iron, and the proportion of carbon is brought down to the desired point or slightly be- low. A charge of Spiegel eisen or ferro-manganese is then added in order that the manganese may act on any oxide of iron slag which remains in the bath, and which would make the steel red-short if allowed to form a part of the charge. The mangan- ese separates the iron out from the oxide, returns it to the bath, while the carbon joins in with that already present, and thus produces the desired proportions. Here as with the similar operation with the Bessemer con- verter there is no removal of either sulphur or phosphorus, and only materials nearly free from these ingredients can be used for steel of satisfactory quality. With very low carbon, how- ever, a little phosphorus seems to be desirable to add strength to the metal. This limitation of the available materials has led, as with the Bessemer process, to the use of calcined limestone, which unites with most of the phosphorus and holds it in the slag. Here, as in the Bessemer process also, it is necessary to use a basic lining for the furnace, and it is known as the basic open-hearth process. By distinction the method without the use of the limestone has come to be known as the acid open- hearth process. As between the products of these two kinds of open-hearth process, there is much difference of opinion among engineers. Either will produce good steel with proper care, and neither will without it. It is usually considered sufficient to specify the al- lowable limits for the proportions of phosphorus and sulphur and leave the choice of the acid or basic processes to the maker. (5) Open-hearth and Bessemer Steels Compared. Open- hearth steel is usually preferred for structural material in mar- ine engineering. This is because : (a) It seems to be more reliable and less subject to un- MATERIALS. 15 expected or tmexplainable failure than the Bessemer product. (b) Analysis shows that it is much more homogeneous in composition than Bessemer steel, and experience shows that it is much more uniform in physical quality. This is due to the process of manufacture, which is much more favorable to a thorough mixing of the charge than in the Bessemer process. (c) The open-hearth steel may be tested from time to time during the operation, so that its composition may be determined and adjusted to fulfil specified conditions. This is not possible with the Bessemer process, and the latter product is therefore not under so good control as is the open-hearth. (6) Influence of Sulphur on Steel. Sulphur makes steel red-short or brittle when hot, and interferes with its forging and welding properties. Manganese tends to counteract the bad ef- fects of sulphur. Good crucible steel has rarely more than .01 of one per cent. In structural steel the proportion may vary from .02 to .08 or .10 of one per cent. When possible it should be reduced to not more than .03 or .04 of one per cent. (7) Influence of Phosphorus on Steel. Phosphorus increases the tensile strength and raises the elastic limit of low carbon or structural steel, but at the expense of its ductility and toughness or ability to withstand shocks and irregularly applied loads. It is thus considered as a dangerous ingredient, and the amount allowable should be carefully specified. This is usually placed from .02 to .10 of one per cent. (8) Influence of Silicon on Steel. Silicon tends to increase the tensile strength and to reduce the ductility of steel. It also increases the soundness of ingots and castings, and by reducing the iron oxide tends to prevent red-shortness. The process of manufacture usually removes nearly all of the silicon, so that it is not an element likely to give trouble to the steel maker. The proportion allowed should not be more than from .10 to .20 of one per cent. (9) Influence of Manganese on Steel. This element is be- lieved to increase hardness and fluidity, and to raise the elastic limit and increase the tensile strength. It also removes iron oxide and sulphur, and tends to counteract the influence of such amounts of sulphur and phosphorus as may remain. It is thus an important factor in preventing red-shortness. The propor- tion needed to obtain these valuable effects is usually found be- tween .20 and .50 of one per cent. 16 PRACTICAL MARINE ENGINEERING. (10) Semi-steel. A metal bearing this trade name has in recent years attracted favorable attention among engineers and has come into considerable use where somewhat greater strength and toughness are required than can be provided by cast iron. Semi-steel is made by melting up mild steel scrap, such as punchings and clippings of boiler plate, with cast iron pig, in the proportion of about 25 or 30 per cent of the former to 75 or 70 per cent of the latter. The presence of manganese and other special fluxes in small proportions is also found to add essen- tially to the strength, toughness and good machining qualities of the product. In this way is obtained a material having a tensile strength of 35,000 Ib. or over, and a toughness and ability to withstand shocks decidedly greater than for cast iron, and with fairly good machining qualities. Semi-steel casts as read- ily as most grades of cast iron, and its shrinkage and genera! manipulation are about the same. The chief drawback seems to lie in the danger of hardness under the lathe, planer or bor- ing tool, but with the proper mixtures this is avoided, .and a material very satisfactory for many purposes in marine engi- neering is thus produced. (n) Mechanical Properties of Steel. The tensile strength of the lowest carbon steel, say about .10 of one per cent carbon, is usually not above from 50,000 to 55,000 Ib. per square inch of section. The strength increases with the increase of carbon, and with not above the usual proportions o sulphur and phos- phorus, quite uniformly. Experiment shows that under these circumstances the strength will increase up to 75,000 Ib. per square inch, or higher, at the rate of from 1,200 to 1,500 Ib. per .01 of one per cent of carbon added. At the same time, with the increase in strength the ductility decreases, so that a proper choice must be made according to the particular uses for which the steel is intended. With the best grades of tool steel with carbon ranging from y 2 to i per cent and over, the strength ranges from 80,000 Ib. upward to 120,000 Ib., and even higher in exceptional cases. Flange and rivet steel must be tough and ductile in the high- est degree. Such steel has usually a tensile strength between 50,000 and 60,000 Ib. and an elastic limit of 30,000 to 40,000 Ib. Its elongation in 8 in. is from 30 to 35 per cent, and reduction of area at the ruptured section from 50 to 60 per cent. It will MATERIALS. 17 bend cold ort itself and close down flat under hammer or press, up to a thickness of 1/4 in. to I in. without a sign of fracture. Shell steel, used for boiler shells, etc., has usually a strength between 55,000 and 65,000 Ib. ; elastic limit from 33,000 to 45,- ooo Ib. ; elongation in 8 in. of 25 to 30 per cent, and reduction of area of 50 to 60 per cent. For shafting the quality of the steel is about the same as for shell plates. For piston and connecting rods the strength is rather higher, and ductility somewhat lower. For steel castings the strength required is usually from 60,- ooo to 65,000 Ib., with an elongation in 8 in. of from 10 to 15 per cent. (12) Various Specifications for Structural Steel. U. S. Navy. COMPOSITION OF BOILER PLATES. Phosphorus : Not over .035 of one per cent. Sulphur : Not over .040 of one per cent. STRENGTH OF SHELL PLATES. Tensile Strength: Between 65,000 and 73,000 Ib. per square inch. Elongation (transverse) : Not less than 22 per cent in 8 in. Elongation (longitudinal) : Not less than 25 per cent in 8 in. Elastic Limit : Not less than 35,000 Ib. per square inch. Cold Bending Test. One piece cut from each shell and curved head plate, as finished at the rolls for cold-bending test, must bend over flat on itself without sign of fracture. STRENGTH OF FURNACE AND FLANGE PLATES. Tensile Strength : Between 52,000 and 60,000 Ib. per square inch. Elongation : Not less than 26 per cent in 8 in. Quenching Test. One piece shall be cut from each furnace or flange plate as finished at the rolls for quenching test, and after heating to a dark cherry red plunged into water at a tem- perature of 82 deg. F. The piece thus prepared must be bent double round a curve of which the diameter is not more than the thickness of the piece tested, without showing any cracks. The ends of the pieces must be parallel after bending. i8 PRACTICAL MARINE ENGINEERING. BOILER RIVETS. Kind of Material. Steel for boiler rivets must be made by the open-hearth process and must not show more than .035 of one per cent of phosphorus, nor more than .04 of one per cent of sulphur, and must be of the best composition in other re- spects. Tensile Tests. These specimens for rivets for use in the longitudinal seams of boiler shells shall have from 62,000 to 70,000 Ib. per square inch tensile strength, with an elongation of not less than 25 per cent in 8 in. ; and all others shall have a tensile strength of from 54,000 to 62,000 Ib. per square inch, with an elongation of not less than 28 per cent in 8 in. Shearing Tests. From each heat, rivets must show a shear- ing strength of at least 51,000 Ib. per square inch for rivets to be used in longitudinal seams of boiler shells, and at least 44,000 Ib. per square inch for all other boiler rivets. Rivets to be driven at the same heat used for working. Hammer Test. From each lot six rivets are to be taken at random and submitted to the following tests : (a) Two rivets to be flattened out cold under the hammer to a thickness of one-half the diameter of the part flattened with- out showing cracks or flaws. (b) Two rivets to be flattened out hot under the hammer to a thickness of one-third the diameter of the part flattened without showing cracks or flaws the heat to be the working heat when driven. (c) Two rivets to be bent cold into the form of a hook with parallel sides without showing cracks or flaws. RODS, SHAPES AND FORCINGS FOR BOILER BRACING. Kind of Material. Steel for stay rods and braces must be made by the open-hearth process, and must not show more than .035 of one per cent of phosphorus, nor more than .04 of one per cent of sulphur, and must be of the best composition in other respects. Treatment. All material for boiler bracing must be an- nealed after working. Tensile Test. Bracing coming into contact with the fire must have a tensile strength of from 50,000 to 58,000 Ib., and an elongation of not less than 28 per cent in 8 in., or of 33 per cent in 2 in. in case 8-in. specimens can not be secured. Other MATERIALS. 19 bracing must have a tensile strength of not less than 65,000 lb., and an elongation of not less than 24 per cent in 8 in., or of 30 per cent in 2 in. in case 8-in. specimens can not be secured. Bending Test. One bar l / 2 in. thick, cut from each lot of the bracing coming in contact with the fire, must stand bending double to an inner diameter of i in. after quenching in water at a temperature of 82 deg. F., from a dark cherry-red heat with- out showing cracks or flaws. A similar piece cut from each lot of the other bracing must stand cold bending double to an inner diameter of i in. without showing cracks or flaws. Opening and Closing Tests. Angles, T bars, etc., are to be subjected to the following additional tests : A piece cut from one bar in twenty to be opened out flat while cold ; a piece cut from another bar in the same lot shall be closed down on itself until the two sides touch without showing cracks or flaws. CONNECTING AND PISTON RODS AND VALVE STEMS. Tensile Strength : Not less than 80,000 lb. per square inch. Elongation : Not less than 26 per cent in 2 in. Elastic Limit : Not less than 50,000 lb. per square inch. Bending Test. One longitudinal bar y 2 in. thick, cut from each forging, must stand bending double, when cold, to an in- ner diameter of i in. without showing cracks or flaws. THRUST LINE AND PROPELLER SHAFTING. Tensile Strength : Not less than 80,000 lb. per square inch. Elongation : Not less than 25 per cent in 2 in. Elastic Limit : Not less than 50,000 lb. per square inch. CRANK SHAFTS. Tensile Strength : Not less than 58,000 lb. per square inch. Elongation : Not less than 30 per cent in 2 in. Bending Test. Bars y 2 in. thick, cut from each length of shaft, must stand bending double to an inner diameter of i in. without showing cracks or flaws. STEEL CASTINGS. Phosphorus : Not more than .06 of one per cent. Tensile Strength: Not less than 60,000 lb. per square inch. Elongation (for moving parts): Not less than 15 per cent in 8 in. 20 PRACTICAL MARINE ENGINEERING. Elongation (other castings) : Not less than 10 per cent in 8 in. Bending Test. A bar I in. square shall bend cold without showing cracks or flaws, through an angle of 120 deg. for cast- ings for moving parts of machinery, and 90 deg. for other cast- ing, over a radius not greater than i l / 2 in. U. S. Inspection Requirements for Boiler Plate. Phosphorus : Not more than .06 of one per cent. Sulphur : Not more than .04 of one per cent. Elongation (J4 m - and under) : 25 per cent in 2 in. Elongation ( l /4 in. to 7-16 in. inc.) : 25 per cent in 4 in. Elongation (7-16 in. to I in. inc.) : 25 per cent in 8 in. Elongation (i in. and over) : 25 per cent in 6 in. Reduction of Area at Rupture (y 2 in. and under) : Not less than 50 per cent. Reduction of Area at Rupture ( l / 2 in. to 34 in.) : Not less than 45 per cent. Reduction of Area at Rupture (fy in. and over) : Not less than 40 per cent. American Boilermakers* Association Requirements. Phosphorus : Not over .04 per cent. Sulphur : Not over .03 per cent. Tensile Strength : 55,000 to 65,000 Ib. Elongation (3/ in. and under) : 20 per cent in 8 in. Elongation (3/ in. to 3/^ in.) : 22 per cent in 8 in. Elongation (34 in. and over) : 25 per cent in 8 in. Cold Bending. For plates y 2 in. thick and under, specimen must bend back on itself without fracture. For plates over y 2 in. thick, specimen must bend 180 deg. around a mandril one and one-half times thickness of plate without fracture. British Board of Trade Requirements. Tensile Strength of Plates Not Exposed to Flame : 60,480 to 71,680 Ib. per square in. Tensile Strength of Plates Exposed to Flame : 58,240 to 67,200 Ib. per square inch. Elongation: From 18 to 25 per cent in 10 in. MATERIALS. 21 Standard Specifications Adopted by the Association of Ameri- can Steel Manufacturers. Special Open-hearth Plate and Rivet Steel. Steel shall be of four grades, as follows : Extra Soft, Fire- box, Flange or Boiler, and Boiler Rivet Steel. Extra Soft, Fire-box and Boiler Rivet Steel: Maximum phosphorus, .04 per cent ; maximum sulphur, .04 per cent. Flange or Boiler Steel : Maximum phosphorus, .06 per cent ; maximum sulphur, .04 per cent. PHYSICAL PROPERTIES. Extra Soft and Boiler Rivet Steel. Ultimate Strength : 45,000 to 55,000 Ib. per square inch. Elastic Limit : Not less than one-half the ultimate strength. Elongation : 28 per cent. Cold and Quench Test : Bends 180 deg. flat on itself with- out fracture on outside of bent portion. Fire-box Steel. Ultimate Strength : 52,000 to 62,000 Ib. per square inch. Elastic Limit : Not less than one-half the ultimate strength. Elongation : 26 per cent. Cold and Quench Test : Bends 180 deg. flat on itself with- out fracture on outside of bent portion. Flange or Boiler Steel. Ultimate Strength : 52,000 to 62,000 Ib. per square inch. Elastic Limit : Not less than one-half the ultimate strength. Elongation : 25 per cent. Cold and Quench Test: Bends 180 deg. flat on itself with- out fracture on outside of bent portion. (13) Special Properties of Steel. Mild or low carbon steel may be welded, forged, flanged, rolled and cast. It can not be tempered or hardened with a proportion of carbon lower than about 24 f one P er cent. High carbon steel can be welded only imperfectly and if very high in carbon not at all. It can be forged with care, and cast into forms as desired. It can be tempered or hardened by heating to a full yellow and quenching in cold water or by other means, and then drawing the temper to the point desired. Mild steel should not be worked under the hammer or flanging press at a low or "blue" heat, as such working is found 22 PRACTICAL MARINE ENGINEERING. in many cases to leave the metal brittle and unreliable. Steel in order to weld satisfactorily should have a low proportion of sulphur, and special care is required in the operation, because the range of temperature through which the metal is plastic and fit for welding is less than with wrought iron. In the operation of tempering, the steel after quenching is very hard and brittle. In order to give to the metal the prop- erties desired, the temper is drawn down by heating it up to a certain temperature, and then quenching again, or, better still, allowing it to cool gradually, provided the temperature does not rise above the limiting value suitable for the purpose desired. If the reheating is done in a bath of oil the conditions may be kept under good control and the final cooling may be slow. If the reheating is in or over a fire the control is lacking and the piece must be quenched as soon as the proper temperature is reached. This is usually determined by the cplor of the oxide or scale which forms on a brightened surface of the metal. The following table shows the temperatures, corresponding colors, and uses for which the various tempers are suited : 4 4 5o S$l:} Hardest and keenest cutting tool, 470 Full yellow. ) Cutting tools requiring less hardness 490 Brown yellow or orange, f and more toughness. 510 Purplish. ) Tools for working softer materials, or those required 530 Purple, f to stand rough usage. 550 Light blue. ] Spring temper. Used for tools requiring great 560 Full blue. [ elasticity or toughness, or for working very soft 6oo c Dark: blue. J materials. (14) Special Steels. In the common grades of steel the valuable properties are due to the presence of carbon modified in some degree by other ingredients as already described. There are other substances which by uniting with iron in small proportions are able to give to the combination increased strength or hardness or other valuable properties. We have thus various special steels in which the properties may be due to the presence of both carbon and other ingredients, or due chiefly to special ingredients other than carbon. Of these special steels we may note the following : Nickel steel, containing somewhere about 3 per cent of nickel and varying amounts of carbon, is found to have in- creased strength and toughness as compared with ordinary steel. Nickel steel is most extensively used for armor plate, MATERIALS. 23 though to some extent it has been employed in Government work for screw-shafts and for boiler plates. For the former purposes it has given excellent satisfaction, but for the latter use difficulty has been met with in obtaining plates free from surface defects. Chrome steel, containing from .5 to 1.5 or 2 per cent of chromium may be made excessively hard, but it is not always reliable, and is not regarded with general favor. Tungsten steel or mushet steel is a steel containing carbon and tungsten, the latter in proportions as high as 8 to 10 per cent. This steel must be forged with .care and is excessively hard. The hardness is not increased by tempering, but is naturally acquired as the metal cools. Hence it is said to be self-harden- ing. Some specimens contain also small amounts of mangan- ese and silver. Its chief use is for lathe and planer or other cutting and shearing tools where excessive hardness is required. (15) Uses of Steel in Marine Construction. In modern practice mild or structural steel is used entirely in the con- struction of ships. The same general class of material is used for all parts of boilers, though the tubes are still sometimes made of wrought iron. Cast steel is used for various parts of engines such as pis- tons, crosshead blocks, columns, bed-plates, bearing pedestals and caps, propeller blades, and for many small pieces and fit- tings. Pistons are made almost exclusively of cast steel. For most of the other items mentioned cast iron is still used, prob- ably to a larger extent than cast steel, especially where the cast- ings are large and complicated in form, as with columns and bed-plates. Forged, steel is used for columns, piston-rods, connecting- rods, crank and line shafting, and for many other smaller and minor parts. Sec. 6. I,EAD. Lead is a very soft, dense metal, grayish in color after ex- posure to the air, but of a bright silvery luster when freshly cut. Commercial lead often contains small amounts of iron, copper, silver and antimony, making it harder than the pure metal. It is very malleable and plastic. In engineering, lead is chiefly of value as an ingredient of bearing metals and other special al- loys. Lead piping is also used to some extent for water sue- 24 PRACTICAL MARINE ENGINEERING. tion and delivery pipes where the pressure is only moderate, and where the readiness with which it may be bent and fitted adapts it for use in contracted places. Sec. 7. TIN. Tin is a soft, white, lustrous metal with great malleability. Commercial tin usually contains small portions of many other substances, such as lead, iron, copper, arsenic, antimony and bismuth. It is largely used as an alloy in the various bronzes and other special metals. Tin resists corrosion well and in con- sequence is often used as a coating for condenser tubes. It is also used for coating iron plates, the product being the so- called "tin plate" of commerce. It melts at about 450 deg., which corresponds to a steam pressure of about 400 Ibs. per square inch. Due to this low melting point tin is often used as the composition for safety plugs in boilers. Sec. 8. 3INC. Zinc, or "spelter," as it is often called commercially, is a brittle and moderately hard white metal with a very crystalline fracture. The impurities most commonly found in zinc are iron, lead and arsenic. It is used chiefly as an alloy in the various brasses, bronzes, etc., and as a coating for iron and steel plates, rods, etc. The process of applying zinc for such a coating is called "galvanizing," and the product "galvanized" iron or steel. Electricity, however, is not used in the process, the articles, after being well cleaned, being simply dipped in a tank of melted zinc and then withdrawn. Slabs of zinc are also used in marine boilers to prevent corrosion. Sec. 9. AI,I,OYS. A mixture of two or more metals is called an t a//0;y. The properties of an alloy are often surprisingly different from those of its ingredients. The melting point is sometimes lower than that of any of the ingredients, while the strength, elastic limit and hardness are often higher than for any of them. Mixtures of copper and zinc are called brass. Mixtures of copper and tin, or copper, tin and zinc, with sometimes other sub- stances in small proportion, form gun metals, compositions and bronzes. These terms are, however, rather loosely employed. Various mixtures of two or more of the metals copper, tin, zinc, lead, antimony form the various bearing metals. MATERIALS. 25 Brass and composition are used for piping and pipe-fitting; globe, gate, check and safety valves ; condenser tubes and shells ; sleeves for tail shafts, and for a great number of small fittings and attachments for which the metal may be suited. The bronzes are employed for many of the uses of brass where more hardness, strength or rigidity are required. They are used with especial success as a material for propeller blades. The white metals, supported or backed by some other metal, such as brass, cast iron or cast steel, to give the neces- sary strength, are now very largely used for bearing surfaces. PROPORTIONS OF INGREDIENTS FOR VARIOUS ALLOYS. In the following proportions the numbers after the ingred- ients denote the number of parts in 100 of the mixture. They represent either the usual proportions, or the results of special analyses of samples, and have been collected from various sources. The alloys are arranged in the alphabetical order of their names to facilitate ready reference : Admiralty Bronze. Copper 87, tin 8, zinc 5. Aluminum Brass. Copper 63, zinc 34, aluminum 3. Aluminum Bronze. Copper 89 to 98, aluminum n to 2. Anti-Friction, A. Zinc i, iron .65, lead 78.75, antimony 19.6. Anti-Friction, B. Copper 1.6, tin 98.13, iron trace. Anti-Friction, C. Copper 3.8, tin 78.4, lead 6, antimony 1 1.8. Babbitt (Light'}. Copper 1.8, tin 89.3, antimony 8.9. Babbitt (Heavy). Copper 3.7, tin 88.9, antimony 7.4. Brass, Common Yellow. Copper 65.3, zinc 32.7, lead 2. Brazing Metal. Copper 84, zinc 16. Brazing Solder. Copper 50, zinc 50. Bush Metal. Copper 80, tin 5, zinc' 10, lead 5. Delta Metal. Copper 50 to 60, tin I to 2, zinc 34 to 44, iron 2 to 4. Deoxidized Bronze. Copper 82, tin 12.46, zinc 3,23, iron .10, lead 2.14, phosphorus trace, silver .07. Gun Metal. Copper 89, tin 8.25, zinc 2.75. Magnolia. Tin ?, zinc trace, iron trace, lead 83.55, anti- mony 16.45. Manganese Bronze. Copper 88.64, tin 8.7, zinc 1.57, iron .72, lead .30. 26 PRACTICAL MARINE ENGINEERING. Muntz Metal. Copper 60, zinc 40. Navy Brass. Copper 62, tin i, zinc 37. Navy Composition. Copper 88, tin 10, zinc 2. Navy Journal Boxes. Copper 82.8, tin 13.8, zinc 3.4. Parsons White Metal. Copper 1.68, tin 72.9, zinc 22.9, lead 1.68, antimony .84. Phosphor Bronze. Copper 90 to 92, phosphide of tin 10 to 8. Steam Metal. Copper 85, tin 6.5, zinc 4.5, lead 4.25. Tobin Bronze. Copper 59 to 61, tin i to 2, zinc 37 to 38, iron .1 to .2, antimony .30 to .35. White Metal. Lead 88, antimony 12. Sec. 10. THE TESTING OF METALS. [i] Different Kinds of Tests. Metals may be tested for strength in various ways in ten- sion, by pulling apart a test piece of specified pattern and size ; in compression, by crushing a piece of suitable dimensions ; in cross breaking, by supporting a bar at two points and breaking or bending it in the testing machine by a load applied at an inter- mediate point; in torsion, by twisting apart a bar in a machine especially designed for the purpose ; in direct shearing, by break- ing a riveted or pin joint connection in the usual machine; for impact or shock, by letting a weight drop through a certain height and by its blow develop suddenly the stress in the ma- terial. [a] Explanation of Terms Used. Ultimate Strength. The ultimate strength, of a test piece is the load required to produce fracture, reduced to a square inch of original section; or in other words, the ultimate or highest load divided by the original area. Thus if the area of the cross-section of a test piece is .42 sq. in. and the load producing fracture is 28,400 Ib. , the ultimate strength equals 28,- 400 -T- .42 = 67,620 Ib. per square inch. Elastic Limit. The elastic limit is the smallest load, reduced to one square inch of area, which will produce a permanent set or distortion of the material. Thus in a tension test if the cross- section is .68 sq. in. and a permanent elongation or set is just produced by a load of 27,600 Ib., the elastic limit is at 27,600 -i- .68 == 40,600. Elongation. A certain length being marked off on the test piece as described in [3], [4], the percentage of elongation is MATERIALS. 27 found by dividing the actual extension of the Jength just before rupture by the original length, and reducing to per cent. Thus if a length of 8 in. is marked off on the test piece and if the length between the same marks at fracture is 10.2 in., the actual elongation is 2.2 in. and the percentage elongation is 220 -f- 8 = 27.5 per cent. When a test piece is first put under load the f " i r\ Fig. 1. Test Piece for Iron Plate. elongation is distributed nearly uniformly over its length. This continues until the piece begins to neck down near the point of final fracture. Nearly all of the remaining elongation is re- stricted to the immediate vicinity of this point. Hence the per- centage elongation with short length of test piece may be much CO 1 H g- M U 16'Vo 20" *J Fig. 2. Test Piece for Steel. greater than with a long piece. A few years ago, for example, when test pieces 2 in. long were not uncommon, the actual elon- gation might be nearly i in., and thus percentage elongations approaching 50 per cent were found. In modern practice the length of a test piece is usually 8 in. and values of the percent- age elongation over 30 per cent even with vastly superior ma- terial, are rarely met with. In reporting elongation the length used should always be stated. ,t \ i-1 f\AOIOS ( CM 1 i 1 r* 1 i- *j II * I " * i- 31-0 6 * u 3T 6 * Fig. 3. Test Piece for Steel. Reduction of Area. The percentage reduction of area is found by substracting the final area of the section at the point of fracture from the original area at the same point, dividing the PRACTICAL MARINE ENGINEERING. difference by the latter, and reducing to per cent. Thus if the original area is .68 sq. in. and the final area is .36 sq. in., the actual reduction is .68 .36 = .32 sq. in., and the percentage reduction is 3200 -=- 68 = 47.5 per cent. [3] Test Pieces for Iron. In modern practice the form of test pieces for iron is usually Fig. 4. Plate with Coupon. the same as for steel, and as described in [4] . The form of test piece for wrought iron plate prescribed by the U. S. Board of Supervising Inspectors of Steam Vessels is, however, somewhat different, and is illustrated in Fig. I. If the plate is 5-16 in. thick or less, the width at the reduced section must be one inch. U---8- Fig. 5. Round Test Piece. If the plate is over 5-16 in. in thickness, the width of the piece must be reduced so that the cross-sectional area at the reduced section shall be about .4 sq. in., but it must not be greater than .45 sq. in. nor less than .35 sq. in. r Fig. 6. Bending Test. Fig. 8. Angle Test. [4] Test Pieces for Steel and Other Materials. Fig. 2 shows the form of test piece for tension prescribed by the Navy Department for tests of steel plate for naval uses. Fig. 3 shows the form prescribed by the Association of American Steel Manufacturers, and adopted by the U. S. Board of Supervising Inspectors of Steam Vessels. The test piece for MATERIALS. 29 plates is cut from a "coupon," as it is called, left on one corner of the plate as shown at A, Fig. 4. The U. S. law requires fur- ther that: "Every, iron or steel plate intended for the construction of boilers to be used on steam vessels shall be stamped by the manufacturer in the following manner : At the diagonal corners, at a distance of about 4 in. from the edges and at or near the center of the plate, with the name of the manufacturer, the place where manufactured, and the number of pounds tensile strain it will bear to the sectional square inch." Fig. 5 shows the usual round form of test piece for all ma- terial except plates. [5] Bending, Quenching and Hammer Tests. The nature of these tests has already been described in Sec. S, [51, (n), (12). Fig. 6 illustrates a cold bending test on a piece of steel plate. A drift test is also sometimes required. This is illus- trated in Fig. 7, and consists in driving taper drifts of con- Fig. 7. Drift Test. tinually increasing size into a punched or drilled hole until the diameter is increased to at least twice its original size. The metal must stand this test without sign of fracture about the edges of the hole. Bending tests for angle and Tee irons, as referred to in Sec. 5, [5], (12), are also illustrated in Fig. 8. PRACTICAL MARINE ENGINEERING. li: P 2 J O 88 88 "1 CO CO VO 88 8 co vo O 8 8 CO CO 7 7 . o o 00 O O "- M CO Tf to M O vo CO O l MM N M MM M M 8 0^ CO * H i! O O CO LO CO CO O O ^O i^ ON m O O O t-r\ CO CO m ui if\ CO vO co >-n CO O 00 O M CO to E | cd ca ,4 a: U BC PL. go O CO co VO t^ CO M M M rh rj- CO co vo "i MM CO t*x tx, O O QQ CO CO i f r ^ co ON CO ^ CO Tt" ON vovO O MM O co >- rh M co W * * CO CO to W SPECIFIC GRAVITY. M t^ OO t^ I s ** t"^ ON ^ 3 oo' ON m to co' co' co* vo oo o oo" t^. co" 10 M tN. CO VO ON *^ ^ vo M CO- > 00 ^^A -s ^ A ^ ,^A_^-,,^A^ ^^ -, */} _ fH *rt rG n ^-H in 2 o +* 8 w O bfi,4_i t/0 O <2JQ . . : , H O C O "^ * OOO0 O0000 0OO0OO0 00'' J 000000 "^ ^ ' -^ *+" *** -^ \_X V-X ^ ' tDl'i W\ ^^ v ' ^^ *~* 000000O000ffl40CfcDC 0OOOOOOOO0 x< 00000000000^!: 0OO0OO0OO00 0OOOOOOO0O0 0000000000 0OOOOOOOOO0S 1 !! 0000 3000 0000 0000 Reinforcing Plate Thick. l"Rivets Fig. 10. Scotch Boiler, End View. sub-division is obtained by the use of a large number of tubes or tubular elements surrounded by a shell or casing. The chief classification of boilers is made according to the relation of the water and hot gas to these tubular elements. If the gas is led through the inside and the water is on the outside, the arrange- ment is known as a fire-tube boiler. If, on the contrary, the BOILERS. 49 gas is on the outside and the water circulates through the inside, the arrangement constitutes a water-tube boiler. Fire-tube boilers may be divided into the Return tubular or Scotch boiler, the Direct tubular or gunboat boiler, the Locomotive boiler, the Flue and return tubular or leg boiler, and the Flue boiler' Fig. 11. Scotch Boiler, Longitudinal Section. as used on western river steamers. These are illustrated in Figs. 9-14. Water-tube boilers are found in great variety, depending on the details of arrangement of the tubes, and drums or head- ers of which they are composed. A few representative types are shown in Figs. 15-26. We will first give brief descriptions 5 o PRACTICAL MARINE ENGINEERING. of the important features of these boilers, and then take up at a later point the subjects of their design and construction. [i] The Scotch Boiler. In present practice, for marine purposes, the Scotch boiler is used more than any other one type, and, in fact, more than all other types combined. This boiler, as illustrated in Figs. 9, 10, ii consists essentially of a cylindrical shell containing one or more cylindrical furnaces, usually corrugated circumferentially for strength, opening into combustion chambers at the back end, from which a large number of small tubes lead again to the front end or head of the boiler. The grates are placed at about the center of the height of the furnace, and the fire and hot gases occupy the upper part of the furnaces, the combustion cham- bers, and the inside of the tubes, while the water and steam fill all the remaining parts of the shell, the water level being usually some 6 in. to 8 in. above the highest part of the tubes or combustion chambers. The hot gases pass from the fire on the grate-bars into the combustion chamber, thence forward through the tubes and out through the uptake or front-connection to the smoke-stack or funnel. Several varieties of this boiler are in common use. Thus the number of furnaces may be one, two, three, or four. They may be fitted with separate combustion chambers, or there may be one combustion chamber for all fur- naces, or, as is common with four furnaces, there may be two combustion chambers one for the two furnaces on either side. Again, the boilers may be single-end or double-end. Fig. 11 is an example of the first. A double-end boiler consists of two sets of furnaces opening from either end of a shell of double length. It is evidently equivalent to a pair of single-end boilers placed back to back with the back heads removed and the shells joined. Such boilers may also have either separate combustion chambers for each end, or a common combustion chamber for both ends. The former arrangement is to be preferred, and becomes necessary where forced draft is used. * [2] Direct Tubular Boiler, Gunboat Type. This boiler is rarely used except in war ship practice, where with low head room it has been occasionally employed. It con- sists of a shell with furnaces and combustion chamber some- what as in the Scotch boiler, but the tubes, instead of returning to the front, fead on to the farther head. To this head is fitted BOILERS. 51 a smoke-box or uptake leading to the funnel. In such cases the boiler for the same power is of smaller diameter and greater length than the Scotch type, and it is readily seen that the whole arrangement is simply a mode of exchanging diameter for length. [3] Direct Tubular Boiler, I/ocomotive Type. The locomotive type of marine boiler as illustrated in Fig. 12 consists of a cylindrical shell extended to the front and modi- Fig. 12. Locomotive Type Boiler. fied in form with flat sides and bottom, and flat or rounded top. The furnace is of rectangular cross-section, and is surrounded by the shell at the front, leaving on the sides a narrow space known as the water-leg and sometimes a like space underneath known as the water bottom. The gases take the same general course as in the gunboat type, the chief difference in the two being in the form of the furnaces and in the absence of the combustion chamber in the locomotive type. [4] The Flue and Return Tubular or I/eg Boiler. In this boiler, as illustrated in Fig. 13, the hot gases pass from the furnace through large tubes or Hues, as they are termed, to a combustion chamber at the farther end. They then return to the front through small tubes, and are led by an appropriate uptake to the funnel. The furnace is of rec- tangular cross-section, and the front end of the boiler is modi- fied on the sides and bottom to correspond to this form, as in the locomotive type. Water legs are also formed in the same way on the sides of the furnace, and from this feature the boiler receives its common name. This form of the front end of the boiler with flat sides and rounded top is sometimes known as a wagon-top. Very commonly, as shown in Fig. 13, an attachment to the shell, known as a steam chimney, surrounds the lower part 52 PRACTICAL MARINE ENGINEERING. of the funnel, the office of which is to subject the steam to the drying and superheating effects of the gases on their way Fig. 13. Leg Boiler. through the funnel. Boilers of this type have been used to a considerable extent on tug and river boats. [5] The Flue Boiler. In Western River practice use is quite commonly made of the return flue boiler as illustrated in Fig. 14. This boiler is externally fired. The flames and hot gases pass back along the outside of the boiler to a back connection and then enter the flues and return through them to the front, and thence to the uptake and funnel. Boilers of the locomotive type, or tubular fire-box boilers as they are often called, are also used to* a considerable extent in western river practice. BOILERS. 53 [6] Water Tube Boilers. Turning now to this type, a brief description will be given of the leading features, which may be combined in the greatest possible variety, thus giving the vast number of forms of such boilers on the market at the present time. To aid in the descrip- Fig. 14. Return Flue Boiler. tion a few typical forms of such boilers are shown in Figs. 15-26. Most boilers of this type have one or more cylindrical drums or chambers on top and one or more similar drums be- low, the two sets of drums being connected by sets of tubes. The feed usually enters first the upper drum, frequently passing on its way through a coil heater in the base of the stack or top of the boiler. It then flows down certain of the tubes to the lower drums. If these tubes are of extra large size and specially intended for down flow, the boiler is said to have special down flow or down cast tubes or pipes, as shown in Figs. 15, 16, 17, 18, 20. In some cases such tubes are omitted, and the feed must descend through part of the small inner tubes. In any case, after finding its way to the lower drum it enters the up How or steam forming tubes, which are surrounded by the hot gases coming from the furnace below them. During the passage of the water upward it is partly converted into steam, and the mixture issues from the upper end of the tubes into the upper drum. There the steam is separated and led to the engine, while the water joins that already in this drum, and thus begins another round. In some cases the upper ends of the steam forming or delivery tubes are below the level of the water in the upper drum, and they are then said to be drowned or wet. In other cases they are above the water level and are said to be dry. In still other forms they enter at about the middle of the drum or about the water level, and may be wet or dry as the level varies. See the various cuts for examples. Water tube boilers are often divided into two general classes : large tube and 54 PRACTICAL MARINE ENGINEERING. BOILERS. 55 56 PRACTICAL MARINE ENGINEERING. small tube boilers. In the former they are usually 3 or 4 or even 5 in. dia., while in the latter they are usually from ij4 to \y 2 or 2 in. dia. Again, the tubular elements may be made up in a great variety of forms. In some they are straight, in others curved, as shown in the various figures. In small tube boilers they are very commonly curved or bent, while in the large tube types they are straight. Also in some types the elements are con- tinuous between drums or headers as in Figs. 17, 18, 19, 20, while in others, as in Figs. 15, 16, 26, they are made up of lengths or of different parts with screwed joints, elbows, re- turns, junction boxes, etc. In some they are expanded into the shells of the drums ; in others screwed. In some all joints are carefully protected from the direct action of the flame ; in others screwed joints are freely exposed to the flame. In some the general direction of the tubes is nearly horizontal ; in others nearly vertical, and in others bent or curved in various forms. In some types, as illustrated in Figs. 24, 25, the lower drums are omitted, or consist merely of the lower portions of the tubes and headers, or members to which the tubes are connected. In all cases the grate lies below the tubes and frequently between the lower drums, as shown in the various figures, while the whole is surrounded by a casing intended to prevent, so far as possible, the loss of heat by radiation. [7] Relative Advantages of Different Types of Boilers. For large ships under ordinary conditions and where the extremes of lightness or of speed on a given displacement have not to be attained, the Scotch boiler seems at present to be considered as fulfilling most satisfactorily the all around re- quirements for a marine boiler, and in consequence it is found almost universally in the mercantile deep sea marine, as well as on the Great Lakes, and to a large extent on inland craft of all descriptions, except those of small size. It is also used to some extent in naval practice, though the use of water-tube boilers is at the present time extending quite rapidly into this field, where their special features become of marked value. The pres- ent is a time of change with regard to types of boiler. It is not too much to say that in most of the modern naval construc- tion the water tube boiler is accepted as the standard type to the exclusion of the fire-tube boiler. The water-tube boiler is also making large advances in the mercantile field, and not a BOILERS. 57 PRACTICAL MARINE ENGINEERING. BOILERS. 59 1 60 PRACTICAL MARINE ENGINEERING. few modern ships of the mercantile marine are now equipped with this type of boiler. For tugboats, river steamers, and a variety of small craft, the various types of direct fire-tube and flue boilers have been much used. These boilers are more readily adapted to a var- iety of demands regarding size, form and arrangement, and in small sizes are perhaps more cheaply built than Scotch boilers. In many cases, however, the preference for boilers of this type has doubtless depended on local and special conditions quite in- dependently of their relative value from the engineering stand- point. For fast yachts, launches, all craft of the torpedo-boat type, and in fact in all cases where the highest speed is to be attained on the least weight, the water-tube boiler has become a neces- sity, and in one or another of its many forms is universally em- ployed. The weight of Scotch boilers without water, per square foot of heating surface, is usually from about 25 to 30 Ib. ; of water-tube boilers of the lighter types from 12 to 20 Ib. The weight of the contained water per square foot of heating surface is usually from 12 to 15 Ib. for Scotch boilers, and from, say 1.5 to 3 Ib. for water-tube boilers. It results that Scotch boil- ers with water will weigh from, say, 35 to 50 Ib. per square foot of heating surface, while water-tube boilers will similarly weigh from 13.5 to 23 Ib. These figures are not to be considered as giving absolute limits, but simply as representative values for average types. It should be noted, however, that a square foot of heating surface in a Scotch boiler seems to be somewhat more efficient than in a water-tube boiler. It is difficult to es- timate the difference numerically, but other conditions being equal, it would probably be safe to give to the water-tube boiler additional heating surface to the extent of from ten to twenty per cent. On the other hand, it must be remembered that water-tube boilers can stand forcing to a much higher degree than fire-tube boilers. With the latter supplying steam to triple expansion engines the ratio of heating surface to I. H. P. can hardly be recluced below 2, while with the former this ratio has been reduced in many cases to less than one and one-half, and, as reported in certain extreme cases, to between one-half and one. Water-tube boilers have the further advantage that they are more readily constructed for the higher and higher steam BOILERS. 61 PRACTICAL MARINE ENGINEERING. BOILERS. 64 PRACTICAL MARINE ENGINEERING. pressure which modern practice is continually demanding. With water-tube boilers, due to the construction and to the smaller amount of contained water, there is also less danger from disastrous explosion. With water-tube boilers steam may be raised much more quickly than with fire-tube boilers ; from one-quarter to one-half hour is sufficient with the former, while from three to four hours should be taken with the latter. Water-tube boilers are also much more portable than fire- tube. In many forms spare parts or even the whole boiler may be shipped in elements or sections across country by rail or to Fig. 23. Lagrafel and D'Allest Boiler. foreign ports by ship transport, put on board the steamer for which they are intended, and erected in place without difficulty. On the other hand, the water-tube boiler imperatively re- quires fresh water feed. Under modern conditions this should be provided no matter what the type of boiler in use, but if in emergency salt water must be used, the fire-tube boiler will re- ceive the lesser injury. Again, from the small amount of water contained as a stock upon which to draw, the water-tube boiler requires a more uniform feed than the fire-tube boiler, and is generally more sensitive to variations in the conditions under which it works. Again, the rupture of a tube is a more serious BOILERS. Fig. 24. Babcock and Wilcox Boiler. ^"ESCAPE PIPE CARRIED AROUIfO SMOKE PIPE TO BE AFT OF IT ABOVE UPPtR OECK <>0 55 50 45 40 Fig. 25. Arrangement of Fireroom with Babcock and Wilcox Boilers. 66 PRACTICAL MARINE ENGINEERING. FEED OUTLET PROM ECONOMISER STEAM OUTLET FEED INLET TO BOILER AFTER LEAVING ** ^ ECONOMISER Fig. 26. Belleville Boiler. BOILERS. 67 matter in the water-tube than in the fire-tube boiler. In the latter it may be plugged without disturbing the water and steam in the boiler, and with only a momentary interruption to its operation. In the former it is usually necessary to disconnect the boiler, draw the fires, blow down the water, and plug or in- sert a new tube. Water-tube boilers are also not readily made in large sizes or units. Scotch boilers may be made in 2,000 horse power units or even larger, while half of this or less is about the maximum for the water-tube boiler. An outfit of the latter for large power requires, therefore, a large number of boilers with a corresponding increase in the fittings and attach- ments. On the other hand, the temporary removal of one boiler for repair is of less importance, as the size is decreased and number increased. To summarize the general comparison between water-tube and fire-tube boilers, the former have relative advantages in the following chief points : Weight, ability to stand forcing, suit- ability for high pressures, greater safety from disastrous explo- sion, and quickness of raising steam. On the other hand they have relative disadvantages in these points : A more rigid re- striction of the feed to fresh water, the necessity of greater regularity of feed, greater difficulty in dealing with leaky tubes, and general sensitiveness to variation in the conditions of use, to which may be added the present feeling of uncertainty as to their durability and efficiency under the conditions prevailing on deep water voyages. Sec. 15. RIVETED JOINTS. The various joints in a boiler are usually of the riveted form. The use of welded joints in various parts of boiler con- struction is increasing somewhat as greater skill is acquired in making them, but in ordinary practice the joints are riveted, and of various types, as follows : Riveted joints are divided into lap joints and butt joints, according as the plates lap over each other (see Figs. 31-34), or butt together at the edges, and are covered by one or two butt straps (see Figs. 35-39). They are also divided according to the number of rows of rivets into single, double or triple riveted joints (see Figs. 31-33). The rivets are usually staggered in arrangement, as shown in Figs. 32-39. Sometimes, though rarely, the chain arrange- 68 PRACTICAL MARINE ENGINEERING. ment, as shown in Fig. 27, is used. While chain riveting is as strong, or ( perhaps even slightly stronger, than staggered rivet- ing, the latter gives a better disposition of rivets for making a steam or water-tight joint, and this fact leads to its more fre- quent use in boiler construction. In butt joints the arrange- ment of rivets is duplicated on each side of the joint, and the style of riveting is named according to the arrangement on one side. Thus, Fig. 35 shows a double-riveted and Fig. 36 a triple- riveted butt joint. A riveted joint may fail : (i) In the plate by tearing out or across from hole to hole, see Figs, 28, 29; (2) In the rivet by shearing; (3) in the plate or rivet by a crushing of the material. Fig. 27. The failure of a joint by the tearing out of the plate in front of the rivet, as in Fig. 29, is safely guarded against by placing the row of rivets at a proper distance from the edge of the plate. This, by experience, is found to be about one diameter in the clear, or one and one-half diameters from edge of plate to center line of rivets. In lap joints and butt joints with one cover, as in Fig. 30, the rivets resist shearing at one section only. In butt joints with double covers, as in Figs. 35-38, the rivets re- sist shearing at two sections. The total shearing strength of a rivet in double shear is usually taken as somewhat less than twice the strength in single shear. The British Board of Trade rules give ij4 as the ratio to be used. With usual proportions the last mode of failure mentioned above is the least likely to occur, so that so long as the proper limits are not exceeded the resistance to crushing needs no es- pecial examination. These limits will be given in detail at a later point. The strength of a riveted joint is, of course, determined by BOILERS. 69 whichever is the weaker of the two, the plate or the rivets. In a properly designed joint the strength of the plate and that of the rivets should be equal, so that there will be no more likeli- hood of failure in one way than the other. It may be remarked, however, that since corrosion usually affects the plate only, it is often considered good practice to give to the plate a slight ex- Fig. 28. Fig. 29. cess of strength, so that even after some wasting by corrosion the joint may still be in fair proportion as to the relative strength of plate and rivets. No exact directions can be given for this increase, as it is simply a matter of judgment. The investigation of the strength of riveted joints by any simple theory is necessarily quite imperfect, because we do not know in just what way the stress is distributed through the re- maining part of the plate, nor through the section of the rivet, Fig. 30. nor what allowance to make for the frictional grip of the joint. The proportions given by the following equations, however, are those which will give practically equal strength of plate and rivets, using the British Board of Trade rules. These rules represent standard and reliable practice, based on wide experi- ence, and are substantially adopted by the United States inspec- tion authorities. In thus considering a joint we take simply an element such as that between AB and CD in the following diagrams. It is clear in each case that the whole joint may be considered as made up of a series of such elements : PRACTICAL MARINE ENGINEERING. Let p denote the pitc h of the rivets : that is, the distance from center to center. Where the rivets in one row are pitched twice as far apart as in another (see joints D, H, etc.), p denotes the larger of the two values. " d denote the diameter of rivet. * " n =: p -r- d = number of rivet diameters in the pitch. " t = thickness of plate. a = t + d. " T = tensile strength of plate per square inch of section. " S = shearing strength of rivet per square inch of sec- tion. The ratio of 5 to T is taken as 23 : 28 or 5" = .821 T. The efficiency of the joint is the ratio between the strength of the joint and the original strength of the plate. It will be seen by the formulae given later that the efficiency of a joint is increased as d and p are made larger. There is, however, a practical limit to the increase in d, due to the difficulty of head- ing up very large rivets, and a limit to the increase in p, due to the necessity of guarding against leakage. If the general pro- portions between d and /, as indicated later in connection with the various joints, are observed, the result will be a pitch within safe limits, and a joint agreeing well with the best practice. The largest permissible values of the pitch, according to the Board of Trade rules, are given by the following formula : p = Ct + if where C is drawn from the following table : FORM OF JOINT AS SHOWN BELOW. C FORM OF JOINT AS SHOWN BELOW C A I "*! F 463. B 2 62 G 5C2 C 7 47 H 6 oo D 4. 14 I 6 oo E i CQ In no case should the pitch exceed 10 inches. We will now proceed with the equations and proportions for various forms of riveted joints. * Strictly speaking the diameter of the rivet hole should be used, as it is about 1-16 inch larger than the rivet before heading up. In the Board of Trade Rules, however, the diameter of rivet is used. The difference in proportion of joint is quite small, and probably not of practical importance. Joint A. BOILERS. Lap Joint. Single Riveted. h h Q Q P i E Fig. Z r 1. Joint D ' A. ) B 3 d The element is A B D C, containing one rivet. We have in this case : Strength of Plate = t (p d) T Strength of Rivet = $xd 2 S For equal strength of plate and rivet, --or;/= i + -645-7 Efficiency = n i 645 a -f- .645 The ratio d -r- t may vary from 1.5 to 2.5, the lower values being more commonly employed with very thick* plates on ac- count of the difficulty of heading up excessively large rivets, and the necessity of a moderate pitch to insure against leakage. In order, furthermore, to guard against danger of rupture by crushing, the upper limit, 2.5, should not be exceeded. The foregoing operations may be expressed also by the following : Rule, (i) Select a diameter of rivet according to the thick- ness of the plate and the directions given. (2) Multiply this diameter by .645 and divide by the thickness of plate. (3) Add i to the result obtained in (2). (4) Multiply the diameter of rivet by the result ob- tained in (3), and the result will be the pitch suited to the diameter chosen. 72 PRACTICAL MARINE ENGINEERING. (5) Select the nearest working dimension, going usually above in order to give slight excess of strength to the plate. (6) To find strength of plate in the joint, subtract the diameter of rivet from the pitch, multiply by the thickness and by the tensile strength per square inch of section. (7) To find strength of rivet, find area of section, multiply by the same strength per square inch as in (6), and then by .821. (8) To find original strength of plate multiply pitch by thickness of plate, and by the tensile strength per square inch, as in (6). (9) To find the efficiency, divide the lower of the two results found in (6) and (7) by that found in (8). Example. To lay out a single riveted lap joint for J/ inch plates, using % inch rivets. Then 7/e X .645 -*-*== 7 X '^ X ' = 1.13 O And 1.13 + i.oo = 2.13. And 2.13 X J = 1.86 = pitch. Take the nearest eighth above and we have pitch = i% inch. Then taking strength of plate at 60,000 Ibs. per square inch we have : Strength of Plate in Joint =(ij J) X -J X 6,000 = 30,000. Area of inch rivet = .60 sq. in. Strength of rivet = .60 X 60,000 X -82! = 29,550. Original strength of plate = if X -J X 60,000 = 56,250. Efficiency = 29,550 -f- 56,250 = .525. Similarly, if we should take 15-16 inch rivets, we should find for equal strength in plate and rivet a pitch of 2.07 inches. If we take a pitch of 2 T / 8 inches we shall find an efficiency of .533. If we take the 2.07 exact the efficiency will be .548. Joint B. BOILERS. Lap Joint. Double Riveted. 73 Fig. 32. Joint B. q not less than (. 6 / -|- . 4 d~} Hence H not less than y (i. i / -1- .4 d) (. i / -f .4 d) Where there are two or more rows of rivets they must be placed at a sufficient distance apart, so that there may be no danger of rupture along a zig-zag line, as indicated in the di- agram. To this end the British Board of Trade rules give cer- tain values for the distance q as given above for this case. This distance is known as the diagonal pitch. The rules are derived from experiment. The distances resulting may be considered as the smallest allowable. In practice the values of q are often made somewhat greater than would result from the rules. Having selected the distance q, the location of the second row of rivets is easily found from the first by constructing a triangle with base equal to />, and the two other sides each equal to q. In this case the element A B D C contains one whole rivet and two halves, or two rivets in all. We have then : Strength of Plate t (p d) T Strength of Rivets = y*7td*S For equal strength of plate and rivets : - -,- or n = i + i. 29 Efficiency = n i 1.29 a -f- 1.29 The values of d -.- t may vary through about the same range as in joint A, above, and for the same reasons as there 74 PRACTICAL MARINE ENGINEERING. explained. These operations may be expressed by a rule similar to that for joint A, the numbered sections referring to that rule as given above : Rule: (1) Same as for joint A. (2) Use 1.29 instead of .645. (3), (4), (5), (6) Same as for joint A. (7) Take twice the strength of one rivet, found as for joint A. (8), (9) Same as for joint A. Example. To lay out a double riveted lap-joint for y 2 inch plates, using J4 inch rivets. Then % X 1.29 *- % = 3 X 1 '' 9X 2 = 1-935 4 And 1.935 + LOO = 2.935. And 2.935 X f = 2.201 = pitch. Taking the nearest eighth above we have p = 2^4 inches. Then taking strength of plate at 60,000, we have : Strength of plate in joint = (2j - - f ) X i X 60,000 = 45,000. Area of J4 mcn rivet = .4418 sq. in. Strength of rivets = .4418 X 2 X 60,000 X -821 = 43,520. Original strength of plate = 2.\ X 4 X 60,000 = 67,500. Efficiency = 43,520 -f- 67,500 = .645. Similarly with % inch rivets, pitched 2% inches, the strength of plate and rivets will be nearly equal, and the effi- ciency will rise to .687. Joint C. Lap Joint. Triple Riveted. h = a d q not less than (.6/ -}- .4^) Hence //"not less than y (i. i / -f .4 -f .4 <^) B = 3 rf + 2 // In this case the element A B D C contains two whole rivets and two halves, or three rivets in all. We have then : Strength of Plate t (p d) T Strength of Rivets %nd*S For equal strength of plate and rivets : BOILERS. P d -or n = i -r- 1.935 75 "R flfi r* i i^n r\7 ?35 ^_ AC -935 t P 11 Q' /~ t i C ** \ --^7- ^ B r H X Q v /\ *s, r 11 h i U i 11 ;.__ p ^ I Fig. 33. Joint C. The values of d -r- t may vary through about the same range as in joint A, above, and for the same reasons as there explained. These operations may be expressed by a rule sim- ilar to that for joint A, the numbered sections referring to that rule as given above. Rule : (1) Same as for joint A. (2) Use 1.935 instead of .645. (3), (4), (5), (6) Same as for joint A. (7) Take three times the strength of one rivet found as for joint A. (8), (9) Same as for joint A. Example. To lay out a triple-riveted lap-joint for y 2 inch plates, using 1/4 inch rivets. 3 X 1-935 X 2 Then ^ X i-935 =2.903 And 2.903 -h i. oo = 3.903. And 3.903 X f = 2.93 inches = pitch. Take p = 3 inches. Then taking strength of plate at 60,000, we have : Strength of plate in joint = (3 3) X i X 60,000 = 67,500. Area of ?4 inch rivet = .4418. Strength of rivets = .4418 X 3 X 60,000 X -821 == 65,280. Original strength of plate 3 X X 60,000 = 90,000. Efficiency = 65,280 -f- 90,000 .725. PRACTICAL MARINE ENGINEERING. Similarly with % inch rivets, pitched 3% inches, the effi- ciency becomes .764. Joint D. Lap Joint, inner row spaced one-half p. Triple Riveted, with rivets in h -4- H "I" 1 H -i- mi II a^St/7/ _.^5? Fig. 34. Joint D. h = q not less than (.$/ + d) Hence H not less than -\/ (. 5 5 / -f d} (. 05 p -\- d) B = 3 d + 2 H As seen below, the efficiency of this joint is superior to that of joint c, but it is perhaps slightly inferior as regards tightness against leakage. We have in this case : Strength of Plate t (p d) T Strength of Rivets = xd 2 S For equal strength of plate and rivets : P or n Efficiency = n i 2.58 a + 2.58 The values of d -T- t may vary through about the same range as in joint A above, and for the same reasons as there explained. These operations may be expressed by a rule sim- ilar to that for joint A, the numbered sections referring to that rule as given above. Rule : (1) Same as for joint A. (2) Use 2.58 instead of .645. (3)i (4), (5) ( 6 ) Same as for joint A. BOILERS. 77 (7) Take four times the strength of one rivet found as for joint A. (8), (9) Same as for joint A. Example. To lay out a triple-riveted joint as in D for l / 2 inch plates, using % inch rivets. Then % X 2.58 % = 3J< 2 -5* X 2 = ^ 4 And 3.87 + i. oo = 4.87. And 4.87 X t = 3.65 inches = pitch. Take p = 3 11-16 inches. Then /> = i 27-32 inches. Then taking strength of plate at 60,000 we have : Strength of plate in joint = (3---- J) X i X 60,000 = 88,125. Area of f inch rivet = .4418. Strength of rivets = .4418 X 4 X 60,000 X -821 =. 87,050. Original strength of plate 3--X i X 60,000 = 110,625. Efficiency = 87,050 -r- 110,625 = .787. With % inch rivets spaced 2 7-16 inches in the middle row and 4% in the outer rows, the strength of plate and rivets would be nearly equal, and the efficiency would rise to .81. Joint E. Double Butt-Straps. Double Riveted, h = ij d q not less than (.6 p -f- .4 d) Hence //"not less than j/ (i. i / 4. .4 d) (. i / -j- .4 d) B = 6 d + 2 H. Thickness of each butt-strap not less than ^ the thickness of plate. The arrangement of rivets is duplicated on either side of the joint line P Q. We need only to investigate the part of the joint on one side of P Q. The element is then A B D C, as in joint B, except that the rivets are in double shear instead of single shear. For the total shearing strength of a rivet in double shear, as previously explained, it is customary to take 1 24 times the strength for single shear instead of 2 times, or to take the two strengths in the ratio 7 : 4. We then have : Strength of Plate t (p d) T Strength of Rh'cts = Ind'S PRACTICAL MARINE ENGINEERING. For equal strength of plate and rivets : -^-or ;/ = i 4- 2.26- d t n i 2.26 Efficiency 2.26 I If ^ Fig. 35. Joint E. In all double butt-strap joints d -i- / usually varies from i to ij4- The lower range of values, as compared with joints in which the rivets are in single shear, is required in order to in- sure the joint against danger of failure by crushing. These operations may be expressed by a rule similar to that for joint A, the numbered sections referring to that rule as given above. Rule : (1) Same as for joint A. (2) Use 2.26 instead of .645. (3)> (4) (5) (6) Same as for joint A. (7) Take 35^ times the strength of one rivet, as found for joint A. (8), (9) Same as for joint A. Example. To lay out a joint as in E for I inch plates, using ij/s inch rivets. Then ij X 2.26 -5- i = 9X2 ' 26 = 2.54. o And 2.54 + i = 3.54. And 3.54 X-f-== 3.98 inches = pitch. Take pitch = 4 inches. BOILERS. 79 Then taking strength of plate at 60,000 Ibs., as before, we have: Strength of plate in joint = (4 - - ij) X I X 60,000 172.500. Area of i-J inch rivet -994- Strength of rivets = .994 X 3i X 60,000 X ,821 = 171,350. Original strength of plate = 4 X i X 60,000 = 240,000. Efficiency = 171,350 -=- 240,000 = .714. Similarly with i inch plates and \ l /\ inch rivets, pitched 4^4 inches, the strength of plate and rivets will be about the same, and the efficiency is .737. oint F. Double Butt-Straps. 7 >/>/< R '/ z/^ I n n n c '/f 1 1 ^ ^ ^ ^ _A__ ..C c J -- -, i q' H B c i ^ 1 ^g . -^ .^. ^ ^ q H h c i 1 11 1 Fig. 36. Joint F. k Ij d q not less than (.6 p -f- .4 d) Hence H " " " i/(i.i/ + .4 (4), (5), (6) Same as for joint A. (7) Take ^/\ times the strength of one rivet, as found for joint A. (8), (9) Same as for joint A. Example. To lay out a joint as in F with I inch plates , using i 3-16 inch rivets. Then i -i. X 3-39 - i = And 4.03 + i = 5.03. And 5.03 X I -|-= 5-97 inches = pitch. Take pitch = 6 inches. Then with strength of plate at 60,000, as before, we have : Strength of plate in joint = (6 - - i-^-) X i X 60,000 = 288,750. Area of i- 3 -inch rivet = 1.108. 16 Strength of rivets = 1.108 X 5l X 60,000 X -821 =286,500. Original strength of plate 6 X i X 60,000 = 360,000. Efficiency = 286,500 -f- 360,000 = .796. BOILERS. Joint G. Double Butt-Straps. Rivets as in Joint D. 81 c: c d ; g IP I I 1 Fig. 37. Joint G. A = Ij rf <7 not less than (.3 /> -f 5/ + <0 5 = 6 rf + 4 //. Butt-straps to be of thickness not less than as given by the formula : Thickness of strap == g 5 , ~ , X (thickness of plate) 5 (/ 2ft) The element of the joint is A B D C, as in joint Z), except that the rivets are in double shear. Taking, as before, the strength in double shear to that in single shear in the ratio 7 : 4, we have : Strength of Plate t (p d) T Strength of Rivets =^-nd 2 S . For equal strength of plate and rivets : A or + 4-52 Efficiency = 52 82 PRACTICAL MARINE ENGINEERING. In this joint d -f- t usually varies from about I to ij4, as explained for joint E. These operations may be expressed by a rule similar to that for joint A, the numbered sections re- ferring to that rule as given above. Rule : (1) Same as for joint A. (2) Use 4.52 instead of .645. (3), (4), (5), (6) Same as for joint A. (7) Take 7 times the strength of one rivet, as found for joint A. (8), (9) Same as for joint A. Example. To lay out a joint as in G with i l / 2 inch plates, using i^i inch rivets. Then ,| X 4.52 -H ii = I3 X */' X -'- 4-9 X 3 And 4.9 + i = 5.9. And 5.9 X i f = 9-6 inches = pitch. Take pitch for outer rows 9^3 and for inner rows 4-||- Then, with strength of plate at 60,000, we have : Strength of plate in joint = (9f - - i J) X ij X 60,000 = 731^50- Area of iJ/ inch rivet = 2.074. Strength of rivets = 2.074 X 7 X 60,000 X -821 = 715,200. Original strength of plate = 9! X ij X 60,000 = 866,250. Efficiency = 715,200 -r- 866,250 = .826. Joint H. Double Butt-Straps. Triple Riveted, with double spacing in outer row on each side. h = ij d q not less than .3 p -f- .4 d g, " " " -3/ + ^ Hence H ^(.55 p + .4^) (.05 /> + .4 Thickness of butt-straps found by same formula as for joint G. The element of the joint is A B DC, containing four whole rivets and two halves, or five in all. These are all in double BOILERS. shear. Taking, as before, the strength in double shear to that in single in the ratio 7 : 4, we have : Strength of Plate = t (p d) T Strength of Rivets = -2|_;r d 2 S For equal strength of plate and rivets : p d -^-or= i + 5.64 Efficiency n i 5.64 n ~ a 4. 5.64 h 't H --*< H, m- h p Fig. 38. Joint H. In this joint d-- t usually varies from i to i%, as explained for joint E. These operations may be expressed by a rule sim- ilar to that for joint A, the numbered sections referring to that rule as given above. Rule : (1) Same as for joint A. (2) Use 5.64 instead of .645. (3). (4), (5) ( 6 ) Same as for J int A - (7) Take 8^4 times the strength of one rivet, as found for joint A. (8), (9) Same as for joint A. Example. To lay out a joint as in H with i^J inch plates, using I 7-16 inch rivets. 84 PRACTICAL MARINE ENGINEERING. And 5.9 + i = 6.9. And 6.9. + i -^-= 9.92 inches =. pitch. The limiting pitch by the. Board of Trade rule for this case would be 9.87. This means that a pitch of 9.92 or larger would not be passed without special permission. If necessary to re- duce below the limit, the joint should be re-designed with a smaller rivet. This case illustrates the point that these limiting values of the pitch, if rigidly adhered to, would prevent the at- tainment of the best joint efficiencies with thick plates. We shall here assume the right to proceed with the pitch derived from the formula which we will take as 10 inches for the outer and 5 inches for the inner rows. Then taking strength of plate at 60,000 we have : Strength of plate in joint = (10-- i-) X if X 60,000 = 706,400. Area of i-- inch rivet = 1.623. Strength of rivets = 1.623 X 8f X 60,000 X -821 =699,600. Original strength of plate = 10 X if X 60,000 = 825,000. Efficiency = 699,600 -r- 825,000 = .848. Joint I. Double Butt-Straps. Triple Riveted, outer row on each side being double spaced, and passing through inside butt- strap only. h=i$d q not less than .3 p + -4 d _ Hence H " " " T / (.55 p + .4 d ) (.05^ + .4 d) 11 #i" " " i/(-55/ + ^)(-o5/ + ^) B=6d+ 2 H ,= 64+ 2 H+ 2 H, Thickness of butt-straps found by same formula as for joint G. The element of this joint is A B D C, with four rivets in double shear and one in single shear. Taking, as before, the strength in double shear to that in single in the ratio 7 : 4, we have: Strength of Plate t (p d) T Strength of Rivets = 2 xd 2 S For equal strength of plate and rivets, we have : BOILERS. 85 / <: d -^- or;/=i -f 5.16 Efficienc " i 5.16 a 4- 5- 16 t [ ^ B, * 1 E P A CO H q H, i "q, \*m 1 fr (.-- _.n__ --H, t 1 ! ( 1 i ^ > k \ I :( i \ B, I 11 c \ 1 1 ^ f I + 1' 1 1 ^ Fig. 39. Joint I. In this joint d -f- t usually varies from I to 1^4, as explained for joint E. These operations may be expressed by a rule sim- ilar to that for joint A, the numbered sections referring to that rule as given above. Rule: (1) Same as for joint A. (2) Use 5.16 instead of .645. (3)> (4), (5), (6) Same as for joint A. (7) Take 8 times the strength of one rivet, as found for joint A. (8), (9) Same as for joint A. Example. To lay out a joint as in I with i^ inch plates, using i 7-16 inch rivets. Then i-- x 5> l6 -^ 23x5.16x8 16 ii o And 5.40 + J = 6.40. And 6.40 X i -^- = 9- 2 inches = pitch. 86 PRACTICAL MARINE ENGINEERING. We will take 9^ for pitch of outer row, and hence 4^ for pitch of inner rows. Then, taking strength of plate at 60,000, we have : Strength of plate in joint = (9^ l^-) X if X 60,000 = 644,530. Area of i-^- inch rivet 1.623. Strength of rivets = 1.623 X 8 X 60,000 X -821 = 639,600. Original strength of plate = 9J X if X 60,000 = 763,125. Efficiency = 639,600 -f- 763,125 = .838. An examination of the values of the efficiency will show that these various joints for the same value of d ~- t stand, in this respect, in the order : H, I, G, F, D, E, C, B, A. Sec. 16. MATERIALS AND CONSTRUCTION. [i] Materials. Open hearth mild steel is used almost universally as the material for boiler construction, and in standard practice is used exclusively for shells, drums, heads, furnaces, combustion chambers and braces. Both steel and wrought iron are used for tubes, though solid drawn steel tubes may be considered as the better representing advanced engineering practice. Wrought iron is also used to some extent for rivets, though in the best modern practice steel rivets are preferred. [2] Joints. The various plates of a boiler are fastened together by riveted joints. These are of several varieties, as discussed in Sec. 15, and to which reference may be made. The holes in the plates are either drilled or punched. The former method is much the better. In the operation of punch- ing, a thin skin of metal about the hole is so severely strained that its strength, and especially its ductility and toughness, are reduced far below what they are in the remainder of the plate. This is not the case with the operation of drilling, or, at least, not to anything like the same extent. Drilled holes may also be located more accurately than punched holes, and thus with the former the parts of a riveted joint may be more perfectly fitted than with the latter. The operation of drilling leaves, BOILERS. 87 however, a sharp edge, which should be removed by a reamer in order to avoid any tendency to cut the rivet. In spite of the greater cost of drilled holes they are now generally accepted as the best for all high-class work, and in many specifications no holes are allowed to be punched. Riveting is either by hand or by machine ; usually hy- draulic. The latter gives much the better result, and is pre- ferred where the machine can be made available. In many cases the construction is such that the jaws of the machine cannot be brought to bear on the joint, and in consequence hand riveting must be employed. After being riveted the joints are calked to insure tightness against leakage. This operation consists in beating down the edges of the metal against the face of the opposite plate by means of special pneumatic driven or hand tools, as shown in Fig. 40. These are known as calking tools, and are of two \ \ \ Fig. 40. Calking Tools. types, square and round nosed, as shown in the figure. The latter form is usually employed in modern practice. For op- erations on board ship the common hand tool is, of course, most commonly used ; but for extensive calking, as in the con- struction of boilers in the shop and where compressed air is available, the pneumatic driven tool is very largely displacing the hand tool. [3] Construction of Fire-Tube Boilers. We will now consider the chief features of the construction of a Scotch boiler. This will, at the same time, sufficiently il- lustrate the operations involved in the construction of other types of fire-tube boilers. In the best practice the longitudinal joints are double butt- strapped and triple-riveted in order to give to the boiler in this direction the highest possible proportion of the strength of the plate itself. The circumferential joints, those which run around the shell, are lapped and double or triple riveted. So far as in- 88 PRACTICAL MARINE ENGINEERING. ternal pressure is concerned the boiler is twice as strong to re- sist rupture around the girth as lengthwise so that a lapped cir- cumferential or girth joint is quite enough for strength alone, and it only remains to make it steam and water tight and to in- sure the necessary stiffness of the boiler as a whole. (See Sec. 63.) Single-ended boilers are usually made with two courses of plates, as in Fig. n. Double-ended boilers are usually made with three courses. Each course consists of two or three sheets, varying with the diameter of the boiler. The heads are flanged, as shown in Fig. u, and thus secured by riveting to the shell. In some cases the shell has been flanged instead of the head, but such form of construction is rare. The head flanges are sometimes turned out, and sometimes in, as shown by the figure. Where machine riveting is to be used they must be turned out in order to allow the riveter to do its work. The back head is made usually in two pieces, with double or triple- Fox. Purves. Morrison. Fig. 41. Styles of Corrugation. riveted lap joints. The front head is made in two or three pieces, according to size of boiler, usually with double-riveted lap joints. The furnaces, as shown, are corrugated in order to give greater strength and elasticity. There are three styles of cor- rugation in common use, as shown in Fig. 41. The furnaces are riveted to flanges formed on the front furnace sheet, and are connected by flanging to the sheets of the combustion chamber. Several different modes of connection are in use for this pur- pose. In one the furnace end is left plain and the flange is all on the combustion chamber sheet, as in Fig. 9. In another the combustion chamber sheets are left plain and the flange is on the furnace, as shown in Figs, u, 42, 44. In some forms pro- vision is made for removal and renewal without disturbing the furnace head sheets. Thus, in Fig. 9 the diameter at the front BOILERS. is the same as, or slightly larger, than that on the outside of the corrugations, and so the furnace may be withdrawn through the opening in the front sheet. In other forms of connection, where the furnace is flanged, especial provision must be made for removal, as shown in Fig. 43. Here the back end of the furnace is necked in on the bot- tom and sides, and a flange is thus obtained which only extends outside the outer diameter of the corrugation at the top. This Fig. 42. Flanged Furnace. flange serves to attach the furnace to the combustion chamber, and on cutting the joint loose the furnace may be taken straight to the front until the upper flange strikes the front sheet, and then swung upward and out of the front opening, as may be readily seen. In some cases where it is difficult to obtain the necessary room on the front head for the greater diameter of the outside Fig. 43. Removable Furnace. of the corrugation, or where, for other reasons, it is not con- sidered preferable to have the furnaces removable without dis- turbing the front sheet, the furnace end at the front runs out on the smaller diameter, as shown in Fig. 44. Some one of the forms favoring easy removal may be recommended as prefer- able in all ordinary cases. The combustion chamber, as shown, is built up of steel plates flanged and riveted together. The details of the con- PRACTICAL MARINE ENGINEERING. stniction vary somewhat with the form of furnace attachment adopted, with the size of the boiler, and with the choice of the designer. The front plate is known as the back tube sheet. The top of the combustion chamber is sometimes flat, as in Figs. 9, 65, and sometimes rounded up, as in Figs, n and 45. Fig. 44. Non-Removable Furnace. The tubes are secured into the tube sheets by "expanding," and "beading" or turning over at the back or at both the back and front ends. See Figs. 46, 47, 48. Tubes are expanded by means of a tool as shown in Fig. 49, representing the Dudgeon expander. The tool is introduced into the mouth of the tube and the small steel rolls are forced out by means of the tapering steel mandrel on which they rest. The mandrel is then turned Fig. 45. Rounded Top Combustion Chamber. around, and this by means of the frictional contact with the rolls causes them to turn also, and thus to roll around on the inner surface of the tube, carrying the whole tool slowly round and round. The mandrel is continually forced in and thus the rolls are forced otitward against the tube. The action is thus a roll- BOILERS. ing of the tube out against the tube sheet, and in this way the joint is made thoroughly tight. The Prosser expander, which was generally employed in former years, is now but rarely used. It consists, as shown in Fig. 47. Tube End. Fig. 46. Tube End. Fig 50, of a hollow tapering plug divided up into separate ele- ments or sections which are held together by a steel band. These are forced outward against the inner surface of the tube by driving a. taper mandrel into the hollow between the ele- Fig. 48. Tube Ends. ments. The action of the expander is thus to force the metal of the tube out against the edges of the sheet in a form of cir- cular ridge as shown in Fig. 46. Beading over the tube ends is usually done with a tool, as Fig. 49. Roller Tube Expander. shown in Fig. 51, and the result is as shown in Figs. 46-48. In some cases the tube sheet is recessed out for the beaded end of the tube, as shown in Fig. 47. The front ends of the tubes, as shown in Fig. 48, are usually swelled slightly larger than the rear ends to facilitate removal. The thickness of the metal of plain 92 PRACTICAL MARINE ENGINEERING. boiler tubes is usually from 8 to 12 wire gauge, or from about .17 to .10 in. In addition to the plain tubes fitted as before described, Fig. 50. Prosser Tube Expander. stay-tubes are also frequently fitted. These are of extra heavy metal, usually about % m - thickness, and specially fitted to the Fig. 51. Beading Tool. tube sheets by screw joints, as shown in Fig. 52. These tubes act as stays between the tube sheets. Further reference to this Fig. 52. Stay Tube with Ferrule. point will be found under the head of bracing. When stay tubes are fitted, it is customary to bead over only the back ends of the plain tubes, as in Fig. 48. Not infrequently, however, no stay tubes are fitted, and in such case the plain tubes must be beaded over on both ends in order that they may securely sup- BOILERS. 9.3 port the tube sheets. Instead of the ordinary form of boiler tube, the Serve tube of cross-section, as shown in Fig. 53, is frequently fitted. The ribs of metal reach down into the column of hot gas moving through the tube and furnish additional sur- face to absorb the heat and help it through into the water. The surface on the fire side is thus much greater than the surface on the water side, while with the plain tube it is somewhat less. Fig. 55. New Admiralty Ferrule. Fig. 53. Serve Tube. Such tubes usually show an increased evaporation per square foot of surface measured on the water side, of from 15. to 20 per cent. Their increased weight, however, offsets in a measure this increase of evaporative efficiency per square foot of surface. Reference may also be made at this point to the use of re- tarders in boiler tubes. These are long twisted strips of thin sheet steel, as shown in Fig. 54. They are simply laid in the tubes and serve to give the gases more or less rotary motion Fig. 54. Retarder. and to assist in throwing them outward against the surface of the tube. With forced draft and high rates of combustion the use of retarders has been accompanied with a marked increase of economy. In some cases both Serve tubes and retarders have been fitted, but the special advantages of the combination may be called in question. As a measure of protection for the back ends of tubes un- der forced draft, cast iron ferrules are sometimes fitted. Fig. 94 PRACTICAL MARINE ENGINEERING. 52 shows the so-called Admiralty ferrule in place in a stay tube. In Fig. 55 is shown an improved type of ferrule which by rea- son of the air space is believed to act still more efficiently to protect the tube sheet than the form shown in Fig. 52. Bracing. We must now consider the bracing needed to make the boiler perfectly secure and safe under the pressures Fig. 56. Adamson Ring. Fig. 57. Bowling Ring. to which the various parts will be subjected. The general prin- ciples to be kept in mind are as follows : (a) Cylindrical surfaces subjected to pressure on the concave side are not helped by bracing. They must be made sufficiently strong by giving to the material a suitable thickness, (b) Cylindrical surfaces sub- jected to pressure on the convex side may be stayed like a flat Fig. 58. Main Head Brace. surface, or they may be stiffened by ribs running around them in planes at right angles to the axis, (c) Flat surfaces will sup- port themselves if their area is sufficiently small in relation to their thickness and to the load per square inch, and it follows that large, flat surfaces must be sub-divided into parts of such size that they may thus become self-supporting. BOILERS. 95 As an illustration of (b), furnaces were formerly strength- ened in this way, and the long favorite Adamson ring, as shown in Fig. 56, or the Bowling ring, as shown in Fig. 57, may be taken as good illustrations of this mode of adding support to cylindrical surfaces loaded .on the convex side. The present corrugated furnace, especially the Purves type, as shown in Fig. 41, may be considered as a further illustration of the same prin- ciple. In modern marine boilers, aside from the furnaces, this mode of support is chiefly used to stiffen the bottom of single combustion chambers where screw stay bolts could not be read- ily fitted, and also in some cases the curved tops of combustion chambers. See Fig. 45. Coming next to flat surfaces as referred to under (c), the necessary sub-division is provided by the fitting of braces con- necting the part to be supported to some point where the sup- port can be provided, or by connecting together two surfaces urged by the steam pressure in opposite directions, as for ex- ample the two opposite heads of a boiler, as shown in Figs. 9, ii. Occasionally also flat surfaces are aided by attaching to them stiffening ribs of angle or tee bar, as on the front tube sheet, between the nests of tubes, or between the tubes and the shell. Plates which are subjected to the direct action of the fire, as in the furnace and combustion chambers, are made relatively thin. This is done because a thin plate transmits heat better than a thick one, and is subjected to less severe internal stresses due to the difference in temperature of its two faces. The thin- ner the plate, however, the less the area which will be self sup- porting. Hence the braces for thin flat plates are relatively small and closely spaced, while those for thick plates are larger and spaced at greater intervals. The main head braces are secured as shown in Fig. 58. A washer is fitted on the outside to increase the supported area, and a nut is fitted both inside and outside so that the joint may readily be made tight, and that the brace may, if needed, act as a strut against pressure from without as well as a tie against pressure from within. In some cases a relatively thin plate is supported by a brace connecting it to a thicker or perhaps to a double plate, or to a place not requiring support itself, but which furnishes a convenient point for carrying the load. In such case the attachment to the thin plate is often made, as shown in 96 PRACTICAL MARINE ENGINEERING. Fig. 59, in order the better to sub-divide and distribute the sup- port. In double-ended boilers, certain parts of the head, as for example those between the furnaces, are supported by braces running obliquely back to the shell and attached as shown in Fig. 60. It often thus happens that braces must run at a slight obliquity in order to connect the parts to be sup- ported with convenient points of support. Other instances are Fig. 59. Forked End Brace. often found in the braces connecting parts of the back tube sheet below or between the tubes to the boiler head. In all such cases, wedge-shaped washers, as shown in Fig. 61, must be fitted under the nuts in order to get a good bearing between the nut and the shell. The braces connecting the relatively thin plates of the com- bustion chamber to the back head and shell of the boiler and to BOILERS. 97 each other, are fitted by screwing them through into both plates, as shown in Fig. 62. The ends are sometimes riveted over and sometimes fitted with nuts. In some cases thev are left thread- OO| o oj Fig. 60. Flange Foot Brace. ed the entire length, in others the threads are raised on the ends, as in the main head braces. The latter practice is much to be preferred. These braces are commonly known as "screw Fig. 61. Oblique Brace. stays," or "screw staybolts." This mode of fitting enables the screw stay bolt to act both as strut and as tie, or to resist pres- sure in both directions. In some cases the older form of "socket bolt," as illustrated in Fig. 63 is still fitted. In such PRACTICAL MARINE ENGINEERING. case the head is riveted and the part of the bolt between the plates is provided with a hollow "socket." This acts as a strut and as a protection to the bolt proper. In modern approved practice screw stay bolts are either hollow or are drilled in at Fig. 62. Screw Stay Bolt. each end (see Fig. 64), to a point well beyond the inner face of the supported plate. The expansion and contraction of such parts of the boiler often have the effect of bending these bolts Fig. 63. Socket Bolt. back and forth, and they may thus in time become broken off, the break naturally occurring near the thicker of the two sheets where the bolt is held more rigidly. If this should occur, or Fig. 64. Improved Screw Stay. if the bolt should become badly corroded or pitted, especially near the plate, warning will be given of the fact by the escape of water or steam, and proper means must be taken for replac- ing the bolt. In this way timely warning may be given of a BOILERS. 99 condition of affairs, which if allowed to go unnoted, might re- sult in a collapse of the plate, or in a disastrous explosion of the boiler as a whole. The usual spacing of stays, such as that shown in Fig. 58, o o o o COMBUSTION CHAMBER 0000 O O O O Fig. 65. Girder Brace or Crown Bar. and supporting plates not directly exposed to the hot flames or gases is from 14 to 16 inches between centers, while for screw Fig. 66. Flanged Manhole and Fitting. stays supporting plates more or less directly exposed to the fire, the spacing is usually between 6 to 8 inches. See also on this point Sec. 62. For the support of the top of the combustion chamber, gird- IOO PRACTICAL MARINE ENGINEERING. ers or crown-bars are used, see Fig. 65. The load is transferred by means of the bolts from the combustion chamber plate to the Fig. 67. Reinforce Plate. girder, while the latter is supported by the edges of the vertical plates forming the front and back of the chamber. These girders are made of two pieces of steel plate, usually from y 2 to 3.4 in. thick, bolted or riveted together with distance oooooo Fig. 68. Manhole and Fitting in Shell of Boiler. Fig. 69. Reinforce Plate. pieces between so that the bolts which take the load from the flat plate may pass up between them as shown in the figure. The combustion chamber is sometimes secured to the back head of the boiler, or in double-ended boilers the two combus- tion chambers are secured together by plate braces fitted as shown in Fig. 45. Such are usually called gusset braces. In the general internal arrangement of the tubes, furnaces BOILERS. and combustion chambers, care must be taken to allow, as far as possible, a ready examination of the various parts. In good modern practice a space of from 10 to 12 inches is left between the nests of tubes and between the tubes and shell, so as to al- low the passage of a man from the steam space down through these spaces to the furnaces. Manholes and Covers. For the purpose of entering, ex- amining and cleaning the interior of a boiler, man or hand holes are cut in the head or shell. These are then covered by man- hole covers, plates or doors, as they are variously called. These Fig. 70. Manhole Plate and Fittings. are secured by bolts and dogs, as shown in Figs. 66-70. The usual size of a manhole is n by 15 inches, which are the dimen- sions required by the U. S. rules. It is of oval or elliptical shape, so that the cover with its lip extending over the edge may be gotten in and out without difficulty. The joint is made on the inside in order that the pressure may tend to keep the joint tight. A hand-hole is entirely similar in shape and fitting, and is simply smaller in size. In order to provide local strength and stiffness and to help support the load which comes on the feet of the dog, and also when the hole is cut in the shell ic^^U PRACTICAL MARINE ENGINEERING. to restore in some measure the metal taken out, a reinforce ring of metal is fitted about the hole. Such a ring of cast steel for a hole in the shell is shown in Fig. 68. The inner face is planed, so that the joint with the cover is readily made. In order that the removal of the metal may affect as little as possible the strength of the shell, the longer axis of the hole should run around the boiler rather than lengthwise. For holes in the head of a boiler the metal is often flanged inward, as shown in Fig. 66, the joint being made against the dressed edge of the ring. Where a manhole or handhole comes close to through braces, as, for example, near Fig. 71. Furnace Front. the furnaces, the reinforce plate may be formed, as shown in Figs. 67 and 69. At the angles or corners the plate is of suffi- cient width to let the threaded end of the brace come through, and the outside nut is then jammed down on the ring as shown. For heavy pressure the fitting illustrated in Fig. 70 may be rec- ommended. The reinforce ring is of flanged steel, and the cover of steel plate also, somewhat thicker than the metal of the shell. An angle iron, as shown, is riveted to the cover, making a neat fit within the reinforce ring, and keeping the plate ac- curately to its seat. Furnace Fronts and Doors. The furnace front is a fitting at- tached to the mouth of the furnace, and carrying the furnace BOILERS. 103 door. In Figs. 71, 72 a common form of arrangement is shown. The front consists of a steel plate forming the outer part, and made with lugs or a flange for attachment to the furnace. The opening for the door is formed, as shown, within this front or door frame as it is sometimes called. Attached to this frame and with a space between is a second plate of cast iron forming the inner wall. This is pierced with a large number of small holes, while the frame is provided with a smaller number of larger holes. These are provided for the purpose of admit- ting air to the furnace above the grate. The inner plate is sub- ject to the direct action of the fire, and although cooled some- what by the air passing through, it is liable to burn out from /vfv.f.n i\ , i /vTi Fig. 12. Detail of Furnace Front. time to time. It is for this reason that it is made as a separate piece, and so is readily replaced as occasion requires. The door is formed in much the same way as the frame, and is provided with holes in a similar fashion and for the same purpose. Often a small covered peep-hole is provided for examining the fire without opening the door. In some cases also a small opening is made through which a slice bar may be introduced for stirring or breaking up the fire without opening the door. A form of slide or gridiron is also sometimes fitted so as to control the amount of air entering above the grates. In some cases the doors and frames are made entirely of flanged steel plates in- stead of cast iron, while much variety exists in the arrangement 104 PRACTICAL MARINE ENGINEERING. of the holes for the introduction of the air. Certain special fittings necessary to adapt the 'furnace fronts and doors to the application of forced draft will be referred to at a later point. The ash-pit door usually consists simply of a plate of thin sheet steel provided with the necessary lugs and handles, and covering the front opening in the furnace below the grate bars. It is used chiefly as a damper in connection with closed stoke- hold forced draft. Grate and Bridge Walls. The general arrangement of the inside of the furnace is illustrated in Fig. 73. The grate extends from the front of the furnace to the bridge wall as shown. The bottom of the door frame extends back a little Fig. 73. Section of Furnace and Grate. way and drops down, forming a kind of shelf for the support of the front ends of the grate bars. In some cases this exten- sion of the door frame extends back some distance, forming the so-called dead plate, upon which bituminous coal may be piled when first fired, so as to provide for the gradual distillation and combustion of its gases. The great bars may be made in a large variety of forms. In Fig. 74 is shown the standard type of cast iron bar. There are usually two lengths of bar in the length of the furnace, sup- ported by the door frame in front and bridge wall at the rear, and by bearing bars in the middle. These latter in turn are sup- BOILERS. 105 ported at their ends by attachment to the furnace. The bars are usually cast double, as shown, while for convenience in fit- ting grates of varying widths, a small number of single bars are usually provided. The width of air space between the bars is usually made about equal to the width of the bar, or about one- half of the entire grate area, although this proportion should vary somewhat according to the fuel in use. The surface of the grate usually slopes slightly from front to rear, from i in 24 to i in 12, covering the usual range of angle. Cast iron grate bars often have a shallow groove running along the top. This fills with ashes and tends to prevent the clinkers ad- hering to the grate. In addition to the type of bar shown in Fig. 74, square wrought iron bars running the whole length of the furnace are sometimes used, and there is a large variety of patent and spe- cial kinds of shaking grate. The purpose in grates of this char- Fig. 74. Grate Bar. acter is to provide means for breaking up and working the fire without the need of opening the door. Many of them accom- plish this end to a considerable extent, but the greater simplicity and cheapness of the plain cast iron grate, as in Fig. 74, insures for the latter a wide use, and it is still the favorite in ordinary practice. Turning now to the bridge wall, a common arrangement is shown in Fig. 73. A casting extends across the back of the furnace and is supported by attachment at the sides. This sup- ports the back ends of the grate bars, as already referred to, and also a wall of fire brick which forms the back limit of the grate, and over which the products of combustion pass on their way to the combustion chamber. Instead of fire-brick, the use of cast iron for bridges is be- coming frequent in modern advanced practice. Such bridges are of ribbed or channeled form, and in use they become suffi- io6 PRACTICAL MARINE ENGINEERING. ciently covered with ashes to form a protection against the heat of the fire. Front Connections and Funnel. After leaving the tubes at the front end the gases and smoke must be guided to the base of the funnel. This is done by the front connections or smoke boxes and uptakes, as shown in the diagrams. Fig. 75 shows the connection made between two single-ended boilers and one funnel, used in common by both. The boilers are placed front to front in an athwartship fire room. Fig. 76 shows the connec- tions between one double-ended boiler and the smoke pipe. Fig. 75. Front Connections, Uptakes and Funnel Base. These connections are formed of sheet metal riveted up in two or more thicknesses with an air space or non-conducting ma- terial between. The term front connection refers more especially to that part of the passage directly in front of the tubes. This is provided with doors swinging upward to allow examination, cleaning and repair of the tubes. A swinging damper is often placed in the uptakes for controlling the draft as may be de- sired, especially where two or more boilers are connected to one stack. The funnel or stack is also made of sheet metal riveted up, and in good practice in two thicknesses with a considerable BOILERS. 107 air space between. This tends to prevent loss of heat by radia- tion, and thus the temperature of the gases is kept as high as possible while in the funnel, as is necessary for good draft. It may be remembered that for boiler economy the temperature of the waste gases at the front connection should be as low as possible, while for the sake of the draft all further loss of heat while in the funnel should be prevented. Around the base of the funnel is fitted an additional air screen or passage, known as the air casing. See Fig. 77. This serves to ventilate DO JBLE ENI BOILER fl ED n n Fig. 76. Front Connections and Uptakes. the fire-rooms and to protect the neighboring parts of the ship from the heat radiated by the funnel. The air casing is pro- tected from the weather by a sloping ring of metal attached to the funnel, as shown in the figure, and known as the umbrella. The weight of the funnel is usually carried by straps or lugs attached to the structure of the ship, and it is furthermore stayed by guys on deck in order to provide the necessary steadiness and support in a sea-way. In small craft, however, the weight of the funnel is often taken simply by the uptakes and boilers. io8 PRACTICAL MARINE ENGINEERING. The funnel is often provided with a cover, which may be placed over the top when the ship is laid up, or when for other reason the funnel is not in use. The cover is usually kept a lit- tle distance above the top so as to allow the escape of smoke from small fires used for warming and airing the boilers. A ladderway should also be provided on the funnel to assist in ex- amination, adjustment of guys, fitting of cover, etc. In small OUTER STACK DECK DECK Fig. 77. Funnel. craft a damper is often fitted in the funnel near the base, to as- sist in controlling the draft. [4] Construction of Water- Tube Boilers. Only a few points will require special notice under this heading. We have already seen that many types of water-tube boiler consist of one or more cylindrical drums above and one or more below, joined by a series of tubes. See Figs. 15-26. These drums, which are rarely more than 18 to 24 in. diameter, BOILERS. iog> are made from steel plates usually by flanging and riveting in the usual manner. The heads alone of such drums require con- sideration as regards bracing. If of sufficient size to require it they may be braced by through bolts as with boiler heads. In most cases, however, the heads are bumped or made of dished form, either concave or convex on the outside. The lat- ter is preferable, as the pressure is then carried on the concave side, and according to the United States law such heads are allowed without bracing a pressure the same as that for a cylindrical shell of a diameter equal to the radius of the sphere of which the head forms a part. It is much preferable to form the heads in this way, avoid- ing the need of bracing, and thus leaving the interior of the drum free for examination, at least so far as bracing is con- cerned. To allow access to the interior, manholes or hand- holes with appropriate cover plates are fitted to the heads. In- stead of forming these drums with riveted joints, drums with welded joints have recently come somewhat into use, especially in naval practice. With boilers having headers formed by the space between two parallel sheets, the necessary arrangements are quite differ- ent. These sheets require special support, and this is usually provided by screw stay-bolts or other equivalent stays worked between the two sheets attached to the tube sheet between the tubes as convenient, and securely tying the two sheets together. In some cases the outer sheets are supported by rod stays pass- ing from head to head through the tubes. In such case the tube sheets are left to be supported by the tubes which are thus thrown into compression, and the tubes must, therefore, be carefully expanded, especially on the inner side of the sheet, in order to give sufficient hold to support the sheets in this direc- tion. In Sec. 14 [6] in speaking of the operation of water-tube boilers, reference was made to a separation in the upper drum of the water and the steam as they are delivered from the upper ends of the tubes. This is usually effected by some form of baffle plate, as illustrated in Fig. 17. A plate pierced with small holes is placed just in front of .the tube openings, and against this the escaping jets of water and steam are directed. The water is supposed to collect on the plate and to run down to the lower edge, or to the water in the lower part of the drum, i io PRACTICAL MARINE ENGINEERING. while the steam passes through the holes and enters the steam pipe beyond. In the Bellville boiler, as in Fig. 26, there is a series of baffle plates forming a more or less tortuous passage through which the steam must pass on its way to the outlet, while at the last there is a plate with holes which exercise a straining action in the manner described just above. Special separators, as described in Sec. 35, are sometimes fitted in ad- dition to these internal separating devices. The tubes of water-tube boilers are of wrought iron or steel, and welded or solid drawn. For the bent-tube boilers solid drawn steel tubes are to be preferred. For straight tube boilers welded iron tubes are still in common use. The tubes are secured to the tube sheets either by expanding or by special fittings with screwed joints. In general there is a force tending to draw the tubes out of the tube sheet or junction box or other form of header, equal for each tube to its cross-sectional area multiplied by the steam pressure. This force must be re- sisted by the tube fastening, and while it is not usually serious in amount, its existence should not be forgotten, and the need of care in the fastening is shown. The furnaces of water-tube boilers are formed of grate-bars with a space below for ash-pit, all inclosed in the same general casing which surrounds the boiler as a whole, and as shown in the various figures referred to in the foregoing. Often a considerable amount of fire-brick is used as a lining to the furnace, and for protection to the lower ends of the tubes. Due to the great variety of forms of water-tube boilers, the details of construction often present the widest variation, and they cannot be so readily reduced to standard forms as in boil- ers of the fire-tube type. [5] Common Sizes and Dimensions of Scotch Boilers. The furnace diameter for Scotch boilers is usually found be- tween 42 and 48 inches. The upper limit comes about in the following manner. Taking into account the extreme ranges of temperature to which this part of the boiler is subjected, and based on general experience, it is usually considered that from Y-2 to y% inch is about as far as it is desirable to carry at present the thickness of the metal for the furnace. Again the strength of the furnace increases with the thick- ness and decreases with the diameter. Hence for a given pres- sure and limit on the thickness, the diameter will be limited as BOILERS. in well. With modern pressures and a general limit on the thick- ness as above, the limit on the diameter, therefore, results. Rarely furnaces are met with up to 54 in., but only with the more moderate steam pressures. The lower limit for furnace diameter is given by a consideration of the necessary space be- tween the fire and the furnace crown. If this space or height is not sufficient the fires cannot be properly worked and the combustion will be incomplete, due to insufficient space for the admixture of air with the gases given off from the coal. In fact for efficiency of combustion we should probably pre- fer the diameter of the furnace larger than we are actually able to fit. As a lower limit, however, it may be considered inad- visable to fit furnaces much smaller than 42 inches, though they are sometimes found down to 36 inches. The length of fire grate is usually found between 5 and 6 feet, though occasionally it extends to 6 ft. 6 in., or may be found as short as 4 ft. 6 in. The chief limitation here comes from the limit in the capacity of the average fireman to efficient- ly work his fire beyond a certain length. For average practice 5 ft. 6 in. may be considered a good length, while it is doubtful if grate area added beyond this length will be of any great value for steam production. It is more than likely to become partially choked with ashes and clinker, while a shorter grate of 5 ft. or 5 ft. 6 in. length may be kept bright and efficient over its entire surface. The length of the furnace itself being equal to the tubes will be somewhat longer than the grate. The difference is usually from 12 to 24 or even 30 inches. This gyves for the usual length of furnace and of tubes from 7 to 9 feet. The usual depth of the combustion chamber is from 24 to 30 inches. This will usually give a suitable volume, and will also provide a sufficient space within which a man may swing a hammer or make use of such other tools as may be necessary in caring for the back ends of the tubes. The usual thickness of the water leg or space between the back of the combustion chamber and the back head of the boiler is from 6 to 9 inches. It will thus be seen that the usual length of a Scotch single- end boiler will be found between 10 and 12 feet ; 10 ft. 6 in. and IT ft. are quite common values. ii2 PRACTICAL MARINE ENGINEERING. Comparing the construction of a single and double end boiler it is clear that the length of the latter will be slightly less than twice the length of a single end. This gives for the usual length of a double-end boiler from 18 to 21 feet. The diameter of the boiler will depend largely on the num- ber of furnaces to be fitted, and, of course, on the steam pres- sure and on any limitations in the thickness of the plates em- ployed. Modern four-furnace boilers are usually found between 15 and 17 feet in diameter. For three-furnace boilers the di- ameters will similarly range from 13 to 14 feet, while for two- furnace boilers the diameter may vary from 10 feet or less to ii or 12 feet. The usual diameter for tubes is from 2% to 3 inches. The smaller sizes are used with forced draft and the higher rates of combustion. For natural draft 2^4 and 3 inches are common sizes. The thickness of boiler tubes is usually specified by sheet metal gauge number. Plain tubes are usually No. 8, 10 or 12, corresponding to .17 to .10 inch. Stay tubes are usually about No. 3 or J4 mcn m thickness. [6] Common Proportions for Scotch Boilers. Grate Surface (G. S.) 10 to 15 I. H. P. per sq. ft. G. S. Heating Surface (H. S.) 2 to 5 square feet per I. H. P. or 25 to 40 square feet per sq. ft. G. S. Coal Burned. 15 to 30 Ibs. per sq. ft. G. S. per hour, or J / 2 to i lb. per sq. ft. H. S. per hour. Water Evaporated. 6 to 10 Ibs. per lb. of coal, or 4 to 10 Ibs. per sq. ft. H. S. per hour. Section of Passage Over Bridge Wall. 1-6 to 1-8 G. S. Sectional Area of Tubes. 1-5 to 1-7 G. S. Sectional Area of Funnel. 1-6 to 1-8 G. S. Volume of Combustion Chamber. 3 to 4 cu. ft. per sq. ft. of G. S. Steam Volume. .3 to .4 cu. ft. per I. H. P. [7] Weights of Boilers. A modern four-furnace single-end Scotch boiler will weigh in the neighborhood of 40 tons, or upward, while the water will weigh not far from 20 tons, making 60 tons or more for the boiler as a whole. A four-furnace double-end boiler will similarly weigh not far from 70 tons, while the water will weigh BOILERS. 113 not far from 40 tons, making no tons more or less for the boiler as a whole. For a modern three-furnace single-end boiler the weights would be similarly about 25, 15 and 40 tons, respec- tively, for boiler, water and total, while for a three-furnace double-end boiler they would be about 45, 25, and 70 tons, re- spectively, for boiler, water and total. Wide variations, of course, are found in the weights of boilers, and the above figures are only given to show the general nature of the weights in- volved. The weight of boilers with and without water, per square foot of heating surface, has already been noted in Sec. 14. From these various figures and proportions it results that Scotch boilers may be expected to develop from 20 to 30 I. H. P. per ton according to conditions, while for water-tube boilers the figures will" run from 30 or 40 for the heavier types to 6c or 70 and even more for the lighter types, and with extreme rates of forced draft. [8] Western River Boat or Flue Boilers. As noted in Sec. 14 these boilers are in common use on the western rivers of the United States. A few additional points may here be given regarding their construction and installa- tion. The length of such boilers varies from 20 to 30 feet, with a diameter of about 4 feet and with from 4 to 6 flues 10 to 14 inches in diameter. The shells are made up of several courses as shown in Fig. 14, the circumferential seams being single riv- eted and the longitudinal seams double riveted. The flues are usually made also in lengths, lap welded and telescoped to- gether. Such a boiler, for example, of 26 feet length and 47 inches diameter with six 10 inch flues has about 580 sq. ft. heating surface and will provide steam for about 275 I. H. P. in engines of the type commonly used and described in Sec. 24. When such boilers are arranged in battery they are placed side by side and are usually provided w^ith a single setting, thus giving a common furnace for the entire battery. The length of grate bar is short, being usually about 4 ft. 6 in. The boilers are furthermore usually connected by a steam drum on top and by one or more mud drums at the bottom. The steam drum for the size of boiler referred to above may be from 18 to 24 inches in diameter, connected by legs 12 to 16 inches in diameter ii 4 PRACTICAL MARINE ENGINEERING. and spacing the boilers so as to give flame room of 9 to 12 inches between the shells. In order to make the setting of such boilers as light as pos- sible the brick work may be kept down to a single thickness of fire brick supported by a sheet iron casing. The ash pan is preferably of steel plates lined with fire brick laid in cement. An interesting feature of the ash pan is the ash well which is frequently fitted. This consists of a 10 or 12 inch cylindrical passage leading from the surface of the ash pan down through the bottom- of the boat, and through which the ashes are dis- charged overboard without further handling. The boiler fronts are of cast iron with suitable fire-door and ash-pit openings. The uptakes, and funnels, or chimneys as they are more com- monly called, are made of heavy sheet iron and are supported by bracing carried down to the main deck beams which carry the boilers themselves. As noted below the engines work non-condensing, and the exhaust, as a rule, is led first through the feed heaters to the ''Doctor" as described in Sec. 24, and then to the base of the chimneys for forming a blast and forcing the combustion. Connections may also be provided for carrying the exhaust to an exhaust pipe leading to the air, and also in part to the stern wheel if desired, in order to prevent the formation of ice in cold weather. Lever safety valves, as illustrated in Fig. 78, are usually employed on these boilers, while gauge cocks, fusible plugs, steam gauges, and blow-off cocks are provided in accordance with usual practice. The steam piping is usually of lap-welded wrought iron with flanged joints. One of the chief features of western river prac- tice is the flexibility of the boat under different conditions of lading, and the necessity for allowing for such flexibility in the connections between the boilers and engines, and between the engines and wheel. Between the boilers and engines this is usually provided by the introduction of long bends or special connections intended to allow for changes due to expansion, contraction, twisting, etc. In addition to the flue boiler, as illustrated above, the di- rect fire tubular or locomotive type of boiler, as illustrated in Fig. 12, is sometimes used on the western rivers, each boiler be- ing thus self-contained, and the brick-work setting of the flue BOILERS. 115 boilers being dispensed with. The flue boiler, however, is the more used and must be considered as the typical boiler in this field of practice. Sec. 17. BOILER MOUNTINGS AND FIRE ROOM FITTINGS. [i] Safety Valves. The purpose of the safety valve is to provide for the escape of the steam in case the pressure should tend to rise above the safe working limit for which the valve is set. There are two kinds of safety valves, known as lever and spring valves, accord- ing as the valve is kept down on its seat by a weight on a lever or by a powerful spring under compression. Fig. 78 shows the construction of the standard U. S. lever valve. The valve itself has a plain conical face, and fits to a corre- sponding seat as shown. In its motion up and down it is guided by the double stem, so that it can by no means become jammed Fig. 78. Standard Lever Safety Valve. in the chamber. The pressure of the steam comes on the bot- tom of the valve, and as it reaches or passes the limit for which the adjustment is made the valve lifts and the steam escapes about the edge, and thence is led by the escape pipe to the deck. The actual lift of a safety valve is very small, l /% in. being usually a large lift. The opening for the escape of the steam depends, therefore, on the circumference of the valve and on the lift, rather than on the area and lift. Safety valves are, however, usually designated and determined according to their area. The weight acts by means of the lever, as shown, and may be ad- justed so as to allow the valve to open at the pressure desired. On this point consult further Sec. 61. In modern practice the lever valve is infrequently used, ex- cept in vessels engaged in smooth water (river) service, the spring valve being fitted almost universally. In this form of n6 PRACTICAL MARINE ENGINEERING. valve, which is shown in Fig. 79, the chief point of difference is in the substitution of the spring for the weight and lever. The tension of the spring is adjusted by a screw at the top, so that the valve will not open until the limiting pressure is reached or exceeded. It is readily seen that as soon as the valve rises the spring is compressed and the tension is increased. It is also found that with the plain form of valve, as shown in Fig. 78, the m Fig. 79. Double Spring Safety Valve. pressure on the face decreases the instant the valve lifts. Due to these facts it follows that such a valve, especially when con- trolled by a spring, is apt to seat itself the instant after rising, lifting again the next instant in answer to the restored value of the pressure. This irregular action will lead to a rapid opening and closing of the valve, producing a chattering noise very un- desirable in passenger boats, and interfering with the continuous and regular escape of the steam. To avoid this a lip of one BOILERS. 117 form or another, as shown in Figs. 79, 80 and 81, is fitted to the valve at or beyond the edge, so that it may catch the escaping jet of steam, and thus increase the effective area of the valve after it has lifted from the seat. In such case the valve is forced farther from the seat, and while it still vibrates, it remains defi- nitely open until the pressure has fallen some 4 or 5 Ib. below that for which it opens. The valve then touches the seat in one of its vibrations downward, and remains closed until the pres- Fig. 80. Enlarged Section of Lip. Fig. 81. Safety Valve and Muffler. sure again rises to the point for which it is set. The safety valve s'hould always be fitted with a hand lifting gear, so that it may be opened by hand when desired, and the spring adjustment should be protected by lock and key, so that it cannot be changed by unauthorized persons. For large boilers, instead of one large valve, safety valves are often fitted in groups of two or three. This reduces to the smallest possible limit the danger from sticking or other de- rangement of the valve. The safety valve or valves should al- ways be attached to a fitting leading direct to the boiler, and ii8 PRACTICAL MARINE ENGINEERING. with no possibility of closing it off by a stop valve. If both stop and safety valves are attached to the same fitting the'latter must always be placed inside or nearer the boiler than the former. [2] Muffler. This fitting, though not in the fire-room, may be properly referred to at this point. It consists of a metal chamber filled with bits of metal or stone, marbles, wire-gauze, small spiral springs, or with thin plates in layers pierced full of holes and ar- ranged in staggered fashion so as to provide a series of zig-zag passages for the steam. The steam from the safety valves and escape pipe makes its way to the air through this chamber, the purpose of the filling being to muffle or deaden the noise, which might otherwise seriously interfere with the giving of orders on deck. Fig. 81 shows a combined safety valve and muffler, the latter with plates as above described. Such an arrangement would be applicable for small or open craft having but one boiler, such as launches, small yachts, etc. [3] Stop Valve. Each boiler is connected through a separate boiler steam pipe to the main pipe. The entrance of steam to this pipe is controlled by the boiler stop valve, which thus provides for the regulation of the supply of steam to the engine, and for closing the boiler off entirely from the main steam pipe if necessary. The usual type of valve employed is shown in Fig. 82, and con- sists of a valve disc guided to its seat by wings, and raised or lowered by its connection with the screw spindle and handle as shown. As also shown in the figure the valve seat with wings and guide for the valve is very commonly a separate piece of gun metal or bronze, specially fitted for its strength and wearing qualities. Commonly in warship practice, and to some extent in mer- cantile practice, such valves are made self-closing in case of rupture of the boiler. In fundamental principle such a valve is a form of non-return valve, as illustrated by the check valve of Fig. 83. The screw stem does not open the valve, but limits simply the extent to which the valve can open. A second plain stem passing through the first then allows of the valve being pulled open by hand, even if there is no definite difference of pressure to force it open. In case of accident which reduces BOILERS. 119 the pressure back of the valve so that the rush of steam is in the reverse direction to its usual flow, the valve will be closed by this rush and held securely on its seat by the excess of pressure on its outer face, thus shutting off the injured boiler, and retain- ing the others intact for use. If such an arrangement is not fitted and the valve cannot be closed by hand, or until it can be thus closed, an entire battery of boilers may be thrown out of Fig. 82. Boiler Main Stop Valve. use by the rupture of any one of them, all of the steam formed escaping through the one opening. Such form of valve should be placed with the spindle horizontal, so that its own weight may not enter as a direct factor in the movement of the valve toward and from its seat. In warships, where the pipes or boilers may be pierced by the fragments of exploding shell, such a safety provision may be of the utmost importance and value. 120 PRACTICAL MARINE ENGINEERING. [4] Dry-Pipe, or Internal Steam Pipe. This is a pipe of relatively thin metal placed within the boiler, extending lengthwise, and close to the top of the shell. At the inner end it is closed, and at the outer end connects with the pipe leading to the safety valve chamber, stop-valve and boiler steam pipe. Along the top of the pipe are cut a large number of narrow slits, through which the steam enters the Fig. Boiler Check Valve. pipe. This arrangement has the effect of drawing the steam from the highest part of the steam space, and of straining out some part of the entrained water. A small hole in the bottom of the pipe provides for draining off the water which may grad- ually collect. The uniform draft of steam from the whole length of the boiler tends also to prevent the priming which might be caused by drawing it all from one point. BOILERS. 121 [5] Feed Check Valve and Internal Feed Pipe. The water from the feed pump conies to the boiler through the feed pipe, and then at the boiler passes through the feed- check. This is a screw-down, non-return valve, as shown in Fig. 83. The valve itself is entirely disconnected from the spindle, and the latter simply limits the height to which the valve can rise, while by screwing down sufficiently, the valve may be forced shut and held there. This construction is adopted so that should the feed pump stop working or between the strokes of the pump there may be no escape of water backward from the boiler into the pipe. Two such check valves are usually Fig. 84. Combined Check and Stop Valve. fitted to each boiler, one connecting with the main and the other with the auxiliary feed pumps. In modern practice a stop valve is usually fitted between the check valve and boiler, in order that, if necessary for ex- amination or repair, the check may be shut off from communi- cation with the boiler. Such combined stop and check valves are frequently fitted in a single casing, the stop valve, of course, being placed next the boiler (see Fig. 84.) After passing through the check-valve the water enters the internal feed pipe, by which it is led to the point or points of delivery. The end of the pipe is usually closed, and the water is delivered through a large number of small holes distributed 122 PRACTICAL MARINE ENGINEERING. along the pipe. The delivery is usually below the water level, and often between the nests of tubes where it meets with the rising currents of water heated by them. In some cases it is led to the bottom of the boiler, where it mixes with the rela- tively cool water there found; but this plan cannot be recom- mended, as it retards rather than assists circulation. In some cases also the water has been introduced as a spray into the steam space, but, while this plan has some advantages, it has not met with general favor. Fig. 85. Blow-off Cock. In water-tube boilers the feed water is usually fed into the upper drum, whence it joins the circulation in the boiler as noted in the description of boilers of this type. [6] Surface and Bottom Blows. Cocks or valves and connecting pipes are fitted for blow- ing grease and scum, or mud sediment and water, out of the boiler into the sea Fig. 85. The surface blow consists of a valve or cock attached to an internal pipe lying just below the normal water level, and either perforated with holes or leading to a shallow open pan. Outside the boiler there is a discharge pipe leading to an outboard valve, through which the discharge is effected. The scum and grease which collect on the surface of BOILERS. 123 the water may by means of this arrangement be blown out of the boiler, and thus disposed of. In early engineering practice the bottom blow was of great importance, as it was used not only to discharge mud and sediment, but also the relatively dense water in the boiler when blowing down to reduce concentration, or when emptying the boiler of water for purposes of examination or cleaning. In modern practice with the surface condenser and the evaporator, blowing off to reduce concentration is no longer necessary, and blowing the water out of a boiler with its own steam is no longer considered good practice. The preferable plan is to allow the steam to condense and the water to cool down, and to then run it into the bilge or remove it by pump connections suitably arranged. Due to these facts, bot- tom blow valves have been sometimes omitted. There may still, however, be occasion to use such valves for the discharge of mud and sediment, and, therefore, they are still quite gen- erally fitted. In any event, there should be some valve and pipe connected with the lowest part of the boiler, and through which it can be emptied in one way or another. Both surface and bottom blows are usually fitted to water- tube boilers, especially to those types consisting of upper and lower drums with sets of connecting tubes. The surface blow is for scum and grease, while the bottom blow is essentially for mud and sediment, and is often attached to a special mud-drum provided to collect such substances. In many cases the inner end of the surface blow pipe ter- minates in a shallow pan located near the low water level in the boiler. The water within this pan will tend to remain more quiet than that outside, and the scum and impurities will thus collect therein, ready for removal by the use of the blowv The arrangement thus serves as a collecting pan for the surface blow, and by most engineers is believed to be quite efficient for the purpose in view. In other cases the pipe terminates in a closed end and is provided with a number of longitudinal slits through which the scum is drawn from the surface of the water. The cross-sectional area of the bottom blow may be so proportioned as to give about one square inch for every 5 tons of water contained by the boiler, with perhaps somewhat larger area in the case of small boilers. The area for the surface blow may be usually made from y 2 to 1-3 that of the bottom blow. 124 PRACTICAL MARINE ENGINEERING. [7] Steam Gauges. The steam pressure within the boiler, or rather the excess of the pressure within over the atmospheric pressure without, is shown by some form of steam gauge, of which the best-known and most used are those employing a Bourdon tube. In Fig. 86 is shown such a gauge and tube, the cross section of the latter Fig. 86. Bourdon Steam Gauge. being an ellipse as shown. When the inside of the tube is sub- jected to the pressure of the steam it tends to become round in section, and as a result of this the tube as a whole tends to straighten out. This carries the free end outward, and this movement, by means of suitable connections, is made to give motion to the needle. These gauges are graduated by compari- son with a mercury column or other form of gauge tester, or with a standard gauge which has been thus graduated. Steam should not be allowed to enter these gauges, as the change in temperature may affect the accuracy of the reading. To pre- BOILERS. 125 vent this the pipe leading to the gauge is always provided with a loop or U bend, called a "goose neck," which serves as a trap for the water condensed beyond this point. In this way the Bourdon tube and part of the connecting pipe are kept filled with water, which in turn is acted on by the steam, and thus the pressure is indicated without the actual presence of steam within the gauge. Steam gauges require comparison with a standard gauge from time to time, in order to make sure that their indi- cations are correct. They are often provided in duplicate, and Fig. 87. Water Gauges. frequently one gauge, at least, is provided of sufficient range to allow of use in the hydrostatic boiler test. [8] Water Gauge and Cocks. The level of the water within the boiler is shown by a ver- tical glass tube connected to fittings at each end, which in turn connect the one with the steam space and the other with the water space. As shown in Fig. 870, the entire arrangement of glass and fittings is attached to a hollow mounting called the stand-pipe, water-column, or water-gauge mounting. To the top and bottom of this are attached pipes, one leading to the steam space at or near the top, and the other to the water space at or near the bottom. In conne.cting the pipe with the steam space care must be taken that the opening is not near a steam outlet, as the rush of steam past such an opening might disturb the 126 PRACTICAL MARINE ENGINEERING. pressure and render the indications inaccurate by showing a higher level of water in the glass than actually exists in the boiler. At the bottom of the mounting a drain cock and pipe are provided, so that the glass may be blown through and cleaned as occasion requires. Screw plugs are also fitted above and below in a line with the base of the tube, so that if necessary a wire and swab may be run through the glass. Instead of the connections, as shown in Fig. 870, and which are to be considered as preferable, the ends of the water column are sometimes con- nected by horizontal passages directly to the boiler, as in Fig. 8/b, which shows the fitting attached to the curved shell of boiler. With such a mounting the level of water in the glass is more liable to fluctuation and disturbance due to rolling of the ship or to priming than with the arrangement of a. Gauge glasses are usually from 12 to 15 in. in length, and y% to J4 in. diameter. Due to the fluctuations in temperature and the accompanying expansion and contraction, they are liable to occasional breakage. To avoid danger or trouble from the escaping jet of water and steam, it is quite customary in modern practice to fit the connection carrying the ends of the glass with ball non-return valves, working on a similar principle with the safety stop valve described above. So long as the glass is in place and the pressure equalized, the balls by their weight remain away from the seat and leave the passages open. Upon the breakage of the glass, however, they are carried by the rush of water and steam, each against its seat, thus closing the openings and stopping the escaping jets of water and steam. In addition to the gauge glass, small cocks, three or four in number, are usually provided. In some cases such cocks are attached to the mounting, and in other cases to the boiler itself. These cocks serve as a check on the gauge glass, or for use in case the glass is not to be depended upon. The glass is usually so adjusted that when the water is at the bottom it is still some 3 or 4 in. above the level of the highest heating surface. The water cocks cover about the same vertical distance, though in some cases the lowest cock is placed nearly on a level with the top of the heating surface. On single-end boilers two such water gauges are often fitted, one on either side at the front, and with water cocks at the back. Similarly on double-end boilers three would be fitted, two on one end and one on the other. BOILERS. 127 i 9 1 Hydrokineter. This is an appliance used to force the circulation of the water in the boiler, more especially when raising steam. It con- sists, as shown in Fig. 89, of a steam jet and series of nozzles Fig. 88. Hydrokineter. with frame perforated at the back for the entrance of water. The steam is furnished from another boiler, and by its inducing action a current of water is set up and driven along, as shown by the arrows. This arrangement is placed near the bottom of the boiler, and thus serves to drive out the cold water which tends to collect there, and which is only slowly heated by the opera- tion of natural circulation. [10] Hydrometer. The density of the water in the boiler is determined by an instrument known as the hydrometer, and shown in Fig. 90. It c I II II II II Fig. Hydrometer. may be of either glass or metal, and consists essentially of two bulbs with stem as shown. The upper and larger bulb is filled with air, and serves to give buoyancy to the instrument; while the lower and smaller bulb is weighted and keeps it in the 128 PRACTICAL MARINE ENGINEERING. upright position. When a body floats freely, wholly or partly immersed in a liquid, the weight of the body equals the weight of the liquid displaced. Hence, in this case the denser the water the less the volume displaced, and the higher the stem out of water. Average sea water contains about i part in 32 of solid matter, and hydrometers are usually graduated relative to this as a unit. That is, 2 means twice as much solid matter relative- ly as sea water ; 3, three times as much, etc., while o, of course, means fresh water'. The density of water depends, furthermore, on its temperature, so that the scale on the hydrometer can only be used with the temperature for which it was graduated. This is usually 200 deg. F., though frequently three scales are pro- vided; for 190 deg., 200 deg. and 210 deg., respectively. The water is drawn from the boiler through an appropriate pipe and connections into a deep, slender vessel called a salimometer pot. Soon after drawing, the water cools down through the tempera- ture corresponding to the hydrometer scales, and thus its den- sity is observed. [11] Boiler Saddles. The weight of the boiler is supported on saddles, or bearers, which in turn are attached to the structure of the ship. A modern form of boiler saddle is shown in Fig. 90, and consists Fig. 90. Boiler Saddle. of two or more supports on each side of the boiler of the lorm shown, and extending each one for some little distance longi- tudinally. An older form shown in Fig. 91 consists of a plate on edge connected with the structure of the ship, extending transversely under the boiler, and cut out to fit the round of the BOILERS. 129 shell. The upper edge of this plate is fitted with angle irons on one or both sides to give a broader surface of support for the boiler. The form of saddle shown in Fig. 90 gives a better longitudinal support, and, moreover, makes access and exam- ination of the bottom of the boiler more easy than with the other I Fig. 91. Boiler Saddle. form. Single-end boilers usually have two such saddles on each side, while double-end boilers are given three or four. In addition, the boiler is held in place in its saddles by stays adjustable by screw turnbuckles, or by other like means. A knee-piece, or chock, is also often riveted to the structure of the ship, projecting just above the end of the boiler at the bottom, and thus preventing endwise motion. [la] Boiler Jigging. To prevent loss of heat by radiation the boiler is covered with non-conducting, non-combustible felting, which in turn is held on by iron straps, or in some cases by a complete covering of sheet metal. This covering is known as boiler lagging. Sec. 18. DRAFT. Draft is due to a difference in pressure between the uptakes or base of the stack, and the ashpits. Due to this difference the air is driven up through the grate, thus supplying the amount re- quired for combustion, see Sec. u [2]. We must first inquire what it is that causes this difference of pressure. To make the case simple let AB Fig. 92, denote a grate with burning fuel, and ACDB the funnel. Then the pressure downward on the top of the fuel will be equal to the weight of a column of air and gas of cross section equal to AB, and extending up to the limits of PRACTICAL MARINE ENGINEERING. the atmosphere. The pressure upward at the bottom of the grate will be the regular pressure of the external air, and this will equal the weight of a column of air of the same cross-sec- Fig. 92. Showing Principle of Natural Draft. ig- 93- Draft Gauge. tion GH, and extending also up to the limit of the atmosphere. The difference in the weight of these two columns is seen to lie in their lower ends, the bottom of one being composed of hot gas and the other of common air. The difference in pressure will, therefore, equal the difference in weight between the col- umn of hot gas CDBA, and that of air EFHG. Actually the column of liot gas will extend some distance above the top of the funnel before losing its heat or mingling with the air, so that the real height of the column is greater than the funnel. This difference is, however, usually neglected, and the difference in pressure is usually taken as the difference in weight between the column of hot gas extending from the grates to the top of the funnel, and a like column of external air. The pressure per square inch will, of course, be likewise equal to the difference between two similar columns of one square inch section. This shows the conditions for producing the so-called natural or fun- nel draft pressure. In order that the combustion may proceed, however, it is BOILERS. 131 not enough to produce simply a column of hot gas. Care must also be taken to provide for a free and full inflow of the outside air to the grates in order that the amount necessary for combus- tion may be on hand as required. Draft pressures are usually measured by an instrument known as a draft gauge. As illustrated in Fig. 93, it consists of a bent U- tube partly filled with water as shown, and with a scale between the legs. In use the two legs are connected by appropriate means to the two places between which the differ- ence of pressure is desired, as for example, the ash-pit and fun- nel-base, or external air and funnel-base. In the latter case one leg is open to the air and the other is connected by a flexible pipe or other similar means to the uptake or funnel-base. With equal pressure in both places the water will stand at the same height in both legs, but with a difference of pressure it will rise in one leg and fall in the other, the movement being toward the lesser pressure. The difference in pressure is then measured by the weight of a column of water equal to the difference in height between the two legs. This is usually read in inches, and hence draft pressures are usually expressed in inches of water. With ordinary funnel draft the pressure is usually from 54 to ^ or ^4 inch, with assisted or light forced draft from y 2 inch to I inch, with forced draft on large ships from I to 3 inches, while on fast yachts and torpedo boats the pressure may rise to 5 or 6 inches or more. In this connection it may be well to remember that an inch of water pressure is equal to a pressure of about 2-3 oz. per square inch. Since as above explained, natural draft is dependent on the difference in weight between the hot gas in the funnel and the outside air, it follows that the lighter, and, therefore, the hotter the gas the stronger the draft ; also the higher the funnel the greater the difference and the stronger the draft. A strong nat- ural draft with moderate height of funnel requires, therefore, a high temperature of escaping gases, and since these carry away heat to the outside air, this means a loss of heat and hence of economy. Strong natural draft requires, therefore, either a very high funnel, or a very high temperature of escaping gases with the resulting loss in economy. The usual temperature of the gases in the funnel base is from 600 cleg, to 800 deg. Fah. At a lower temperature the draft will be very poor, while with a higher temperature, the increase of draft will be obtained at 132 PRACTICAL MARINE ENGINEERING. the expense of economy. With natural draft the rate of com- bustion will usually range from 12 or 13 to 20 Ib. of coal per square foot of grate surface, dependent on the quality of the coal and other circumstances. From the preceding it is clear that with natural or funnel draft the power which can be obtained from a square foot of grate surface soon reaches a limit, and under present conditions this is usually found at from 10 to 12 I. H. P. In order to ob- tain more power per square foot of grate area, or in general more per pound of boiler, some form of assisted or forced draft is necessary. In all cases where very high speed is required as in torpedo boats, fast launches, yachts, etc., the application of forced draft is a necessity, as the boilers required to develop the power under natural draft would occupy far more weight and space than could be assigned them. With assisted or mod- erately forced draft the power per square foot of grate surface may be raised to from 15 to 18 I. H. P., and if properly installed, without sacrifice of economy. W r ith harder forcing the power may be raised to 25 or 30 I. H. P. per square foot of grate sur- face, or even more in extreme cases, but necessarily at the ex- pense of a loss in economy. The immediate object of all forced draft appliances is to in- crease the difference in pressure between the ash-pit and uptake over what it would be with the funnel alone, at the same time taking care to provide for the full supply of air to the grates as required by the rate of combustion desired. To this end there are four fairly distinct means as follows : (1) Closed fire room. (2) Closed ash-pit. (3) Exhaust fans in the uptakes, or between them and the funnel. (4) Steam jets in base of funnel. In the closed fire-room system the air is forced by means of blowers into the fire-room, which is closed air tight except for the outlet into the furnaces. The fire-room is hence under a pressure greater than the other parts of the ship, and to enter or leave it, an air lock is necessary, as illustrated in Fig. 94. Small air valves are provided by means of which the pressure in the lock may be equalized with that on either side, as may be desired, and this being done the door may be opened. To leave the fire-room, for example, both doors of the lock being closed, BOILERS. 133 the pressure inside is equalized with the fire-room and the door being opened the person enters and closes it behind. The pres- sure in the lock is then equalized with that outside, the door is opened, and thus exit is effected. The chief advantages of this system lie in the fact that the boilers are left unchanged as for Fig. 94. Showing Principle of Air Lock. natural draft, and the shift from one system to the other is read- ily made. The necessary structural arrangements are also sometimes more readily effected than for the other systems, es- pecially in warship practice, and this reason may in some cases largely determine the choice. Its chief disadvantages lie in the difficulty of making the fire-rooms air tight, in the necessity of fitting air-locks as above described, and in the more severe strain placed on the fire-room force than with other systems. In the closed ash-pit system the air is forced by means of blowers into conduits leading directly to the ash-pits and fur- naces, which are closed air tight from the fire-room. The latter are, therefore, under a pressure greater than in the fire-room, and if the furnace, doors were opened with the draft on, the flames and gas would be driven out into the fire-room. To pre- vent this the draft must be shut off when the furnace or ash-pit doors are opened, and to avoid accidents a locking arrangement is often provided which prevents the door from being opened while the draft is on, or the draft from being turned on till the doors are closed. The Hotvdcn forced draft, which is representa- tive of this system, provides also for heating the air by means of the waste furnace gases before it enters the ash-pits and fur- naces. The general arrangement for the Howden draft is shown in Fig. 95. In the uptake is fitted a nest of vertical tubes through which the furnace gases pass on their way to the funnel. The air from the blower is delivered into a conduit which leads 134 PRACTICAL MARINE ENGINEERING. BOILERS. 135 across the front of the boiler and within which these tubes are placed, as shown in the figure. The furnace gases pass, there- fore, through the tubes while the entering air passes about them on the outside, and thus absorbs a part of their heat which would otherwise escape through the funnel. The heated air then passes downward to a kind of special front over the ash-pits and furnaces. From these passages openings controlled by either sliding or hinged valves lead into the ash-pits and into the fur- naces above the grates. The supply of air to the fire may thus be regulated, and the relative amounts delivered above and be- low the grate may be adjusted as required for the best combus- tion. The ash-pit and furnace doors are, of course, air tight to the fire-room, and arrangements may be provided for insuring the closure of the valves before opening the doors as above ex- plained. Induced draft is represented by the Ellis and Eaves system, as illustrated in Fig. 96. A large exhaust fan is so placed as to draw the gases along the uptakes and discharge them to the funnel, thus producing the draft by means of a defect of pres- sure in the uptakes, rather than by an increase in the ash-pit or fire-room. Considering the uptakes and funnel base as repre- senting the main passage, the fan is so placed as to draw from the former and deliver into the latter. Between the inlet and delivery is a slide or damper in the main passage, while the fan inlet may similarly be closed off. When the blower is in opera- tion the former of these is closed while the latter is open and the products of combustion are thus drawn from the uptake and delivered to the funnel-base on the other side of the main slide. On the other hand, if it is desired to run without the fan the inlet may be closed off and the main slide or damper opened, thus giving the usual arrangement for natural draft. The entering air which in this case is supplied either by nat- ural ventilation or by special blowers is heated before reaching the furnaces usually by being drawn around nests of tubes through which the gases pass on their way to the fan. These tubes are sometimes arranged vertically in front of the boiler as in the Howden system, and as shown in the figure, and some- times horizontally in the spandrels over or between the boilers. The air thus heated is then led through passages at the side of the front connections to the ash-pits, and to the spaces around the furnace frames. The furnace and ash-pit fronts are closed 136 PRACTICAL MARINE ENGINEERING. BOILERS. 137 from the fire-room, and a certain proportion of the air is ad- mitted above and below the grates according to the needs of the combustion. This system has the advantage of leaving the fire- room open and of working the ash-pit under practically atmos- pheric pressure. Furthermore all leaks between the fire-room and the fire side of the boiler are inward, and thus the fire-room is kept free from escaping gas, or from flame and gas when the furnace doors are opened. Its chief disadvantage lies in the large size and weight of fan necessary to handle the gases, as compared with the smaller size needed for the air alone in the closed fire-room and closed ash-pit systems. The action of steam-jets in the base of the funnel is to pro- duce a defect of pressure in the uptake, thus giving a form of in- duced draft. Turning the exhaust of a non-condensing engine into the funnel produces the same result, and may also be con- sidered as a form of induced draft. The latter arrangement is sometimes met with in tugs and other small craft, while the steam jet is much used throughout the whole range of tugs, yachts, launches, tenders and all forms of small craft. One of the special advantages of the steam jet is its readiness for use as soon as a small head of steam is formed, and independent of any special auxiliary machinery. It is, however, a wasteful and ex- pensive mode of obtaining increased combustion, and is only to be recommended when simplicity and the saving of weight and space are of more importance than economy of steam. In this connection it must not, of course, be forgotten that the operation of the blowers used in the closed fire-room, closed ash-pit, or induced systems of draft requires also the consump- tion of steam and hence of coal, so that in no case can forced draft be obtained without paying for it in one form or other. General experience shows, however, that for a given increase in the rate of combustion, the use of a steam jet requires more steam than blowers, so that the latter are to be preferred except in such special cases as are referred to above. Reference may also be made to the practice of introducing jets of air under considerable pressure into the combustion chambers or furnaces of steam boilers. The result of such an arrangement is two fold : (1) It places the air at the immediate point where it may be of the most value in aiding to complete the combustion. (2) Its introduction under pressure insures its thorough 138 PRACTICAL MARINE ENGINEERING. mingling with the gases and the latter with each other, and thus still further aids in bringing about the conditions necessary for complete combustion. The introduction of air in this manner has met with considerable favor in many cases where it has been tried, especially in certain forms of water-tube boilers where the volume available for the combustion of the gases before they pass among the tubes is often limited or insufficient in amount. Sec. 19. BOILER DESIGN IN ACCORDANCE WITH THE RUIZES OF THE TJ. S. BOARD OF SUPERVISING INSPECTORS OF STEAM VESSELS. In the present section extracts are given from the United States Rules relating to the design of Marine boilers. To give here the Rules entire would require more space than is avail- able, but those of chief importance are given, though in some cases the wording is slightly changed to aid in condensation. Rivet Holes to be Drilled. All boilers built for marine purposes after July i, 1898, shall be required to have all the rivet holes "fairly drilled" in- stead of punched. Pressure Allowed on Cylindrical Shell Boilers. Rule. Multiply one-sixth (1-6) of the lowest tensile strength found stamped on any plate in the cylindrical shell by the thickness expressed in inches or parts of an inch of the thinnest plate in the same cylindrical shell, and divide by the radius or half diameter also expressed in inches and the quo- tient will be the pressure allowable per square inch of surface for single riveting, to which add 20 per cent for double riveting, when all the rivet holes in the shell of such boiler have been "fairly drilled" and no part of such hole has been punched. Test Pressure. The hydrostatic pressure applied must be in the proportion of 150 pounds to the square inch to 100 pounds to the square inch of the steam pressure allowed. Butt Straps. Where butt straps are used in the construction of marine boilers, the straps for single butt-strapping shall in no case be less than the thickness of the shell plates; and where double butt straps are used, the thickness of each shall in no case be less than five-eighths (^) the thickness of the shell plates. BOILERS. 139 Stays and 'Flat Surfaces. In allowing the strain on a screw stay bolt, the diameter of the same shall be determined by the diameter at the bottom of the thread. No braces or stays hereafter employed in the construction of boilers shall be allowed a greater strain than six thousand (6,000) pounds* per square inch of section, and no solid or hol- low screw stay bolt shall be allowed to be used in the construc- tion of marine boilers in which salt water is used to generate steam unless said screw stay bolt is protected by a socket. But such screw etay bolts without socket may be used in staying the fire-boxes and furnaces of such boilers, and elsewhere when such screw stay bolts are drilled at each end with a hole not less than Y% inch diameter to a depth of at least ]/ 2 inch beyond inside sur- face of sheet, when fresh water is used for generating steam in said boilers (to take effect on and after July I, 1898, on all boil- ers contracted for or construction commenced on or after that date). Water used from a surface condenser shall be deemed fresh water. The flat surface at back connection or back end of boilers may be stayed by the use of a tube, the ends of which being expanded in holes in each sheet beaded and further se- cured by a bolt passing through the tube and secured by a nut. An allowance of steam shall be given from the outside diameter of pipe. For instance, if the pipe used be i l / 2 inches diameter outside, with a i l /\. inch bolt through it, the allowance will be the same as if a i l / 2 inch bolt were used in lieu of the pipe and bolt. And no brace or stay bolt used in a marine boiler will be allowed to be placed more than io l / 2 inches from center to center to brace flat surfaces on fire-boxes, furnaces, and back connections ; nor on these at a greater distance than will be determined by the following formulas. Flat surfaces on heads of boilers may be stiffened with doubling plate, tees, or angles. The working pressure allowed on flat surfaces fitted with screw stay bolts riveted over, screw stay bolts and nuts, or plain bolt with single nut and socket, or riveted head and socket, will be determined by the following rule : When plates 7-16 inch thick and under are used in the con- struction of marine boilers, using 112 as a constant, multiply * This limit is understood to refer only to the use of iron as a material. 140 PRACTICAL MARINE ENGINEERING. this by the square of the thickness of plate in sixteenths of an inch. Divide this product by the square of the pitch or dis- tance from center to center of stay bolt. Plates above 7-16 inch thick, the pressure will be deter- mined by the same rule, excepting the constant will be 120. v On other flat surfaces there may be used stay bolts with ends threaded, having nuts on same, both on the outside and inside of plates. The working pressure allowed would be as follows : A constant 140, multiplied by the square of the thickness of plate in sixteenths of an inch, this product divided by the pitch or distance of bolts from center to center, squared, gives work- ing pressure. Flat part of boiler-head plates when braced with bolts hav- ing double nuts and a washer at least one-half the thickness of head, where washers are riveted to the outside of the head, and of a size equal to % of the pitch of stay bolts, or where heads have a stiffening plate either on inside or outside covering the area braced, will equal the thickness of head and washers, the head and stiffening plate being riveted together * * * * shall be allowed a constant of 200, rivets to be spaced by thick- ness of washer on the stiffening plate. Boiler heads so rein- forced will be allowed a thickness to compute pressure allowed of 80 per cent of the combined thickness of head and washer, or head and stiffening plate. Plates fitted with double angle iron and riveted to plate with leaf at least two-thirds thickness of plate and depth at least one-fourth of the pitch would be allowed the same pressure as determined by formula for plate with washer riveted on. But no flat surface shall be unsupported at a greater dis- tance in any case than 16 inches, and such flat surfaces shall not be of less strength than the shell of the boiler, and able to resist the same strain and pressure to the square inch. Steel stay bolts of a diameter of ij4 inches and not ex- ceeding a diameter of 2^ inches at the bottom of the thread may be allowed a strain not exceeding 8,000 pounds per square inch of cross-section. Steel stay bolts exceeding a diameter of 2y 2 inches at bottom of thread may be allowed a strain not exceeding 9,000 pounds per square inch of cross-section, but no forged or welded steel stays will be allowed. Any steel stay brace of the Huston type, or similar thereto, BOILERS. 141 prepared at one heat from a solid piece of plate without welds, intended for use in marine boilers, to be allowed a strain ex- ceeding 6,000 pounds per square inch of cross-section, shall be tested as hereinafter provided for steel bars intended to be used as stay bolts ; and any brace formed in this way, with an area of cross-section of 1.227 an d not exceeding an area of 5 inches, may be allowed a strain not exceeding 7,000 pounds per square inch of cross-section ; exceeding this area, may be allowed a strain not exceeding 8,000 pounds to the square inch. All steel bars intended for use as stay bolts to be allowed a strain exceeding 6,000 pounds per square inch of cross-section shall be tested by the inspectors, in lots not to exceed fifty bars, in the following manner : Inspectors shall promiscuously select one bar from each lot and bend one end of such bar cold to a curve, the inner radius of which is equal to one and one-half times the diameter of the test bar ; and should any such test bar break in the bending process the lot from which the bar was taken shall not be allowed to be worked into stay bolts for mar- ine boilers. Corrugated Furnace Flues. Corrugated furnace flues constructed with corrugations 8 inches from center to center, the radius of outer corrugation being not more than one-half of the reverse or suspension curve, the plain parts of the ends not exceeding 9 inches in length, made of plates not less than five-sixteenths of an inch thick, when new, corrugated with practically true circles, shall be allowed a steam pressure in accordance with the following formula : Pressure in pounds Where T = thickness in inches. D = mean diameter, in inches. The strength of all corrugated flues, other than described in the preceding paragraph, when used for furnaces or steam chimneys (corrugation not less than i l / 2 inches deep, and not exceeding 8 inches from centers of corrugation) and provided that the plain parts at the ends do not exceed 9 inches in length and the plates are not less than five-sixteenths inch thick when new, corrugated, and practically true circles, to be calculated from the following formula : i 4 2 PRACTICAL MARINE ENGINEERING. 14000 X T = pressure. T = thickness, in inches. D = mean diameter, in inches. Ribbed Furnace Flues. The strength of ribbed flues, when used for furnaces or steam chimneys (rib projections not less than i^ inches deep), and not more than 9 inches from center to center of ribs, and provided that the plain parts at ends do not exceed 9 inches, and constructed of plates not less than seven-sixteenths inch thick, with practically true circles ; and The strength of corrugated flues, when used for furnaces or steam chimneys, corrugated by sections with flanged ends overlapping each other and riveted with ^4 inch rivets, 2 inch pitch, corrugated projection not less than 2y 2 inches from inside of flue to outside of lap, and not more than 18 inches between centers of corrugation, provided plain parts at ends do not ex- ceed 12 inches in length, constructed of plates not less than 7-16 inch thick, with practically true circles ; and The strength of ribbed flues, when used for furnaces or steam chimneys, when made in sections of not less than 12 inches in length, measuring from center to center of said pro- jections, and flanged to a depth not exceeding 2^ inches, and substantially riveted together with wrought-iron rings between such flanges, and such rings have a thickness of not less than double the thickness of the material in the flue, and a depth not less than 2^ inches, when straight ends do not exceed 12 inches in length, shall, in each of the above cases, be calculated from the following formula : C = 14000, a constant. T = thickness of flue in decimals of an inch. D = diameter of flue in inches. P = pressure of steam allowable. C x T Formula : P = ^. When plain horizontal flues are made in sections of less than 8 feet in length and flanged to a depth of not less than 2 1/2 inches, and substantially riveted together with wrought-iron rings between such flanges, and such rings have a thickness of not less than half an inch and a width of not less than 2^ inches, BOILERS. 143 or, in lieu thereof, angle-iron rings are employed, and such rings have a thickness of material of not less than double the thick- ness of the material in the flue and a depth of not less than 2 l / 2 inches, and substantially riveted in position with wrought-iron thimbles between the inner surface of the ring and the outer sur- face of the flue, at a distance from the flue not to exceed 2 inches, with rivets having a diameter of not less than one and one-half times the thickness of the material in the flue, and placed apart at a distance not to exceed 6 inches from center to center at the outer surface of the flue, the distance between the flanges, or the distance between such angle-iron rings, shall be taken as the length of the flue in determining the pressure allowable, which pressure shall be determined in accordance with the following formula : 89600 X T 2 P = L X D Where P = pressure of steam allowable in pounds. T = thickness of flue in decimals of an inch. L = length of section in feet. D = diameter of flue in inches. All vertical boiler furnaces constructed of wrought iron or steel plates, and having a diameter of over 42 inches or a height of over 40 inches, and crown sheets of flat-sided furnaces, if made with a radius of over 21 inches, and all cylindrical shells of back connections having a radius of over 21 inches, shall be stayed as provided ***** f or fl a t surfaces. But the cylindrical shell or bottom of back connections may be stiff- ened by angles or tees secured with rivets spaced no more than 6 inches from center to center, the distance from center of rivets at edge to center of tee, or from center to center of tees, not to exceed 24 inches, tees and rivets to be of suitable section for the pressure and radius of surface braced. And the thick- ness of material required for the shells of such furnaces shall be determined by the distance between the centers of the stay bolts in the furnace and not in the shell of the boiler ; and the steam pressure allowable shall be determined by the distance from center of stay bolts in the furnace, and the diameter of such stay bolts at the bottom of the thread. Where steam chambers are formed in such vertical boilers at the upper end thereof by a sheet in form of a cone between the upper tube sheet and upper 144 PRACTICAL MARINE ENGINEERING. head of such boiler, the pressure allowed shall be determined by the diameter of such cone at the central point between the tube sheet and upper head of such boiler. Steam chimneys or superheaters formed of a flue, with an inclosing shell, shall be built as follows : The outer shell subject to internal pressure shall be con- structed under rules governing the shells of boilers, without al- lowance for any bracing to lining or flue. For lanings. The lining of flue subject to external pressure shall be con- structed as follows : Plates under 30 inches in diameter shall be at least 5-16 inch thick. Thirty inches and under 45 inches diameter, plates shall be at least ^ inch thick. Forty-five inches and under 55 inches diameter, plates shall be at least 7-16 inch thick. Fifty-five inches and under 65 inches diameter, plates shall be at least J^ inch thick. Sixty-five inches and under 75 inches diameter, plates shall be at least 9-16 inch thick. Seventy-five inches and under 85 inches diameter, plates shall be at least y% inch thick. Eighty-five inches diameter a corresponding increase in thickness of plate of 1-16 inch for every 10 inches increase in diameter. The linings of flues shall be braced as follows : On or for all boilers using salt water, carrying a steam pres- sure of 60 pounds and under per square inch, the lining shall be braced with socket bolts, with heads, and with ends of bolts threaded for nuts, with plate washers not over 12 inches be- tween centers (or equivalent) on the inside of the lining; bolts to be at least I inch diameter. On or for all boilers using salt water, carrying a steam pres- sure over 60 pounds per square inch, the lining shall be braced with socket bolts, with heads, and with ends of said bolts thread- ed for nuts, with plate washers not over 10 inches between cen- ters (or equivalent) on the inside of lining; bolts to be at least ij^j inch diameter, the diameter of the bolts to be determined by the diameter at the bottom of the thread of said bolts. On or for all boilers using fresh water, the lining may be BOILERS. 145 braced as described for boilers using salt water, or as hereafter described (or equivalent thereto), viz., with iron or steel angle rings, properly riveted to lining, and properly connected to outer shell by plate braces. These plate braces shall be of suffi- cient number and width to make space between plates not over 20 inches on the lining; the angle rings shall be at least 2 l / 2 inches by 2 l / 2 inches on lining, 5-16 inch and $ inch thick; 3 inches by 3 inches on linings, 7-16 inch and y 2 inch thick ; 3^ inches by 3^ inches on linings, 9-16 inch and ^ inch thick, and 4 inches by 4 inches on linings, 11-16 inch or more in thickness. Provided, // inches, measuring from the outer surface, the reinforcement rings may be dispensed with. 148 PRACTICAL MARINE ENGINEERING. Also plates constructed of plate steel of corrugated form, without opening in plate for bolt, corrugation forming support for bolt, will be allowed for use for manhole and hand-hole openings. No connection between shell of boiler and mud drum ex- ceeding 6 inches in diameter will be allowed. Safety Plugs. All steamers shall have inserted in their boilers plugs of Banca tin, at least one-half inch in diameter at the smallest end of the internal opening, in the following manner, to wit : Cyl- inder boilers with flues shall have one plug inserted in one flue of each boiler; and also one plug inserted in the shell of each boiler from the inside, immediately below the fire line, and not less than 4 feet from the forward end of the boiler. All fire-box boilers shall have one plug inserted in the crown of the back connection or in the highest fire service of the boiler. All up- right tubular boilers used for marine purposes shall have a fusible plug inserted in one of the tubes at a point at least 2 inches below the lower gauge cock, and said plug may be placed in the upper head sheet when deemed advisable by the local in- spectors. All fusible plugs, unless otherwise provided, shall have an external diameter not less than that of a i inch gas or steam pipe screw tap, except when such plugs shall be used in the tubes of upright boilers, plugs may be used with an external diameter of not less than that of a three-eighths of an inch gas or steam pipe screw tap, said plugs to conform in construction with plugs now authorized to be used by this Board ; and it shall be the duty of the inspectors to see that these plugs are- filled with Banca tin at each annual inspection. Gauge Cocks. All steamers having one or two boilers shall have three suitable gauge cocks in each boiler. Those having three or more boilers in battery shall have three in each outside boiler and two in each remaining boiler in the battery ; and the middle gauge cocks in all boilers shall not be less than 4 inches above the top of the flues, tubes, or crown of the fire box. Safety Valves. Lever safety valves to be attached to marine boilers shall have an area of not less than I square inch to 2 square feet of BOILERS. 149 the grate surface in the boiler, and the seats of all such safety valves shall have an angle of inclination of 45 degrees to the center line of their axis. The valves shall be so arranged that each boiler shall have one separate safety valve, unless the arrangement is such as to preclude the possibility of shutting off the communication of any boiler with the safety valve or valves employed. This arrange- ment shall also apply to lock-up safety valves when they are em- ployed. Any spring-loaded safety valves constructed so as to give an increased lift by the operation of steam, after being raised from their seats, or any spring-loaded safety valve constructed in any other manner so as to give an effective area equal to that of the aforementioned spring-loaded safety valve, may be used in lieu of the common lever-weighted valve on all boilers on steam vessels, and all such spring-loaded safety valves shall be required to have an area of not less than I square inch to 3 square feet of grate surface of the boiler, except as hereinafter otherwise provided for water-tube or coil and sectional boilers, and each spring-loaded valve shall be supplied with a lever that will raise the valve from its seat a distance of not less than that equal to one-eighth the diameter of the valve opening, and the seats of all such safety valves shall have an angle of inclination to the center line of their axis of 45 degrees. All spring-loaded safety valves for water-tube or coil and sectional boilers re- quired to carry a steam pressure exceeding 175 pounds per square inch shall be required to have an area of not less than I square inch to 6 square feet of the grate surface of the boiler. Nothing herein shall be construed to prohibit the use of two safety valves on any water-tube or coil and sectional boiler, pro- vided the combined area of such valves is equal to that required by rule for one such valve. But in no case sha'll any spring- loaded safety valve be used in lieu of the lever-weighted safety valve without first having been approved by the Board of Su- pervising Inspectors. The first paragraph of this section applies to valves con- structed in material, workmanship, and principle according to the drawings for a safety valve printed with these rules, and all common lever safety valves to be hereafter applied to the boilers of steam vessels must be so constructed. i 5 o PRACTICAL MARINE ENGINEERING. Copper Steam Pipe. All copper steam pipes shall be flanged to a depth of not less than four times the thickness of the material in the pipes, and all such flanging shall be made to a radius not to exceed the thickness of the material in such pipes. And all such pipes shall have a thickness of material according to the working steam, pressure allowed, and such thickness of material shall be de- termined by the following rule : Rule. Multiply the working steam pressure in pounds per square inch allowed the boiler by the diameter of the pipe in inches, then divide the product by the constant whole number 8000, and add .0625 to the quotient ; the sum will give the thick- ness of material required. The flanges of all copper steam pipes over 3 inches in di- ameter shall be made of bronze or brass composition, shall be securely brazed to pipe, and shall have a thickness of material of not less than four times the thickness of material in the pipes plus .25 of an inch; and all such flanges shall have a boss of sufficient thickness of material projecting from the back of the flange a distance sufficient to be properly riveted to the pipe, and of a thickness of not less than one-half inch ; and all such flanges shall be counterbored in the face to fit the flange of the pipe; and the joints of all copper steam pipes shall be made with a sufficient number of good and substantial bolts to make such joints at least equal in strength to all other parts of the pipe. Steel and Iron Pipe. The terminal and intermediate joints of all wrought iron and homogeneous steel feed and steam pipes over 3 inches in diameter, other than on pipe or coil boilers or steam generators, shall be made of wrought iron, homogeneous steel, or flanges of equivalent material ; and all such flanges shall have a depth through the bore of not less than that equal to one-half of the diameter of the pipe to which any such flange may be attached ; and such bores shall taper slightly outwardly toward the face of the flanges ; and the ends of such pipes shall be enlarged to fit the bore of the flanges, and they shall be substantially beaded into a recess in the face of each flange. But where such pipes are made of extra heavy lap-welded steam pipe up to and including 5 inches the flanges may be at- BOILERS. 151 tached with screw threads ; and all joints in bends may be made with good and substantial malleable iron elbows or equivalent material. All feed and steam pipes not over 2 inches in diameter may be attached at their terminal and intermediate joints with screw threads by flanges, sleeves, elbows, or union couplings ; but where the ends of such pipes at their terminal joints are screwed into material in the boiler, drum, or other connection having a thickness of not less than y 2 inch, the flanges at such terminal joints may be dispensed with. Where any such pipes are not over i inch in diameter and any of the terminal ends are to be attached to material in the boiler or connection having a thick- ness of less than y 2 inch, a nipple shall be firmly screwed into the boiler or connection against a shoulder, and such pipe shall be screwed firmly into such nipple. And should inspectors deem it necessary for safety they may require a jam nut to be screwed onto the inner end of any such nipple. The word "terminal" shall be interpreted to mean the points where steam or feed pipes are attached to such appliances on boilers, generators, or engine, as are placed on such to receive them. All lap-welded iron or steel steam pipes over 5 inches in diameter or riveted wrought iron or steel steam pipes over 5 inches in diameter, in addition to being expanded into tapered holes and substantially beaded into recess in face of flanges, shall be substantially and firmly riveted with good and sub- stantial rivets through the hubs of such flanges, and no such hubs shall project from such flanges less than 2 inches in any case. No cast iron nozzles, branch pipes, or elbows shall be used in connecting steam drums, superheaters, branch pipes, or steam pipes to boilers, and in no other part of steam pipes. Flanges welded to wrought iron, Bessemer, or other steel pipe may be used. No cast iron flanges will be allowed to be used on boilers for marine purposes unless such cast iron has been officially tested and test on record in the office of the local in- spectors where boiler with such appliances was constructed, and no cast iron with a tensile strength of less than 30,000 pounds will be permitted to be used for such purposes. Semi- steel of not less than 24,000 pounds tensile strength may be used for nozzles, stop-valves, branch pipes, elbows, slip-joints, flanges i 5 2 PRACTICAL MARINE ENGINEERING. to boilers, tee pipes, and water and gauge cock pipes or columns, when said semi-steel has been officially tested, and test on record in the office of the local inspectors, same as is required of cast iron. Coil and Ttibulous Boilers. All coil and pipe boilers hereafter made, when such boiler is completed and ready for inspection, must be subjected at in- spection to a hydrostatic pressure double that of the steam pressure allowed in the certificate of inspection to take effect on and after July I, 1897. The use of cast-steel manifolds, tees, return bends, or el- bows in the construction of pipe generators shall be allowed, and the pressure of steam shall not be restricted to less than one-half the hydrostatic pressure applied to pipe generators, unless a weakness should develop under such test as would ren- der it unsafe in the judgment of the inspector making such inspection. All drums attached to coil, pipe, sectional, or water-tube boilers not already in use or actually contracted for, to be built for use on a steam vessel, and its building commenced at or before the date of the approval of this rule, shall be required to have the heads of wrought iron or steel or cast steel, flanged and substantially riveted to the drums, or secured by bolts and nuts of equal strength with rivets, in all cases where the di- ameters of such drums exceed 6 inches. Except steam drums not exceeding 15 inches diameter at- tached to coils or pipe generators may be used when heads are made of malleable iron or cast steel, said drums being threaded on outside of such shell with a good full U. S. standard thread, eight to the inch, for a distance of at least I inch on such shell, the thread on head to correspond with the same and well fitted ; the end of shell projecting beyond the threaded part and screwed against a packing that will prevent water or steam to come in contact with the threaded part : PROVIDED, Such steam drums are placed outside of and not brought in contact with the heat or gases used in generating steam, and have been subjected to a hydrostatic pressure of double the steam pressure allowed. Drums and water cylinders constructed with bumped head at each or either end, any opening in the shell or heads to be re- inforced as required by the rules of the Board, the circumfer- BOILERS. 153 ential and horizontal seams to be welded and properly annealed after such welding is completed, and when tested with a hy- drostatic pressure of at least double the amount of steam pres- sure allowed, may be used for marine purposes. 154 PRACTICAL MARINE ENGINEERING. CHAPTER IV. MARINE ENGINES. Sec. 20. TYPES OF ENGINES AND ARRANGEMENT OF PARTS. The various types of marine steam engine may be classi- fied in different ways, according to the particular feature under special consideration. A typical modern marine engine as in Fig. 98 may be defined as a vertical, inverted, direct-acting, multiple-expansion, condensing, engine. Let us first examine the significance of these various terms. In the early days of marine engineering the engines were often horizontal, as shown in Figs. 101, 102, and such are still met with occasionally in special types of warship practice and elsewhere. An intermediate type, as shown in Fig. 103 and known as the inclined or diagonal engine, has been used to a considerable extent with paddle wheels. In modern practice, with rare exceptions, the marine screw engine is vertical, as in Figs. 97-100. In the earlier vertical marine engines the cylinder was at the bottom and the motion of the parts proceeded upward either directly to the crank shaft, as in the oscillating engine, Fig. 104, or to a beam or intermediate mechanism, Fig. 105,. whence it came back to the shaft. In the modern engine the cylinders are on top and the motion of the parts proceeds down- ward to the shaft. Hence in comparison with the earlier types the modern engine is called inverted. Where the connecting-rod and crank lie beyond the cross head or farther end of the piston-rod, as in Figs. 97-101, the engine is said to be direct-acting. In certain early types of hori- zontal engines in single screw ships, as represented in Fig. 102, the cylinder was sometimes placed close to the shaft and two piston-rods were fitted passing beyond the shaft, one above and the other below. Then from a crosshead at this point the mo- MARINE ENGINES. 155 tion came back to the crank pin by a connecting-rod in the usual way. Such engines were called return connecting-rod or back-acting. In still earlier times the same type of engine placed on end, with the cylinder at the bottom, and known as the stee- Fig. 97. Longitudinal Section, Compound Engine, Mercantile Type. pie engine, was frequently fitted in side-wheel paddle steamers, and a modification of this is occasionally met with abroad at the present time. In early marine engines the expansion of steam always 156 PRACTICAL MARINE ENGINEERING. MARINE ENGINES. 157 took place in one cylinder only. In the typical modern engine the steam is passed through a series of cylinders from one to another of increasing size. Such engines in general are termed Marine Engineering Fig. 99. Triple Expansion Engine, End View Looking Aft. multiple expansion. If the steam is thus used successively in two cylinders or the expansion occurs in two stages, the engine is said to be a compound; if in three cylinders or three stages, it 158 PRACTICAL MARINE ENGINEERING. is a triple or triple expansion; if in four cylinders or four stages, it is a quadruple or quadruple expansion, etc. Where the steam after being used in the cylinder is ex- Fig. 100. Triple Expansion Engine; End View Showing Condenser in Back Fr ramng. hausted into the air, the engine is said to be high-pressure or non-condensing. In the typical modern engine the steam is ex- hausted to a condenser, thus giving the advantage of an in- MARINE ENGINES. 159 Such creased ratio of expansion and a decreased back pressure, engines are called condensing. Engines are often given special names according to the nature of the mechanical movements employed. In the usual type, as we have already seen, the motion is direct-acting and proceeds through piston, piston-rod, crosshead, connecting-rod, Fig. 101. Horizontal Direct Acting Engine, Outline. crank-pin and crank-shaft. In the beam engine, as shown in Fig. 105, the motion passes from the piston-rod to a crosshead and then by link or parallel motion to the beam. Thence from the other end of the beam it passes by the connecting-rod to the crank-pin and crank-shaft. Such engines are especially suited to side-wheel paddle steamers, and for many years were Fig. 102. Horizontal Back Acting Engine, Outline. considered the standard engine for use on river, bay and lake steamers. In more recent practice, however, the vertical direct- acting engine with screw propeller is to a considerable extent displacing the beam-engine with paddle-wheel, even in its own territory. In the oscillating engine, a favorite in British practice for side-wheel paddle steamers, the cylinders are located below the 160 PRACTICAL MARINE ENGINEERING. shaft and are swung on trunnions, as shown in Fig. 104. The piston-rod is connected directly to the crank-pin, the piston-rod and connecting-rod forming thus but one member. This mo- tion is made possible by swinging the cylinder on trunnions, as may be readily seen by the diagram. The trunk type of hori- zontal engine, as shown in outline in Fig. 106, was often fitted in former years where economy of transverse or athwartship dimension was necessary. In this engine the use of the piston- rod was avoided by the large trunk, to which the connecting- rod was directly attached, as shown. The stern-wheel western river boat engine, as shown in Fig. 155, is a direct-acting horizontal engine connected to the stern wheel, and provided with a peculiar type of valve gear. Fig. ]03. Inclined Engine, Outline. Further reference to some peculiar features of this engine will be made in Section 22. The various members of a multiple-expansion marine en- gine may be arranged in a great variety of ways as regards the location of the cylinders, the crank angles, and the way in which the cranks follow each other around in the revolution. These are illustrated in Figs. 107-110. Of the many combinations which might be made, only the more important are men- tioned. Throughout these diagrams the high-pressure cylinder is denoted by //, the low-pressure cylinder by L, the interme- diate cylinder of a triple-expansion engine by /, and the first and second intermediates of a quadruple-expansion by/!,and/ 2 , respectively. Where the total cylinder volume is divided be- MARINE ENGINES. 161 tween i\vo, each of half size, both of the latter are given the same letter. The course of the steam through the engine is also indicated by the arrows. For compound engines the usual ar- rangements are illustrated in Fig. 108. We may have two or three cylinders and one, two or three cranks. In the latter case the entire volume of low-pressure cylinder is divided between two cylinders, each of half the total volume. The first arrange- ment with high-pressure cylinder on top of low-pressure is known as a single-crank tandem compound, but is rarely met Fig. 104. Oscillating Engine, Outline. with in marine practice. The other arrangements may be placed, of course, with either end forward. The various crank angles are shown in Fig. 107 at I, 2, 3, 4 and 5, the crank marked / in No. 5 being in this case for one of the L. P. cylin- ders. With two cranks the angle between may be either 90 deg. or 180 deg., or slightly greater or less than 180 deg., as 175 deg. or 185 deg. The 90 deg. angle is undoubtedly the best for all-around service. The 180 deg. angle gives a better balance to the moving parts and admits of a simplification of valve gear. 162 PRACTICAL MARINE ENGINEERING. and is sometimes preferred for these reasons. There is, how- ever, a liability of the engine's sticking on the center and the general readiness of handling is less than with cranks at 90 deg. To overcome this, angles of 175 deg. or 185 deg., as shown at 2, are sometimes used, the balance of moving parts in such case being substantially as good as with an angle of 180 deg. Fig. 105. Beam Engine, Side Elevation. With three cranks the angles are usually equal, and hence 120 deg. each. Occasionally they are slightly varied from these values in order to give a more uniform rotative effort, or to give a better balance to the forces causing vibration. MARINE ENGINES. 163 For the triple-expansion engine the more important ar- rangements of cylinders are shown in Fig. 109. We may have three cylinders or more, and two, three or more cranks. The Fig. 106. Trunk Engine, Outline. most common types have either three or four cranks, in the lat- ter case the total L. P. volume being divided between two cylin- (DCDG'OO 8 9 10 11 Fig. 107. Various Crank Angles. ders, each of half the total volume. The crank angles are usually 1 20 deg. with three cranks, and 90 deg. with four, ; * \ / ^^ 1 # L H / ^ L L H L 7 2 / / Fig. 108. Cylinder Arrangements for Compound Engine. though occasionally slight variations from these values are adopted in order to obtain a better balance of the forces causing vibration. Of the various arrangements of cylinders shown in i6 4 PRACTICAL MARINE ENGINEERING. Fig. 109, each may, of course, be placed either end forward in the ship. We may also have the various sequences and arrange- ments of cranks as indicated in Fig. 107, the changes of letter- ing where necessary being readily seen. For the quadruple-expansion engine the more important cylinder arrangements are shown in Fig. no. The number of ^_I I L I / 1 L L T x /h Fig. 109. Cylinder Arrangements for Compound Engine. I L z I / / 3 / Fig. 110. Cylinder Arrangements for Quadruple Expansion Engine. cylinders may be four, five or six, with four or five cranks. With five cranks the angles are usually equal, and hence of 72 deg.,. though as with three and four cranks slight departures might be made to obtain a better balance of the forces producing vibra- tion. The arrangements of cylinders shown in Fig. no may l>e placed in the ship either end forward, and various crank se- MARINE ENGINES. 165 qucnccs in addition to those shown in Fig. 107 may be easily arranged. One of the chief tendencies of modern practice is to pay especial attention to the balancing of the forces producing vibration. The use of irregular crank angles in this connection lias been already referred to. In addition, and of not less im- portance, the larger cylinders with the larger and heavier pis- tons are now frequently placed inside, with the lighter moving parts on the outside, as in Fig. 109, Nos. 3 and 5, or Fig. no, No. 2. Sec. 21. DESCRIPTION OF PRINCIPAL PARTS OF A MARINE ENGINE. In describing the principal parts of the typical modern marine engine, we may take first the stationary, and then the moving parts. [x] Cylinders. As shown in Figs. 97-100, the cylinders are at the top of the engine and consist each of a cylindrical chamber containing the moving piston. The steam is received from the steam chest alternately in either end and thus forces the piston up and down. The motion is then transmitted through the piston-rod and con- necting-rod and thus the revolution of the crank and the crank- shaft is produced. Cylinders are made of cast iron of the highest grade. Each one, as shown in the figures, consists essentially of a cylindrical body or barrel, with which is usually cast the lower or bottom head. With the barrel are usually cast also the valve casings and chests and all ports and passages, as well as the necessary feet for attachment to the columns, lugs for attaching braces, etc. The top head or cover is cast separately and is secured to an appropriate flange on the barrel by means of stud-bolts. In some cases the head is made in a single thickness, conical in form to correspond to the piston, and ribbed on top for strength. In other cases it is made by a double shell or in two thicknesses with connecting ribs between. The lower head is formed in the same general way, but, as noted above, is usually cast in one piece with the barrel. In many cylinders, as shown in Fig. in, liners are fitted within the barrel or cylinder proper. These are of extra hard and fine grained iron, and are fitted for one or both of the fol- lowing purposes: (i) To provide a working surface admitting of replacement in case of excessive wear. (2) To provide a i66 PRACTICAL MARINE ENGINEERING. jacket space between the barrel and liner in case the cylinders are to have steam jackets. The space thus formed is filled with steam from the boiler, thus providing a jacket or layer of steam entirely surrounding the steam cylinder. Such an arrangement is known as a steam jacket, and is used to increase the economy of the engine as noted in Section 59. The liners are usually secured at the lower end by a flange, as shown in Figs, in, 113, Marine 'Engineering Fig. 111. Cylinder with Liner and Double Valve Chests. the joint between the end faces of the liner and barrel being carefully made in order to prevent leakage, especially if the space between the barrel and liner is to be used as a steam jacket. At the upper end the joint between liner and barrel may be made in a variety of ways. As shown in Fig. 112, a packing space is formed between the liner and barrel. This is filled with some form of elastic MARINE ENGINES. 167 packing held in place by a ring attached to the liner as shown. In this way the tipper end of the liner is free to come and go as expansion and contraction may require, while the packing main- tains the joint steam tight. In another mode of fitting, a groove of dovetailed cross section is turned out partly in the liner and partly in the barrel, and a ring of soft metal or packing is ex- panded into the space thus formed. The bore of the cylinder or liner is made uniform except near the top and bottom, where it is counterbored out slightly larger, so that at the extreme ends of the stroke the piston rings may overrun the counterbore, and thus avoid wearing a shoulder in the metal. Fig; 112. Joint Between Liner and Barrel, Top. Fig. 113. Joint Between Liner and Barrel, Bottom. Cylinders as well as steam jackets are usually provided with drain cocks and valves with suitable piping, so that water collect- ing within them may be drained away In addition, automatic relief cocks or valves (see Sec. 24) should be fitted, set to open under an appropriate pressure, and thus furnishing relief in case a large quantity of water may find its way into the cylinder. The cylinders are supported directly upon the columns which are attached to facings on the lower head, or to lugs cast on the lower part of the barrel in case its diameter is not suffi- cient to reach out over the tops of the columns Sec Fig. 114. For mutual support the cylinders are quite commonly tied to- i68 PRACTICAL MARINE ENGINEERING. gather by braces, or flanged and bolted to each other. In some cases, however, the cylinders are allowed to stand alone and in- dependently, while in the other cases of recent practice a form of connection has been adopted, consisting of a vertical tongue and grooved joint. This allows differences of expansion ver- tically and fore and aft, but provides mutual support trans- versely. Fig. 114. Double Inverted Y Columns. The valve chests with the various ports, passages, etc., are also cast with the cylinders, as shown in the figures. These parts will receive further notice in connection with valves. See Sec - 46. [a] columns. The columns serve to support the cylinders and to connect them with the bed-plate. They also serve to support the guide surfaces for the crossheads, and thus receive the transverse MARINE ENGINES. 169 thrust of the connecting-rods. Columns are made either of cast iron, cast steel or forged steel. When of cast metal they are usually in the form of an inverted Y, as shown in Figs. 114, 115, and of a box or I-formed section. When forged, the col- umns are usually cylindrical or slightly tapering, and sometimes hollow. Cast inverted Y columns both front and back of the en- gine, as shown in Fig. 114, for many years constituted standard practice. More recently, however, cast inverted Y columns at the back of the engine and cylindrical forged columns in front, Fig. 115. Inverted Y and Cylindrical Columns. as in Figs. 115, 116, are commonly employed in representa- tive marine practice. In such case either one or two columns may be fitted in front and one in the rear. When the columns are all cylindrical, it is customary to provide four for each cyl- inder. Such columns are usually placed vertical, as in Fig. 117, though occasionally they are spread somewhat at the base, as in Fig. 115. In some cases of modern practice four vertical columns of T section have been provided for use with a crosshead as shown in Fig. 134. The columns stand in pairs, one forward and one 170 PRACTICAL MARINE ENGINEERING. aft, and the wings of the crosshead carrying the slide surfaces work between them on the guides carried on their inner faces. In some cases the condenser is placed back of the engine Fig. 116. Inverted Y and Cylindrical Columns, Warship Type. and on the bed-plate, as in Fig. 100. In this case the back col- umns are either cast with the condenser shell or consist of short vertical columns standing on top of the condenser; which thus constitutes a part of the support of the cylinders as shown. MARINE ENGINES. 171 To resist the racking and cross-breaking stresses to which the columns may be subject, it is necessary, especially with plain cylindrical columns, to provide transverse and even longitudinal ties and braces. The usual arrangement of such bracing is shown in Figs. 115, 116, 117. It will be noted in particular that the transverse bracing between a pair of columns as in Fig. 117 unites them into a single girder, thus providing vastly more strength to resist lateral stresses due to rolling of the ship, etc., than could be furnished by the columns themselves and without the assistance which the bracing is able to provide. Fig. 117. Cylindrical Columns. The guide surface for a crosshead is fitted in various, ways according to the style of crosshead, the style of column and type of practice. The simplest arrangement is as shown in the cross- section of Fig. 118, in which the guide surface is fitted directly on the inner face of the Y column. In the arrangement of Fig. 115 the guide surface is fitted on a separate slab of rather harder and finer grained cast iron, and hence better adapted for bear- ing purposes. Between this slab and the face of the column a 172 PRACTICAL MARINE ENGINEERING. space is left as shown, and through this may be circulated a stream of water to absorb the heat generated by the friction, and thus to keep the bearing surface cool. With cylindrical col- umns the guide c urface must be fitted as a separate slab for each crosshead, and usually in the manner shown in Fig. 117. These slabs may be of cast iron, steel or bronze, and are carried on longitudinal bars attached to the columns. The form of cross- section may be either hollow for water circulation, or plain or ribbed on the back for strength, as the case may require. A common form is that shown in Fig. 117, thinner towards the Fig. 118. Section of Cast Column Showing Guide Surface. ends and thicker in the middle as a girder, to provide the neces- sary strength at this point. For further details of the guide surfaces which depend on the form of crosshead used, reference may be made to [7]. [3] Bed-Plates. The purpose of the bed-plate is to support the feet of the columns, and thus to carry the weight of the cylinders and at- tachments, to provide seatings and support for the crank-shaft bearings, and generally to serve as the foundation piece upon MARINE ENGINES. 173 which the engine rests, and through which its weight and the various stresses developed are transferred to the structure of the ship. As usually formed it consists of a series of transverse box Fig. 119. Bedplate for T Marine Enginttrlng pie Expansion Engine in one Casting or I girders, one for each crank-shaft bearing, these being con- nected together by fore and aft members, as shown in Figs. 119, 121. Bed-plates are usually made of cast iron or cast steel. Fig. 120. Details of Bedplate in Fig. 119. Sections Showing Main Pillow Block. Rarely bronze or special forms of plate girder may be em- ployed. Large bed-plates instead of being made in one casting are often made in sections and bolted together. The bed-plate is secured to the ship by holding doivn bolts passing through the 174 PRACTICAL MARINE ENGINEERING. flanges of the plate and of the specially strengthened structure of the ship underneath, known as the engine seating or foun- dation. Further examples of bed-plates may also be noted in Figs. 97-100, 114, 116. o o o o o lo Fig 1 . 121. Bedplate in Sections. End View of one Section. [4] Engine Seating. This structure is a part of the ship, and serves to give the final support to the weight of the engine, and to lead the stresses due either to its weight or to its operation, into the structure of the ship as a whole. The usual character of the seating is shown in Fig. 122. It consists of a cellular construction formed o \0 E 101 i e LONGITUDINAL SECTION. TRANSVERSE VIEW. Fig. 122. Engine Seating. by longitudinal and transverse vertical plates, stiffened and con- nected at the corners by angle irons, and usually forming a con- tinuous structure with a part, at least, of the regular internal members of the ship itself. We will now turn to the chief moving parts of the engine. MARINE ENGINES. 175 [5] Pistons. The piston is the moving part of the engine upon which the steam directly acts, and which by the steam pressure is driven back and forth in the cylinder, and from which, through the piston-rod, crosshead and connecting-rod, the motion is trans- Fig. 123. Conical Marine Piston. mitted to the crank and crank-shaft. The requirements for the piston are therefore : (i) It must be able to support the load which the steam pressure brings upon it. (2) It must be of such form as to admit of movement up and down in the cylinder, at the same time making a steam tight joint between its outer edge Fig. 124. Marine Piston, Enlarged View, Showing Packing Rings and Follower Plate. and the cylinder walls. (3) Provision must be made for its se- cure attachment to the piston-rod, through which the forces are transmitted to the remaining moving parts of the engine. The usual form of marine piston is shown in Fig. 123, and consists of a shell of conical form with a central boss or body for carrying the piston-rod as shown. Around the outer edge of i 7 6 PRACTICAL MARINE ENGINEERING. the piston the metal is thickened up to provide for the packing- rings, which are fitted to make a steam tight joint between the piston and cylinder walls. The fitting of these rings is shown in 124. The rings are usually two in number, and are formed TOP-RING w-J Fig. 1.25. Marine Piston, Joint in Packing Rings. of cast iron turned first to an outside diameter slightly larger than the bore of the cylinder.- They are then cut as shown in Fig. 125, and enough is taken out so that they may be sprung together sufficiently to allow their entrance into the cylinder bore. Care is taken to so locate the two rings that the cuts Marine Engineering Fig. 126. Marine Piston, Steel Springs for Packing Rings. shall not come opposite, and thus the opportunity for a direct leak through from one side to the other is avoided. In order to still further prevent such leakage, a tongue as shown in the figure is usually fitted across the opening. The tongue piece, which is usually of brass, is attached to the ring and overlaps MARINE ENGINES. 177 the slit, as shown. The joints between the ring and tongue piece are carefully fitted so that in this way the ring may open and shut as circumstances may require, while the opening into the slit remains closed to the entrance of steam. When the pis- ton is of any considerable size it is customary to aid the natural elasticity of the rings by steel springs, as shown in Fig. 126. These bear on the bottom of the recess formed in the piston, and on the inner surface of the rings, and thus the latter are forced outward against the surface of the cylinder. The body of the piston itself, as shown in Fig. 124, is turned slightly smaller than the diameter of the cylinder, so that it clears the latter at all times, while the rings extend beyond and make the joint with the cylinder wall. The rings and springs Fig. 127. Ramsbottom Rings. are fitted as shown between the lower flange of the piston body an-1 a plate known as the follower plate or ring. By removing the latter the rings and springs may be removed when necessary for overhauling ana refitting. The follower plate is secured to the piston by stud bolts and nuts, as shown in the figure. In the best class of work all joints between the piston and rings, be- tween the follower plate and rings and between the two latter are carefully made by hand scraping and fitting, in order to re- duce the chances of leakage to the smallest possible limits. Many variations are met with in the details of the form and fittings of pistons. In some cases they are flat and either solid or hollow, as shown in Figs. 97, 128. PRACTICAL MARINE ENGINEERING. In some cases ramsbottom rings are fitted instead of the rings of Fig. 123. These consist of two or three narrow rings turned slightly larger than the cylinder with a piece cut out so that they may be sprung on over the body of the piston, and into grooves, as shown in Fig. 127. No special springs are fitted, and the natural elasticity of the rings is depended upon to give the necessary pressure between the ring surface and the cylinder. It is easily seen that no follower plates being fitted, the rings cannot be examined or removed without removing the piston. To avoid this difficulty the arrangement of Fig. 128 is sometimes used. Here the rings are carried on a larger solid ring, as shown, and sometimes known as a bull ring. This is carried between the faces of the piston flange and follower plate, and thus by the removal of the latter the whole arrangement may be withdrawn and examined. There is usually some clearance be- tween the inner surface of the bull ring and the body of the pis- Fig. 128. Piston with Ramsbottom Rings on Bull Ring. ton, as shown in the figure. This allows the whole arrange- ment of rings to move transversely independent of the piston body, thus making allowance for lack of alignment between the axis of the- piston-rod and the axis of the cylinder, or for wear in the latter. While light packing rings of cast iron fitted as above de- scribed without the assistance of steel springs may prove satis- factory for small pistons, the more standard method of Fig. 123 is to be recommended for all cases where the pistons are of any considerable size. In present practice pistons of the form shown in Fig. 123 are made of cast steel. Pistons of the form shown in Figs. 97, 128, are more commonly made of cast iron. The chief advantage of the conical form of piston lies in the saving of weight for the necessary strength and stiffness, as compared with other forms. This superiority has gained for it MARINE ENGINES. 179 almost universal adoption in modern practice, and it may be considered as the present day representative form of marine piston, and the one which will naturally be adopted unless there may exist special reasons for the adoption of the older type. [6] Piston-Rods. The piston-rod is that member of the moving parts which serves to support the piston, to carry the forces due to the steam pressure through the stuffing box outside the cylinder, and through the crosshead to communicate them to the connect- ing-rod and other moving parts. The requirements are there- fore as follows : (i) It must have sufficient strength and stiffness to safely carry the load coming from the piston. (2) It must be provided at the upper end for attachment to the piston, and at the lower end to the crosshead. (3) It must be of such form as to admit of readily making a steam tight joint where it passes out of the cylinder. To fulfil these conditions the piston-rod, as |inmi|iiniii|ii c&m liUii,i;iii,|j!|ii I 'II iim ; 1 1 ^\& !i;i;:. : !'!i : ' ! 1 1 1 i ! ! i Marine Engineering Fig. 129. Piston Rod. shown in Fig. 129, has the form of a uniform cylindrical rod ex- cept at the ends where it joins the piston and crosshead. The common form of attachment to the piston is shown in the figure. The rod is sometimes tapered where it lies in the piston, and sometimes parallel. It is often relieved from direct bearing ex- cept near the top and bottom, so as to give definite points of bearing where it is most needed. A shoulder or ring is also fitted, as shown, so as to give a definite stop against which the Dody of the piston rests. The end of the rod is threaded and a nut on top completes the fastening. This nut is sometimes hexagonal and sometimes cylindrical with longitudinal grooves, a spanner wrench being used in the latter case to set the nut down. The fitting at the lower end of the piston-rod depends on the style of crosshead used, and may be more appropriately de- scribed under that heading. In modern practice with conditions requiring the highest grade of material and most careful design, the piston-rod is i8o PRACTICAL MARINE ENGINEERING. often made hollow. This practice also extends to most of the other cylindrical elements of the engine such as cylindrical col- umns, crosshead pins, connecting-rods, crank-pins, crank, line, Fig. 130. Marine Crosshead. thrust, and propeller shafts. Inasmuch as this style of construc- tion was first commonly introduced in connection with shafting, the reasons for such practice and its advantages may properly be discussed under that heading. Fig. 131. Marine Crosshead, Slipper Type with Cotter Fastening for Piston Rod. [7] Crossheads. There are several types of crosshead to be met with in marine practice. In Fig. 130 is shown one of the more com- MARINE ENGINES. 181 mon forms. It consists essentially of a cubical body A, through which in a vertical direction is the hole for the piston-rod. Ex- tending out on either side longitudinally are the two crosshead VERTICAL VIEW. TRANSVERSE VIEW. Fig. 132. Marine Crosshead, Slipper Type. pins B and C. Then attached to the two remaining sides trans- versely are the slides as shown. The connection between the crosshead and the piston-rod is commonly by means of thread and nut, as shown in the figure, in the -same way as for the con- Marixt Engineering Fig. 133. Crosshead formed on Lower End of Piston Rod. nection to the piston. In some cases a pin or cotter joint, as shown in Fig. 131, is used instead of the thread and nut on the end. The slide surfaces D and E rest on the guide surfaces of the columns, as above described, one side taking the load when 182 PRACTICAL MARINE ENGINEERING. going ahead and the other when backing. A crosshead of this type is therefore suitable for double inverted Y columns where there is a guide surface on both back and front sides of the en- gine. Where cylindrical columns are used, as in Figs. 115-117, the slipper form of crosshead is commonly fitted. This is shown in Fig. 132, and so far as the part connected with the piston- rod and carrying the crosshead pins is concerned may be the same as in Fig. 130. Instead of two wings carrying slides, how- ever, there is but one with the form shown in the vertical view. The corresponding form of guide is shown in Figs. 115, 117. Marine Engineering Fig. 134. Marine Crosshead, Special Type. When going ahead the face A of the slipper bears against the face B of the guide. Cheek pieces or gibs C and D are se- cured to the column, thus forming guide surfaces on their in- ner faces E and F. Against these the faces G and H of the slip- per bear when in backing motion. The go-ahead surface is therefore formed on the faces A and B of the guide and slip- per, as with Fig. 130, while the backing surface, instead of be- ing provided on the opposite column and on another slide piece on the other side of the crosshead, is formed on the reverse side, G and H, of the slipper, and on the cheek pieces, as shown. These types of crosshead are suited to the so-called forked type of connecting-rod, as described below, for which the cross- MARINE ENGINES. 183 head pins are a part of or fast in the crosshead, and are naturally two in number, one on either side fore and aft, as shown. In the other type of connecting-rod which is frequently met with, the rod is not forked, and the pin is fast in the upper end, and is single rather than double, while the crosshead member fur- nishes the bearing. This arrangement is shown in Fig. 133. The crosshead body is usually forged up on the lower end of the piston-rod, and together with a suitable cap and bearing brasses forms the bearing for the pin which is fast in the upper end of the connecting-rod, as shown. The wings for carrying the slides may be attached and the slides may be fitted in the same d Fig. 135. Marine Crosshead, Special Type. general manner as in Figs. 130, 132, either double or of the slipper type. A third form of crosshead occasionally found in modern practice was referred to in [2], and is here shown in Fig. 134. This type of crosshead is a marine adaptation of a type very common in stationary engine practice. The slide surfaces are formed on the opposite faces of webs or wings extending out from the body of the crosshead, and bearing on the guide sur- faces formed on the columns. In Fig. 135 is shown a somewhat different form of the same type of crosshead, the latter being suited to two columns and the former to four. As noted in [6], the crosshead-pins, in the most advanced practice, are often made hollow. In some cases the hole is 1 84 PRACTICAL MARINE ENGINEERING. parallel ; in others its diameter decreases from the outer end inward, thus giving the most metal at the inner end, where the greatest stresses are likely to be found. See Fig. 130. I if a Marine Enyineeriny Fig. 136. Marine Connecting Rod. [8] Connecting-Rods. Fig. 136 illustrates perhaps the more common type of con- necting-rod. At the upper end it is forked or formed into a U Fig. 137. Marine Connecting Rod. shape, each branch being provided with a bearing and connec- tions for one of the crosshead-pins. This type of end corre- sponds therefore to the type of crosshead shown in Figs. 130, 132. MARINE ENGINES. 185 For connection to the crank-pin, the lower end of the rod is fitted with brasses and cap, all secured to the forged out foot of the rod by through bolts as shown. For the type of crosshead shown in Fig. 133 the rod is formed, as shown in Fig. 137, with a U-shaped upper end fitted to receive the two ends of the crosshead-pin, which is thus made fast to the rod. This pin is then seated in a bearing in the cress- head, as described under that heading. The lower end of the rod is usually of the same form as shown in Fig. 136. Rarely the gib and key form of connecting-rod end as illus- trated in Fig. 138, is found in marine practice. In external form marine conecting-rods usually increase in transverse dimension from top to bottom. In some cases they are given a uniform taper from one end to the other, as in Marine t-nginetring Fig. 138. Marine Connecting Rod with Gib and Key Connections. Figs. 136-138, while in others the extra metal is slabbed off on the forward and after sides until the thickness in the fore and aft direction is uniform from top to bottom. As noted in [6], the connecting rod, in the most advanced practice, is often hollow, a hole of uniform bore being drilled from one end to the other, as shown in Fig. 137. [9] Crank Shafts. Modern marine crank shafts are of two principal types, forged and built up. Fig. 139 shows a portion of a built-up crank shaft. It consists, as shown, of two crank urbs or throws, A and B, one crank-pin C and two portions of shaft D, E. Built-up crank-shafts are usually made contiuous for the whole engine, and in such case the piece of shafting D connects i86 PRACTICAL MARINE ENGINEERING. the crank shown with the one next to it, and thus serves as a common member for the two. In this type of crank-shaft the various sections of shaft, the crank-pin and the webs, are all made separately, and then fitted and secured together. This is usually done by shrinking and keying the various cylindrical members into the sections of web as shown in the figure. Fig. 140 shows a section of a forged crank-shaft. In this case a- forging of suitable form is made, and the various parts are then formed by cutting out and machining this forging. In many cases, moreover, the series of such sections for the entire engine are forged and machined in one piece, the result being a continuous forged crank-shaft. In other cases the section for each crank, as shown in the figure, is forged and made sep- Fig. 139. Section of Built Up Crank Shaft. arately, the various sections being then secured together by flange couplings, as shown in Figs. 140, 141. The advantage of making the shaft in sections lies in the fact that in many cases the sections may be made interchangeable, and thus a single spare section is sufficient for the replacement of any section which may become disabled through accident, and in any event a break will usually require the refitting of a single new section instead of an entire shaft. Forged crank-shafts are commonly used in naval practice, and in general where the type of construction is of specially- high grade and the saving of weight an important feature. Their use in all departments of marine practice seems, more- over, to be on the increase. Built-up crank-shafts, however, are still much used in the mercantile marine, especially where the MARINE ENGINES. 187 conditions are easily fulfilled, and their somewhat greater weight is not a serious objection. As noted in [6], the cylindrical members of marine engines are often made hollow, especially in the more advanced types of design. Fig. 140 shows a crank-shaft section with hollow pin and shaft. As this feature was first commonly introduced in connection with shafting, and is more often met with here than elsewhere, the advantages of such construction may be now considered. The advantages of a hollow cylindrical member such as a piston-rod, connecting rod, crank-pin, or length of shafting, are two in number, (i) It is stronger for a given weight, or for a given strength less weight is required. (2) The central core of metal is removed, and this is the most liable to contain cracks or flaws, which might in time extend out into the remaining Marine Engi>-Mring " Fig. 140. Section of Forged Crank Shaft. metal, and thus seriously weaken the member. Furthermore, the hole gives opportunity for the inspection of the metal on the inside, and thus increases the opportunity for the detection of a flaw which might not extend to the outer surface, or which might there be so small as to be overlooked. For cross-breaking or for torsion the metal in the ii-- terior of a cylindrical member is of comparatively small value. Thus in a lo-inch shaft, the inner core 5 inches in diameter is worth no more than a shell of metal about .16 inch thickness lying next the outer surface. Or, as a further illustration, a 16- inch shaft with a lo-inch hole is equal to a 1 5-inch solid shaft. In other words, a shell of metal 1-2 inch in thickness all around added on the outside of the 1 5-inch shaft will make up for the removal of the inner core of 10 inches diameter. In the latter case the hollow shaft would weigh about 65 per cent of the equivalent solid shaft. The saving in weight for a desired i88 PRACTICAL MARINE ENGINEERING. strength may thus be very considerable, but it is probable that the advantages noted above under (2) are of still greater im- portance, and in some cases might justify the added cost of making the member hollow where such addition could not be justified by the saving of weight only. Fig. 141. Detail of Flange Coupling and Bolt. [10] I/ine Thrust and Propeller Shafts. From the crank-shaft the motion is carried on to the pro- peller by means of a number of lengths or sections of shafting according to the distance from the engine to the stern of the ship. Of these sections the one to which the propeller is at- tached is known as the propeller shaft. One length must also I Fig. 142. Flexible Coupling. be specially fitted to transmit the forward thrust to the thrust bearing and thence to the ship. This section is known as the thrust shaft. Other intermediate lengths form the line shafting. These various lengths, with the exception noted below, are usually connected by flange couplings, as in Figs. 140, 141. The coupling from the engine to the next section of shafting aft is MARINE ENGINES. 189 often made of such form as to allow a certain degree of flexi- bility between the line shafting and the crank shaft. A form of such coupling is shown in Fig. 142. One of the coupling flanges is faced off, as shown like the segment of a sphere, with a ball and socket joint at the center to keep the two parts in line. The coupling bolts are then set up with nuts bearing on some form of spring washer which will take up the slack as the shaft re- volves, even when not exactly in line. The action of the coup- ling will be readily seen from a study of the figure. Various other styles of coupling are in use, but the one shown will suffi- ciently illustrate the principles involved. The thrust shaft will more naturally find its description with the thrust bearing. See [ 1 1 ] . The propeller shaft is formed with the after end tapered Marine Enyinetring c Fig. 143. Outboard Shaft for Twin Screw Ship. and fitted with screw thread for a nut, as shown in Fig. I43C. The propeller is fitted with a corresponding taper, and is held in place by a nut and prevented from turning on the shaft by one or more keys, as indicated in the figure. In the case of twin screws, where the propeller shafts pass outside the skin of the ship some distance forward of the stern it often becomes necessary to form the outboard shaft in more than one length, coupled together by flange couplings as above described. In all cases it is necessary to form one end of the section of shaft which passes through the skin of the ship with a plain end, so that it can be passed through 'the outboard bear- ing as described in [n]. In cases therefore where the propeller ipo PRACTICAL MARINE ENGINEERING. cannot be attached directly to the plain end, as in single screw ships, it becomes necessary to provide a special form of socket coupling connecting the after end of the last inboard length of shafting with the forward end of the length which passes through the ship. The general plan of this arrangement is shown in Fig. I43b, and the details of the coupling in Fig. 144. Such couplings vary somewhat in detail, but the form shown in 'Marine Enginetring SECTION ON C-D Fig. 144. Detail of Socket Coupling. the figure will serve to illustrate the type. It consists, as shown, of the enlarged end of the inboard shaft, in which is bored out a tapering socket of appropriate size to take the tapered for- ward end of the first outboard length of shaft. The two are then secured together by keys and locking ring, as shown in the figure. [11] Bearings. The various types and forms of bearing and bearing surface to be found in a marine engine may be conveniently examined under one heading. (i) Crosshead and Guides. The stationary part of this bear- ing has been already referred to in [2], and as there noted is usually of a hard and fine grained cast iron. The moving sur- face on the crosshead is usually of brass, bearing-bronze or white metal. When of brass or bronze it is in the form of a bearing piece secured to the crosshead, as shown in Fig. 130. When of white metal a suitable slab of brass, cast i-on or cast steel, with shallow pockets formed in its surface, forms the bear- ing piece. These pockets have slightly overhanging edges, and into them molten white metal is run, the general layout and arrangement being similar to that for the main pillow block bearings shown in Fig. 146. The white metal is then machined down to a bearing surface, in some cases being hammered with a round pene hammer in order to compress or harden the metal. MARINE ENGINES. 191 The spaces between the pockets thus become spaces between the sections of white metal, and serve for the circulation and supply of oil to all parts of the bearing surface. In some cases shallow channels or oil grooves are cut in the guide surface or stationary part as well, but this is the least necessary with the arrangement of white metal as described. Liners or packing pieces are often placed between the bear- ing piece and the crosshead, so as to allow for adjustment and take up in case of wear. (2) Crosshead Pins. The general arrangement for the bearings are indicated in Figs. 133, 136, 137. The crosshead Marine Engineering SECTION THROUGH A-S Fig. 145. Main Pillow Block, Cap. SECTION THROUGH C-D pins are steel, and the bearing surface is brass, bronze or white metal. The bearing pieces are two in number, forming between them the hollow cylindrical bearing, and are held in place by steel caps as shown. From the fact that in former practice such bearing pieces were almost universally made of some grade of brass, they are still usually known as brasses. When white metal is used it may be fitted in the same gen- eral manner as above described for the crosshead slides, or in some cases, especially for small surfaces, the white metal sec- tions are turned down until a continuous bearing surface is ob- tained on both white metal and brass. For the distribution of IQ2 PRACTICAL MARINE ENGINEERING oil, grooves or channels are then cut to serve in place of the channels between the sections of white metal, as in Fig. 146. (3) Crank Pin. The usual arrangement of this bearing is sufficiently shown in Figs. 136, 137. In modern practice the material used is commonly white metal in a brass backing or bearing piece, as already described. In older practice brass or bronze was commonly employed. (4) Pillow Block or Crank Shaft Bearings. The usual ar- rangements are shown in Figs. 120, 145, 146. Here likewise in modern practice the usual surface is white metal in a brass backing piece. In all bearings for cylindrical elements, as the ^-Hjj^' SECTION ON C-D SECTION ON Fig. 146. Main Pillow Block Bearing. crosshead pin, crank-pin, crank-shaft, etc., the two brasses are held from separating by a cap and bolts as shown, and from pinching the pin or shaft too tightly by filling pieces or liners. These by adjustment allow of take up for wear. In modern practice the lower pillow block brass is often made in the form of a half cylinder, as shown in Fig. 146, so that by the removal of the cap and upper brass the lower one may be slid around the shaft and so removed for adjustment or repair, or a new brass replaced without disconnecting the crank shaft and lift- ing it from its bearings, as is necessary when the lower brasses are of the shape shown in Fig. 120. MARINE ENGINES. 193 (5) Line-Shaft or Spring Bearings. In these bearings the chief load is the weight of the shaft, at least so long as the bear- ings and shaft are in line and adjustment. It is therefore quite common to provide for such bearings simply a lower brass or bearing piece, usually in modern practice of white metal backed by brass, or in some cases by cast iron or steel. A bearing cap or cover is then fitted, not in contact with the shaft, and serving Fig. 147. Plain or Spring Bearing. simply to protect the bearing surface and to support grease cups or other lubricating arrangement. A bearing of this type is shown in Fig. 147. (6) Thrust-Bearing. At this bearing the thrust coming from the propeller is taken off the shaft and transferred to the ship. The length of shafting which is specially fitted for this purpose is known as the thrust-shaft. The special provision on the thrust-shaft consists of a series of rings or collars, as shown 194 PRACTICAL MARINE ENGINEERING. in Figs. 148-150, while the bearing of the type shown in Fig. 149 has a corresponding series of channels into which the shaft rings enter when the thrust-shaft is in place. The bearing thus comes on the forward faces of the shaft rings and after faces of the in- termediate bearing rings when the propeller is turning ahead, and vice versa when backing. The faces of the bearing rings are usually of white metal, thus giving a steel on white metal pair of surfaces. In order to take the weight of the thrust-shaft, a support of brass or white metal of the usual spring bearing form is usually provided at the forward and after ends of the bearing casing. The casing is furthermore commonly made in the form of a rectangular box, so that it can be filled with oil and thus flood the bearing with lubricant. Where the shaft passes through the ends of the casing, a stuffing-box or form of pack- ing ring is provided to prevent the oil from leaking through. At the bottom of the casing a hollow space is often provided con- necting freely with the general oil receptacle above, and through c z If ft -) (- ' ^ i Hl ^c ~~ ij a ~* - .._ _ _ _ Marine Engineering Fig. 148. Thrust Shaft. which a pipe of copper or thin brass is led back and forth. Through this pipe cold water is circulated for cooling down the oil, and thus absorbing the heat of the bearing. The base of the bearing is secured to the ship through a seating specially strengthened and stiffened to take the thrust from the shaft and thus transfer it to the structure of the ship. In Fig. 150 is shown a bearing somewhat more modern in type and very commonly met with in present day practice. It is known as the horseshoe collar bearing. The shaft is fitted the same as in Fig. 149, but the bearing, instead of being fitted with series of fixed rings and intermediate channels, is provided with a series of separate collars of the form shown in Fig. 151. These collars are provided with ears or lugs A and B, by means of which they are carried on side rods attached to the bearing casing, as shown in Fig. 150. These lugs in turn bear against adjusting nuts on the side rods as shown. In operation the thrust is transferred from the shaft rings to the faces of the col- MARINE ENGINES. 195 196 PRACTICAL MARINE ENGINEERING. lars, thence through the lugs and nuts to the side rods, thence to the bearing casing, and thence to the ship. It is readily seen that this arrangement allows of the indi- vidual adjustment of each collar as may be required by wear, or, if need be, of its removal and replacement by a spare collar even when under way, and without interfering with the action of the other parts of the bearing. The collars are usually of cast steel, or, in some cases, of brass or bronze, and the bearing surface of white metal, carried in pockets, as explained above. Marine ngiiieerinf Fig. 151. Detail of Collar Thrust Bearing. The arrangement of the casing as a receptacle for oil, the provision for spring bearings at the ends, and the provision of circulating pipes for cooling water, are similar to those above described in connection with Fig. 149. The thrust bearing is variously located. In some cases it is placed immediately aft of the engine with its base connected directly to the engine bed-plate. In other cases it is placed at the after end of the inboard shaft, or just forward of the after shaft-alley bulkhead, and in others at some intermediate point. (7) Stern Bearing, The general arrangement of the stern MARINE ENGINES. 1 37 bearing for a single screw ship is shown in Fig. 152. The en- tire distance through the stern of the ship from the stern-post to the after bulkhead of the shaft alley is lined with a tube A B, usually of cast iron. Within this are placed brass tubes C D, each perhaps about one-third the total length. These bearing tubes are provided with longitudinal channels slightly dovetailed in sec- tion, as shown in the figure, and into these are forced blocks of lignum vitae for a bearing. The arrange- ment is therefore somewhat similar to that for white metal, as described above, except that lignum vitae is substituted for white metal, and is placed in continuous channels run- ning the entire length of the bearing tube with intermediate spaces be- tween. The shaft itself is cased with a brass sleeve or casing, so that the bearing surfaces are brass on lignum vitae. It is found by experience that water is a lubricant for such a pair of surfaces, and it is chiefly for this rea- son that lignum vitae is so common- ly used as the material for the sta- tionary part of the bearing. The brass sleeve, which preferably ex- tends the whole length of that part of the shaft within the tube, also pro- tects the shaft from corrosion. This part of the shaft is known either as the tail shaft or propeller shaft. It is usually made a little larger than the line shaft to provide for corrosion, and also for the more violent shocks to which it is subject. At the forward end of the tube A is fitted a stuffing- box, through which the shaft passes to the after end of the shaft alley. At the after end of the tube the water enters freely through the 198 PRACTICAL MARINE ENGINEERING. spaces between the lignum vitae and flows forward, thus serv- ing to cool and lubricate the bearing. At the forward end the stuffing-box prevents leakage through into the ship. It is de- sirable, however, to fit a small pipe and cock so that water may be drawn from the tube as desired, in order to judge by its temperature as to the condition of the bearing. Instead of a pipe and cock the stuffing-box follower is sometimes loos- ened up so as to allow a sufficient leakage to insure circula- tion through the tube, and to serve as an index of the condi- tion of the bearing. In some cases, instead of water lubrication, the after end of the stern tube is closed against the water, and the tube is filled Fig. 153. Stern Brackets. with heavy oil or tallow. Or. if desired a stand pipe may be run up to a sufficient height, so that when filled with oil it will pro- duce a pressure in the tube slightly greater than that of the water outside, and thus the leakage will be outward rather than inward. With oil lubrication the lignum vitae bearing surface is replaced by white metal. In small craft the steel shaft without casing is often fitted directly in a brass bushing or bearing. In such case oil lubri- cation is to be preferred, but very commonly the bearing is left to run with such lubrication as the water can provide. For twin screw ships, as shown in Fig. 143, the same gen- eral arrangement 'is used, except that the length of the tube MARINE ENGINES. 199 where it passes through the skin of the ship is shorter, and fre- quently the lignum \itae bearing extends the entire length in- stead of over a part of the forward and after ends. A similar form of bearing is also provided in the shaft brackets or struts just forward of the stern post. The general form of such brack- TCP VIEW LONGITUDtNAL SECTION Fig. 154. Stern Bracket Bearing. ets is shown in Fig. 153. On each side is a heavy steel casting secured firmly at top and bottom to the structure of the ship, and carrying at the apex a boss for the bearing, as shown in Fig. 154. This bearing is formed by a tube carrying lignum vitae strips as previously described, and in this way, with twin screws, the extreme after ends of the shafts are supported. Sec. 22. WESTERN RIVER BOAT PRACTICE. The peculiar conditions existing on the western rivers of the United States have resulted in the development of a special type of boat and propelling machinery. In the early days of river navigation the raft was first employed, and then came the flatboat, which has stood as the type of all later developments. On the rivers where at certain seasons of the year the water is shallow, the current swift and the channel narrow and tortuous, the usual style of keel boat would be of small service, while the light draft flat bottom craft seems admirably adapted for navi- gation under such difficulties. 200 PRACTICAL MARINE ENGINEERING. Of the two varieties of boat, side wheel and stern wheel, the latter is preferred as on the whole the better suited to the all-around conditions of river navigation, and the flat-bottomed stern wheel craft may to-day be considered as the typical boat for western river navigation. Indeed this type of boat has met *Vrwte Engineering Fig. 155. Western River Engine, Elevation and Section through Valve Chests. with much favor for river navigation in all parts of the world, and especially in South America, where they are largely employed. The type of engine used on western river boats is shown in Figs. 155-157. It is horizontal and of the simple non-con- densing type. Two such engines are usually employed, .one on each side placed close to the guards, with the axis of the cylin- Fig. 156. Western River Engine. Top View. ders fore and aft, and with the connecting-rods coupled to the cranks on the stern wheel paddle shaft. The cylinders are of relatively small diameter and long stroke, the dimensions in a typical case being 24-inch diameter by 96-inch stroke. The most peculiar feature of the engine, however, is found in the valve gear. The valves themselves are usually of the double-beat poppet form, as shown in Fig. 155, MARINE ENGINES. 201 and each cylinder is provided with four, two for steam and two for exhaust. These valves are actuated by a cam valve gear mechanism, as briefly described below. The steam valves with their connecting pipes are located on one side of the cylinder, while the exhaust valves and con- nections are on the other side. Each set of valves is operated by separate rocking cams or levers, which receive their motion through rockers and connections from a special cam located on the main paddle shaft. The cam type of valve gear possesses peculiar advantages, especially for long stroke, slow revolution engines such as are used in these cases. The motion of the valve may thus be made intermittent, giving a quick opening and closure, with interme- Marine Enyliieering Fig. 157. Western River Engine, End View and Section Showing Valves. diate periods of rest or very slow motion. It is also peculiarly adapted to the elastic movements of the boat during the process of loading, unloading, etc., movements which continually vary the distance between the main shaft and rock shaft, and which, with almost any other type of gear, would introduce serious dis- turbance into the movement of the valve and the distribution of the steam. For the operation of these valves in the common type of gear two cams are used ; one known as the full stroke cam and one as the cut-off cam. When the engine is in full gear the full stroke cam operates all four valves, raising one exhaust and one receiving valve at opposite ends of the cylinder at the same moment, and alternately at each end, thus distributing the steam 202 PRACTICAL MARINE ENGINEERING. as required to carry the piston back and forth continuously. The one cam does all the work in the full gear motion of the engine both ahead and astern, and is hence in its neutral posi- tion when the crank is at its dead point. The cut-off cam is so arranged as to be hooked on after the full stroke cam has given Fig. 158. Full Stroke Cam with Yoke. headway to the boat, and is used in the go-ahead motion only. This cam is so designed that the steam is cut off at any desig- nated point in the stroke, as at J^, JH$, 3^, etc. The form of a full stroke cam with its yoke is shown in Fig. 158, and of a ^ stroke cut-off cam in partly dotted lines. Fig. 159. Full Stroke Cam. In Fig. 159 is shown the usual type of construction of the full stroke cam, and in Fig. 160 similarly the 3,4 cut-off cam. With this arrangement of gear the exhaust is opened and closed just at the end of the stroke, and hence neither early ex- haust opening nor closure for cushion can be obtained. A MARINE ENGINES. 203 means of obtaining the former has been found by blocking up the exhaust lifters somewhat, so that the valve will be slightly open when the engine is on the dead point. This insures an earlier opening of the exhaust and so clears the cylinder for the return stroke, but it gives likewise a later exhaust closure, so that with the engine on the center both ex- haust valves are slightly open, and in full gear operation a slight "blow through" will occur. This disappears, however, when the cut-off cam is engaged, because the opening movement of the latter is much slower than that of the full stroke cam. Various modifications of this simple cam gear have been introduced with a view of improving the general operation, especially by the provision of means for obtaining both steam and exhaust lead and compression, as well as independent move- ments for the go-ahead and backing motions. Fig. 160. Three Quarter Cut-off Cam. In the Sweeney valve gear two full stroke cams are em- ployed, one for go ahead and one for backing, each set so as to give suitable exhaust lead and compression, while a separate cut-off cam is fitted for the go-ahead motion. The crossheads of these engines are usually of the locomo- tive type, with long brass gibs bearing on the top and bottom guides. The connecting-rods are commonly of wrought iron or wood, with iron or steel fittings, and form one of the most pe- culiar features of these engines. Wood is often thus preferred over metal because it seems to be better capable of standing the shocks and peculiar twisting strains which come upon the rod, and in spite of the strangeness of the combination, we find in some modern boats a fluid compressed nickel steel paddle shaft with a wooden connecting-rod. The rods are very long, fre- quently as much as eight times the crank, and the best rods are 204 PRACTICAL MARINE ENGINEERING. made of Oregon fir, reinforced with iron straps which are let into the body of the rod and through bolted. The ends of the rods are fitted with brass boxes with straps, gibs, keys, etc., in the usual manner of fitting up such form of rod, and as illus- trated in Fig. 138. In some cases of modern river boats on the Pacific Coast many changes have been introduced looking toward a closer approach to usual marine practice. In a typical example of such improved practice the engines are horizontal tandem compound, the high-pressure cylinder having piston valves and the low- pressure cylinder slide valves, both operated by excentrics and link work in the usual way. In this case there are two engines developing about 1,500 I. H. P. each. The cylinders are 22^/2 in. and 38^4 in. diameter, with a stroke of 8 feet, and are intended to make thirty revolutions per minute. The crank shaft for such engines is built up in structure, the two cranks being separately forged and secured to the pad- dle shaft by shrinking and appropriate keys. The shaft is usually fitted with hexagonal bosses where the wheel flanges are to be secured. The latter are usually of cast iron, heavily ribbed and reinforced by wrought iron bands shrunk on their hubs and outer circumference. These flanges are fitted to the hexagonal bosses on the shaft, and are secured with suitable keys. They are provided on one face with sockets for the wheel arms, which are of wood. These latter are further strengthened by circular bands of iron bolted near the outer ends, and also by oblique bracing which is worked between them. The buckets are also of wood, 2-inch oak plank of suitable width and length being a standard material. They are secured to the wheel arms by special clamp bolts, and are so located relative to the draft of the boat as to be immersed only some 4 to 6 inches when the steamer is running light. In some cases the buckets are divided at the center, forming really two sets, staggered with reference to each other, and thus reducing the shock of the wheel as it enters the water. DOCTOR. This peculiar feature of western river practice as illus- trated in Fig. 161, is a combination of feed pump and feed water heater. As here shown, the doctor consists of a vertical beam engine with crank and flywheel operating four pumps. Two of MARINE ENGINES. 205 these are simple lift pumps drawing water from the river and delivering it into the heating chambers overhead, while the other two are feed pumps proper, taking their supply from the heaters and forcing the water into the main boilers. Each lift and force pump is designed of sufficient capacity to supply the entire battery of boilers, so that one of either kind may be dis- Marine Engineering Fig. 161. Western River Boat "Doctor." connected for examination or repair without disturbing the regularity of boiler feed supply. The various parts of the ma- chine are erected on a deep cast iron base plate which contains various ports and passages, forming the water connections be- tween the various pumps. The suction pipe from the river is connected with a vacuum chamber, and communicates through a passage in the base cast- 206 PRACTICAL MARINE ENGINEERING. ing with the suction side of the lift pump. The discharge from these pumps is then led by other passages to the columns, which serve as discharge pipes, supports for the engine beam and for the heaters. Valves are also located in these columns, by closing which the water in the heaters may be prevented from returning at such times as it is necessary to open up a pump for examination or repair. The heaters themselves consist of wrought iron shells riv- eted to cast iron heads, through which the exhaust steam from the main engines is led on its way to the exhaust pipe. The ex- haust steam thus comes in direct contact with coils of copper pipe that lie in the lower part of the heaters, and through w r hich the feed water is forced and finally discharged below a dia- phragm. Beyond this the exhaust steam and water are to some extent in direct contact, the latter being finally lead down through the pair of columns on the opposite side of the machine to the feed pump inlet valves in the base-plate. The head of water in the columns is thus sufficient to flood the valves and prevent the pump from missing stroke, even with the hottest feed water which the heaters can furnish. The lift pumps are fitted with long pistons having either cup leather or square gum packing, while the feed pumps are of the common plunger type. The pump valves are flat disks of brass made quite thick so as to avoid the need of springs, and also to allow metal for re-facing. The engine part of the doctor is very simple and will call for no special comment, consisting simply of a steam cylinder for actuating the beam and thus giv- ing motion to the four pumps as described. In some cases of recent river practice injectors have taken the place of the "doctor," and if they can be depended upon they are of course much preferable, being easy to handle and occupying little or no space otherwise valuable. While it is probable that they can thus be used to advantage on certain of the upper portions of the western rivers, it is hardly possible that they could be used at all in many other localities on ac- count of the sand and grit which is held in suspension by the water, and which would cut out the injector tubes so rapidly that their use would be out of the question. For this reason it seems likely that the "doctor" will hold its own in all such locali- ties and that it will continue to be an important detail of west- ern river practice. MARINE ENGINES. 207 Sec. 23. THE STEAM TURBINE. Within the past few years the application of the steam tur- bine to marine propulsion has produced results which have at- tracted world-wide attention, and it seems at present not un- likely that the part taken in the future developments of marine propulsion b> this form of mo- tor will be one of increasing im- portance. The present develop- ment is represented by the Par- sons' steam turbine as fitted on the Turbinia, and later on the British torpedo-boat destroyers Cobra and Viper, and Clyde passenger steamer King Ed- ward. This type of motor, one form of which is represented in Fig. 162, consists of a cylindrical case carrying rings of inwardly projecting oblique guide blades, while within these revolves a shaft carrying rings of outward- ly projecting oblique blades. There is a clearance of about 1-16 inch between the successive rings of blades and guides, and between the ends of the former and the case, and the ends of the latter and the body of the shaft. There is thus left between the shaft and the case an annular space filled with alternate rings of blades attached to the shaft and guides attached to the case. The steam when admitted passes first through a ring of fixed guides by means of which it is given a rotational motion, and then projected on to the first ring of blades. It is then thrown on to the following ring of 208 PRACTICAL MARINE ENGINEERING. guides, by means of which its direction is again changed, and it is then thrown in the same direction as at first upon the second ring of blades, and so on, passing from one ring to the next, and giving to each a part of its energy and thus maintaining the rotation of the shaft. It must be especially understood that the steam in a turbine acts by impact or reaction, and not by pressure. As the steam rushes against the blades and its direc- tion of flow becomes thereby changed, it exerts a reaction on the blades, and this constitutes the force which produces the rotation. The energy which the steam possesses in virtue of its temperature and pressure cannot therefore be directly used in the turbine as in the common steam engine, but it must first be transformed into the energy of motion as in the rushing jet. This transformation is effected by the gradual expansion of the steam as it passes through the turbine. This gradual expansion keeps up a continual transformation of heat energy into the energy of motion, and this energy is as constantly transferred to the moving blades, and thus the original heat energy of the steam is transformed into mechanical work. In order that the expansion may be carried on continuously, the cross-sectional area occupied by the blades is increased from time to time, as shown in the figure, thus making a series of steps of increasing diameters for the rings of blades and guides. In a moderate sized motor there may be 50 to 80 successive rings thus ar- ranged in from three to five groups. The steam pressure acting on the annular rings separating these steps, and also on the blades themselves, would set up a severe end thrust. This may be balanced, as in Fig. 162, by ar- ranging two sets of such steps on the same shaft varying in op- posite directions, and thus balancing each other in end thrust. In another method special disks are fitted on the shaft with grooves in their outer surface, within which project rings car- ried in the frame. These rings and grooves form a nearly steam tight joint, and the annular area is so adjusted in amount that the steam acting on it will balance the thrust acting on the blades and corresponding annular area of the main shaft. In addition a special thrust bearing is fitted for taking any residual end thrust and for making the necessary adjustments. The arrangement thus briefly described constitutes a sim- ple turbine. By combining two or three such in series and leading the steam from one to another through them, the so- MARINE ENGINES. 209 called compound turbine is formed. In a simple turbine the steam may be expanded some six or eight times, so that by compounding a total expansion of, say, 30 to 60 could be ob- tained, and by a triple combination a total expansion of 200 and more may be effected. The revolutions of the turbine are high. This is a necessity of its efficient performance. The Turbinia has three each of about 600 to 700 horse power, and the revolutions run up to about 2,000 per minute. In the Viper and Cobra there are four turbines, each of about 1,500 H. P., running at about 1,200 revolutions per minute. With the former a speed of about 34 knots has been reached, while with the latter speeds of over 35 knots were reached. The efficiency of the compound type of turbine is not very different from that of good compound or triple expansion en- gines of the usual type. The weight for the same power is somewhat less, though the difference is not great when com- pared with light reciprocating engines forced in a manner cor- responding to the conditions on these boats. In other words, the turbine shows no very great saving over the weights of the lightest types of reciprocating engines as designed for torpedo craft ancl fast launches. The great advantages of the turbine are found in its com- pactness and absence of reciprocating motions, and thus in the entire absence of the forces which cause vibrations. With ex- treme speeds and in many conditions of modern practice the vibration forces become a serious question, and a motor en- tirely free from them becomes immediately of great importance in all such cases. In regard to questions of durability, maintenance, liability to derangement or accident, etc., the experience available at present is too small, and we must wait for the future to answer these and many other questions which bear on the applicability of the turbine to the various conditions of marine practice. Sec. 24. ENGINE FITTINGS. [i] Throttle Valve. The purpose of the throttle valve is to provide a means for quickly opening or closing the main steam-pipe near where it connects with the high pressure valve chest, and thus to provide for the quick control of steam to the engine when stopping and 210 PRACTICAL MARINE ENGINEERING. starting. A great variety of valves have been employed for this purpose. The necessity for quick operation, especially by hand gear, requires usually some form of balanced valve, though in very small sizes an ordinary globe or straight-way or gate valve, as shown in Figs. 166, 168 may be used. Of these the straight- way valve is much to be preferred, as when open it leaves prac- tically an unobstructed passage for the flow of the steam. (i) Gridiron Valve. The gridiron is another form of unbal- anced valve sometimes employed as a throttle. This valve, as shown in Fig. 163, consists of a series of bars and ports corre- sponding to a like series in the valve chest, and giving a series of openings for the steam, wider or narrower according to the position of the valve. With such an arrangement a considerable area of opening may be obtained with a comparatively small Fig. 163. Gridiron Valve. Fig. 164. Double Beat Poppet Valve. movement of the valve, and a screw or some other form of slow motion gear may be employed without loss of quick opening and closure. This form of valve is, however, but rarely met with in modern. practice. (2) Double Beat Poppet. The double beat poppet valve, as shown in Fig. 164, has been much employed as a form of bal- anced throttle. The upper disc is slightly larger in area than the lower, so that if the live steam is on the outside the net load on the valve is that due to the difference of the two areas, and this may be made very small. The resistance to opening is thus no more than can be readily overcome with a direct hand gear, as for example, a simple lever or other like arrangement. The chief difficulty with this valve is in keeping it tight, var- iations of temperature and the consequent expansions and con- tractions often tending to slightly unseat one disc or the other. (3) Butterfly Valve. The butterfly valve has also been wide- MARINE ENGINES. 211 ly used as a balanced throttle. It consists of a disc of elliptical form carried on a spindle and swinging within a cylindrical casing. When closed it rests obliquely on the inner surface of the casing, thus closing the passage around its outer circumfer- ence. When full open it swings into a position with its plane lying along the pipe, thus leaving the passage nearly free for the flow of steam. This form of valve is quite perfectly balanced, but it is difficult to keep tight. If the angle of obliquity with the surface of the casing is too small, it may also be liable to stick fast, due to unequal expansion of the valve and casing. In an- other form of butterfly valve, as shown in Fig. 165, however, the Marine Enginitrmg Fig. 165. Combined Stop and Throttle with Balance Piston. disc is circular and when closed swings square across the line of flow, just fitting within a corresponding ridge of the casing. In such case the diameter of the opening must be made enough larger than that of the disc to avoid the danger of striking, and considerable leakage will usually result. (4) Disc Valve With Balance Piston. A plain disc with bal- ance piston attached to the stem is quite commonly employed in modern practice for the throttle or for the stop and throttle com- bined. Such an arrangement in combination with a butterfly valve is shown in Fig. 165. By this means the pressure on the piston nearly balances the load on the valve, and it may thus be operated by hand gear. Steam may also be admitted back of the piston by a pipe with stop-valve operated from the working platform. By this means the disc may be balanced when once off the seat, and closure effected as easily as opening. 212 PRACTICAL MARINE ENGINEERING. (5) Power Operated Throttle. In some cases 1 with large en- gines the throttle is operated by steam power instead of by hand, steam being admitted to an operating cylinder by means of a hand lever or other like arrangement. Here the steam acts upon an auxiliary piston and by suitable connections produces the movement of the throttle as desired. In such cases the con- nections are often of the "floating lever" type, as in the reversing Fig. 166. Globe Valve. gear described in [5,] so that the valve will follow the hand lever in its movement back and forth, and the combination becomes thus equivalent to a direct operation of the throttle by hand. [a] Main Stop Valve. The throttle valve from its construction can rarely be closed sufficiently tight to prevent leakage of steam, often considerable in amount. To provide a shut-off without sensible leakage a MARINE ENGINES. 213 stop valve is often fitted in addition. Such valves may be of various types, as shown in Figs. 166, 167, 168. (i) Globe Valve ^ This valve, as shown in Fig. 166, consists of a metal chamber of globular or spherical form with flanges for connecting to the line of piping. Within the body is a partition separating the portions connected with the two openings, and in this partition is a hole with conical seat upon which the valve with corresponding conical face bottoms when closed. The valve is attached to a threaded spindle which works in a nut either formed in the neck which contains the stem, or carried Marine Engineering Fig. 167. Angle Stop Valve. outside on a girder supported by stud bolts, as shown in the fig- ure. To the end of the stem a handle is attached, and by this means the valve is opened or closed as desired. The stem is packed by means of a stuffing-box and soft packing compressed by a gland of the usual form as shown. In small sizes the gland is usually replaced by a form of nut threaded to the neck, which contains the stem, and compressing the packing between the nut and the bottom of the packing space. (2) Angle Valve. In this type of valve, which is an angle or elbow and a valve combined, the seat and valve-face, as shown 214 PRACTICAL MARINE ENGINEERING. in Fig. 167, are placed square across one of the openings, thus shutting off all flow through it when the valve is closed. When the valve is opened, however, the passage is left free, according to the degree of opening, for the flow of the liquid or vapor around the angle and on into the following section of pipe. When the stop valve is of the disc form it is very commonly of the angle type and arranged to go in at a turn of the pipe, as shown in Fig. 167. In this case also the valve is attached to a bulkhead and the arrangement will serve to show the method of Marine Engineering SECTIONAL ELEVATION SECTIONAL PLAN SHOWING BY-PASS Fig. 168. Gate Valve. carrying steam through a bulkhead and of making up the joints connecting together the steam pipe, the stop valve and the bulk- head plate. (3) Straight-way or Gate Valves. In this form of valve, which is shown in Fig. 168, the moving part consists of a special form of slide which is moved by a screw back and forth across the opening of the pipe. There are various special forms and de- vices for securing tight contact between the valve and its seat when closed, and thus making the valve tight under steam pres- MARINE ENGINES. 215 sure. The general arrangement of Fig. 168 will, however, serve to show the main features of valves of this type. When closed and with pressure on one side of the slide only, there is some- times some difficulty in opening the valve. To relieve this con- dition a small by-pass, as shown, is often fitted. This admits steam to the farther side of the valve, thus balancing the load and making the operation of opening much easier. In another form the valve slide is made of two parts, hinged together and with the end of the spindle working between them in such way that when screwed hard down it is forced as a wedge between the two parts thus forcing them against their seats. When the handle is turned in the reverse way the first action is to partly withdraw the stem from between the two parts of the slide, thus easing them from their seats and allowing them to be readily withdrawn as the stem is turned farther back. When the throttle takes the form of a plain disc with bal- ance piston, as in Fig. 165, no additional stop is thought neces- sary, and such an arrangement is often known as a combined stop and throttle valve. In such case, however, a screw stem may be provided with connections for bringing it into use when closing the valve down as a stop. [3] Cylinder Drain Gear and Relief Valves. A certain amount of water is likely to collect in the steam chests and cylinders, either carried in with, or condensed from the entering steam, especially when warming up the engine pre- paratory to getting under way. Provision must be made for getting rid of this water as occasion may require, and to this end the so-called cylinder drains and relief valves are fitted. The drains are usually plain cocks piped up and connected to the parts to be drained, and with the valve stems connected by levers and bell-cranks to operating handles at the starting plat- form. The drains in the bottom of the cylinder or valve-chest will naturally be placed at the lowest point at which water can collect, or as near to such point as is practicable. Those in the upper end of the cylinder will be placed at such a height that the opening will not be covered by the piston when at the top of the stroke. For small engines, auxiliaries, pumps, etc., the drain valves are often plain globe valves piped into the cylinder at convenient points, and operated independently by hand. 216 PRACTICAL MARINE ENGINEERING. The discharge of the drains is piped away either into the bilge, or into a fresh water collecting tank. In addition to such gear, which is operated by hand, and when judgment may calMor its use, it is necessary to provide automatic relief valves for the discharge of water in larger quan- tities should it find its way into the cylinder by priming or in other ways. Such a relief valve is in the form of a safety valve, and may be set to open at any pressure desired. Such valves are sometimes connected up with operating levers, also led to the starting platform, so that they may be operated by hand from that point. In such cases only the one set of valves is often fitted, automatic when necessary, and under hand control when desired. In some cases with large engines a double set of automatic relief valves is furnished, a pair of large valves not under hand control, and a smaller pair under hand control, as described above. [4] Starting Valves. In order to assist in starting the engine, especially if the high pressure piston happens to be on or near the center, a valve and pipe are usually provided for admitting steam direct from the steam pipe or high pressure valve chest, to the first receiver, or intermediate pressure valve chest. This will give sufficient load on the intermediate pressure piston to start the engine, and carry the high pressure piston off the center, and thus give the engine a chance to start in the regular way. In case the high pressure and intermediate pressure cranks should be opposite, and thus both pistons on or near the center at the same time, the auxiliary pipe will lead to the second intermediate piston, or to the first cylinder, whose piston is not on the center with the high pressure. In some cases the passage of the steam to the next cylinder beyond the high pressure is effected by the open- ing of a valve connecting the steam and exhaust sides of the high pressure valve chest. Such valve being opened the steam finds its way directly to the point where it is needed. Valves for this general purpose are variously called pass- over, or starting valves, or monkey tails. They are either in the form of a cock or of a small slide valve, in either case admitting of full opening by a single short stroke of a convenient hand lever, to which they are connected by suitable rods and con- nections. MARINE ENGINES. 217 [5] Reversing Gear. The various links of a Stephenson valve gear, as will be seen in Section 53, are connected by side or bridle rods to arms on the rock or "weigh" shaft. To reverse or link up with such a gear, therefore, it becomes necessary to provide some means for turning this shaft back and forth, and for holding it under complete control at any position desired. The form of reverse gear most commonly employed in American practice is of the so-called "floating lever" type, and is illustrated in Fig. 169. It consists of a cylinder, AB, with piston and rod, D, con- nected by a link from E to an arm on the engine rock shaft, and thus connecting with the links. Fig. 169. Floating Lever Reverse Gear. As the piston is moved back and forth by the steam this arm will evidently be carried with it, and the various Stephenson links, or like parts of other types of valve gear, will be moved as desired, each through its connection with the rock-shaft. The steam to the cylinder, AB, is controlled by a slide valve, V, either plain or of the piston type. This valve has very small lap so that from the position when covering both ports but slight movement is needed to uncover. To the stem of the valve is at- tached a link, LI, which at the latter point is joined to a bar, KH. The lower end, H, of this bar is attached to a lug, Q, on the piston rod, and, therefore, moves with the piston. The upper end, K, is connected through a link, KN, to a hand lever, which is provided with means for clamping in any position desired. 2i8 PRACTICAL MARINE ENGINEERING. Suppose now the gear in the position shown and with the valve covering both ports. Let the hand lever be moved so as to throw KN to the left. For the moment H will be a fixed center, and with the connections shown the valve will be moved to the left also. With this arrangement of connections an in- side valve (Section 46 [7] ) must be used, and, therefore, steam will be admitted to the left hand end of the cylinder, AB, and the piston forced to the right. Let the hand lever, carrying with it the valve, be thus moved over a certain distance and then held or clamped there, thus fixing NK. The point, K, will thus become for the time a fixed center, and the movement of H to the right will carry the valve in the same direction, and thus finally close the ports, shutting off the supply of steam at one end and closing the exhaust at the other. ' The movement of the piston will thus be stopped and the gear will be held in the po- sition reached. It is clear that for every position of the hand lever there will thus be some position of the piston, rock shaft arm and main valve gear, for which the valve will be brought to mid position and the piston and gear thus brought to rest, and that the steam will carry the gear to this position and then automatically shut off and stop. If the hand lever is moved but slightly so as to barely displace the valve, the piston will move but a small distance before again covering the ports antl coming to rest. If the handle be moved to an extreme position the valve will be moved far over and the steam will rush the piston and gear over into the extreme corresponding position. In short, the position of the gear for equilibrium under steam will correspond exactly to that of the hand lever, and wherever the latter may be placed, the gear will run to the corresponding position and then stop. It is also clear that if the hand lever be moved slowly, the piston and main links will follow along at equal pace, stopping when the handle is stopped and moving when it moves. Also if the handle be slightly displaced and left to itself the friction of moving the valve will be usually more than that of moving the handle, and in consequence the point, I, will become for the time a fixed center, and the piston will move along, the valve remaining open and the connection, HKN, moving the handle over at equal pace with the link. This will continue till the handle comes against a stop at the end of its path. The point, K, will then become fixed, and the further movement of the piston will move the valve into mid-position, MARINE ENGINES. . 219 thus shutting off steam and bringing the gear to rest in the position corresponding to that of the hand lever. To take up sudden shocks and provide a safeguard against putting the link over too rapidly and thus overrunning at the end through the inertia of the parts, spring stops or buffers, R, are provided on a rod, S, against which the lug, Q, comes at the end of its run. It is thus seen that this gear furnishes a very perfect con- trol over the main valve gear, the action being the same as for a man operating the gear directly, and thus giving him readiness of control with the least mental effort, and the least liability of error in a moment of hurry or excitement. In addition to the spring buffers, as shown in Fig. 169, a form of plunger control is sometimes added. In this arrange- ment the piston rod of the reverse cylinder is continued back- ward and connected to a second piston or plunger working in a cylinder filled with oil. The operation of the plunger is to trans- fer the oil through a suitable pipe connection from one end of the cylinder to the other, and as this passage may be throttled at will by a stop valve, all possibility of slamming or of violent motion may be removed. A further advantage of this arrange- ment lies in the fact that with suitable pipe connections to a hand pump, the oil may be drawn from one side of the plunger and forced in on the other, thus giving a control over the valve gear by hand power in case of derangement of the power con- trol. Of other forms of reverse gear the so-called all around gear is quite commonly met with in English practice. The main links are connected up to a small engine which makes a large number of revolutions in running the link over from one extreme to the other. This engine is under the control of a small link which is directly operated by hand. A form of lever stop is usually provided which will either reverse or middle the small link and bring the engine to rest when the main links have reached either extreme of their travel. In engines for small yachts, launches, etc., the links are placed directly under the control of a hand lever. The various other types of valve gear may be operated by any of the forms of reverse described. With all valve gears, as described in Chapter VII, the reverse is effected by the move- ment of some piece of the gear from one position or location into 220 PRACTICAL MARINE ENGINEERING. another, and so back and forth for the various degrees of linking up, etc. By suitably connecting such piece to the power re- verse gear the control may, therefore, be obtained in the same manner as for the Stephenson link as described above. [6] Turning Gear. It is always necessary to provide some means for turning the engine other than by steam on the main pistons. This is necessary for moving the engine when in port for adjustment of bearings, setting of valves, etc. The turning gear usually con- sists of a large worm wheel placed on the main shaft just aft of the bed-plate, geared down through worm and spur gearing to a small engine, usually a double simple engine with cranks at 90. The gearing ratio is such that many hundred revolutions of the turning engine may be required to one of the turning wheel or main engine shaft. This gear must be so ar- ranged as to be readily thrown in and out of connection with the main turning wheel. This is usually accomplished by carry- ing the main worm on a shaft which is pivoted, and which can thus be locked in either of two positions, in one of which the worm is in gear, and in the other out of gear, or else by driving the worm on a shaft with a feather, thus providing for endwise motion, and for fixing it in either of two locations on its shaft, in one of which it is in gear and in the other out of gear. The latter is the arrangement more commonly met with. Where a turning engine is not provided the turning wheel is usually arranged for operation by hand through worm gear- ing operated by a lever with pawl and ratchet arrangement, or by some similar device. In some cases the engine is turned by a hydraulic jack placed under a movable chock piece located in sockets cast in the turning wheel. This chock is shifted from one socket to an- other as the jack shoves it upward, and thus the engine is slowly turned. In small engines the turning wheel is often simply a form of gear wheel with shallow teeth in which a pinch bar is worked, and by this means the engine may be slowly pried around. Such a wheel is known as a pinch wheel. [7] Joints and Packing. The joints to be considered under this head are of two kinds, (i) Fixed joints as those between a cylinder or valve MARINE ENGINES. 221 chest cover and flange, and (2) Sliding or slip joints as those be- tween a piston rod and the stuffing box, or the slip joint in a length of steam piping. For making up stationary joints a great variety of packings are in use, the difference depending to some extent upon the temperature to which the joint is to be subjected. Thus for joints to stand high temperature, as with boiler man- holes, cylinder heads, etc., sheet asbestos either plain or in combination with other materials is used. There are also various kinds of packing in which rubber in one form or another is used either in combination with some fibrous ma- terial as sheet canvas, or as a constituent of some form of compound. The tendency of rubber by itself is to grow dry, hard and brittle, especially under the action of heat, and the purpose of the modern forms of rubber compound is to avoid this tendency, at the same time retaining its elasticity and joint making qualities. For joints not subject to the action of high temperature, similar forms of packing are used, though with a greater proportion of rubber, if desired. The strip or ring of packing which is cut out and fitted for the joint is called a gasket. In making up such a joint it is well to smear the surfaces of the gasket with a mixture of black-lead and grease or oil. This will aid somewhat in making the joint, and very much in the removal of the cover and gasket at a later time without tear- ing the latter. With such precaution and when the temperature is not high the same gasket may be used several times over with- out loss of its joint making qualities. In addition to gaskets made of such materials as described above, joints are also made with gaskets of corrugated sheet copper, or of plain copper wire. For high pressures such gas- kets have proved quite successful. The soft copper is expanded between the harder metals of the flanges, and spreads, filling the surfaces where it touches, thus making a tight joint. For sliding joints as between a piston-rod and stuffing-box, the greatest variety of packings is likewise in use. They may be broadly divided, however, into the two classes, fibrous and metallic. The fibrous packings are made of the same material as the sheet packings above described, and are either round, square or triangular in section. For use. they are cut to such lengths as 222 PRACTICAL MARINE ENGINEERING. may be necessary and placed in the stuffing-box in layers or turns, the joints between the ends being shifted so as not to come one above another. The stuffing-box, as shown in section in Fig. 170, consists of a cylindrical chamber or box, EF, with cavity B. This is bolted by means of the flange, F, to the lower cylinder head. The part, CC, is known as the gland or follower and is carried by two or more studs, as shown. At the bottom or upper end of the box is a ring, as shown, just filling in the space between the opening in the box and the piston rod. Fre- Fig. 170. Plain Stuffing Box. quently this ring is omitted and the metal of the box fits about the rod. The packing is placed in the box as described above, thus filling the space, BB, between the bottom of the box and the gland. The packing may then be compressed as de- sired and as may be necessary by means of the nuts on the stud- bolts, thus forcing the gland down on the packing and making the joint tight. This is the general type of all such joints made with compressible packing, with, of course, variation in details. Joints of this character are used for piston and plunger MARINE ENGINES. 223 rods, slide valve stems, globe and disc valve-stems, joints about the shaft where it goes through a water-tight bulkhead, joint in the thrust bearing casing, as noted in section 21 [n], in slip and expansion joints, as noted in section 25 [2], etc., etc. For metallic packing with joints of this character the form of the box is in general the same. In fact in some cases the box is so made that either soft or metallic packing may be used. Here again the greatest variety in detail is to be found, but a Fig. 171. Metallic Packing. single instance will serve to illustrate the essential features of such packing. In Fig. 171 is shown an example of metallic packing. The box or casing contains at its bottom, or upper end in the cut, a spiral spring, as shown. Next comes a brass ring, and next a series of babbitt or white metal rings carried in a casing or shell, as shown. These rings are conical on the outer cir- cumference, and fit to a corresponding form of the containing 224 PRACTICAL MARINE ENGINEERING. shell. Next below is a second brass ring which supports the shell above, the joint between the two being ground to a tight fit. This ring rests on a casing below, the joint between the two being spherical and ground to a fit. The latter cas- ing contains another spiral spring and then follows another series of rings, etc., similar to those above. The whole box contains, therefore, two similar sets of packing ele- ments, each consisting of a spiral spring, white metal rings con- taining shell, etc. Each of the white metal rings consists of two separate halves, the whole arranged so as to break joints from one ring to the next. It is readily seen that the action of the spring is to crowd the white metal packing rings into the conical shell and hence against the rod, thus keeping the joint tight be- tween the two. It is further seen that with this way of carrying the packing the latter is entirely unconstrained laterally, and may move in any way to accommodate itself to any slight ir- regularity in the rod without danger of disturbing the tight- ness of the joint. The two systems of packing, as a whole, are held up into place by an outer ring, secured to the cylinder head by stud bolts. The joint between the packing systems and the cylinder is made by a ring of copper wire, as shown, thus shut- ting off all leakage of steam from the packing space in this di- rection, while the various ground joints and packing ring sur- faces close it off in other directions. Among the various conditions which an ideal packing for piston and valve rods should fulfil those of chief importance may be stated as follows : (1) The packing should make a steam tight joint between rod and stuffing box, at the same time opposing the minimum frictional resistance to the motion of the former. (2) It must be durable even under the temperature of modern high pressure steam, and also easily removed or replaced with new when necessary. (3) The packing should be free to move about transverse- ly to a sufficient extent to follow the rod, even if it is slightly bent or out of line, at the same time maintaining the joints steam tight between the rod and the packing, and between the packing and the stuffing-box. Requirement (3) has given the greatest trouble and has led to many varieties of design intended to cover the point, one of which is illustrated as above in Fig. 171. No packing can be MARINE ENGINES. 225 considered satisfactory for modern requirements which does not possess in good degree the qualities detailed above. [8] Reheaters. A reheater is a collection of pipes placed in a receiver or ex- haust passage from one cylinder to the next. Within these pipes high pressure steam is circulated, and around them the exhaust steam passes. The high pressure steam will, therefore, give up its heat to the cooler exhaust steam, and thus tend to dry or even to superheat it as it passes on into the next cylinder beyond. The office of the reheater is, therefore, to exercise a drying and heating action on the exhaust steam as it passes from one cylinder to another in a multiple expansion engine. Under most conditions this will exert a beneficial influence on the economy of the engine by decreasing the amount of cylinder condensation, and to such action may be referred the benefit which the reheater seems to give. See further Section 59. [9] Governors. In order to control the revolutions of the engine and to prevent violent increasing or racing when the propeller is par- tially lifted out of the water by the pitching of the ship, some form of governor is frequently fitted. The early types of mar- ine engine were usually governed by hand at the throttle, which was commonly of the butterfly variety (see Section 24 [i]), though occasionally automatic means of moving the valve were employed. With modern multiple expansion engines, however, it is impossible to satisfactorily control the revolutions by the throttle. With such engines the control must come from the slide valve gear, the links of which may be linked up more or less, as required when the propeller is uncovered, and linked out again as it is submerged. Where no automatic governor is fitted, this must be done by hand control of the reversing gear. The modern automatic governor is intended to take the place of this hand control. There are two modes of actuating marine governors. (1) By utilizing the varying pressure under the stern. (2) By utilizing a variation in the revolutions from the reg- ular speed. In the first type a pipe is run from the outside water at the stern to some form of pressure chamber near the engine, within which is a flexible diaphragm held in position by a spring or 22 6 PRACTICAL MARINE ENGINEERING. other equivalent means. The water being admitted to this pipe, the air within is compressed according to the head of water over the outer end. The apparatus is so adjusted that at normal draft the diaphragm is in equilibrium between the two forces, due to the water pressure on the one side and the spring on the other. A change in the depth of the water will cause a varia- tion in the pressure which will be transmitted through the air and thus destroy the equilibrium, throwing the diaphragm in one direction or the other. This may be made to actuate a steam valve and thus through an auxiliary steam piston control the reversing lever and through this the links. In former practice this type of gear was sometimes made sufficiently large to actuate the steam throttle directly, or sometimes a like valve in the exhaust pipe. The other type of governor is found in various forms. In many of them use is made of the centrifugal force of revolving balls or weights somewhat as in the ordinary stationary gover- nor. Through the force thus available a small valve is oper- ated, thus leading through a series of steps to the control of the reverse lever or other part which it is desired to operate. Again in other forms a revolving fan or propeller working in a box filled with liquid maintains the apparatus in a certain condition at a certain speed. With a sudden change of speed a corre- sponding change of resistance to the motion is met with, and this difference of force may be used to operate a small valve, and then, as before through the proper steps, the reversing lever is controlled. In another form a pump continually forces air into a chamber from which it escapes through a cock whose opening may be regulated at will. For a given size of outlet and speed of pump the pressure will rise until finally as much escapes as enters and the pressure remains constant. If the speed changes, however, the pressure will change correspondingly, and this difference of pressure will give a force which may be used as already explained. A still different type of gear operated by a change of speed but not driven by the use of a belt employs the forces due to inertia. As usually installed it consists of a weighted vertical rod pivoted at the top so that if unrestrained it could swing to and fro between a pair of stops. This weight with its point of suspension is then given a movement of reciprocation horizon- tally by attachment to any suitable part of the engine. If not MARINE ENGINES. 227 prevented, it would therefore swing to and fro between the stops, due to the change in momentum imparted by the re- ciprocating motion. It is, however, held by a spring against one of the stops, and the tension is so adjusted that movement will not result until the engine exceeds its normal speed, when the inertia forces overcome the spring, and the weight moves away from the stop. This motion, by means of an attached lever, may operate an auxiliary valve, piston, etc., and thus control the links. This type of governor is sometimes used only as a safety gear to quickly stop the engine in case of a breakage of the shaft or other accident permitting violent racing. In such case the gear is sometimes so arranged that the movement of the weight away from the stop will cause it to engage as a clutch with an arm or lever connected with the reverse lever, and so adjusted that the motion given will just bring the links to the mid posi- tion. The instant the weight leaves the stop, therefore, the levers will be suddenly thrown over, the links middled and the engine stopped. All forms of marine governor are somewhat slow in control- ling the variations of speed. The ideal governor would antici- pate the motion and close down or open up just in advance of the rise in speed. Instead of this they act only after the stern has risen or fallen, or after the change of speed has become more or less pronounced. It is considered good practice, however, to fit some form of governor, at least as an emergency control, so as to prevent an excessive increase of revolutions from any cause whatever. For this purpose only those forms which de- pend on a change of speed are suitable, and such are commonly fitted in modern practice. [10] Counter Gear. The revolutions of the engine are automatically registered by a counter of the common type, and consisting of a series of discs with numbers from o to 9 on their circumferences. The motion for the counter is taken from any reciprocating piece which has a convenient location and a motion of small range. This is connected up to the counter by appropriate links, bell cranks, etc. The motion operates directly on the disc to the right and moves it along one notch or figure for each revolution. As each disc reaches o it engages with the one of next higher order on the left and throws it over, thus carrying the count continuously along the discs from the first to the last. 228 PRACTICAL MARINE ENGINEERING. In this way the revolutions are registered one by one, the total number for any period of time being found by taking the difference of the two readings for the beginning and end of this period. By this means the revolutions per minute, per hour or per day are readily found as desired. (n] Lagging. The cylinders, cylinder-heads, valve chests and covers are usually provided with some form of covering intended to prevent the loss of heat, and thus conduce to economy as well as render the engine less disagreeable to work near and about. Such covering is known as lagging and consists usually of either wood in strips or polished sheet brass or Russia iron. When of wood the strips are narrow, I to 2 inches in width, and often of alter- nate light and dark color to give a pleasing effect. They are usually matched together and secured by bands of brass or pol- ished iron, or by brass headed screws taking into foundation pieces held in place by countersunk tap bolts. [12] Lubrication and Oiling Gear. (i) Lubricants. For the lubrication of the various rubbing surfaces and turning joints, except within the cylinder, olive oil, castor oil, and the lubricating grades of mineral oil are used. Olive oil when pure is a most excellent lubricant, especially for machinery of moderate or light weight, but it is liable to adul- teration by peanut oil or other oils of an inferior quality. For the lubrication of the internal surfaces nothing but the best min- eral oil must be used. (See Sec. 40.) The grade commonly employed is known as cylinder oil, and is heavy and viscid at ordinary temperatures, becoming quite fluid, however, at the usual temperatures of the steam. It is usually fed in by means of a sight feed lubricator, as described in (9). In addition to the liquid oils, various lubricating greases are used, often in combination with a certain proportion of graphite (black lead.) Graphite alone or in combination with oil is also used, and its lubricating qualities are of the highest order. It seems to possess the property, especially with cast iron, of filling the pores of the iron, and of thus forming a kind of graphite-metal skin on the surface, with a very small co- efficient of friction. The place where the lubricant should be supplied to the bearing is a subject which has attracted considerable attention MARINE ENGINES. 229 in the past few years. It seems now to be very well established that the following principles should govern : (a) The oil should always, where possible, be led into the bearing at a point which is under the smallest pressure. (b) The continuity of the oil film, where it is under the greatest pressure, should not be interrupted by oil channels or grooves. (c) The oil should be prevented, as far as possible, from escaping at those points which are under the greatest pressure. For journals such as main pillow-blocks, etc., these princi- ples are very commonly violated, and in fact it can hardly be said that practice has as yet come to act upon them, though their correctness seems to have been well demonstrated. According to these principles the oil for the main pillow block bearings should be introduced near the division between the upper and lower brasses, and the oil scores or grooves in the metal of the bearing at the top and bottom should be omitted. Similarly for the crank-pin and other cylindrical journals, the oil should be admitted at those points where there is the least pressure, and at the points where the pressure is greatest the bearing surface should be smooth and not interrupted by grooves, or scores, or oil channels of any kind whatever. (2) Amount of Lubricant Required.. As to the amount of oil to be used, practice differs widely, but from 5 to 8 Ib. of oil per ton of coal may be taken as a fair allowance, or say from 5 to 8 Ib. per looo I. H. P. per hour. In small sizes, for engines of the torpedo boat type, etc., the consumption will go up to consider- ably larger figures. Of this total amount some 5 to 10 per cent, may be required for internal lubrication, and the remainder for the various joints, bearings, etc. In the opinion of many good engineers, after a ship has been at sea for a few days and the machinery has settled into a steady running condition, the amount of internal lubricant may be gradually decreased to perhaps one-half the amount first used. With regard to the frequency of lubrication no definite rules can be given. The ideal system is, of course, as nearly con- tinuous as possible. Where, however, the continuous system is not in use and intermittent oiling must be depended on, the vari- ous joints and stuffing boxes will require attention and a fresh supply of lubricant at intervals of from perhaps twenty minutes 230 PRACTICAL MARINE ENGINEERING. to one hour. For the various pin and turning joints, main guides, etc., the lubricant is usually supplied by oil cups or cans of character suited to the particular use for which intended, while the piston and valve rods are lubricated by means of a swab charged with cylinder oil or special grease. The main guides are also in some cases lubricated by the swab rather than the can. There is also a growing tendency in engines of the high speed type as used on torpedo boats, etc., and where the steam is always more or less moist, to depend on water lubrication, and to avoid, so far as possible, the use of internal lubricant. This end may be furthered by careful workmanship in the fitting up of valves and pistons, and by driving the engine by belt or otherwise in the erecting shop with the surfaces charged with graphite. The minute pores of the metal are thus filled with the graphite, and rubbing surfaces are developed which run very well without further lubrication. (3) Adjustment of Bearings. For a bearing in good adjust- ment the clearance or distance between the journal and bearing surface is proportioned to the size of the journal, and may be made about .002 or 1-5 of i per cent, of the diameter. With a lubricant of proper consistency and a load per square inch not too great, say not over 400 to 500 Ib. per square inch of project- ed area, the film of oil will retain its place, and insure the proper lubrication of the bearing. If too thin a lubricant is used the bearing may heat and pound simply because the journal is not supported by the film of oil. The proper consistency of the oil as influenced by its natural viscosity and by the temperature of the bearing may, therefore, determine to a considerable extent the smooth running or pounding of the various joints and jour- nals. DEVICES EMPLOYED FOR SUPPLYING LUBRICANT TO BEARINGS. We will now describe the more important devices for sup- plying oil and grease to the bearings, or to the points where re- quired. (4) Wick Cup. The plain wick cup consists of a receptacle, usually of cast brass, fitted with a cover, and placed at a conven- ient point for the delivery of the oil to the bearing. It is also frequently formed as a part of the bearing cap, as in Fig. 147. MARINE ENGINES 231 A tube, as shown, enters through the bottom of the oil reservoir and rises within to a point above the level at which it is expected to carry the oil. This tube leads downward to the duct which carries the oil to the point of delivery to the bearing. The "wick" consists of a few threads of cotton wicking, one end of which is wrapped with a bit of wire, which then serves as a handle for pushing it down the tube or for pulling it out. In op- eration, one end of the wick is pushed down the tube and the other end dipped in the oil. Through the action of capillary at- traction the oil rises in the wick on the outside, and then by a combination of capillary and siphon action descends and drips down the tube to the bearing. The end of the wick within the tube should be pushed down below the level of the bottom of the cup so that this shall form the longer leg of the siphon. The size of the wick should be adjusted according to the amount of oil which it is desired to feed and to the quality of the oil as well. This adjustment of size is most easily effected by varying the number of strands of cotton in the wick. The Fig. 172. Wiper. Fig .173. Oil Cup with Adjustable Feed. amount fed may also be varied to some extent by regulating the distance to which the wick is pushed down the inner tube. For a sudden flush of oil the cups may be filled until they overflow into the inner tube, by which means the bearing may be flooded if desired. (5) Wiper. A wiper is shown in Fig. 172. It consists of 232 PRACTICAL MARINE ENGINEERING. an oil cup with a central blade or plate, A, extending above the edge, and attached to one of the moving parts of the engine. At a convenient point is placed a strip of fibrous material on to which the oil is fed from the source of supply. The strip and wiper are so adjusted that the latter in its motion to and fro wipes or scrapes along the lower surface of the former, and thus as soon as the strip is saturated with oil the wiper takes off a drop or more which then runs down into. the cup and thence to the surfaces to be lubricated. Naturally this mode of lubrica- tion is more especially suited to parts having a horizontal mo- tion. Fig. 174. Marine Engineering Oil Cup with Screw Cover. Marine Engineering Fig. 175. Oil Cup with Sight Feed. (6) Plain Oil Cup With Adjustable Feed. This consists of a simple cup, as shown in Fig. 173, mounted where convenient and connected by pipe or duct to the bearing to be supplied. The rate of feed is regulated by a needle or conical valve, which controls the size of opening through the discharge passage in the base. A cover is usually fitted to prevent spilling or the ad- mission of impurities. Where such a form of cup is used to ad- mit oil to a steam chest or other chamber under pressure, a strong screw cover is necessary, as shown in Fig. 174. To fill the cup in such case the valve is closed, the cover unscrewed, and MARINE ENGINES. 233 the cup filled. The cover is then replaced and the valve opened according to the rate of feed desired. ^ Another variety of cup used for this purpose has a body of cylindrical or globular form terminating at top and bottom in a neck or tube, each of the latter being closed by a valve. The lower neck joins the tube leading to the bearing as in other cups, while to the upper is fixed a shallow open cup. The chamber between the two valves is filled by closing the lower valve, opening the upper and pouring into the shallow cup which serves thus simply as a funnel. When filled, the upper valve is closed and the lower one opened according to the rate of feed desired. (7) Sight Feed Oil Cup. As shown in Fig. 175, this is es- sentially a plain cup with the addition of the "sight-feed" attach- ment or feature. When in adjustment, the flow of oil is regu- lated by the conical valve to a drop at a time at such interval as may be desired. The space below the outlet of the cup is cut away so as to show the drop as it falls into the mouth of the feeding tube. Very frequently a glass tube is fitted inside the brass framework, thus closing in the oil completely, but allowing the drop to be seen as it falls. For a sudden flush of oil it is only necessary to open up the conical valve sufficient to let the oil descend in a stream and flood the bearing. (8) Compression Grease Cup. In addition to oil, various forms of hard grease in cakes, or balls, or in bulk, are some- times used for lubricating purposes. For feeding such lubri- cating material to bearings two means are made use of. (i) If the bearing tends to become heated the heat de- veloped will soften the grease and allow it to run to the spot where it is needed. (2) Compression cups are used containing a piston or plunger on top of the grease and acted on by a spring under control by a screw operated by hand. (See Fig. 176.) The grease is thus forced either automatically or by hand through the feeding tube and to the bearing. The spring ar- rangement may be made adjustable so as to force the grease more or less rapidly, according to its degree of hardness, and to the rate of feed desired. (9) Lubricator. For the introduction of cylinder oil into the valve chests or steam pipes, an apparatus known as a sight-feed lubricator is very commonly employed. Such devices have been made in great variety of form, but the description of one will be 234 PRACTICAL MARINE ENGINEERING. sufficient to show the principle upon which they operate. The lubricator, shown in Fig. 177, consists of a main chamber, A, with connections for attachment to the steam pipe or throttle valve casing at B, and for the attachment of a length of vertical pipe, P, leading in to the main steam pipe at C. D and E are two fittings for a short length of glass tube, as shown. From the top of the chamber a passage or pipe leads down to the lower fitting, E, while from D the passage leads into the steam pipe Marine Engineering Fig. 176. Compression Grease Cup. Fig. 177. Automatic Lubricator. through the connection at B. The lower part of the chamber is connected to the vertical pipe leading up to C. There are also two connections, F, G, with glass gauge between to show the level of the oil and water within the chamber. The operation of the lubricator depends on the difference in density between the oil and water. The lubricator is first filled with oil through the plug H. The steam is then admitted to the pipe, P, where it will slowly condense and collect at the base of the chamber, in the pipe between D and E, and in the pipe P, thus furnishing a head of water acting on the oil and forcing it upward. As MARINE ENGINES. 235 soon as the head is sufficient, oil will be forced a drop at a time as regulated by the valve V, out through the passage leading from the top of the chamber down to E and up through the water in the tube, DE, and so on to the steam pipe, where it is caught by the flow of steam and carried to the valve chest and cylinder. The passage of the oil drop upward is plainly seen, and thus the operation of the lubricator is under ready observa- tion. Such lubricator may be placed on the steam pipe or throt- tle valve chamber, or at any convenient point where the oil will be carried by the inflowing steam to the points where needed. (10) Oil Pump. A simple arrangement for forcing cylinder oil into a steam chest is sometimes used when it is not conven- ient to fit a lubricator. This consists, as shown in Fig. 178, of Marine Fig. 179. Oil Pump. an oil pump operated by hand. The chamber being filled with oil the delivery valve is opened and the oil forced in as may be desired, through a connection attached to the pump delivery, as shown. (n) Modern Systems of Oil Distribution. In the preceding section we have described the principal devices used for supply- ing oil to a bearing, or to a steam pipe or chest. We will now describe briefly the general oiling system for the engine as a whole, involving such combination of these devices as may be found most desirable. The leading features of the modern system consists in the provision of a small number of distributing centers from which oil is taken by piping as directly as possible to the various places 236 PRACTICAL MARINE ENGINEERING. where needed, each place having its own independent pipe and set of connections. Following is a brief description of such a system of oiling gear, and will serve to illustrate the methods now in use in good practice. A light cast brass box is provided for each cylinder placed at a point higher than any joint or bearing to be reached by the oil, and having a capacity sufficient to last several hours without refilling. These oil boxes are provided with sight feed cups with protected glass tubes from which pipes lead to wipers on the moving parts, or to tubes in the bearings and guides. Union joints are fitted where necessary, so that the oil pipes may be quickly taken down and cleaned. With few exceptions the oil for the various moving parts of the cylinder is supplied from this box. The main crank pin is oiled by means of a pipe and cup carried on the cross-head and taking oil from a drip supplied from the oil box as described. The pipe runs down the side of the rod, or frequently inside if the rod is hollow, and connects with the oil duct leading through to the pin. The cross-head guides are provided with oil through pipes connected with holes at about the middle of each forward and backing guide. The main pillow-blocks are oiled by one or more wick cups deliver- ing the oil at the points desired. A cup for tallow or grease is also usually provided, and like- wise sometimes a hole through which the hand may be passed to feel of the shaft as may be desired. The presence of this hole, however, is not in accord with the principles given above in (i), and the practice cannot be recommended. If anything of the kind is to be fitted it is better to carry the hole simply through the cap, thus leaving the brass continuous. The latter may then be felt as desired, and a tendency to heat may be thus observed. The excentric straps are fed from long narrow oil cups, receiving their oil through the drip pipes from the reser- voir. The length of the cup is made such that some part of it is always under the drip in any position of the excentric. and it will, therefore, always receive its supply. The various other parts of the gear are similarly supplied with oil either from a drip or a wiper as may be more convenient. The chief advantages of such a system consist in the cer- tainty and regularity of operation which may be assured with the minimum of time and attention on the part of the oiler. MARINE ENGINES. 237 Sec. 25. PIPING. [i] Systems and Materials. The principal systems of piping are as follows : (1) The main steam piping from boilers to engine. (2) The auxiliary steam piping from the auxiliary boiler or from one or more boilers specially selected, to the various auxiliaries which are to be operated by steam. (3) The main exhaust piping from cylinder to cylinder and from the L. P. cylinder to the condenser. (4) The auxiliary exhaust system, providing each auxil- iary with its exhaust, either to the condenser or overboard, as desired. (5) The feed system, main and auxiliary for returning the condensed steam to the boilers. (6) The condensing system for bringing the condensing water to the condenser and for carrying it from the condenser to the sea again. (7) The drainage and bilge pump delivery systems for lead- ing water to the bilge pumps and from the pumps to the sea. (8) The fire system for leading water to the fire pumps and from the pumps to the fire plugs. (9) The sanitary system for delivering water to the W.Cs. and heads. (10) The steam heating system. We may otherwise classify all pipes under three heads : steam pipes, exhaust pipes, and water pipes, while of the latter we have a further division into those carrying water to a pump or induction pipes, and those carrying water from a pump or educ- tion pipes. For steam pipes the materials in present use are copper, wrought-iron, and steel. Copper pipes in small or moderate sizes may be made of seamless or solid drawn tubing ; in large sizes they are made of sheet copper with brazed joints. Wrought iron pipes are lap welded, while steel pipes are also lap welded and are sometimes further fitted with a riveted longi- tudinal strap covering the line of the weld. Seamless or solid drawn steel pipes have also been made to some extent. For the various junctions, elbows, bends, tees, etc., steel or malleable iron castings are used with steel pipe, while with copper pipe sheet copper is used for these parts, bent and formed 23 8 PRACTICAL MARINE ENGINEERING. up by hammering into shape, and secured at the joints by brazing 1 . The advantages of copper are its great ductility, freedom from corrosion, and the readiness with which it may be used to make pieces of an irregular form, such as the elbows, junctions, etc., referred to above. Its disadvantages are, greater cost, low tensile strength, the possibility of damage to the quality of the material in the process of pipe manufacture, and the possibility of a loss of ductility in service by repeated strains due to the expansions and contractions which result from changes in tem- perature. The metal close about a flanged joint seems especially liable to lose its strength in this way. This is probably due to the concentration of the strains due to expansions and con- tractions in the vicinity of a rigid connection such as a flanged joint, and to the development in this way of a line of weakness running around the pipe. To render copper pipe more secure under high pressure it has been wound with copper or steel wire, or reinforced by wrought-iron or steel bands. Such bands may be from ^ to 2 inches wide by y& to J4 inch thick, and spaced with intervals of from 6 to 10 inches. These methods, especially the latter, have proven quite successful in strengthening copper piping for mod- ern advancing pressures. The chief advantage of wrought iron and steel pipes are, less cost, greater tensile strength, less liability of the mater- ial to damage in quality in the processes of manufacture, and less liability to lose strength or ductility in service. Their disadvantages . are, greater liability to corrosion, and greater weight of cast junctions and fittings than for copper. Welded pipe is made from rolled strips the edges of which are machine beveled for a lap joint. The requirements of manu- facture are such that for all except the largest sizes the thickness is in excess of that needed for strength alone, at least with the pressures at present in use, so that when such material is employed there is always an excess of strength. 1 With wrought-iron pipes the welded joint is trusted without reinforcement. With mild steel a covering strip or butt strap is sometimes riveted on, though with the later improvements in the welding quality of such material, experience shows that these joints are quite as reliable as those of iron. Flanges for MARINE ENGINES. 239 wrought-iron or steel pipes may be welded on, but more com- monly they are riveted or screwed to the pipes. In the latter cases the flanges are caulked on both sides to make a steam tight joint. In small sizes and in a relatively cheaper grade of practice, ordinary commercial steam piping is used, fitted up with the usual fittings and screwed joints. For exhaust piping the same general character of pipe is used as for steam, with such differences as the decreased strength necessary may indicate. For water piping steel, iron and copper, and in cheaper practice the ordinary commercial pipe are all used. Steel and iron are usually considered less suitable for water than for steam piping on account of the greater danger from corrosion. This is especially true for feed piping, and in case such material is used for this purpose it is considered good practice to care- fully galvanize the pipe both inside and out. It is likewise good practice to tin all copper piping which is under the floor plates or in the bilge, but this is rather to protect the ship than the pipe, the former being in danger of attack by electro chemical action (see Sec. 40) in case the copper and the metal of the ship obtain connection through a medium such as bilge water. In connection with piping see also that heading under Section 19. [2] Expansion Joint. The expansion and contraction of a length of piping under a change of temperature require some kind of joint or connec- Fig. 179. Expansion Joint. tion which will allow of the change of length without buckling or straining the pipe. This is usually provided by an expansion joint, as shown in Fig. 179. This consists of a recessed portion on one part of the joint into which the other fits, as shown. The 240 PRACTICAL MARINE ENGINEERING. space left between the two thus forms a stuffing-box into which packing is compressed by means of the gland. The two parts of the joint are thus free to slip a little way, one relative to the other, while the joint is kept tight by means of the stuffing box and gland in the usual manner. It is readily seen that the steam pressure within the pipe, especially if it contains a bend or el- bow, will tend to force the two portions of the joint apart, and thus open the pipe at the joint. To guard against this, safety stays or ties should be fitted. In the figure one of three such stays is shown by the bolt at the top. Care must be taken in adjusting such stays that sufficient freedom is left for the expan- sion and contraction which the joint is intended to provide for. In special and more complicated forms, known as balanced or equilibrium expansion joints, these forces are more or less completely balanced within the joint itself. [3] Globe Angle and Straightway Valves. For controlling the flow of a liquid, vapor or gas through a line of piping, various forms of valve are used. Chief among these are the Globe, Angle and Straightway or Gate types, as de- scribed in Section 24 [i], [2], and to which reference may be made. AUXILIARIES. 241 CHAPTER V. AUXILIARIES. Sec. 26. CIRCULATING PUMPS. The office of the circulating pump is to draw the condensing water from overboard, force it through the condenser tubes, as explained in Section 29, and thence overboard through the con- denser discharge pipe. The principal resistance to be n/w Engineering Fig. 180. Centrifxigal Pump. come by the pump is the resistance to the llo\v of the water through the tubes, and this is but slight measured in pounds per square inch or in feet of head. On the other hand, the quantity of water to be handled is large, and hence the requirement is for a type of pump which shall be able to handle large quantities of water against a small head or resistance. These require- ments are very perfectly fulfilled by the centrifugal pump, as shown in Fig. 180. The moving part consists of a number of 242 PRACTICAL MARINE ENGINEERING. vanes or arms attached to a shaft and forming what is called the runner. This revolves within a casing furnished with inflow and outflow passages, as shown in the figure. The pump being primed or filled with water and started, the rotary motion gives rise to a centrifugal force, in obedience to which the water moves outward toward the tips of the blades, where it escapes through the outflow passage into the discharge pipe. There is a corre- sponding defect of pressure about the hub of the runner and a resulting inflow of water from the sea to take the place of that which leaves at the outflow. The operation thus becomes con- Fig. 181. Outboard Discharge Valve. tinuous and results in a steady flow of water from the pump through the condenser tubes and back to the sea through the condenser discharge pipe and outboard delivery. In order to prevent the water from "short circuiting" or slipping back from the discharge space about the tips of the blades to the inflow space about the hub, a running fit is provided between cor- responding faces on the runner and casing as indicated in the figure. The discharge or outboard delivery valve is usually a plain type of angle stop valve, as illustrated in Fig. 181. Its office is AUXILIARIES. 243 simply to allow when open the discharge of the water from the condenser, and prevent when closed the inflow of the sea to the pump. Sec. 27. CONDENSERS. The purpose of the condenser is to provide for converting the exhaust steam back into water. Condensers are of two types jet and surface. The jet condenser consists simply of a chamber of rec- tangular or cylindrical form in which the steam and the conden- sing water are mingled together, the steam giving up its heat to the relatively cool water, and thus being reduced to the liquid state again. The water is usually led into the top of the chamber and allowed to fall upon a plate pierced with a large number of small holes, and known as the scattering plate. This divides the water into small streams or jets and enables it to mix intimately with the steam which enters just below the plate. The condensed steam and condensing water then fall together to the bottom of the condenser. From here the water is removed by the air-pump which delivers it overboard, the feed-pump in the meantime taking enough for the boiler feed and returning it to the boilers. The usual type of surface condenser consists of a chamber commonly of cylindrical form if separate from the main engine (see Fig. 182), or rectangular if forming a part of the engine columns. (See Fig. 100.) This chamber contains, as shown, a large number of small brass tubes running between the inner walls of the heads, which are double, thus providing a connec- tion between the ends of the various tubes. The condensing water is driven by the circulating pump through the tubes, the usual run being, as shown in the figure. The water enters at the lower left hand end and fills the lower half of the head, be- ing prevented from filling the whole head by a partition half way up, as shown. It thus finds its way into the lower half of the tubes and flows through them to the right hand head. It then rises into the upper half of the tubes, flows back to the left and out at the opening in the upper part of the left hand head. The water thus traverses twice the length of the condenser forward and back, and from the bottom upward. The steam, on the other hand, enters at the top into the body of the chamber, and thus around the outside of the tubes. The steam and the condensing water are thus kept separate, and the steam is condensed simply 244 PRACTICAL MARINE ENGINEERING. by the surface action of the tubes. The steam thus condensed to water falls to the bottom of the condenser, whence with some air and vapor it is removed by the air-pump and delivered to the hot- well, whence it is taken by the feed-pump and sent back to the boilers. Baffle or diaphragm plates, as shown, are often fitted in the condenser to prevent the steam from rushing directly through from the inflow on top to the air pump passage on the bottom. The steam is thus forced to fill the condenser as com- pletely as possible, and thus the condensing surface is more uni- formly brought into action. In order to facilitate the rush of steam downward into the body of the tubes, thus bringing more AIR PUMP SUCTION - Fig. 182. Surface Condenser, Longitudinal Section. quickly into action those in the lower part of the condenser, a few rows are often omitted in the upper part, thus forming branching passages leading from the top downward, as shown in Fig. 183. In order to support the heads against the pressure from without, a certain number of longitudinal braces or struts are necessary, as shown in the figures. Condenser shells are made of cast-brass, cast-iron, or sheet brass or steel. When of rectangular form the sides are cast with the necessary webs to give them strength to stand the pres- sure from without. When of cylindrical form the necessary strength can be given bv a suitable thickness of metal rein- AUXILIARIES, 245 forced if necessary by ribs running around the shell. When rela- tively thin sheet metal is employed, as in torpedo-boat practice and the like, it is customary to fit one or more angle-iron or Tee-iron stiffeners running around the shell in order to provide the necessary strength. Condenser tubes are of thin sheet brass, usually > to y^ inch outside diameter. In order to make a water-tight joint be- tween the condenser tubes and the inner heads or tube plates, and at the same time to avoid a rigid constraint of the tube, a great variety of condenser tube packings have been employed. The most common type of packing in present practice is shown in Fig- .184. The tube plate is counterbored, as shown, and threaded for a ferrule with a tapering outer end. The hole in the outer end of the ferrule is thus of about the same size as MR PUMP SUCTION 3fartnt Engineering Fig. 183. Surface Condenser, Cross Section. that inside the tube, and hence smaller than the outside of the tube. Between the other end of the ferrule and the bottom of the counterbore is usually a ring of rubber or a few turns of some other elastic or fibrous material as packing. Screwing clown on the ferrule compresses the packing, and thus makes the joint, while at the same time the tube is free to expand and contract to a slight extent. The outer ends of the ferrules, however, pre- vent the tube from crawling to such an extent as to free either end, a result liable to occur without some method of prevention. Sec. 28. AIR PUMPS. It is. the purpose of the air-pump to remove from the con- denser the water and such small quantities of air as may enter by leakage or with the steam, and which would ultimately de- 2 4 6 PRACTICAL MARINE ENGINEERING. stroy the vacuum if riot removed. As often stated, it is the office of the air pump to maintain the vacuum formed by the condensation of the steam. The usual type of air-pump is shown in Fig. 185. A is the piston or bucket moving in the barrel B, and carrying bucket valves, D, opening upward, as shown. The foot valves at C also open upward and admit the contents of the condenser from below. Beginning with the piston in the position shown the operation is as follows : As the piston rises, the air and vapor between its lower face and the foot valves become rarified with a resultant decrease Frg. 184. Ferrule and Tube Packing, Surface Condenser. of pressure. Soon a point is reached where the pressure in the condenser is decidedly greater than in the space above the foot- valves, and in answer to this difference of pressure the valves open and admit air, vapor and water from the condenser. This* operation terminates with the piston at the top of the stroke. On the return stroke the foot valves close and the contents of the barrel are forced through the bucket valves at D to the space above. On the next stroke the contents are lifted and forced out through the delivery or head valves at E, w r here the air and vapor escape, and the water flows to the hot-well, whence it is sent by the feed-pump back to the boiler. AUXILIARIES. 247 Fig. 185. Vertical Attached Air Pump. 2 4 8 PRACTICAL MARINE ENGINEERING. It is evident that the pressure in the condenser cannot be reduced below that necessary to raise the foot-valves, so that for this reason, as well as for their more ready response to varia- tion of pressure, they should be made as light as is consistent with a proper performance of their duty. As shown in Fig. 186, such valves in modern practice are usually made of light sheet metal discs controlled by spiral springs. In older practice vul- canized rubber was quite commonly employed. It is also evi- dent that the foot valveb will respond the more quickly, the more rapidly the pressure above them decreases as the piston begins to rise, and hence the less the clearance space between the valves and the piston when in its lowest position. The air-pump has this peculiarity in its action, that the load per stroke and hence the resistance often dUreases with an increase of speed, and increases with a decrease of speed. Hence when the pump is operated by an independent engine, it may Fig. 186. Air Pump Valve, Guard and Spring. be liable, unless carefully designed, to race or run away to ex- cessively high speeds with an increase of pressure in the steam cylinder, or to slow down and stop with a corresponding de- crease. It is apparent also that a certain time will be needed for the foot valves to open, and for the air, water and vapor to flow through. Hence, with excessive speeds, the valves may not have time to open between strokes, the vacuum will become poorer, 'and the condenser may become flooded with water. It thus fol- lows that with too high, as well as with too low a speed, the vacuum will be poor, and the operation of the pump unsatis- factory. The air-pump may be driven either by an independent en- gine, or by attachment to the main engine. The attached air- AUXILIARIES. 249 pump is usually operated by air pump levers, which derive their motion in most cases from the L. P. cross-head, as shown in Fig. <*<;. The stroke of the pump is thus reduced to usually less than one-half that of the main engine. One of the advantages of the attached air-pump is that the number of strokes per min- ute is necessarily the same as for the main engine, and it can neither race nor slow clown on account of variations in its own resistance. A further advantage is that the power required for its operation is obtained more economically than when operated by a separate engine. The chief disadvantage of the attached air-pump is that with the modern increase of revolutions, the speed may be too great "for the best results from the pump as Fig. 187. Air Pump for High Speeds. usually designed. This, together with the advantage of having the condition of the condenser under control independent of the main engine furnish the chief reasons for the use of the inde- pendent air-pump. When thus fitted as an independent auxil- iary the number of double strokes per minute usually varies from 15 or 20 to 30 or more, while the revolutions of the main engine may be from 100 to 200 or more. For special cases where the revolutions are very high, as in torpedo boat practice, but where for simplicity or for the saving of space it is desirable to use an attached air-pump, the Bailey type of pump is employed. In this pump, as shown in Fig. 187, 250 PRACTICAL MARINE ENGINEERING. the water flows by gravity into the barrel through ports alter- nately opened and closed by the piston itself, which thus serves as its own valve. The air and vapor naturally expand and enter with the water, and the whole contents are forced out of the end of the barrel through delivery valves similar to those in the pump of usual type. In some cases the delivery valves are car- Fig. 188. Vertical Independent Air Pump. ried on movable heads, which thus become valves in themselves, and available to relieve the barrel in case the smaller valves give insufficient opening. In some cases, as shown in Fig. 187, the smaller valves are omitted and the entire head serves as the de- livery valve. With this design air-pumps may be successfully operated at speeds of 400 or 500 revolutions and higher. AUXILIARIES. 251 When operated independently the air pump is very com- monly made double, and operated by one form or another of special steam valve gear. A typical form of independent air pump is shown in Fig. 188. The general operation of the valve gear is as follows : The beam which positively connects the main piston rods of the pumps operates from a point near its center and by means of rod and bell cranks, the slide valve of the hori- zontal cylinder which lies between the main steam cylinders, as shown. The piston of this horizontal cylinder is really the driv- ing engine of the main steam valves, a function which it per- forms by means of a system of internal levers. See further Sec- tion 33 regarding the operation of such types of pump valve gear. The adjustable collars on the valve stem of the "valve driving engine" afford a means for regulating for full stroke at any speed, while suitable cushion valves give a further control over the action during the stroke, in regulating the distribution of the work and preventing the slamming of the foot valves. Sec. 29. FEED PUMPS AND INJECTORS. Comparing the feed and circulating pumps we find that the former has to handle a very much smaller quantity of water usually from 1-25 to 1-40 the amount but against a very much higher pressure, viz., that in the boilers. In consequence an entirely different type of pump is required. The feed-pump may be attached to the main engine, or run as an independent auxiliary. When attached to the engine it is usually of the type known as the plunger pump and shown in Fig. 189. The moving part consists simply of the plunger, AB, working in the stuffing box, KL, and operated usually from the air-pump levers. There are two valves or sets of valves, in- flow and outflow, as shown at F and E. The level of the pump is usually below that of the hot-well so that the water stands ready to enter through the inflow valves as the plunger rises and makes room for it. This is aided by the partial vacuum formed within the barrel as the plunger rises. On the other hand, as the plunger descends on the next stroke the inflow valve closes and the water flows out through the outflow valve in order to make room for the descending plunger. It is thus seen that the pump is single acting ; that is, that it delivers but once in two strokes, and that the amount delivered is measured by the volume of the plunger displacement. 252 PRACTICAL MARINE ENGINEERING. This in turn equals the cross-sectional area of the plunger multiplied by the length of the stroke. The actual delivery per stroke will be somewhat less than this due to leakage, and to failure of the barrel to completely fill on the up stroke. The stuffing box, K L, is of course accessible and adjustable from the outside, and with proper design the inflow and outflow valves may be examined by the simple removal of a bonnet. The strong points of this pump are its simplicity, and the ready accessibility for examination and adjustment, of all parts on which the operation of the pump may depend. Fig. 189. Plunger Feed Tump. In fitting up the attached feed pump it is necessary to pro- vide it with some form of safety or relief valve, else should the discharge or check valve jam or fail to operate, the feed pipe or pump or some part of its operating gear would become broken. Such a relief valve is usually a simple form of spring loaded safety valve, and similar to the engine relief valves re- ferred to in Section 24. In order that the valve may be ef- fective in relieving the pump and entire line of pipe it should be placed on the pump chamber or in any event not beyond the pump discharge valve. AUXILIARIES. 253 Where the feed pump is operated as an independent auxil- iary it is usually of the direct acting or positive motion type, as described in Section 33, and to which reference for details may be made. For feed-pump purposes the area of the steam piston is made from 2 to 3 times the area of the water piston or plunger in order to give on the steam side a pronounced excess of total pressure over the resistance on the water side. This will enable the pump to overcome the resistance to the flow of the water through the feed-pipe and check valves, and thus to force water into the same boiler from which it draws its steam, or even into a boiler with a pressure somewhat higher than that from which its steam is drawn. For the general purposes of a feed pump the vertical or admiralty style, as illustrated in Section 33, has come to be very generally used. Its chief advantages over the horizontal type are two in number. (1) It occupies less floor space and may be conveniently put up on a bulkhead or elsewhere, in such manner as to occupy but little space otherwise available. (2) The valves in the water end, as shown in the figure, are more conveniently arranged for examination by the removal of a bonnet than with the horizontal type of pump. These considerations and especially the latter, have made this general type of feed pump the standard in modern marine engineering practice. In addition to feed-pumps of the plunger and piston types, an injector is often fitted as an auxiliary means of feeding the boilers. There are many different varieties of injector, but a description of one will suffice to illustrate the principles in- volved. Referring to the diagram. Fig. HJO. S. is a nozzle con- nected with the upper pipe, I>, leading steam from the boiler. When steam is turned on by means of the handle, K, and at- tached valve-stem and valve, it escapes in a jet which enters the. slightly tapered passage VC. The air in the space around and between these two orifices is caught and drawn along with the jet, thus causing a reduction of pressure at this point. This space is connected through the lower pipe, B, to the water reser- voir, and when the loss of pressure is sufficient, the water rises the same as in the case of a pump. The water and steam are thus brought into contact, and pass on together into the com- bining and delivery tube CD. The steam is here condensed and the resultant jet of water attains a very high velocity. A little 254 PRACTICAL MARINE ENGINEERING. further on, when this is reduced to the relatively low velocity of the water in the feed pipe, the pressure developed is sufficient to overcome the boiler pressure, to open the check valve, and to force the water into the boiler. It may aid the understanding of this seemingly puzzling re- sult if we remember that it is the energy of the steam which is the real motive power. This is transformed largely into motion in the combined jet, and this, when arrested, gives the pressure, as stated before. In the steam pump a steam piston is provided much larger than the water plunger in order to give a force suffi- cient to overcome the resistance of the feed pipe and at the check valve. So in the injector, in a somewhat similar manner, Fig. 190. Injector. the energy of the steam in a relatively large pipe is concen- trated on a small jet of water, giving it the high velocity and later the pressure, as described. In passing it may be noted that as a boiler feeder a good injector has practically a perfect efficiency, all heat used being carried back again into the boiler, except the small amount lost by radiation from the instrument and connecting pipes. An injector of the type shown in the figure is known as an automatic injector. This signifies that once .the injector is ad- justed and working, should the jet of water become broken by a jar or other accidental circumstances, it will restart itself without further adjustment. The capacity and working range of an in- AUXILIARIES. 255 jector are decreased as the lift is higher and as the water is warmer. With cold water and a moderate lift, say not exceed- ing 5 to 8 feet, a good automatic injector will start up with 25 or 30 Ib. steam pressure, and will work with little or no further adjustment over a range of perhaps 100 pounds pressure. With feed water at about 100 deg. F, the same injector would start at 30 or 35 Ib. steam pressure, and will work over a range of per- haps about 70 Ib. or up to about 100 Ib. In addition to the automatic injector there is another type having two sets of tubes, one for lifting and one for forcing. Such instruments are often termined inspirators to distinguish them from the ordinary automatic injector. When properly ad- justed the lifting set of tubes acts as a governor to the forcing set, supplying under a great range of steam pressure the proper amount of water to condense the steam in the final set of tubes. Such an injector handling cold water with a short lift, will work through a range of over 200 Ib., while with water as hot as 100 deg. F and small lift it will work through a range of from 150 to 200 Ib. The operation of each set of tubes is on the same general principles as above described for the automatic injector. Sec. 30. FEED HEATERS. The office of the feed heater is to raise the temperature of the feed-water from that of the hot-well as nearly to that within the boiler as may be practicable before the feed enters the boiler proper. Feed heaters are of two fundamentally different types, according as the heat used is drawn from waste furnace gases or from steam. If the former, as is very common with water- tube boilers, as described in Section 14, the feed heater is really a part of the boiler. The entire operation is thus performed in two stages, one in the heater, and one in the boiler proper. In the first stage it is sought to raise the water as nearly as possible to the boiling point by use of the furnace gases after they have passed the main steam generating tubes. In the second stage, carried out in the boiler proper, the previously heated water is transformed from liquid into vapor. The resulting economy comes from being thus able to re- duce the products of combustion to a temperature lower than they would otherwise have before finally getting rid of them. The addition of the heater will, of course, affect the draft, and the extent to which heating surface, either in the form of steam 256 PRACTICAL MARINE ENGINEERING. generating tubes or feed heating' tubes, can be added without seriously interfering with the draft is a point which must receive consideration. Morever, since the feed-heating surface might be put into additional main boiler tubes, thus giving the same total surface without a feed-heater, the question may naturally be asked whether in such case the results would be as good. In other words, is it better to put the total heating surface all into main boiler tube surface, or to divide it up and put a part (usually quite small) into a feed-heater located beyond the mail? part of the boiler? Experience seems to indicate the latter as the better design of the two, and the fundamental reason is that given above viz., that we are thus able to reduce the products of combustion to a lower final temperature than with main boiler tubes of the same aggregate surface. The reason for this is found in the fact that the temperature of the feed water as it en- ters the heater is much lower than that of the steam and water within the main tubes. Hence with such a heater the gases as they leave the boiler pass over relatively cool surfaces, and the flow of heat will be much more pronounced, and the gases will be more effectively cooled than by passing over an equal area of main boiler tube surface. Turning now to the other type of heaters we have an en- tirely different mode of operation. Here the heat given the feed-water comes from steam which is drawn either directly from the main or auxiliary steam pipe, or from the receivers, or from the exhaust of some of the auxiliaries on its way to the con- denser or to the escape pipe. There are two styles of heater working on this principle. In one the steam and feed-water are mixed together in the same chamber and the steam is condensed and thus joins the feed-water, raising its temperature as may be determined by the conditions of operation. In the other style the steam is on one side of a coil or nest of tubes and the feed- water on the other side, the heat passing through the metal of the tubes'from the former to the latter while the steam condensed in consequence of the loss of heat is drawn or trapped out as may be required. Where the steam and feed-water are mixed together the feed-heater consists essentially of a chamber or drum, as in Fig. 191, provided with means for introducing the feed as a spray or series of cascades, while the steam is introduced in jets, and the two thus become intimately mingled. AUXILIARIES. 257 In the form here shown the feed enters through C and pass- ing out through a valve, D, falls as a cascade through the an- nular space between the pipe and the steam delivery drum which is pierced, as shown, with small holes. The steam enters through B, and passing through the holes in small jets becomes mingled with the water and thus imparts to it its heat. The t\Vo then fall to the bottom of the chamber from whence the feed TO CONDENSER Fig. 191. SUPPLY TC SECOND PUMP Feed Water Heater, Direct Contact. pump takes its supply, and by means of which the water is finally sent to the boiler. The advantages of such a form of heater are simplicity in the apparatus itself and a quicker action than with tubes, as in the other form. The chief disadvantage lies in the fact that an ad- ditional feed pump must be provided ; one for forcing the water from the hot-well to the feed-heater and the second for taking it from the heater and forcing it into the boiler. 25S PRACTICAL MARINE ENGINEERING. Turning to the other style of heater, as illustrated in Fig. 1 92, we have a chamber or drum containing a nest of corrugated copper pipe. The feed-water passes on one side of the pipes and the steam on the other, as shown, the heat passing through from the one to the other as above described. Where such a heater is fitted to utilize the steam from an auxiliary exhaust, the heater forms simply a part of the exhaust passage and the steam passes through continuously, simply leaving a part of its heat behind. RELIEF VALVE SURFACE BLOW-OFF ^"AFEED OUTLET EXHAUST ELOW-OFF- Fig. 192. Feed Water Heater, Surface. In other forms of heater there is no continuous flow of steam through, but the steam is led to the steam side from the source selected and there gradually condensed by the loss of heat, while the water thus formed is drawn off as may be necessary. The heater is thus kept cleai for efficient operation, and the water is returned to the hot-well or otherwise into the feed system. In heaters of this type the flow of water is continuous from the feed-pump through the heater to the boiler, and no additional pump is required as with the other type referred to above. The difference is due to the fact that where the water and steam are AUXILIARIES. 259 separated, the water side of the heater can be operated under the full pressure in the feed-pipe and thus made part of the feed circuit. Where the water and steam are mixed the interior of the heater cannot be operated under any such pressure, and thus two separate pumps are required. In heaters using steam from the steam pipe or from the re- ceivers, it is clear that all such steam would ultimately go to the condenser and thence back to the boiler as feed-water, and hence that no heat is saved which would otherwise have been thrown away. In such cases it is not at first sight clear where the gain can come in, for the operation seems to be a simple shifting of heat from one part of the cycle to another without gain or loss in total amount. As a matter of fact the operation does consist of just such a shifting of heat, and here is where the gain in work comes in. This shifting of heat from one part of the cycle or routine of the steam to another introduces a change which brings the cycle a little nearer that for the highest efficiency as described in 59. While therefore there will be no saving of heat as such, the engine may be enabled to better use the heat which is pro- vided and thus to show a larger return in useful work. These points cannot be here discussed in detail, but it seems at least worth while to note in general terms the chief source of the economy experienced with such heaters. Especially will heaters of this type affect the routine of the steam favorably when they are arranged on the compound or step by step principle. In this arrangement the feed passes through a first chamber and receives heat from steam drawn from the low pressure receiver. It then passes on to a second chamber and there receives heat from steam drawn from the next higher receiver, and so on, in the last receiving a final addition of heat from steam of full boiler pressure. This type of heater, when of sufficient capacity to raise the tem- perature of the feed nearly up to that of the water in the boiler, will effect a marked economy in the engine, a saving presumably due to the change thus effected in the routine through which the steam is carried. In addition to the saving thus effected by feed heaters, many engineers believe that they are of use in reducing the strain and wear and tear on the boilers by furnishing a hot rather than a cold feed, and hence that they are of distinct advantage to the boiler and well as to the engine. 260 PRACTICAL MARINE ENGINEERING. Sec. 31. FH/TERS. Feed water filters are provided for removing oil from the feed water before it enters the boiler. See further on this point Section 41. Such filters are made in various forms, the chief features being the kind of filtering material employed, and the arrangement of the flow of water through it. Animal charcoal;, sand, gravel, broken pumice stone, etc., form one class of sub- stances, while fibrous materials such as sponges, bagging, towel- ing, etc., form another case. Of the first class, animal charcoal is the best, though somewhat expensive. It may, however, be Engineering Fig. 193. Feed Water Filter. removed from time to time, washed in lye water and replaced r and thus made to do duty for a long period of time. The various fibrous materials, such as sponges or bagging, soon become clogged also with oil and impurities, and require either replace- ment or washing and cleaning. After a few repetitions of cleaning in this manner, such material must be replaced with new. Filters also differ, according to whether the flow of water through the filtering material is forced by the pressure of the feed pump, or is due simply to the flow under the action of gravity. In gravity filters the flow may be up and down, two or AUXILIARIES. 261 three times through the bed of filtering material, the course be- ing determined by suitable partitions or passages within the filter box. When the action is under pressure the filter forms a part of the feed pipe circuit and the water enters and passes through, urged by the action of the feed pump, though at a much lower velocity than through the feed-pipe itself. In such case, if the filter should become choked, excessive pressure might be de- veloped between the feed-pump and filter with the possibility of a rupture of the latter. To avoid this danger a by-pass pipe and safety-valve may be arranged so that the valve will open under an excess of pressure and allow the water to flow around the filter to the continuation of the feed-pipe beyond. The safety- valve may also be maintained open by appropriate means and the filter shut off by stop-valves, thus sending the feed through the by-pass pipe and leaving the filter free for examination and repair. In Fig. 193 a simple form of filter is shown with by-pass pipe and valves for controlling the flow of the feed. From the ex- planation above the operation of the filter will be readily under- stood. Sec. 32. EVAPORATORS. The office of the evaporator is to supply fresh water to make up the loss in boiler feed. Of the steam which the boilers supply not all can find its way back through the feed. Small steam leaks may occur at the various joints and stuffing boxes, some of the auxiliaries may not send their steam to the condenser, the whistle may be used (as in foggy weather), and so in various ways losses of fresh water will occur. The proportion of such loss varies widely with the circumstances, but will often amount to 5 per cent, and more. In order to avoid making up this loss with salt water the evaporator is provided. A modern representative evaporator consists of a series of nests or coils of pipe contained within a chamber, as shown in Fig. 194. The chamber has a salt-water inlet, and steam from the boiler or from one of the receivers is passed inside the tubes. The heat in the steam passes through the tubes and forms steam or vapor of lower pressure on the salt-water side. The chamber is connected with the condenser or with the low pressure re- ceiver, and the steam formed in the evaporator is thus passed into the main circuit and serves to make up the loss as specified before. At the same time the water formed in the coils bv the 262 PRACTICAL MARINE ENGINEERING. loss of heat is drawn or trapped out as it accumulates, and is re- turned to the feed, so that all steam formed on the salt-water side is a net gain for the fresh-water account. The coils on the outer or salt-water side naturally become coated with scale, so that they must be cleaned from time to time. To this end they CROSS SECTION OF EVAPORATOR COIL Fig. 194. Evaporater. are usually made removable or arranged so as to be readily accessible through manhole openings in the shell. It is, of course, essential that the tubes be kept clean for the most effi- cient working of the evaporator. In the operation of the evaporator the chief point requiring attention is the proper proportion between the amount and tern- AUXILIARIES. 263 peraturc of the inflowing steam and the pressure within the chamber on the salt-water side. If the pressure is low and steam is provided in excess, it may give rise to a violent ebullition or foaming, which will carry some of the salt water along with the vapor formed, and thus introduce salt into the circulating sys- tem. This condition must be guarded against by a proper con- trol of the amount of steam admitted. In the way of general maintenance, the tightness of the tube joints and the condition of the tubes as regards scale are the chief points requiring attention. Sec. 33. DIRECT ACTING PUMPS. In early marine practice the fly-wheel pump was a favorite type, and was used for all ordinary purposes where an independ- ent pump was required, as for boiler feed, fire purposes, or for general purposes on shipboard. This pump consisted essen- tially of horizontal steam and water cylinders with the piston and plunger on a common rod and moving together. Attached to the rod was a cross-head with connecting rod leading to a crank and shaft carrying a fly wheel. The fly wheel served to carry the pump past the dead points, and the shaft served to carry an excentric which actuated a simple slide valve on the steam cylinder. This type of pump, however, has almost entirely disappeared from modern practice, its place being taken by the direct acting pump with its greater compactness of form and better adapta- tion to the conditions of service. We will now consider briefly the essential features of this type of pump, with a few examples drawn from modern practice. As illustrated in Fig. 195, the pump is horizontal and con- sists of two cylinders, one for steam and one for water, carried on a common piston rod. The steam end is operated by means of a suitable valve gear as a simple reciprocating engine, and thus communicates the same movement to the pump plunger or piston. Each end of the water cylinder is provided with both inflow and outflow valves, as shown, and thus the pump becomes double acting, that is delivering on each stroke alternately from one end and the other. For operating the steam ends of pumps of this type, a great variety of ingenious valve gears have been devised. The need for special device arises from the fact that there is 264 PRACTICAL MARINE ENGINEERING. no rotating part and no chance to use an excentric, and that the valve cannot be operated directly from the main piston rod. Where it is thus required that a single set of principal moving parts be self operating, the valve gear usually consists of the following chief features : (i.) The main steam valve, often of special form, but usu- ally operating as a simple slide valve. (2.) An auxiliary plunger or piston moving in a cylinder formed in the valve chest, and coupled or connected to the main valve. (3.) An auxiliary valve controlling steam and exhaust to and from the two ends of the auxiliary plunger cylinder. (4.) Means for operating the auxiliary valve from the main piston-rod. Such means may consist of levers, links, rods, cams, etc., operated by tappets on the main rod, whose location or point of operation may be adjusted according to the length of the stroke desired. The chain of operation is then in general as follows : Just before the end of the stroke the tappet or other piece moved by the main piston rod gives motion to the auxiliary valve. This produces an adjustment of steam and exhaust for the auxiliary cylinder which results in a movement of the auxil- iary piston and hence the movement of the main valve as de- sired. The motion of the main piston is thus reversed and the stroke takes place in fhe opposite direction, and so on continu- ously. In Fig. 195 the lower section is horizontal and taken through the auxiliary piston and auxiliary slide valve operated by the levers and links as shown. The upper view shows in vertical section the auxiliary piston and main steam valve. If two such pumps are placed side by side, it is found that the valve of each pump may be operated from the piston rod of the other. Hence by appropriate connections a pair of such pumps may be made self operative, the strokes being made alter- nately, and each piston rod running the valve gear of the other pump. Such an arrangement constitutes a dnplc.v pump, a form which has enjoyed w^ide and continued favor among marine en- gineers for feed-pumps and for other purposes with generally similar conditions. In the so-called "Admiralty" style of pump the motion of these parts is vertical, and the water valves are specially arranged AUXILIARIES. 265 with a view to ready examination and overhauling. As noted in Sec. 29, this general style is quite commonly used for feed-pump purposes. Such pumps may be either simple or duplex, but the duplex type is more commonly met with in this form. In Fig. 196 is shown one member of a duplex admiralty pump, the ar- rangement of the parts and operation of which will be apparent without further explanation. In Fig. 197 is shown similarly a single vertical type of feed-pump with independent valve gear, Marint E.iytnterfng Fig 19"). Direct Acting Independent Feed Pump. the auxiliary piston being operated by the opening and closing of ports due to a rocking motion which is communicated to it by the levers and link work as shown. Bilge pumps when independent, and all general service pumps, are usually of the direct acting form as above illustrated. The chief item of difference is found in the ratio of the areas of steam piston and water plunger. Where the water is to be de- 266 PRACTICAL MARINE ENGINEERING. livered under considerable pressure, as for feed-pumps or for fire purposes, the area of steam piston will be from two to three times that of water plunger. Where the resistance to be over- come is less, as in a pump for freeing the bilge or for circulating Fig. 196. Vertical Duplex Feed Pump. Admiralty Type. Marine Engineering Fig. 197. Vertical Single Feed water through distillers, evaporators, water-closets, etc., the water plunger may be relatively larger and we shall find such pumps with a water end only slightly smaller or equal in size or even larger than the steam end. AUXILIARIES. 267 Such pumps are always so connected up, of course, as to enable them to be run from the auxiliary boiler. Sec. 34. BLOWERS OR FANS. The centrifugal blower is the type universally used on ship- board for all purposes requiring the handling of large quantities of air under light pressure, as for ventilation and forced draft. As indicated in Figs. 95, 96, such a blower consists of a series of flat or nearly flat steel vanes carried on a shaft and sur- rounded by a casing. The principle of operation is the same as with the centrifugal pump, as described in Sec. 26. The rotation of the vanes sets up first a circular current or rotation of the air, and as a result of this motion, centrifugal force is developed which carries the air out toward the tips of the blades and de- velops an increase of pressure from the hub outward. If an out- let is then provided in the outer shell of the casing the air will be delivered at this point and the surrounding air will flow in to take its place at the intake about the hub. So long as the rota- tion is kept up these conditions will continue, and there will be a continuous flow of air in at the hub and out through the delivery passage under a pressure depending on the speed of rotation and other circumstances. Blowers are driven by either steam engine or electric motor direct connected to the shaft, and are made of various forms so as to readily find a place in almost any position desired, thus re- quiring the smallest possible amount of otherwise valuable space. In the operation of blowers the points of chief importance relate to the general care which must be given to the operating motor, whether electric or steam, and to the proper lubrication and care of the fan-shaft bearings. Sec. 35- SEPARATORS. In many types of water-tube boilers, special arrangements are provided for separating the steam from the water. These are usually located in the upper drum or chamber and consist commonly of one or more metal plates pierced with holes through which the steam passes to the stop-valve and steam pipe, and which exercise more or less of a straining or separat- ing action on the water and steam. Reference has been made in Sec. 16 [4] to arrangements of this character. In addition to such arrangements located in the upper drum of water-tube boilers, special devices known as separators are 268 PRACTICAL MARINE ENGINEERING. used wherever the steam is likely to have any considerable pro- portion of water. Such devices are found in great variety of form, and utilize various principles in their operation. The most successful are those which employ for separating the water from the steam the centrifugal force developed by a rotation of the steam as it enters or passes through the separating chamber. The .following description will serve to illustrate the oper- ation of a typical separator of this character : The separator, as shown in Fig. 198, consists of a vertical cylinder with an internal central pipe extending from the top downward, for about half the height of the apparatus, leaving an annular space between the two. e Engineering Fig. 198. Separator. A nozzle for the admission of the steam is on one side, the outlet being on the opposite side or on top as may be most con- venient in making the connections. The lower part of the apparatus is enlarged to form a re- ceiver of some considerable capacity, thus providing for a sudden influx of water from the boiler. A suitable opening is tapped at the bottom of the apparatus for a drip connection, and a glass water gauge shows the level of the water in the separator at all times. The current of steam on entering is deflected by a curved partition and thrown tangentially to the annular space at the side C XI LI ARIES. 269 near the top of the apparatus. It is thus whirled around with the velocity of influx, and a centrifugal force is developed, which throws the particles of water against the outer cylinder. These adhere to the surface, so that the water runs down continuously in a thin sheet around the outer shell into the receptacle below, while the steam, following a spiral course to the bottom of the internal pipe, enters it abruptly, and in a dry condition passes upward and out of the separator, without having once crossed the stream of separated water, all danger of the steam taking up the water again after separation being thus avoided. The water thus separated from the steam collects in the lower part of the chamber and may be drawn out from time to time or it may be led to a steam trap of approved form and Fig. 199. Ash Ejector. trapped out, thus making the operation entirely automatic. The water thus obtained will, of course, be of high temperature and should be led directly to the hot-well where it will aid in raising the temperature of the feed-water. The heat which it contains will thus be returned to the boiler, and saved, and all heat loss in connection with the operation will be avoided. Sec. 36. ASH EJECTOR. Ashes are either hoisted in a bucket by a special hoist to a point on the main deck level and there dumped into an ash- chute leading to the side of the ship and down into the water, or else disposed of directly* from the fire-room by means of an ash ejector. Such a device is illustrated in Fig. 199. A represents a cast metal chute or pipe leading from the fire-room up and out 270 PRACTICAL MARINE ENGINEERING. through the side of the ship near or slightly above the water line. At the lower end this chute connects with a hopper, B, into which is led a pipe from the discharge of a pump. This pipe enters to a point near the lower end of the chute, into which its discharge is directed, and is contracted to a nozzle so that the water issues with a high velocity. The hopper may be closed by a cover, and if in this condition the discharge valve is opened and the pump started, a stream issues with high velocity from the upper and open end of the chute. If then the cover is removed Fig. 200. Ash Gun. and ashes shoveled into the hopper, they are caught by the stream, carried rapidly up, and ejected free of the ship's side in a mingled jet of ashes and water. It is found by experience that at the upper bend the wear on the metal of the pipe, due to the scouring action of the ashes, is very rapid, and it is usually found necessary to make this bend in a separate piece of extra thick metal, and to provide by means of a proper arrangement of joints for its replacement as occasion may require. AUXILIARIES. 271 A similar device known as the ash gun is shown in Fig. 200. Where possible the lead of pipe from the hopper to the ship's side is made straight .so as to avoid all bends and elbows. The principles of operation are the same as above explained. 012 8 4 S 67 8 10 48 Murin* Engineering Figs. 201, 202. General Arrangement Plans. Sec. 37. GENERAI, ARRANGEMENT OF MACHINERY. We shall not here discuss in detail the various questions which may arise in connection with the problem of the general arrangement of marine machinery. It will be sufficient for our 272 PRACTICAL MARINE ENGINEERING. present purpose to note the fundamental principles which must be held in view : (i.) Each piece must be located so as to favor, as far as possible, examination and repair. (2.) Each piece should be located with reference to handi- ness of care and control in routine operation, and in such way as to interfere to the smallest practicable extent with the routine care, examination and repair of other pieces. (3.) Due regard must be had to economy of space and such combinations of the various pieces must be sought as will re- quire the minimum total space, while giving the necessary free- dom in accordance with the principles noted above. (4.) The influence of the location of the various pieces on the arrangement of the piping must be carefully noted and due weight must be given to simplicity, shortness and directness of the various lines of piping. In Figs. 201, 202 are shown illustrations of a general ar- rangement plan in which the condenser is located in the engine framing. The remaining features are independent, and include those most commonly met with in the auxiliary equipment of the engine room. OPERATION, MANAGEMENT AND REPAIR. 273 CHAPTER VI. OPERATION, MANAGEMENT AND REPAIR. Sec. 38. BOII/ER ROOM ROUTINE. In the present section it is the purpose to give brief hints and suggestions regarding the routine of operation and manage- ment in the fire-room in getting under way and on the voyage, first supposing that everything is working smoothly and with- out trouble, and then to notice the chief emergencies which may arise. We shall first suppose that fire-tube boilers are in use, and later give such supplementary suggestions as may be suit- able for water-tube boilers. [i] Starting Fires and Getting Under Way. A general examination must first be made of the boiler and fire-room equipment in order to make sure that everything is in readiness for getting up steam. Among the more important points to be attended to the following may be mentioned : See that the coal bunker doors are in proper working order and if the bunker is partly empty it may be well to air it by open- ing the door and taking off the deck plates. See that the coal handling gear is on hand and in proper condition. See that the necessary fire tools are provided, and dis- tributed as needed. Examine the grate-bars, bridge-walls and back-connections, and note whether the area of passage above the bridge-walls is properly proportioned. For usual conditions it should be from 1-5 to 1-7 the grate area. Note the condition of the tubes both from the front and back connections. 274 PRACTICAL MARINE ENGINEERING. Examine the dampers in uptakes and funnel to see if they are in working order, and open them preparatory to lighting the fires. Examine carefully all valves, cocks, piping and connections and make sure that everything is connected up as it should be, and that no valves are open which should be closed nor closed which should be open. See that no waste or other inflammable substances have been left about by workmen on the tops of the boilers. If the water has not been previously run up in the boilers, this may be under way in the meantime. In modern practice the boilers are always filled with fresh water where possible, ob- tained from a hydrant on the dock or water-boat alongside, and put in usually by a hose through an upper manhole. If, how- ever, the boat is lying in fresh water, or if by necessity the water is to be taken from overboard, it is then run in through the bot- tom blow and Kingston valve. In the meantime examine the connections leading to the water-gauge and cocks. Clean the glass if necessary, and make sure by means of a wire that the opening through the cocks is clear. The packing of the gauge glass should also be examined and renewed if necessary. When the water appears in the gauge glass and shows from one-half to two-thirds full in each boiler, it may be shut off. All open manholes may then be closed, and the boilers are ready for the fires. Notice of the time when steam is required should have been given not less than from six to eight hours in advance, and many engineers prefer a still longer time in which to bring along everything into working condition. With hard coal a certain amount of wood is necessary in starting the fires. With soft coal less wood is required, and if necessary oily waste may be made to answer the purpose. If fires are up in the donkey boiler a little live coal may be taken from them to assist in start- ing. As soon as the fires are going the hydrokineters are put on if such appliances are fitted. In some cases arrangements are made for drawing the water by the donkey or auxiliary feed- pump from the bottom of the boiler by the bottom blow and re- turning it through the feed-pipe, thus producing a forced or as- sisted circulation. Where there are no appliances for forcing the circulation during this period, it is considered good practice to light first the fires in the center furnaces, and later, by one or OPERATION, MANAGEMENT AND REPAIR. 275 two hours, those in the wing furnaces. The natural circulation thus produced will more nearly even up the temperature within the boiler than if all fires are lighted at the same time. After the fires are fairly going the funnel or uptake dampers may be partly closed so as to hold the fires back, and bring them along at a moderate gait as desired. While the boilers are thus warming up and before steam has formed, a last look may be given to the boiler mountings and their connections. The various cocks and valves should be worked, and especially the stop and safety valves, in order to make sure that none are jammed or in any way out of order. The oil lamps for the steam and water gauges may also be trimmed and lighted, or the electric bulbs cleaned, if such are provided. During this period the steam-pipe drains and safety valves are usually open to allow of the escape of the air and of the con- densed vapor as formed. In some cases, however, the safety valves are closed, and the stop valves being open, the air and vapor are expelled along the steam-pipe and through the engine, thus beginning the process of warming up. Many engineers, however, prefer to keep the boiler stop valves closed until steam is formed, and to discharge the air through the safety valve, or in some cases through a specially fitted air-cock. If steam is already up on some of the boilers or if there is no auxiliary steam-pipe and the pressure from the donkey boiler is on the main steam-pipe, then of course the stop valves must be closed on the boilers in which steam is being raised, and they must re- main closed until the pressure on the boiler is equal to that in the steam-pipe. In opening a boiler stop valve connecting with a pipe in which there is no pressure the following precautions should be taken : (1) The pipe should be thoroughly drained and especial care should be taken that there are no sags, bends or U's un- provided with proper drains, and in which a pocket of water may have collected. (2) The valve should be very carefully eased from its seat and opened only from a quarter to a half turn until the pipe is under full boiler pressure and has taken the temperature of the steam, and the drains are discharging steam instead of water. In opening a boiler stop valve connecting with a pipe in which there is approximately the same pressure as in the boiler, it is 276 PRACTICAL MARINE ENGINEERING. simply necessary to ease the valve from the seat and note by the sound whether there is a sufficient difference of pressure to cause any violent flow in one direction or the other. As soon as the absence of such evidence indicates an equality of pressure on both sides of the valve, it may be opened out as desired. The two fundamental principles underlying much of this routine and detail are simply as follows : (1) To prevent as far as possible sudden changes in the temperature condition of the boilers, piping and machinery, and (2) To prevent throughout the steam-pipe system the accu- mulation of water at any point. If these two points are kept clearly in view and good en- gineering judgment used in carrying them out, the life of the boilers and machinery will be prolonged, and danger of ruptured pipes through the effects of water hammer will be avoided. After steam is formed and the pressure has risen to some 40 or 50 pounds the hydrokineters may be shut off, especially if the ship is to get under way as soon as ready. If, however, the boil- ers are to stand some time with steam up, it may be advisable to turn on the hydrokineters from time to time, at least as long as the pressure in the donkey boiler is sufficient for the purpose. The fires in the meantime have been kept simply in good condition without forcing, and even if they work under a forced draft system, only enough air should be provided during this stage to bring them along at the gradual pace which will allow the boiler to properly accommodate itself to the change in tem- perature and other conditions. The fire-room auxiliary machinery should also be examined during this period, and tested under steam from the donkey boiler if possible. The feed pumps should first receive attention, in order that there mav be no question as to the proper supply of feed-water when required. The fan engines should be examined, oiled and turned over under steam. The ash-hoist gear and engine, or ash ejector and pump, should be examined and put in working order. If steam for these purposes is not to be had from the donkey boiler, then as soon as a sufficient head is formed on the main boilers these auxiliaries must be examined, taking in all cases the feed pump first. Soon after lighting fires it may be desirable to slacken up OPERATION, MANAGEMENT AND REPAIR. 277 somewhat on the funnel guys on deck, in order that the expan- sion of the funnel may not bring an undue stress upon the guys and their connections, or upon the funnel and its supports. After the ship is away and the funnel has taken its temperature for running conditions, the guys may be tightened up so as to properly support the funnel in a sea way. [2] Fire Room Routine. At length we may suppose that full head of steam has been formed on the boilers, that the fires have been brought up to proper condition, and that the ship has gotten under way for the voyage. As soon as possible the operations in the fire-room should be brought to a regular routine. This will involve the following chief features, which we shall consider separately: (i) Firing. (2) Water tending. (3) Disposal of ashes. (4) Cleaning fires. (5) Sweeping tubes. Firing. The routine of firing should be so arranged that no two furnaces in boilers connected to the same stack shall be open at the same time. If this is not practicable, then care must be taken to avoid at least firing at the same time furnaces in oppos- ite ends of double-end boilers, especially if there is a common combustion chamber. Two furnaces in a single-end boiler, or in the same end of a double-end boiler will, of course, never be fired at the same time. It is now well understood that firing light and often is better than heavy and at great intervals. There is, however, a limit to this, for the oftener the firing the more are the furnace doors open and the more is the draft subject to disturbance, while the arrangement of a suitable routine be- comes more and more difficult. Light and frequent firing, especially with water-tube boil- ers, is now, however, the rule where the best results are to be obtained. The furnace door should be opened smartly and kept open only the minimum time needed to get the coal on. Hard coal is spread in as even a layer as possible over the grate. For firing soft coal two methods are available. When firing for coal efficiency, that is to get the most heat out of a pound of fuel, the coal should be first charged in front and coked, and then should be pushed back and burned. When firing for weight efficiency, that is to get the most power out of the boiler, the former method would be too slow and the coal must be spread over the fire and burned without waiting for the separate dis- 27 8 PRACTICAL MARINE ENGINEERING. tillation and combustion of its gases. Where the coal runs ir- regular in size the large lumps should be broken into pieces not larger than the fist. The thickness of the fires varies with the conditions, from six to ten or twelve inches, or even thicker un- der a heavy forced draft. With a given speed of fan the air pressure in the ash-pits will vary widely with the thickness of the fire, rising as it is thicker, and falling as it is thinner and the air finds more ready passage through. With a thick fire it will therefore be easy to get a strong draft pressure in the ash-pits, while with a thin fire it will be perhaps impossible, even with a much higher speed of fan. A strong draft pressure will not, however, produce the corresponding rate of combustion unless the thickness and condition of the fire are such that the pressure is able to drive through it the necessary amount of air. For the best combustion the thickness of the fire should be so adjusted to the draft pressure that the latter is able to drive the necessary air through, and keep it in a state of active combustion through- out from fire grate to upper surface. Care must be taken to keep the grates evenly covered, especially at the back, and to prevent the formation of relatively thin or bare spots. A spot which is relatively thin allows of the passage of relatively more air. This further increases the combustion at that point and the spot becomes still thinner, thus allowing more and more air to escape freely instead of passing through the remainder of the fire as it should. In the intervals of firing the pricker and slice bars may be used to clear away the ashes and clinker, if such is forming. Care should be taken to prevent the formation of dull or dead spots due to "the accumulation of ashes or clinker, especially at the corners of the grate. Among old firemen a familiar saying relating to this point is : "Take care of the corners and sides of the fire and the middle will take care of itself." The ash-pits should also be kept clear of ashes, for if allowed to accumulate they will prevent the passage of air to the grate, especially at the back. If the passage of air is thus interfered with to any con- siderable extent there will be also danger of overheating the grates and of bringing them down into the ash-pits. In connection with the use of the slice bar, it must not be forgotten that every opening of the furnace door means an in- rush of cold air into the furnace, a checking of the draft, a distur- bance of the combustion, and often severe strains on the struc- OPERATION, MANAGEMENT AND REPAIR. 279 ture of the boiler, due to the sudden chilling and contraction which the heating surfaces undergo. If shaking grates are fitted much of this cleaning may be done without opening the door, though no form of grate is quite able to deal satisfactorily with coal showing a decided tendency to form clinker. In thus working the fires a certain amount of fine unburned or partly burned coal will be shaken down into the ash-pit. In some cases this forms so large a part of what comes through the grate, that it may be immediately thrown onto the fire and burned over again. In most cases a sifting or washing of the ashes and separation of the combustible from the non-combus- tible would show a surprisingly large per cent, to be available as fuel, and some saving could usually be effected in this way. It is rare, however, that anything of the kind is attempted, as with present prices of coal it. may be doubted whether the additional appliances and labor would be paid for by the saving effected. Water-tending. The care of the water is the most important and responsible of the duties in the fire-room. The ideal is to keep the water regularly flowing inward through the check- valves at about the same rate as it is flowing outward as steam through the steam pipe. This requires constant watch and ad- justment of the valves, closing down where it is entering too rap- idly and opening up where it is entering too slowly. Instead of this method it is often the custom to put the feed on strong first to one boiler and then another, in order, according to the firing, feeding the boiler up when the fire is at its best, and shutting down when it is freshly coaled. The steady and uniform feed is, however, better because it approaches more nearly to a uniform condition of the boiler, especially on the water side. The position of the water is determined, of course, from the water gauge and cocks. It is necessary, of course, that the gauge and its connections be clear of any obstruction in order that the height of the water may be properly indicated. To make sure that everything is clear the gauge glass and connections are blown through by the "double shut off" method as follows : In Fig. 203, G represents the glass, A the drip cock, B and C the cocks connecting to the stand, and D and E those connecting the stand to the boiler. First, B and E are closed, and A is opened. If steam blows through it shows that A G C D are clear. Second, C and D are closed and A is opened. If water blows through it shows that ABE are clear. The action of the 280 PRACTICAL MARINE ENGINEERING. water in the glass will usually show to an experienced eye whether or not the connections are clear. If the water is lively and follows the rolling of the ship it is a good indication that the passages are clear. Otherwise it indicates that an obstruction exists which must be sought out without delay. In the mean- time the water cocks are relied upon, and in fact many ex- perienced water tenders prefer the indications of the cocks to those of the glass, while they should in all cases be freely used as a check on the glass. To those without experience, however, the glass is less apt to be misleading. The indications of the Fig. 203. Marine Ziiyizeeriny Test for Water Gauge and Glass. water cocks are sometimes difficult to interpret, because fre- quently it is not easy to tell whether water or steam is blowing off. With high pressure steam especially, a jet of water issuing at a temperature of 350 degrees to 400 degrees is instantly sur- rounded with a shell of vapor formed by the vaporization of part of the jet. Furthermore, if the water in the boiler is in active ebul- lition near to the surface so that the jet would be drawn from a mixture of steam and water, then on issuing it becomes practical- ly a jet of moist steam. On the other hand if the water is well below the cock so that the jet would be drawn from steam alone OPERATION, MANAGEMENT AND REPAIR. 281 or from moist steam, then on issuing it will become dry and usually super-heated. It is also a fact, especially with water-tube boilers, that due to a kind of lifting action, a cock will often dis- charge moist steam or a mixture of water and steam, even if the water level is somewhat below the mouth of the cock. It is hence readily seen that the indications from the cocks must be interpreted with judgment, and that some experience is neces- sary in order to always draw correct conclusions from them. It is often difficult to distinguish between an empty glass and one entirely full. In order to make sure close the cock B, Fig. 203, and slightly open A. If the gauge is full of water the surface will gradually descend, first coming into view in the top of the glass and then passing out of view at the bottom. If then A is closed and B is slightly opened, the water will rise again in the glass and pass out of view at the top. Blowing off. Blowing off boilers to reduce the concentra- tion or density of the water is now rare in good practice. In- stead of reducing density by introducing sea-water for feed make up, evaporators are installed for providing fresh water make up, or for short runs additional fresh water is often carried in double bottoms or spare tanks provided for the purpose. In modern practice the purpose of blowing off is (i) to get rid of mud or slush in the bottom of the boiler or in the special mud drums of a water-tube boiler, and (2) to get rid of oil and scum at and near the surface of the water. For the former a bottom blow or special mud cock is required, while for the latter the surface blow is used. In ordinary experience on deep sea voyages where evaporators or other fresh water make up is pro- vided, the use of the surface blow is all that is needed to keep the water in good working condition. It must not be forgotten that the use of the blow-off means a direct loss of heat, and hence it should be used with discretion, and no more frequently than is needed for the purpose in view. An idea of the condition of the water in the boiler near the surface may be obtained by drawing off a little water from a cock fitted into the surface blow pipe, or from a gauge cock fitted directly to the boiler. The water being allowed to cool and settle, is then poured into a glass jar, when its condition is readily noted, and the need of using the blow determined. It may be well to speak at this point of the proper method of testing, from the outside, the correct position of a plug cock han- 282 PRACTICAL MARINE ENGINEERING. die for "closed" and for "open." Instances have been known where there was no mark on the head of the plug, and the han- dle becoming bent or being wrongly placed, the cock was left shut when it was supposed to be open, or open when supposed to be shut, with the possibility of most serious consequences, especially in the latter case. A careful examination of the cock, aided if need be by placing the ear to the chamber, will suffice to tell whether or not the cock is open and water or steam passing through. Then the cock being open let it be turned in one direction until it is just closed, and then back in the other direction until it is closed again. Half way between these two positions it will be wide open, and at right angles to the latter position it will be full shut. Taking the Saturation or Testing the Density of the Water. The density of the water is determined by the use of a hydro- meter or salinometer as it is often termed. Under modern con- ditions where evaporators provide fresh water make up, the density rises but slowly, and it is usually only necessary to ob- serve its value once or twice a day. It is usually not allowed to rise above two or two and one-half. See Sec. 17 [10] . Disposal of Ashes. For the disposal of ashes two chief means are in use. According to the older method they are sent up and disposed of through an ash chute leading overboard and down the side of the ship to the water, and this, method is still extensively used in large and deep ships. In the more modern system they are disposed of from the fire-room direct by means of an ash ejector. In either system it is usually sufficient to dispose of the ashes once in a watch, and they are collected, wet down and either hoisted in buckets or shoveled direct into the ash hopper usually between 6 and 7 bells. Cleaning of Fires. The routine working of fires spoken of above will suffice to keep them in fairly good condition for sev- eral hours, provided the coal is of fairly good quality. It usually becomes necessary, however, to give to each fire from time to time a more thorough cleaning than is possible in the manner previously referred to. To this end the fire should be taken when partly burned down, but not too far lest there be nothing left after cleaning on which to build up again. One side may be cleaned first, working the good coal over to the other side, separating out the clinker and ashes, and hauling out the latter. Then similarly with the other side, working the good coal over to OPERATION, MANAGEMENT AND REPAIR. 283 the side first cleaned and pulling out the clinker and ash. The live coal is then spread over the grates, fired lightly, and so brought up again into regular conditions. In some cases there is so little left after a thorough cleaning that live coal must be borrowed from another furnace to save the fire. Only judgment and ex- perience can determine the best point at which to clean a fire so as to insure the minimum loss of heat, and at the same time have enough coal left to nicely build on again. Some engineers prefer to burn the fire almost completely down to the ashes and clinker, and then pull the entire contents of the grate out and start afresh. This method, however, chills the furnace and more seriously interferes with the operation of the boiler, and is not to be recommended. It must of course not be forgotten that heat is lost with the clinker and ashes withdrawn, and the general operation should be so conducted as to keep this loss down to the minimum possible. Under usual conditions the fires will need cleaning in this way at intervals of from 12 to 16 hours, or at least once a day. Sweeping Tubes. In addition to the cleaning of fires the tubes will require cleaning from time to time, dependent on the character of the coal and other circumstances. With soft coal and moderate draft they will soon become partly filled with soot and ashes, thus choking the draft still further, and prevent- ing the transfer of heat to the water through the metal of the tube. To prepare for sweeping tubes the draft is checked, ash-pit doors put up, furnace doors opened and front connection doors raised. Care should be taken to wait until the fire is burned partly down before doing this, so that the circulation of air through the grates may not be shut off while the fires are too heavy, thus endangering the grate bars. For cleaning the tubes the ordinary wire tube brush may be used. This consists of a mounting carrying wire bristles and fitted usually with a jointed handle by means of which it is pushed and pulled through the tubes, thus cleaning out the soot and ashes collected there. A more modern method consists in blowing through tfre tubes with a steam jet. The mounting of this appliance consists of a flange or conical ring fitting closely to the end of the tube and provided with a steam nozzle directed along the center of the tube. A handle is provided for holding and guiding the ap- paratus, and steam is led to it by means of a flexible hose. By 2 8 4 PRACTICAL MARINE ENGINEERING. this means the ashes and soot are driven out of the tubes into the combustion chamber. By still another form of apparatus the jet is not directed into the tube but across the front end pro- ducing a suction, and thus drawing the ashes and soot to the front connection and discharging them up the funnel. The operation of sweeping tubes is one that is necessary to maintain the continued efficient operation of the boiler, but it must not be forgotten that it involves a serious disturbance to the draft of the whole battery, that the chilling of the heating sur- faces and interruption to the regular routine are hard on the boiler itself, and that hence, it should only be done when neces- sary and then as quickly as possible. Stopping Suddenly. With everything going along its regu- lar schedule, suppose that the engine is suddenly stopped. The dispositions to be taken w r ill depend on whether the stoppage is momentary or whether it is expected to last for some time. Here" again the caution regarding a sudden change in the conditions must be kept in mind. If the stop is but momentary it wifl probably be sufficient to shut off the draft, close the dampers and put on the feed strong, standing by to ease open the safety valves in case the pressure rises too near the point of blow- ing off. If the stop is to be longer it may be necessary to still further check the fires by putting up the ash pit doors and open- ing the furnace doors. Caution must be exercised in thus check- ing the flow of air through the grates lest there be danger of overheating the bars, or even of bringing them down into the abh pit. Of these various steps for checking the fires the opening of the furnace doors' and the sudden chilling of the heating sur- faces is the most objectionable and should not be resorted to unless necessary. As an additional means the fires may be freshly coaled, especially with dampened coal. This will check the formation of steam and provide fuel for bringing them into good condition for the next start. A period of stoppage like, this may also be taken advantage of to clean such fires as may be in need of it. In addition to checking the formation of steam, that which is formed may often be used in a variety of ways. If evaporators are provided it may be turned on to them and thus go toward increasing the store of fresh feed water. The bilge pump may also be put on strong, and if its exhaust is saved there will be no loss of fresh water. In some cases with independent air and OPERATION, MANAGEMENT AND REPAIR. 285 circulating pumps a bleeder is provided for taking the steam direct from the main steam pipe to the condenser. Here it is condensed and then sent by the feed pumps back to the boilers, thus avoiding blowing off at the safety valves and the loss of fresh water, and allowing the fires to be gradually reduced to the condition desired for the period of stoppage. Here again in all of these operations general principles aro often worth more than a multitude of minor directions. These principles are (i) Sudden chilling of the boiler heating surfaces must be avoided as far as possible. (2) Fresh water in the form of steam should not be wasted, and (3) Care must be taken not to allow the grate bars to melt down. So far as relates to the general securing of the machinery and gear in the fire-room, the hints given in connection with getting under way will be a sufficient guide in reversing the process. Supplementary Hints Relating to Water. Tube Boilers. In water-tube boilers the circulation is usually more nearly natural than in fire-tube boilers, and circulating devices are not, there- fore, required. Steam may be raised in such boilers in from twenty minutes to one hour, depending on the type, character of the draft, etc. With this type of boiler it is especially neces- sary that for the best results the firing be light, often and regu- lar, and that the fires be kept as nearly as possible in a uniform condition. It is also necessary that the feed be regular, and the water must be carefully watched, since from the small amount contained, any lack of feed in a given boiler will be followed by rapid lowering of the level, and by a rapidly increasing likeli- hood of danger to the tubes. In water-tube boilers it is es- pecially necessary that nothing but fresh water be used as feed, and great care must be taken to keep the condenser tight and the fresh water make up ample in quantity. The tubes of water-tube boilers become coated with soot and ashes on the outer or fire sjfie, and it is usually a very difficult matter to satisfactorily clean them without the use of a steam jet. In continued steaming for long periods, it will usually be found necessary from time to time to let the fires die down some- what and to use what methods are available for blowing off and dislodging the soot from the tubes. When stopping or standing by, the same general means may be adopted as in fire-tube boilers. As regards injury through 286 PRACTICAL MARINE ENGINEERING. sudden change of temperature, the water-tube boiler is some- what less liable than the fire-tube. This is due to the nature of the construction which, especially with curved or built up ele- ments is much more elastic than in the fire-tube boilers. It is always better, however, to avoid sudden temperature changes where possible, and the same principles may be properly applied here as previously discussed in reference to the other type of boiler. Coming Into Port. When coming into port notice will usually be given some hours in advance, so that the fires may be worked into a condition in accordance with their expected disposition after arrival. If they are to be drawn and the boilers opened up for examination and repairs, they will be allowed to burn down as low as possible so as to use no more fuel than necessary, and to leave as small an amount as possible to finally haul, while at the same time sufficient steam must be maintained to bring the ship safely to her anchorage or dock. If, on the other hand, the fires are to be banked, they will not be allowed to burn so low. It may be recommended to bank fires on the front of the grates, as in such case the air is heated as soon as it enters the furnace and the boiler is kept at a more nearly even temperature than if they are banked at the back of the grate. As the fires are banked they should be cleaned and enough fresh coal put on to hold them in the condition desired. If the fires are properly managed there will be little extra steam after the engines are stopped, and this may be readily disposed of by means of the evaporator, bilge pump, bleeder, safety valve, etc. Loss of fresh water at this time is of course less objectionable than when on the voyage, and if desired the steam may all be blown off through the safety valves. Many engineers, however, object to using the safety valves and escape pipe for this purpose except as a last resort, and prefer other means as mentioned. In passenger vessels the noise occasioned is usually considered ob- jectionable, though to obviate this a muffler is frequently fitted in the escape pipe. If the boilers are to be opened fires are allowed to die out or are hauled immediately. If time permits the former plan is pref- erable, as the change in the condition of the boiler is more gradual. When the fires are finally hauled and the furnaces, back connections and tubes cleaned out, the ashes, soot and clinker are wet down and piled away until they can be disposed of to OPERATION, MANAGEMENT AND REPAIR. 287 the ash barge, as few harbor regulations allow the dumping of ashes overboard. In wetting down the fires after they are hauled out on the fire room floor, or in wetting down ashes at any time, care should be taken not to wet the fronts of the boilers or the mouths of the ash pits. The local chilling will not im- prove the quality of the steel, and the alternate wetting and dry- ing will increase the opportunities for surface corrosion. For the same reason damp ashes should never be piled up in contact with the boiler or furnace plates, as in many instances serious cor- rosion has resulted from a neglect of this precaution. The fires being burned out or hauled, some engineers pro- ceed to blow the boilers down immediately. This plan, however, cannot be recommended and should not be adopted unless the time available for examination and repairs is so short as to make it absolutely necessary. It is far better to let the steam condense and the water gradually cool, and then draw it out by means of a pump, or in some cases run it into the bilge. In this way the boiler cools more gradually and the structure is left in better condition, while on the water side the scale and incrustation will usually be made softer and more easily removed than when the boiler is blown down with steam on. [3] Emergencies and Casualties. (i) Foaming and Priming. These terms refer to a disturbed condition of the water in the boiler, of such a nature that the water level is more or less uncertain in location, and the steam space is partially filled with foam or a mixture of foam and water. In severe cases of foaming, steam seems to be given off from almost the entire mass of water in the boiler, causing it to rise bodily as foam and water and fill the whole steam and water space, thence entering the steam pipe and passing on to the engine. In other cases the water seems occasionally to rise in gulps, nearly unmixed with steam, and entering the steam pipe pass on to the engine. The terms foaming and priming are often used as meaning practically the same thing. Where a difference is implied, foaming is understood to apply more especially to the uplifting of the mixed steam and water as foam, while prim- ing may refer more particularly to the lifting of water as such, and its passage over into the engine. There is, however, no clear line of distinction between the two kinds of disturbances, and there are all grades intermediate between the extremes. 288 PRACTICAL MARINE ENGINEERING. Foaming may be due to the presence of certain forms of oil or grease, or to the excess of soda used for scale prevention, or to other impurities in the water, or to the demand for steam too large in proportion to the steam space in the boilers. A sud- den change in the character of the feed water may also produce foaming. In former days when jet condensers were in common use, boilers were liable to foam in passing from sea water to fresh water, especially if the latter was muddy, and again in passing from fresh water back to sea water. In modern prac- tice foaming is due either to the presence of oil, or to the extreme demand for steam from the boiler. In the former case the oil must be removed from the boiler by a free use of the surface blow, and kept out by a proper filter. In the latter case the engine must be slowed and the demand for steam reduced to an amount which the boiler can supply without the danger of such disturbance. As a result of foaming the engine slows down, power and speed are lost, while due to the possible inability of the relief valves to handle all of the water coming into the cylinders, there may be serious danger of breakdown. There is also danger to the boiler in foaming, because the water level cannot be known with certainty, and plates or tubes may become overheated, with danger of collapse and rupture. The tendency to foam is, there- fore, a symptom of serious import, and no steps should be neg- lected to discover and, if possible, to remove the cause. (2) Feed, Pump. In modern practice an auxiliary feed-pump is always provided except perhaps in very small craft. If then the main feed-pump refuses to work, the auxiliary pump must be brought -into use while the other is under examination. The chief causes which may disturb the operation of a feed- pump are the following : (a) Jamming of check valve or other closure in the de- livery pipe. (b) Water in the steam cylinder. (c) Derangement or sticking of the steam valves. (d) Jamming or sticking of the water or steam plunger in its cylinder. In addition to these causes which may affect or prevent the motion of the pump, the following causes may prevent it from throwing water into the boiler, even though its movement may be entirely regular : OPERATION, MANAGEMENT AND REPAIR. 289 (e) Split in the feed-pipe, or valve open, allowing the escape of the water at some unexpected point. (f) Excessive wear of water plunger. (g) Split or leak admitting air on the suction side or into the suction pipe. (h) An excessively high temperature of the feed water. (i) Derangement of the suction or discharge valves. To make sure that the delivery pipe is free, one or more feed-checks and the air-cock on the pump may be opened. If there is no movement of the pump or no discharge from the cock it may be concluded that the trouble is located elsewhere. The drain valves in the steam cylinder should then be blown out freely, and if there is still no inclination to start, the trouble is presumably with the valve gear. A fresh supply of oil should be admitted to the valve-chest, and an attempt may be made to work the tappets or other valve mechanism by hand. In many cases this will suffice to start the pump off at its regular gait. If it does not, the chances are that the trouble is more serious, involving the stopping up or clogging of some of the auxiliary ports or passages, or the sticking, jamming or excessive wear of some part of the valve- gear. A removal of the bonnets and complete overhaul can alone lead to a discovery of the difficulty in such cases. The jamming or rusting of the steam or water plungers in their cylinders could only result from long disuse and gross neglect, and can hardly be considered as of likely occurrence in routine work. If the feed-pump is working properly and throwing water into the boiler, the chamber of the check-valve will be relatively cool, there will be a click as the valve rises and falls, the air cock at the pump will show a stream, and the water will rise in the boiler gauge glass. At the same time an experienced eye and ear will detect by the manner of the pump, by the way it moves and by the character of the sounds, whether or not it is throwing water. If then the pump works, but does not seem to be throw- ing water, we must have resources to causes such as those men- tioned in (e)-(i). There are here two chief questions to be answered. First, is the pump getting water? and second, if it is, where is it going? The air cock will usually serve to answer the first question. If water appears here, and if the pump shows by its action that it 29 o PRACTICAL MARINE ENGINEERING. is handling water, it is evident that there must be escape at some unexpected point. The feed-pipe must then be carefully ex- amined for leaks, and all valves or connections leading to or from it should be examined to make sure that the water is not escap- ing in some such way. In one case coming under the author's notice the main feed-pipe was fitted with a small branch leading to the forward tank. This branch was closed off from the feed- pipe by a globe valve. Due to the ignorance or carelessness of some attendant, this valve was jammed wide open instead of being jammed hard shut. At low or moderate pressure the feed- pump would throw enough water to feed the boiler in spite of this leak. The trouble was therefore not discovered until a full power run being started, the demand for water was greater and the leakage as well, so that the boiler was soon short of water, and the run was lost. If no trouble is found in the feed-pipe, the difficulty may be sought in a very loosely fitting or badly worn water plunger. Such a plunger will discharge water into the air or even against a low boiler pressure, but may not be able to force it against the regular pressure in the boiler. If from the evidence of the air cock and general behavior of the pump it is evident that no watef is being handled, the suction pipe and plunger rod packing should be examined for air leaks. Where there is some considerable lift from the hot well to the feed-pump, an unusually high temperature of feed-water, on account of the vapor formed, will sometimes prevent the pump from taking water. In good practice, of course, the hot-well is above, or at least not below the feed-pump, so that this difficulty is not likely to arise. If such should prove to be the trouble the feed-water must be cooled and the difficulty will be removed. If none of these causes seem to explain the failure to draw or discharge water, then the trouble is probably to be found in the suction or discharge valves, and the necessary bonnets or covers must be removed to allow of their examination. In any search for the cause of the trouble in the feed-pump, the details may, of course, be modified according to the circum- stances, and the above suggestions are more especially intended to illustrate the principle that in such a search the trouble has often to be found by a continued elimination of one thing after another, taking those which are most readily examined, and thus OPERATION, MANAGEMENT AND REPAIR. 291 localizing the difficulty as quickly and as readily as possible. (3) Check-Valve Jammed. If the feed-pump seems to be in proper condition except that it slows down and stops when out- lets excepting a particular check-valve are closed, if furthermore the check-valve chamber is hot, there is no click, and the water does not rise in the glass, we may conclude that the check-valve is jammed on its seat. In former years this was sometimes due to unequal expansion of the valve and seat, and nipping of the former by the latter. In modern practice with good design and an angle of valve seat not steeper than 45 degrees, such an oc- currence is very rare. The valve may also become jammed by the bending or other derangement of the stem or wing guides, or by the lodging of some foreign body within the chamber. If the trouble is due simply to unequal expansion the usual treatment is to wrap the valve chamber in waste or clothes, and then to pour on cool water, thus reducing the temperature. At the same time the chamber may be tapped near the valve seat with a hammer or bar. In any ordinary case of sticking due to unequal expan- sion the result will be to free the valve from its seat. If this does not avail, then the stop-valve between the check-valve and boiler must be closed and the check-valve cover removed, so as to allow an examinaton of the interior. In good, modern prac- tice at least two check-valves, main and auxiliary, are provided for each boiler, so that there should be no danger of low water. If, however, only one check is provided, or if there is any ques- tion of shortness of water while the necessary repairs are being made, the stop-valve should be closed to stop the draft of steam and the usual precautions taken when stopping suddenly. (See [2] above). (4) Bursting of Water Gauge Glass. This occurrence is by no means uncommon, and under ordinary circumstances is of relatively small importance. With the type of gauge glass fitting having self-closing valves, as described in Sec. 17 [8], the flow of water and steam is automatically shut off and the new glass is readily put in. Without such provision the shut-off valves must be shielded from the discharge in the manner most readily effective, and then quickly closed. In setting a new gauge glass care should be taken to see that the fittings are well lined up, so that when screwed down there will be no bending strain on the glass. If any pronounced strain is thus set up on the glass by the fitting, it will be almost sure to break in a short time. 2 9 a PRACTICAL MARINE ENGINEERING. The packing rings should also be screwed down no tighter than barely sufficient to keep the joint tight. To make the closing of the supply valves as short a job as possible, in case it should become necessary, it may be recommended to open them only enough to insure a good supply of steam and water to the glass, rather than wide open. Two turns of the valve will be usually sufficient, and it is then much more quickly closed than when open five or six turns. (5) Low Water. The occurrence of low water or the ab- sence of water from the gauge glass is one of the most serious emergencies which can arise in the fire-room. Immediate ac- tion is called for, and the most serious consequences may result from a mistake, or indeed may result in spite of whatever may be done. If there is reason to believe that the water has but just dis- appeared from the glass and the lower gauge cock gives indica- tions of water or of very moist steam, it may be fairly assumed that the level of the water is not below the tubes or combus- tion chamber tops, and in such case there will be no immediate danger of overheating or collapse, at least so far as the level of the water is concerned. The feed may therefore be put on strong without hesitation, and if the diagnosis has been correct the water will soon reappear in the glass and the incident is at an end. It may be considered prudent, however, to check at the same time the draft of steam from the boiler, and to deaden the fires to some extent by some of the methods referred to below. When the water reappears the boiler can then be put on its regular work as before. In the more serious case when the location of the water is quite unknown and the gauge cocks and glass give no indica- tions, there is some diversity of opinion as to the best procedure. The chief point of difference relates to the propriety of imme- diately putting on a strong feed. It has been claimed that if the plates were red hot, so much steam would be suddenly gen- erated as to rapidly increase the pressure, and burst the boiler. On the other hand, it has been pointed out that the amount of steam which can be thus formed is in reality comparatively small, and that its formation cannot be instantaneous, nor even especially rapid, since its formation will extend over the period while the water is rising over the heated surfaces. In no way then could any great amount of steam be generated with es- OPERATION, MANAGEMENT AND REPAIR. 293 pecial rapidity, and it is hard to see how its formation could take place more rapidly than would be provided for by the natural outflow to the engine, and by the safety-valve, if need arose. To obtain some definite information on these points, ex- periments were carried out by a Steam Boiler Insurance Com- pany some few years ago, in which the plan of putting in cold feed upon overheated plates was followed. The boiler could not be burst by the operation, and no very pronounced elevation of pressure was produced. So far as the results of these experi- ments went, it would seem to be safe to put on the feed imme- diately in such an emergency as we are now discussing. This conclusion seems also to be borne out by the results of such practical experience as is obtainable. There are, however, dif- ferences of opinion on this point, and while the author would follow this plan in such a case, it should not be denied that many good authorities would consider it unwise, at least in the earliest stages of the measures, to be taken. Aside from getting the feed into the boiler as soon as prudence will permit, the other great point is to deaden the fire. If the heating surfaces have not collapsed when the condition is discovered, it is hardly likely that the plates can be at more than a very dull red, and if the supply of heat can be effectually checked, further trouble may be averted. To this end a plan often followed, especially in former years, was to haul the fires. This, however, seems very unwise indeed. While being hauled the fires will burn up all the more fiercely, and for a few moments the heat supply will be in- creased rather than decreased. Instead of hauling directly, some engineers prefer to have the fires dumped into the ash-pits by dislodging a few grate-bars, and then to haul from there. This plan seems but little better than the other, and in any event the immediate result will be to increase the amount of heat given off at the very time when it should be decreased. A far better plan seems to be to deaden the fire with either moist ashes or coal. If a pile of wet ashes is at hand they should be thrown immediately on the fire, and will be found a most effective means of deadening the burning coals. In default of wet ashes, wet or even dry coal may be thrown on and the fir$ simply smothered. At the same time the dampers should be put up and furnace doors left open, thus checking all draft and stopping the formation of heat. 294 PRACTICAL MARINE ENGINEERING. As between these two operations, the deadening" of the fire and the getting in of feed-water, the author is of the opinion that the deadening of the fire is of the more immediate impor- tance, and should be attended to first, because it will produce the most immediate effect over the whole heating surface, and will serve most effectually to rapidly check the further heating of the plates. Putting in the feed water will then complete the cooling, but the direct operation is slower, and more local in its influence, and is therefore of relatively less importance. In all such emergencies much, of course, will depend on the special circumstances, but if the two principles be kept in view that the fire must be deadened and the water restored, the details may be left to good engineering judgment to execute. After the water has again appeared in the glass, and if no ill effects seem to have resulted to the boiler, the fire may be again gotten into condition and the boiler put on its regular routine. If, however, there be any doubt whatever regarding the possible results to the boiler, no chances should be taken, but the boiler should be disconnected from the others, the safety- valve raised and the steam blown down, while the fires should be hauled or allowed to die out and the boiler allowed to cool down. It should then be carefully examined for symp- toms of distress or collapse, and if any such are found they must receive proper attention before the boiler is again set to work. (6) Collapse of Furnace Crounis or Combustion Chamber Plates. The collapse of a part of the heating surface is due either to an overheating of the plates or tubes, or to a gross error in the design. We may dismiss the latter as not liable to occur in good practice. Overheating may result from either low water, or from a coating of scale or of oil and scale on the water side. In the former case with no water to absorb the heat the natural result is an overheating of the plate until it becomes red hot, followed by its collapse and rupture. When the overheating is due to the presence of a coating of scale, the gradual bulge or start toward a collapse may result in cracking off the coating and in letting in the water to the plate. This will cool the metal, restore its strength, and thus put an end to the operation. In some cases when the covering is a mixture of scale and oil, the overheating of the plate will result in burning off or volatilizing the oil, leaving the scale as a fine powdery deposit. This readily admits the water to the plate, and thus the metal OPERATION, MANAGEMENT AND REPAIR. 295 may be cooled and restored in strength, and further bulging prevented. This nice adjustment of heating, burning or crack- ing off, cooling and re-strengthening before final rupture, does not, however, always occur. Before the re-cooling is effected rupture only too often results, and the contents of the boiler are more or less completely emptied into the fire-room, with consequences always severe and sometimes fatal. If it is discovered that the furnace crowns have come down, but without final rupture, or if any portion of the heating sur- face has suffered collapse or bulging, but without final rupture, it may be assumed that the overheating was due to scale or oil, and that the change of form or the overheating has resulted in getting rid of the coating, and in readmitting the water to the plate. So that if rupture has not yet occurred, it is probable that the plate is safe for the time being, and in such case the fire may be first deadened and then hauled, the boiler shut off from the others and allowed to cool down, and then examined as to the nature and extent of the injury sustained. (7) Collapse and Rupture of Furnace Crowns or Combustion Chamber Plates. In the event of rupture following upon col- lapse, the chief thought after the safety of human life must be for the remaining boilers while the fire-room is in such condi- tion that it cannot be entered. The general nature of the steps which may be taken in such case are discussed in the following section, and while naturally judgment must be depended on for many details, it is readily seen that the two main points are as follows : (1) To isolate the injured boiler. (2) To safeguard the remaining boilers from injury due to low water. (8) Serious Leakage in Boiler Tubes. A serious leak may suddenly develop in one or more of the tubes. A split in the metal, a collapse due to overheating, or perforation due to deep pitting or general corrosion may give rise to such an occurrence. If the hole or holes are not too large the immediate conse- quence will not extend beyond a more or less complete filling of the fire side of the boiler with water and steam, and a more or less pronounced checking or deadening of the fire. In such case the feed should be looked after to see that the water does not get low in the boiler, while preparations are made for plug- ging the tubes. For this purpose a tube stopper or plug is used, 296 PRACTICAL MARINE ENGINEERING. of which there are many varieties. A standard type of stopper consists of two heads or tapered plugs which make a joint within or against the ends of the tube, and are held in place by a rod running through the tube, threaded at the ends and pro- vided with nuts for holding them up to their position against the ends of the tube. To fit this stopper it is necessary to enter the combustion chamber to adjust the back end, but once properly fitted, it may be depended upon to fulfil its pur- pose. There are also special forms of tube stoppers which may be inserted and adjusted from the front end only. It is more difficult to make a tight joint with the latter than with the former stopper, but they can be fitted without drawing the fire, and therefore in an emergency may prove of great value. Plugs of soft pine are also used for temporary purposes. These are pushed in from the front until they cover the leak, and the ex- pansion due to soaking with hot water is depended on to make a tight joint. See also Sec. 42 [7]. If, however, the holes in the tubes are of considerable size, so great a quantity of water and steam may be liberated as to make it impossible to remain in the fire-room. In such case the fire will usually be put out as well, or at least so deadened that no further danger of collapse due to overheating need be feared, even should th> water become low in the boiler. The general safety of the boiler itself is thus secured, but the other boilers, connected through the main steam pipe, will continue pouring out their steam through this leak, and as long as this condition continues it will thus remain impossible to return to the fire-room to attend to the other boilers. The first care after escaping from the fire-room, or before effecting escape, if pos- sible, should be to close the stop valve which connects the boiler to the others, and thus to localize the trouble to the one boiler. If the stop valves are arranged so as to be worked from the deck above, as is frequent in good modern practice, this may be readily accomplished. If at the same time the safety valve on the injured boiler can be opened, the pressure will soon be blown down, and with good ventilation from the fire-room it will be possible in a short time to re-enter it and give the needed attention to the other boilers. In the meantime also, the en- gines may be slowed down so as to reduce the demand for steam. Where the feed-pump is located in the engine room, it will OPERATION, MANAGEMENT AND REPAIR. 297 be possible, if the checks have been left open on the other boilers and closed on the injured boiler, to feed by judgment at a rate which will keep these boilers safe from all danger of low water. The object of these various steps is, of course, to isolate the injured boiler and safeguard it from anything more serious, and to provide for the safety of those remaining ; and while cir- cumstances may alter the details of the measures which should be taken, the above suggestions will serve to illustrate the main points to be looked after. When return to the fire-room is possible, and after the other boilers have received the necessary care, attention may be given to the injured boiler; the fires may be hauled, and after cooling down, the nature and extent of the damage investigated. (9) Rupture of Steam Pipe. In the case of a ruptured steam pipe the valves controlling the flow of steam to the point of rupture each way should be closed at the earliest possible moment, as the escape of steam will soon make it impossible to remain in the fire-room with safety. If it is arranged to work the stop-valves from the deck above, this is readily effected, and the trouble thus gotten under control. Self-closing valves are also often provided in modern practice, as referred to in Section 17 [3]. It is not possible, however, to so fit these that they will always act, or that they will shut off the steam in more than one direction. In one way or another, however, the first attempt must be to shut off the escape of steam. The next thought must be for the boilers, to safeguard those which may have been shut off from the engine from danger due to increase of pressure, and those which still remain connected to the engine from danger due to low water. The particular steps suitable for attaining these objects have been already sufficiently dis- cussed, and no further mention will be here necessary. (10) Casualties With Water -Tube Boilers. With water-tube boilers the same general emergencies are liable to arise as with fire-tube boilers, and may be met in the same general way. It should be remembered, however, that, due to the small amount of water carried, the results due to shortness of water will come much more rapidly than with fire-tube boilers, and promptness in action is all the more necessary. In such boilers the tubes are most liable to suffer through shortness of water, and any considerable; overheating is likely to result in their rupture. With the small tube type the most serious results of such an 298 PRACTICAL MARINE ENGINEERING. accident are usually confined to the emptying of the contents of the boiler into the fire, and the effectual deadening or extinction of the latter. Here, as before, however, with more than one boiler the trouble must be localized by shutting off the boiler with the ruptured tubes from connection with the others. In other cases, however, with large tube types especially, or with the rupture of steam or water drums, the consequences may be more serious, resulting in driving every one from the fire-room, or even in loss of life. The same general principles apply here, however, as with fire-tube boilers, and good judgment must be depended on for the details suitable to the occasion. Sec. 39. ENGINE-ROOM ROUTINE AND MANAGEMENT, [i] Getting Under Way. In the engine room the same as in the fire-room, a general inspection is first in order, more or less detailed and extensive, according to the time the machinery has been out of use, and the degree of acquaintance with its various features and pecu- liarities. If the engine has been laid up for any length of time a detailed examination will of course be required similar to that referred to at a later point in Sec. 43. We here assume, how- ever, that no such general overhauling is needed, and that the machinery is to be supposed in a working condition. A good general idea should first be obtained of the lead of the principal piping systems as noted in Sec. 25, and especially of the main and auxiliary steam and feed systems. These lines of piping should be looked over, the location of the valves noted, and where permissible the valves should be opened or closed to insure their being in working order, and then left in the condition desired for getting up steam. The various parts of the main engine will be looked over so as to insure, so far as an external examination can, that everything is in proper working order. The various auxiliaries will be looked over in the same way, and the results of this general examination being satis- factory, steps may be taken to test the various parts of the ma- chinery under steam as soon as dt is ready. We have already in Sec. 38 pointed out the importance of trying the feed-pumps and getting them into working order as soon as possible, in order to insure the proper supply of feed- water to the boiler. Next in order may come the circulating OPERATION, MANAGEMENT AND REPAIR. 299 pump, the engine of which is started at moderate speed, and the main injection and discharge valves opened. In starting all of this auxiliary machinery, proper precautions must, of course, be observed in regard to freeing the steam cylinders of con- densed water by means of the relief valves, as noted in Sec. 38 [3] in connection with the feed-pump. The circulating pump being usually below the level of the water outside the ship, it naturally floods itself so that no trouble should be met with in getting it to take water. Assuming the air-pump independent, this may be started next and put at a moderate pace, or sufficient to main- tain a vacuum of 15 to 20 inches. The electric light engines, if not in operation from the donkey boiler, will also be looked after and started in due time, as well as any other auxiliary machinery whose operation may be required for getting under way. In case the main engine since the last time used has been subjected to any adjustment or overhauling, it will be well to turn it completely over with the turning engine once or twice in order to make sure that everything is clear and in running condition. In the meantime, while the auxiliaries are being gotten into operation, the steam will have been admitted to the jackets, if there are any, and to the cylinders through the main stop and throttle valves. Here, as noted in Sec. 38 [i], the object in view is to avoid any sudden change in the temperature or heat condi- tion of the machinery. A good method of gradually warming 1 up the engine is to just unseat the main stop and throttle valves, and then with the links in the ahead gear, say, to slowly turn the engine over ahead with the turning engine. This will allow the steam to work its way through the engine, warming up the entire series of cylinders and bringing them practically to their working temperatures. The water condensed must, of course, be allowed to escape by opening the relief and drain valves. During this period the reversing gear will also be warmed up and tried under steam until it works properly and throws the links smoothly from one side to the other. When the engine has thus become well warmed up, the turning gear will be disconnected and locked out of gear, and im- mediate preparations made for turning over under steam. At this point the question of lubrication must be borne in mind, and while the regular schedule of oiling, etc., need not be started 300 PRACTICAL MARINE ENGINEERING. until the ship is fairly under way, still a moderate provision of oil may be made to the more important bearings, and if the en- gine has been out of use some little time, it will be well to work oil into the principal bearings during the preceding operation of the main engine with the turning gear as suggested above. Before turning over under steam the deck officer should be notified in order that the hawsers securing the ship to the dock may be looked to if necessary, or the presence of anything about the stern which might foul or jam the propeller may be re- ported back to the engine room. Everything being in readiness, the main stop valve is opened slowly to full opening, and steam is turned on the reversing gear. Then the main throttle being still closed the links are thrown back and forth a few times, the passover or starting valves opened, and the throttle opened moderately. If the engine does not start off in one direction the links are thrown into the other gear, and if everything is in the proper condition the engine will start in one direction or the other after a few see-saws of the links. The hand relief valves are, of course, operated at the same time in order to aid in freeing the cylinders of any water which may collect there, or which may enter with the steam. Often the engine will move a little way, but the high pressure, or one of the other pistons will not pass the center. This is on account of the water in the cylinders, and is especially liable to occur if the engine has not been well warmed up, or if the steam pipe has not been properly drained. In such case the water must be worked out through the relief and drain valves, the links in the meantime being moved back and forth. In answer to this the piston will see- saw up and down, getting gradually nearer the center, and finally when the water is sufficiently cleared out, passing over and continuing the revolution. As the main engine is thus started the circulating pump and air pump, if independent, will be started up at the increased pace suitable to the amount of steam passing through the engine and into the condenser. After thus running for a few minutes, or until everything seems to be in proper running order, the engine is stopped, and the signal for the regular start is awaited. The object of thus turning over under steam is simply to make sure that everything is free and in working condition. Little of course, can be told regarding the adjustment of the various bearings, etc., or their liability to heat or pound. If the machinery is new or has undergone any con- OPERATION, MANAGEMENT AND REPAIR. 301 siderable readjustment, or has been out of use a long time, it should have a dock trial of some considerable time, in order to determine the various points, and to bring out any defects liable to present themselves in the course of a continuous run. Naturally the time when the ship is to start will be known to the engineer, and these various preparations will be so timed that soon after the final turning over under steam, the signal for the regular start may be expected. PASSAGE OF STEAM THROUGH THE ENGINE. In connection with the operation of a marine engine it will be instructive to note in order the names of the various parts through which the steam passes from the boiler until it returns again as feed water to its starting point. Starting, then, with its formation in the boiler, we have the following route for the case of an ordinary triple-expansion engine : Dry-pipe Safety valve chamber Boiler stop-valve Boiler steam-pipe Main steam-pipe Main stop-valve Main throttle-valve High pressure valve-chest Steam ports and passages High pressure cylinders Steam passages and ports Exhaust side of valve Exhaust passage Exhaust pipe to in- termediate valve-chest and cylinder as above for the high pres- sure Exhaust pipe to low pressure valve-chest and cylinder as above for the high pressure Exhaust pipe to condenser Condenser Air-pump suction Foot-valves Air-pump cham- ber Bucket-valves Delivery-valves Hot-well Feed pump suction Induction valves Feed-pump barrel Discharge valves Feed-pipe Check-valve Boiler. In addition a separator may appear between the boiler and the engine, and the filter and feed water heater between the hot- well and the boiler. [a] Routine Operation. In the routine operation of the main engine and of the other machinery in the engine room, the following are the points requiring chief consideration : (a) The proper provision of oil and other lubricant in suit- able quantities and at proper intervals, or continuously, accord- ing to the nature of the oiling gear in use. (b) A constant watch over the general conditions of operation of the machinery in order that any symptom or 302 PRACTICAL MARINE ENGINEERING. sign of derangement or disturbance may be noted, and the proper steps taken for its control or removal. The chief points relating to lubrication have been already discussed in Sec. 24 [12]. The watch over the general condi- tions extends to all features and depends to such an extent upon the special circumstances that only a few general hints can be given. First, regarding the sounds which accompany the opera- tion of the machinery and the part the ear may take in de- tecting symptoms of disturbance. The operation of the main engine and of the various parts of the machinery individually is accompanied by more or less plainly marked sounds or noise or combination of sounds. These in the end tend to combine them- selves into a kind of resultant rumble, click, and rattle, which often remains quite constant in character, and so comes to have a kind of individuality of its own. To a person accustomed to the regular sounds of the engine room, the ear is often a deli- cate means of detecting any departure from the regular routine, and often the first indication of some disturbance will be fur- nished by a change in the character of the sounds produced. In particular, any unusual pound, jar, squeak or rattle should be located as soon as possible, and its cause investigated. In some cases assistance in the detection or location of a pound or knock may be gained by the use of a convenient piece of metal, such as a spanner, or bit of pipe, one end being placed to the ear and the other against the cylinder, valve-chest, or other point nearest to where trouble is expected. At the same time too much reliance must not be placed on the ear to the neglect of other means of observation. In fact in the modern engine room all of the available senses keenly on the alert will be found none too many for the proper watch and care over the machinery in use. The danger of heating, due to insufficient lubrication, poor adjustment or bad condition of bearing, is one which the ear will often aid in detecting, but the chief reliance must be placed on the sense of feeling and on the nose. With the necessary skill most of the important bearings may be felt by the hand. Caution must be used, however, so that the hand may not be caught or jammed. This part of an engineer's training is one which can be learned only by observation and cautious trial. If the heating of the bearing passes beyond a moderate elevation OPERATION, MANAGEMENT AND REPAIR. 303 of temperature, the oil will become correspondingly heated and will give off a burnt odor, or perhaps will smoke freely, thus show- ing plainly the existence of trouble. The nose and eye will thus come in as factors in detecting trouble of this character. Small steam leaks at joints, stuffing-boxes, etc., will make themselves plainly visible, and should receive such treatment as the circumstances may require, in order that they may be closed up. It must not be forgotten that every steam leak means a loss of both heat and fresh water. The vacuum in the condenser will depend not only on the proper operation of the air-pump, but also on the reduction of all possible air leaks which might admit air to the low pressure cylinder during the exhaust, or to the steam side of the conden- ser. All such stuffing-boxes, joints, etc., must therefore receive careful attention, especially if the vacuum is not what it should be. Water coming over into the cylinders from the boilers pro- duces a crackling or snapping noise, which is readily recog- nized. The automatic relief valves may, of course, be depended on, or the hand gear may be operated to aid in removing the disturbing cause. In stopping momentarily the throttle is closed and the links are run to mid-gear, no other change being made, and every- thing remaining ready to start again at an instant's notice. In stopping for a known period of time of any considerable dura- tion, means should be taken to stop the flow of oil to the bear- ings by the closure of the feeding valves or the withdrawal of wicks, according to the means in use. If the stop is only tem- porary, and the engines are to be kept in readiness for starting again, the further steps taken will be only such as will serve to bring the machinery into its condition just previous to getting under way. That is, the circulating and air-pumps, so far as in- dependent, may be slowed somewhat, while by the aid of the steam jackets, if fitted, and steam which is allowed to flow past the stop and throttle valves, the main engine is kept warmed up and ready for operation at short notice. If the stop is to be of longer duration and the steam is to be shut off the engine, the stop and throttle valves will be closed, the air and circulating pumps shut down, and steam shut off the reversing engine, jackets, etc. The various drain valves and drips will be left open so as to free the machinery, 304 PRACTICAL MARINE ENGINEERING. as far as possible, of all the water formed by the gradual con- densation of the steam. At the same time the flow of oil to the bearings will be shut off and such measures taken with respect to the oiling gear as the circumstances may require. [3] Minor Emergencies and Troubles. We will now consider briefly the steps to be taken in the event of the more commonly occurring troubles, some of which have been mentioned in the preceding paragraph. (i) Derangement in the Oiling Gear. In sight-feed apparatus this is readily detected, and without loss of time the trouble must be located and remedied, the oil in the meantime being supplied to the bearing in question by hand. The trouble in such cases usually arises from a clogging up of some of the pipes or passages, and as noted in Sec. 24 [12] all such pipes should be put up with union joints so that they may be readily taken down, cleaned and replaced. (2) Hot Bearing. This is one of the most important of the minor troubles which may arise in the engine room, and one which may lead to serious consequences in case the proper steps for its control are not taken in time. A hot bearing may arise from a variety of causes, among which the following are the more important. (a) Lack of lubrication. (b) Lubricant too thin so that it will not remain in place in the bearing and sustain the load. (c) Improper adjustment, the amount of clearance between journal and brass being too small. (d) Lack of alignment in the machinery, as a result of which the bearing is excessively severe on certain parts, thus forcing out the lubricant and causing the surface to nip and abrade. (e) Bearing surface not of sufficient area to carry the load or take the work put upon it without an undue rise in tem- perature. This means, of course, either that the design is faulty or that the machinery is worked beyond the loads for which it was intended. (f) Bearing surfaces rough and uneven, due to the poor workmanship, or as a result of serious heating on a previous occasion. If the trouble is due to a lack of lubrication simply, and OPERATION, MANAGEMENT AND REPAIR. 305 is discovered in time, an abundant supply of oil will be usually sufficient to control the condition and to gradually bring the bearing back to its normal temperature. If, however, the tem- perature rises considerably, the journal may expand more than the bearing brasses, so that the clearance will be decreased and the brasses will pinch the journal, thus introducing a further source of trouble as noted in (c) above. If this is not soon relieved, the metal surfaces will nip and the softer of the two will begin to abrade or "cut." This is always the bearing metal, and the resulting condition, in consequence of which the smoothness of the surface is destroyed, will tend simply to make matters still worse, to generate more heat, expand the parts still more, perhaps nip the surfaces still more tightly, and so cut the worse, until the bearing metal melts and runs out. The treatment of a heated bearing involves two chief items, viz., the removal of the cause and the restoration of the bearing to its normal condition. We may remove the cause entirely, of course, by stopping the engine, and in an advanced case of trouble, such as just described, this may be necessary. Otherwise we may reduce the cause by slowing down somewhat, and thus decreasing the amount of work thrown on the bearing. We may further de- crease the cause by easing up the bearing cap and thus increas- ing the clearance between journal and bearing surface. This, however, can only be done to a slight extent, else trouble will be met with from too great clearance and the consequent pound- ing in the joint. A plentiful supply of oil, or other lubricant, will also aid in decreasing the cause and in restoring matters to their proper condition. A decrease in temperature will also usually aid in removing the cause, and is, furthermore, of course, one of the chief steps in bringing the bearing back to its normal condition. To this end in the extreme case, it may be considered neces- sary to turn a stream of water on the bearing, thus to absorb and carry away the heat, and in many cases full power trials are run with streams of water playing for a considerable part of the time on various parts of the machinery in order to carry off the heat and so control the temperature. Water, however, is doubt- less used far more than is absolutely necessary, and far more than good engineering would authorize. If sprayed or run from 3 o6 PRACTICAL MARINE ENGINEERING. a hose on the bearings it is almost certain to find its way in and an to the bearing surfaces, where it will prevent action of the lubricant. For this reason its use once begun, it may be neces- sary to continue, simply because the lubricant cannot lubricate in the presence of water. In the best modern practice, as indi- cated in Sec. 21 [n], provision is made for circulating water through hollow bearing blocks, and thus in the most effective way the water is able to remove the heat generated without coming into contact with the bearing surface itself. In case the machinery is not properly lined up, or the bear- ings are of insufficient area, or not in proper condition, only temporary relief can be looked for from the various means sug- gested above, the most effective of which will presumably be the operation of the machinery at a low or moderate power until such time as the needed readjustments, changes or repairs can be effected. To sum up the treatment for a hot bearing, the measures taken may be selected according to judgment and the special circumstances from the following: Lubrication. Easing up bearing caps. Slowing down and consequent reduction of load. Application of water. (3) Pounding. This condition may arise from several causes, chief among which are the following : (a) Bearings not in proper adjustment, too much clearance being allowed between journal and bearing metal. (See Sec. 24 [12].) (b) Lubricant too thin and thus unable to retain its place in the bearing. (c) Valve events not properly adjusted, especially the ex- haust closure and following compression. Furthermore, an engine will often show at different speeds a marked difference in this respect, such difference being chiefly due to the increasing effect of the inertia forces with increase in the revolutions. If the trouble arises from the nature of the lubricant in use a change to a heavier oil may show an improvement. If, however, as is more commonly the case, it is due to faulty ad- justment, either of bearing or valve gear, or both, but little can be done while the engine is in operation, and the first oppor- OPERATION, MANAGEMENT AND REPAIR. 307 tunity for overhauling and readjustment must be taken for a study of the conditions, both as regards the bearings them- selves, and the possibility of improvement by an adjustment of the compression. If the pounding becomes very severe," it may become necessary to slow down the engine and operate under less than the regular or full power until the proper examination and readjustment can be made. (4) Priming or Lifting Water. This emergency has been more particularly referred to in Sec. 38 [3] . In small quantities water produces a crackling or snapping sound in the cylinders, and the automatic relief valves may be allowed to take care of the situation, of if desired, the hand reliefs may be operated as well. If, however, the water comes over in large quantities the engine will slow down and work with an irregular and labored motion, which may be readily recognized as denoting this con- dition. In such case the throttle or main stop valve should be partially closed and the water gotten rid of as quickly as possible by the use of the relief valves. The engine will then operate at the reduced speed permitted by the partially closed valve, pre- sumably without further trouble. If on opening out again the tendency to lift water at full or ordinary power is persistent, the power must be reduced until the trouble is removed and the engine will operate continuously without disturbance of this character. (5) Vacuum Falls and Becomes Poor While the Condenser Be- comes Hot. Following are the chief causes which may lead to such a condition : (a) Insufficient condensing water from any cause. (b) Division plate in condenser head carried away so that water goes directly from inflow to outflow without going through the tubes. (c) Excessive inflow of steam caused by leakage either past low pressure piston or slide valve, or possibly in the ''bleeder" of "silent blow" if such is fitted. (6) Vacuum Falls and the Condenser Remains Cool. In such case the indications are that this condition is due to the presence of air not removed by the air pump, as may be caused by any one or a combination of any of the following : (a) Air-pump valves defective. (b) Leak in the condenser, either at the head joints or through a crack. 3 o8 PRACTICAL MARINE ENGINEERING. (c) Soda or drain cocks open or leaking. (d) Low pressure piston rod stuffing box leaking air inward during exhaust stroke. (e) With "inside" piston valves on the low pressure cylin- der, leaky valve stem stuffing boxes. (f) Leak or obstruction in the pipe leading to the vacuum gauge. Sec. 40. BOH,ER CORROSION. NO sooner has a boiler been completed than the various corrosive and destroying influences with which it is surrounded set to work on its destruction. We may conveniently consider corrosion as of two kinds, that due to oxygen and that due to an acid. These two are, however, by no means independent, and are often combined in very complex ways. The process by which oxygen combines with another substance is called oxida- tion, and the product of the operation an oxide. In the case of iron and steel the typical product is the ordinary red iron rust, or ferric oxide (Fe 2 O 8 ), consisting of about 56 parts -by weight of iron and 24 of oxygen. In order that oxidation or rusting of iron may continuously proceed at ordinary temperatures, how- ever, it is not enough that oxygen and iron shall be in contact. It requires the additional presence of moisture and carbon di- oxide (CO 2 ), small proportions of which are always present in the atmosphere. Oxygen and moisture alone act feebly and very slowly on iron, but when the four substances, iron, oxygen, moisture, and carbon dioxide, are all present together, the operation of rusting proceeds continuously and with vigor. Oxide is first formed, and this is reduced by the carbon dioxide to a carbonate, and this in turn breaks up, forming hydrated oxide (FeHO 2 ), setting free the carbon dioxide to continue the process. The hydrated oxide thus formed is furthermore elec- tro-chemically negative to iron, and thus helps on the operation as explained at a later point. If either the moisture or the car- bon dioxide is absent the oxygen will have little or no effect, and the iron will be protected. This is shown by the non-rust- ing of iron in perfectly dry air, even though there may be some carbon dioxide present ; or again, by its preservation in a weak alkaline liquid, as lime water, in which there can be no free car- bon dioxide. The piano wire used in certain forms of deep sea sounding apparatus, for example, is thus kept from corrosion OPERATION, MANAGEMENT AND REPAIR. 309 under conditions which would naturally soon destroy its regu- larity and value for the purpose used. Acid corrosion means the attacking of a substance by an acid, the breaking up of the latter, and the formation of a new substance known as a salt, and composed of a part of the acid and of the substance attacked. Thus hydrochloric or muriatic acid (HC1), as it is commonly called, is sometimes present in boilers. This is composed of hydrogen and chlorine. When it is brought into the presence of iron or steel the chlorine leaves the acid, and joining with the iron, forms a salt known as ferrous chloride, or chloride of iron (FeCl 2 ). With iron rust and mu- riatic acid the result would be similar, the chlorine would join with the iron and form ferrous chloride, while the hydrogen of the acid would join with the oxygen of the oxide and form water. As before stated, acid corrosion and oxidation are very commonly both present, especially in the latter operation, and in fact the continued progress of oxidation with iron, moisture and carbon dioxide is dependent on the combined action of both operations. W T e shall not, however, deal further with the chemical details of corrosion in general, but proceed to a brief consideration of the causes, effects and remedies as related to corrosion in marine boilers. Taking first the exterior o'f boilers and of all exposed iron and steel work in general, it is clear that the conditions for con- tinued rusting are all present on board ship. The air is moist and there is likely to be present carbon dioxide in abundance. The only safe protection is, therefore, a covering which shall keep the air, moisture and carbon dioxide from contact with the iron. To this end metal paint or other equivalent coating is used wherever possible. Many small fittings, especially about the deck, are of galvanized iron, that is, iron covered with a thin coating of zinc. The latter metal is but slightly affected by the process of oxidation, and it, therefore, forms an efficient protec- tion for the iron. Brass, bronze and copper are also oxidized but slightly, and the oxide formed serves as a protective cover- ing to the metal underneath. For this reason, among others, many of the fittings about boilers and elsewhere are, as we have already seen, made of these metals. Passing in now to the fire side of the boiler, we find the ap- plication of paint or other protective coating impracticable. 3 io PRACTICAL MARINE ENGINEERING. Here we must depend on the heat, which will so dry the air that it is no longer moist. That is, while water vapor may still be present in the air, there is so little compared with the amount the air could naturally contain at that temperature, that it is held by the air and is no longer free to enter as a factor into the operation of oxidation. Rusting in the usual way is, there- fore, very much retarded or prevented. To this fact we owe the general preservation of the furnaces, ash-pits, etc., from serious and continued corrosion. We here, however, run -into another danger in the extreme case when oxygen is present in excess, and both the oxygen and iron are very hot. The oxygen in such cases enters more readily into union with the iron, and if the temperatures should be sufficient, a different kind of oxide is formed, the black, or magnetic oxide (Fc 8 O 4 ), the same as the mill scale or forge scale, which forms when iron is worked at a red heat. The oxide thus formed may presumably be swept away by the scouring action of the draft, thus exposing a fresh surface to renewed attack. The back ends of the tubes seem especially liable to attack in this way, and particularly with hard forced draft. The cure for this trouble is found in the use of cast iron ferrules, as previously described. These ferrules protect the tube ends from the extremes of temperature, and also provide something for the hot oxygen to attack, while they are readily renewed. Turning now to the water side of the boiler, we find more serious trouble than with the fire side. There is likely to be more or less air in the feed water, either entering with the make-up feed, or occasionally drawn into the feed-pump and sent on to the boiler. There may also be free carbon dioxide liberated from the salts entering with the make up feed, and thus all the conditions for continuous rusting may be present. Even if free carbon dioxide is not present the formation of iron oxide, combined with electro-chemical reactions, as referred to later, may result in serious local corrosion. Furthermore, as the feed-water is heated the air is liberated, and the oxygen just at the instant of liberation seems to be especially active chemi- cally, and is thus all the more likely to attack exposed places than if allowed to remain in solution in the water, as at ordin- ary temperatures. Turning next to acid corrosion, mention may first be made of the serious trouble formerly experienced from the use of OPERATION, MANAGEMENT AND REPAIR. 311 animal and vegetable oils for cylinder lubrication. Such an oil is a compound of a fatty acid and glycerine. When exposed to a high temperature the fatty acid and the glycerine become separated. If a substance such as soda or potash is present, the fatty acid combines with it and forms soap. This process is called saponification. If, however, no such substance is present the acid will be free to attack other substances as it may be able. Fatty acids attack iron feebly, but if long continued the result may be a serious corrosion, resulting in the formation of what is known as an iron soap. The temperature within the cylinders and boilers was quite sufficient to thus decompose the oil, and there would, under such circumstances, be set free in the boilers an amount of fatty acid depending on the amount of oil used in the cylinders and finding its way into the condenser and feed-water. There were thus present all the conditions necessary for the corrosion of the interior of boilers by fatty acids, and many seri- ous cases were laid, in part at least, to this cause. These trou- bles appeared especially with the introduction of the surface condenser, and the part which fatty acids might play being un- derstood, the use of animal and vegetable oils for the lubrication of the cylinders was abandoned, and in their place hydrocarbon or mineral oils are now used. Such oils are derived as one of the constituents of crude petroleum, and are not compounds of a fatty acid and glycerine. They are compounds of carbon and hydrogen, and belong to an entirely different class of chemical substances. They do not produce a fatty acid on being heated, and cannot, at least directly, take part in the process of boiler corrosion. In modern practice, therefore, nothing but the best hydro- carbon oil, entirely free from animal or vegetable admixture, should be used for cylinder lubrication. With lubricant of this character modern boilers should be free from corrosion charge- able to the action of fatty acids. These are, however, not the only acids which have given trouble in the way of boiler corrosion. Under certain circum- stances free hydrochloric or muriatic acid is found in boilers. This is presumably due to the breaking up of magnesium chloride, forming hydrochloric acid and magnesium hydrate. The most dangerous feature of the corrosion due to hydro- chloric acid is that under conditions which may exist within steam boilers the chloride of iron first formed may become 312 PRACTICAL MARINE ENGINEERING. broken up, giving rise to other neutral compounds of iron, and setting free the acid to continue its ravages. There are also possibilities of the development of nitric acid from the organic matter which in small quantities may occa- sionally find its way into steam boilers. Except as it may be modified by electro-chemical action, the presence of such an acid usually results in a general surface corrosion, at least of all surfaces not protected by a sufficient layer of lime scale. The most troublesome feature of boiler corrosion has not been, however, a general or more or less uniformly distributed effect, such as would naturally be charged to the action of an acid diffused throughout the boiler. It has been rather in the so-called pitting. This term refers to the formation of small pits or depressions from the size of a pin head upward, and conical or cup-shaped in form. The depth of such pits may be anything from a slight depression to a hole cut entirely through a boiler tube. They are found in no fixed locality, though more commonly on the tubes, furnaces, and combustion chambers than elsewhere. When found they are usually filled with a blackish or brownish pasty mass, consisting chiefly of iron oxide with a slight admixture of lime salts, oily matter, and other substances. This deposit within the pits is often covered with a skin of somewhat different composition, consisting of lime salts and iron oxide in more nearly equal proportions. To account for the formation of these pits, various explana- tions have been suggested, most of them involving electro-chemi- cal action as a more or less pronounced feature. To under- stand the nature of this action a few explanations must first be given. Nearly all substances are in a different electrical condition, or at a different electrical potential, as it is called. This differ- ence is found not only between substances of different kinds, but also between similar substances at different temperatures, or in different physical conditions, as, for example, between two pieces of iron or steel, one of which has been hammered or worked more than the other. Due to this difference of elec- trical potential there is a tendency to set up a flow of electricity from one to the other, and as a further result to so change the two substances as to bring them into electrical equilibrium. In other words, the result of such a difference of electrical con- OPERATION, MANAGEMENT AND REPAIR. 313 dition is always to bring about changes which will cause the dif- ference to disappear, and so bring the two substances into equilibrium. These chemical changes of the two substances, which tend toward electrical equilibrium, may be much helped or hindered by the medium in which the bodies are immersed. If they are in dry air, for example, no such activity takes place, and the difference of electrical condition continues unchanged. If, however, they are immersed in water, or especially in salt or slightly acid water, the operation will usually be much assisted by the activity of the medium for the substances. It may also happen that the medium and substances are so related as to bring about a series of chemical changes, of which the first are those which would naturally be associated with the transfer of electricity and the development of equilibrium, while the second counteract these changes chemically, and bring the substances back to their original condition, and so keep them constantly in the condition of electrical difference. There is as constantly the attempt to restore equilibrium, and hence so long as these conditions continue there will result this continued series of chemical actions, accompanied by a constant flow of electricity from one substance to the other. In order, however, that this flow of electricity may be thus constant and so constitute a cur- rent of electricity, as it is termed, there must be a path for a complete circuit or flow in one direction through the medium which produces the chemical changes, and in the other direction outside of this medium. The substance from which the current flows in the medium is known as the electro-positive element, and the other the electro-negative. The chemical activity pro- ceeds and the current is formed, in general, at the expense of the electro-positive element. These operations are illustrated in the ordinary voltaic cell or battery, such as those used for ringing bells, etc. In most of these batteries, however, the action is not self-sustaining, and if allowed to continue for a little time, a condition of electrical equilibrium is reached, or, as ordinarily stated, the battery is run down. In others used for telegraphy and other purposes the operations are self-sustaining and continuous until the chemical substances are exhausted. In a boiler these conditions for a more or less continued electro-chemical action may be fulfilled in a variety of ways. Parts of the structure of widely differing temperatures or of 3 i4 PRACTICAL MARINE ENGINEERING. different physical or chemical compositions may provide the elements in a different electrical condition. Still more likely is such a difference to be found between iron and its oxides, especially the magnetic oxide or mill scale (Fe 3 O 4 ), or between a particle of carbon in the steel and the surrounding metal, or between a place in the steel where the proportion of carbon is much greater than the average and the surrounding metal, or between a bit of slag or other impurity in wrought iron and the surrounding metal. Copper, either in the form of oxide, or es- pecially in the metallic form, would also supply a substance dif- fering strongly from the iron. The exciting liquid is the water in the boiler, and its action will be more vigorous according as it is more acid in reaction, higher in temperature, and denser in concentration. With a high pressure boiler, water of high density and quite acid in character, and with the usual lack of homogenity or uniformity in the structure of the boiler, we should, therefore, expect the effects of electro-chemical action to be shown in marked degree. It happens, furthermore, that iron is electro-positive to copper, to carbon, and to its own oxides, so that in all cases likely to occur the operation will proceed at the expense of the iron. . From the very nature of these electro-chemical actions their effects are necessarily local in character, and so far as understood they seem to provide a fairly good explanation of the formation of pits as already described. It is not unlikely, however, that in some cases they are due rather to simple chemical action, and that their localization to a small spot is due to special or accidental causes, such as the protection of the surrounding'metal by lime scale, or a peculiar weakness against chemical attack at that point, due to peculiarities in chemical or physical structure. The possibility of deposits of copper on boiler surfaces has been already mentioned. These were first noted in connection with the corrosion accompanying the general introduction of the surface condenser. It was believed that the copper of the condenser tubes was attacked by the pure water resulting from the condensation of the steam, or by the fatty acids formed as above explained, and was then carried over into the boiler and deposited on the surfaces. To prevent such action the con- denser tubes were tinned, thus covering the copper from the action of the water or the fatty acids. Neither this step nor OPERATION, MANAGEMENT AND REPAIR. 315 the substitution of hydrocarbon oil for that containing fatty acids has made any very marked difference in boiler pitting, and at the most the presence of the copper can have been only one among a number of causes as suggested. There has been much difference of opinion and difference in experience regarding the question whether wrought iron or steel boiler tubes were the more liable to corrosion. It was pointed out that wrought iron was less homogeneous than steel, and therefore the latter should be the better. The early experi- ence with steel hardly bore out this claim, and in fact the gen- eral opinion seems to have been that wrought iron tubes were found to corrode less readily than steel. In explanation of this, it may be said that while wrought iron was less homogeneous physically, the steel was perhaps less homogeneous chemically, and in any event contained a larger proportion of carbon than the iron, so that it would by no means follow that it would neces- sarily be less subject to electro-chemical action. The latest and best products of the steel makers for such purposes, however, are extraordinarily low in carbon and very homogeneous, and experience with such grades of material seems to show them superior to wrought iron in this respect. We have thus developed in some detail the causes of corro- sion on the water side of steam boilers, so far as they are under- stood. For the prevention of such effects their causes must be removed or counteracted. For reducing the amount of oxidation and the possible re- sults due to electro-chemical action, the presence of air in the feed water must be avoided by preventing as far as possible the entrance of water from overboard into the feed. The hot-well or feed-tank should also be of good size and kept full, so that there may be no danger of its getting too low 7 from time to time, and thus allowing the pump to take air. The piston rod on the low-pressure cylinder should be kept well packed, so as to pre- vent the entrance of air during the exhaust part of the stroke. The feed pump rods on the water end should be kept well packed for the same reason. To prevent acid corrosion the formation of the acids must be prevented as far as possible, and such as may form must be neutralized within the boiler. The prevention of the formation of fatty acids has been considered above. We have also seen that the formation of other acids is due chiefly to the presence 3 i6 PRACTICAL MARINE ENGINEERING. of salts contained in sea water, or to organic substances. We have therefore simply an additional reason for keeping all such substances out of the boiler as far as possible. To neutralize such acid as may form, bicarbonate of soda, or soda-ash, as it is known in the trade, may be used from time to time, and in such quantities as may be found necessary. To test the water for acidity the litmus test is used. Blue litmus paper turns red when dipped in water slightly acid, while if the water is alkaline it re- mains blue, or the red color caused by an acid is changed to blue. By this means the condition of the water may be tested from time to time and soda used accordingly. Care must be taken not to use it in too great excess, as it may cause foaming. The soda is introduced by means of a soda cock on the con- denser. Instead of keeping the water alkaline by the use of soda, dependence is often placed on the zinc slabs used to pre- vent electro-chemical corrosion. These are gradually dissolved, forming zinc chloride, and this will undoubtedly tend to neutral- ize free acids and to keep the water alkaline. Whether sufficient or not, can of course be readily determined by the litmus test before referred to. For the prevention of electro-chemical action the causes must also be removed or neutralized as far as possible. This cannot be realized entirely, but it is clear that the results will be the better, as the following conditions are the more nearly ful- filled : (1) The structure of the boiler should be of material as homogeneous as possible in its chemical constitution and physi- cal condition. (2) Causes liable to produce oxidation or the presence of foreign substances should be kept out of the boiler as far as possible. (3) The water in the boiler should be made as nearly neu- tral or non-exciting relative to the iron as possible. This in a general way will be attained by keeping it slightly alkaline rather than acid, and by avoiding very high densities. In addition to these means for reducing the causes, there remains one further step, and that is : (4) The provision of a substance which shall be electro- positive to iron, and readily attacked, so that the activity will be diverted from the iron to the protecting substance, and the operation will proceed at the expense of the latter rather than OPERATION, MANAGEMENT AND REPAIR. 317 of the former. Such a substance we find in zinc, and its use for this purpose is very general and seemingly beneficial. It may be also noted that the formation of zinc chloride as referred to in the foregoing will aid in keeping the water alkaline in reaction, thus reducing its natural activity, and contributing further to the general decrease of electro-chemical action. In order to be effective as a protection to the iron in the man- ner described, the zinc must be in actual metallic contact with the structure of the boiler. It is usually in the form of rolled or cast slabs, weighing 8 to 12 Ibs. each. These are often placed in perforated sheet metal baskets hung from the stays or attached to other portions of the boiler. Where the basket is attached to the boiler there should be bright metal contact, and the attach- ment should be by screwed joint or other equivalent means, so that the separation of the two surfaces by the formation of scale or corrosion between them may be prevented. The zinc should also be connected to the basket by through bolts or other means which will insure continuous metallic contact. In some cases the zincs are hung by a through bolt without other means of sup- port. In such case, as the zinc becomes used it may fall apart and the pieces may lodge where they will obstruct the circulation, or be otherwise undesirable. In any event, they will no longer pro- tect the part of the boiler confided to their care, and their period of usefulness may therefore be less than when supported and connected to a basket, as described above. The number of zincs fitted varies greatly, according to the judgment of different engi- neers. In some cases not more than 10 or 12 would be assigned to the protection of a large double-end boiler, while in others as many as 40 or 50 would be used. The latter number is the bet- ter representative of good modern practice. In any case they should be distributed as nearly uniformly as possible throughout the boiler, in order that the latter may be thus subdivided into parts, each more especially, under the influence of a given slab. In connection with the use of zinc it may be noted that for such boilers as may be used for distilling purposes, that is, for the provision of fresh water for drinking and cooking, the zincs should be omitted, as the presence of any considerable amount of zinc chloride will render the water unsuitable for such uses. Instead of depending on zinc to prevent or divert electro- chemical action, as above described, some engineers prefer to depend simply on reducing the activity of the water by keeping 318 PRACTICAL MARINE ENGINEERING. it alkaline by the use of soda, introduced as the litmus test may show to be necessary. When spots are found in a boiler, showing the presence of pronounced corrosion, they should be cleaned off thoroughly, washed with soda solution, and, if not on a heating surface, cov- ered with a thin wash of Portland cement. This will attach itself to the iron and protect it in a manner similar to the lime scale. The beneficial effect of scale in thus protecting the surfaces of boilers from corrosion is well recognized, and there is no doubt that its presence as a thin wash or layer is of great value. In order to be effective, however, it must be so firmly and closely attached to the iron as to prevent contact of the water with the surface, else the corrosive action may proceed under the scale and result all the more seriously because it is protected from in- spection until the scale is thoroughly removed. On the tubes and other heating surfaces of the boiler, with their changes of temperature and consequent expansions and contractions, the scale is especially liable to be cracked off or partially separated from the iron, with possible results, as here noted. This is still more likely to be the case as the scale becomes thicker and the metal more liable to become overheated. It has also been sug- gested that a very heavy scale may result in an overheating of the metal sufficient to decompose the moisture present, thus lib- erating oxygen and forming the magnetic oxide of iron or black mill scale (Fe 3 O 4 ). This is highly electro-negative to iron, and thus it may give rise to harmful electro-chemical reactions. Laying Up Boilers. When boilers are to be laid up, the prin- ciples already explained will indicate the nature of the means suitable for preventing corrosion. On the outside, paint or other like coating may be used, as already noted. On the fire side of water-tube boilers protec- tion is sometimes gained by building a slow fire of tar or resin- ous material, the> tarry smoke from which condenses on the tubes and furnishes protection from the air with its moisture and carbon dioxide. Use is also made of quicklime in trays renewed from time to time. This absorbs the moisture and so keeps the air dry. On the inside, all boilers when laid up should be either empty or entirely full. If a boiler stands for any considerable length of time partly full, corrosion is likely to occur about the water line. If they are to be out of use for a short time only, OPERATION, MANAGEMENT AND REPAIR. 319 they may be filled full of water made slightly alkaline by the ad- dition of soda, the condition of the water being determined by the litmus test already referred to. If they are to be laid up for a longer time it is better to lay them up dry. To this end the water is removed, the manhole-plates taken off and the interior thoroughly dried out by the introduction of trays of burning charcoal or coke. The boiler is then closed up, except a lower manhole, through which a tray of freshly burning charcoal is in- troduced, and the manhole cover is put on. The charcoal will consume most of the remaining oxygen, and the boiler will thus be protected. Instead of the final introduction of a tray of char- coal, trays of quicklime may be used to insure the absence of all moisture, and the boiler then closed as before. It is readily seen that these various methods are simply ways of carrying out the necessary conditions for preventing oxidation, as already discussed, and if these principles are kept clearly in view the means most conveniently at hand may be suitably adapted to provide the protection desired. Sec. 41. BOILER SCAI,E. It is well known that sea water contains in solution a certain amount of solid matter, while even ordinary fresh water is not wholly free from similar substances. As long as the water re- mains in its natural condition these solids remain in solution ; but under the change of condition to which the water in a steam boiler is subjected, they are liable, as explained later in detail, to separate out from the water and thus to form scale or sludge, according as the circumstances may determine. The proportion of the solid matter in ordinary sea water is about (by weight) i part in 32, or 1-32. This is the same as about 5 oz. per gallon, or 2 Ibs. per cu. ft. The solid matter con- sists chiefly of chloride of sodium or common salt, with small quantities of calcium sulphate and carbonate, magnesium sul- phate and chloride, with smaller quantities of other substances. An average composition of this solid matter is about as follows : Chloride of Sodium (common salt) 76 per cent. Chloride of Magnesium 10 Sulphate of Magnesium 6 Sulphate of Calcium (gypsum) 5 " The remaining 3 per cent consists of small quantities of other salts with a little organic matter. The proportion of the solid matter in river and lake water is 3 2o PRACTICAL MARINE ENGINEERING. quite variable with the locality, and no representative or average analysis can be given. The amount held in solution may vary from perhaps 10 to 250 parts in 100,000 or from .015 oz. to .30 oz. per gallon, or .1 oz. to 2.5 oz. per cu. ft. It is composed chiefly of the carbonates of calcium and magnesium with smaller quantities of the sulphates of calcium and magnesium, and other substances. In addition to the substances in solution, quanti- ties of sand, mud, organic matter, etc., may be carried in sus- pension, dependent entirely on the locality and special circum- stances. Boiler scale from sea water is composed chiefly of calcium sulphate or sulphate of lime, as it is commonly called, while that from fresh river or lake water is composed chiefly of calcium carbonate or carbonate of lime, as commonly called. With brackish water, as we might expect, the proportions of the two are more nearly the same. Following are analyses of boiler scale by Professor Lewes which may be considered as typical of the incrustations formed by river water, brackish water and sea water, respectively : CONSTITUENTS. RIVER. Calcium Carbonate 75-85 Calcium Sulphate 3-68 Magnesium Hydrate 2. 56 Sodium Chloride 0.45 Silica 7.66 Oxides of Iron and Alumina 2.96 Organic Matter 3.64 Moisture 3.20 100.00 100.00 100.00 It thus appears that scale from river water may be looked on as an impure calcium carbonate, that from sea water as an impure calcium sulphate, while that from brackish water, as we should expect, is a mixture of the two in more nearly equal pro- portions. Sodium chloride or common salt is soluble in water until the proportion exceeds some 25 or 30 per cent. This corre- sponds to a density of 8 or 10 on the usual hydrometer, and is far greater than that reached by the water in marine boilers. This substance therefore gives no trouble so far as helping to form scale is concerned, and the small amount found in analysis of boiler scale is probably due to the shutting in, so to speak, of a small amount of water during the formation of the scale. In discussing the formation of boiler scale for our present purposes, OPERATION, MANAGEMENT AND REPAIR. 321 it will be sufficient to refer to the behavior of the salts of calcium and magnesium. Calcium carbonate (CaCO 3 ) is practically insoluble in water, while calcium bicarbonate (CaC 2 O 5 ) is quite soluble, and it is in this form that the substance exists in solution in water. If r?ow the \\ater is heated to the boiling point carbonic acid (CO 2 ) is driven away from the bicarbonate, it becomes reduced to the simple carbonate, and being now insoluble it separates out a? a more or less powdery deposit. Mixed with other salts, how- ever, especially calcium sulphate, or if there is a little sulphuric acid in the water, it may collect on the heating surfaces and form a hard and closely adhering scale. Magnesium bicarbonate is in a similar manner reduced to the simple carbonate, which is insoluble, and is then deposited in the same fashion. Calcium sulphate is soluble in cold water to a slight extent, as found in sea water. As the water is heated, however, or as the density becomes greater, the proportion of sulphate which it can retain in solution becomes less and less. When the tempera- ture rises to 280 or 290 (corresponding to from 35 to 45 Ibs. gauge pressure) the water can no longer retain any of the sul- phate in solution, and it is all deposited. It is also largely de- posited, even at a temperature of 212, if the density rises to 3-32 or above. The other sulphates become likewise insoluble and are completely deposited if the temperature rises to about 350 or over, corresponding to about 120 Ibs. gauge pressure.' These sulphates of lime and magnesium thus deposited tend to attach themselves to the surfaces within the boiler, and to form a very hard and crystalline scale. As to the effects of this scale, its presence in a very thin layer is often considered beneficial as a protection to the surface of the boiler from corrosive influences. On the other hand, how- ever, it is a much poorer conductor of heat than metal, and its presence on the heating surfaces retards the transmission of heat from the fire through to the water. In the extreme case the heat may be so effectually shut off from the water that it simply be- comes banked up, so to speak, in the metal, and in this way the tubes and other heating surfaces may become seriously over- heated with resulting damage to the boiler. The scale may also in extreme cases become so collected between the tubes or be- tween the combustion chamber and boiler sheets as to impede the circulation of the water and thus lead to overheating and its 322 PRACTICAL MARINE ENGINEERING. dangers, as referred to above. In water-tube boilers the accu- mulation of scale on the inside of the heating tubes is of special danger, as the circulation becomes in such case rapidly ob- structed and the danger of overheating and rupture is corre- spondingly increased. In a similar manner the accumulation of scale in the interior of tubular feed-water heaters rapidly de- creases their efficiency as heaters, if no worse results follow due to the burning out of coils, or to the resulting shortness of water in the boilers. Scale Prevention, Fresh Water. The only sure way of pre- venting scale is simply to keep it out of the boiler. If the scale- forming substances find entrance to the boiler it will be found very difficult to prevent its formation, at least to some extent. On boats navigating inland waters the jet condenser is still for the most part used, the feed is ordinarily taken from the condenser, and therefore practically from overboard. In such boilers, therefore, we may expect the formation of the usual fresh water scale, consisting chiefly of calcium carbonate. For the treatment of fresh water scale a great variety of methods have been proposed. In some cases the substances proposed act chemically, in others mechanically. From the great variation in the character of the solid matter contained in fresh water, it can hardly be expected that any one method of treatment or sub- stance will prove equally good in all cases. If a feed-water heater is used, and is effective in heating the water, it will be found that most of the scale will be deposited in the heater, especially if it is of sufficient size to allow of proper time. In this way the scale may be kept out of the boiler proper. The heater, .however, should be so made as to readily admit of cleaning, especially if the water contains any considerable pro- portion of scale-forming salts, otherwise it will soon become choked and ineffective. Among the various substances which have been recom- mended for the prevention of fresh water scale the following may be mentioned : Oak and hemlock bark and other like substances which contain tannic acid are more or less effective in waters contain- ing carbonates of calcium or magnesium. The tannic acid, how- ever, will attack the iron of the boiler and may lead to serious corrosion. Molasses, cane juice, fruits, distillery slops, vinegar and OPERATION, MANAGEMENT AND REPAIR. 323 other like substances containing acetic acid have also been used with success where no sulphates are present. The acetic acid, however, is still more injurious to the iron than the tannic acid, and the organic substances will form a scale with sulphates if they are present. Sal-ammoniac when used with a feed water containing cal- cium carbonate brings about an exchange between the two sub- stances as a result of which ammonium carbonate and calcium chloride are formed. The former of these is soluble and quite volatile and passes off mostly with the steam. The latter is quite soluble and thus the deposition of the calcium carbonate is avoided. This operation by itself, however, would result in the gradual accumulation of calcium chloride in the boiler, thus rais- ing the density of the water to a point where ultimately it would begin to deposit. This condition may, of course, be controlled by a suitable use of the blow. Tanate of soda is well recommended for general use, but with water containing sulphates a small amount of soda-ash should be added. Among the substances which act mechanically, crude petro- leum and kerosene oils are probably the most widely used. The latter may be recommended as the better of the two, as the crude oil will sometimes aid in scale formation. They seem to act best in cases where there are some sulphates present, as in slightly brackish water, or in the waters of certain geographical regions. Kerosene seems to act by preventing the particles of scale from sticking closely together or from tightly adhering to the heating surfaces, so that much of the matter will collect as a sludge in the bottom of the boiler, and that on the heating surfaces will be more easily removed. In all cases where there is reason to expect the accumula- tion in the bottom of the boiler of deposits thrown down in a loose or powdery form, the bottom blow should be freely used so as to prevent the accumulation of too great a quantity, or op- portunity for its hardening into scale. In spite of all modes of treatment there will be found some scale on the heating surfaces, and provision must be made for entering the boiler and removing it with appropriate tools as the occasion demands and circumstances permit. In many of our inland waters the amount of scale-forming substances is so small that no special treatment is thought neces- 3 2 4 PRACTICAL MARINE ENGINEERING. sary, and little attention is paid to the matter except to remove the accumulation at the periods of regular inspection and over- haul. Scale Prevention, Salt Water. Turning now to boilers in which sea water may form a portion of the feed, it will be of in- terest to first note briefly the historical development of the mod- ern situation. In the early days of marine engineering, the temperature and pressure of the steam were low, and the jet condenser was in general use. The feed water which was drawn from the min- gled condensing water and condensed steam was but slightly fresher than sea water, so that large amounts of solid matter were thus fed into the boiler. In consequence the density would have risen rapidly had it not been kept down by blowing off a part of the water in the boiler of relatively high density and re- placing it with the salt feed of lower density. Had the sulphates of calcium and magnesium thus brought into the boiler been completely deposited, enormous quantities of scale would have been formed, and this method of operation would have been quite impracticable. Due, however, to the moderate pressure then in use and to the fact that the density was kept usually be- tween i 3-4 and 2, the salts were held fairly well in solution, and but a moderate amount of scale was deposited. As steam pressures advanced, however, beyond 40 or 45 Ibs., conditions were reached under which first the calcium sul- phate and later magnesium sulphate and other salts are com- pletely deposited. Under such circumstances blowing off to re- duce the density of the water will only make matters so much the worse,, for the lower the density is to be maintained the greater must be the amount blown off, and hence the greater the amount of extra feed, and the greater the amount of scale form- ing salts brought into the boiler, all of which will be deposited. It became therefore necessary to abandon the use of the jet condenser and salt feed. Its place was taken by the modern sur- face condenser. So long as this condenser is perfectly tight the feed water consists of the condensed steam, and is therefore al- most perfectly fresh water. Due, however, to steam leaks at the various joints, seams and glands, to the occasional use of the steam whistle, and to the use of steam in certain auxiliaries from which it is not returned to the condenser, there will be a con- tinual shortage in the feed water which under usual conditions OPERATION, MANAGEMENT AND REPAIR. 325 will be found between say 2 and 5 per cent. Until recent years this shortage was made up by the use of sea water obtained usually by opening, as circumstances required, the salt water cock connecting the salt water side of the condenser with tne steam side. It is very difficult to keep the tubes oi a surface condenser packed perfectly tight, and in some cases the con- denser was allowed to run a little leaky, simply to make up in this way the salt feed required. Due to this admixture of salt feed, the scale forming salts of which are all deposited in the boiler, there will be a gradual formation of scale greater or less, according to the length of the run and the proportion of salt feed make up. In recent years experience has clearly shown that the dan- gers of overheating and the general bad effects due to the pres- ence of scale are more and more pronounced as the pressures are higher. It has become therefore more and more important to prevent so far as possible the entrance of any sea water into the boiler, and thus avoid the formation of scale with its troubles and dangers. To this end, in modern practice, the make up feed is provided by an evaporator, or in some cases by feeding one boiler with salt feed and thus restricting the scale formation to this boiler, while the condensed steam from all the boilers is re- turned to the other ones as feed. In all such cases it will be noted that this scheme amounts to a transfer of the use of salt water and the formation of scale from the boilers in general to the evaporator, or to the particular boiler in which it is allowed to accumulate. For short trips as, for example, those met with in bay, har- bor or channel service, or on short coasting voyages, fresh water for make up feed may be carried in tanks instead of providing it by means of an evaporator. By many engineers this is consid- ered the preferable method whenever tanks of sufficient size can be provided, and in some cases with the double bottom style of construction, double bottoms have been utilized to a consid- erable extent for this purpose. It is rare that the condenser can be maintained perfectly tight, so that even under the best practicable conditions there is apt to be some passage of sea water into the steam side of the condenser, and thence into the boiler. Under the best condi- tions the amount of scale formed, however, is so small that com- monly no special treatment is attempted, and the scale is allowed 3 26 PRACTICAL MARINE ENGINEERING. to deposit, and is then removed at the regular periods of inspec- tion and overhaul. Some attempts have been made to prepare sea water by the removal of the calcium sulphate in a separate vessel before en- tering the boiler. This may be done by the use of sodic fluoride which causes the sulphate to separate out and settle to the bot- tom as a fine powder. The remaining water is practically free from this substance and may be used for boiler feed without fear of causing scale. Soda ash and other alkalies have sometimes been used in boilers, with feed water containing sulphate of lime. They act by converting the sulphate into a carbonate, and thus into a somewhat less objectionable form. Barium chloride acts in a somewhat similar fashion by pro- ducing barium sulphate and calcium chloride. The use of zinc in boilers is also by many believed to prevent to some extent the formation of scale by the reaction of the alka- line zinc chloride on the scale forming salts. With sea-going, as with inland boilers, the bottom blow should be used occasionally and as the particular circumstances may demand, so as to remove the accumulation of such sub- stances as may be thrown down as a powder or sludge and thus collect in the bottom of the boiler. However careful the provisions for keeping sea water out of the boilers or no matter what methods may be used to pre- vent scale formation, it is almost sure to gradually accumulate, and assurance of safety from the troubles and dangers which may result can only be obtained from periodical examination and scaling as may be found necessary. All marine boilers must, of course, be provided with manhole plates for this purpose, and the internal arrangement of tubes, braces, furnaces, etc., should be made, so far as possible, with a view to furthering this neces- sary operation. Combinations of Oil and Scale. We have thus far referred to scale formed simply from the solid matter in the feed water. The combinations which may be formed by the deposited salts and oil from the cylinders as it may enter with the feed water are, however, of even still greater importance, and must now be noted. Oil coming in thus with the feed water is caught by the cir- culating currents and distributed more or less throughout the OPERATION, MANAGEMENT AND REPAIR. 327 bailer, though by reason of its lesser weight it will tend grad- ually to rise and accumulate as a scum at the surface of the water. In thus wandering about, a drop may come in contact with a bit of solid matter separated from the water. The two join together, the oil forming a coating about the sulphate, and they journey on meeting and joining with other like particles. The combination of the oil and sulphate may have about the same specific gravity as the water in the boiler, and hence these parti- cles will readily move with the circulating currents, either up or down, as they happen to be flowing. They are thus swept along the heating surfaces, to which they attach themselves all the more readily by reason of their oily -covering, and on either the upper or lower side as they happen to be moving with a down or up-flowing current. In this way the coating gradually in- creases until it has attained a thickness sufficient to seriously interfere with the passage of the heat. In other cases, when the scale and oil are lighter or the water is denser and heavier, there seems to be formed at the surface of the water in the boiler a kind of oil and scale blanket or layer floating about, and perhaps ultimately by the gradual increase of weight sinking and covering some portion of the heating surface. Especially is this oil "pancake," as it has been called, liable to settle should the density of the water in any way be suddenly decreased. Still otherwise should the boiler be blown down by the bottom blow, such an oil blanket would naturally settle and attach itself to some part of the heating sur- face. Should the boiler be then filled again, the coating would remain where attached. This shows that under such circum- stances a boiler should never be blown down with the bottom blow without first using thoroughly the surface blow to remove as far as possible all such accumulations of oil or of oil and scale from the surface of the water. The danger to be feared from this combination of scale and oil is not in its close adherence to the surfaces, but in its non- conductivity for heat. Experiments show that 1-16 to 1-8 inch of such a covering is far worse in this respect than perhaps 1-2 inch or more of scale alone. The danger to be feared is there- fore overheating and collapse, and not a few cases of the col- lapse of furnaces and other parts of marine boilers are believed to be due to this cause. So far as these effects are concerned it is seen that it is bet- 328 PRACTICAL MARINE ENGINEERING. ter to carry a high density in the boilers than a low one, so as to keep such oil and scale combinations at the surface of the water, where they may be disposed of by the surface blow. As it is practically impossible to prevent the entrance of some scale-forming materials into the boiler, the danger of trouble with oil and scale combinations is most surely pre- vented by keeping the oil out. To this end a cylinder oil should be used having a high point of vaporization, as the higher this point the smaller the amount carried into the condenser. Of this oil the minimum amount necessary should be used in the cylinders, and the feed water should be filtered to remove what- ever oil it may contain. Sec. 42. BOII/ER OVERHAULING AND REPAIRS. [i] Inspection and Test. We will suppose that after some considerable term of serv- ice, and preparatory to a general overhauling, a battery of boilers are to be carefully and thoroughly examined. The more important points may now be considered. (1) Furnace Fronts. The furnace fronts and doors may be found warped and cracked, and if this is the case to such an ex- tent as to interfere with the proper closure of the furnaces, or with the proper and convenient care of the fires, the necessary re- pairs or renewals should be made. (2) Grates and Bearers. The grate bars will often be found warped and twisted, or badly burned, and at various points sunk- en below or sprung above their proper level. Such irregularities in the grate may occasion loss of coal at some points, while they will further the accumulation of ash and clinker at others, and will make it almost impossible to give to a fire the proper atten- tion, or to get from a square foot of grate surface the power which it should be able to give. The bearers may also be the cause of trouble by warping or settling from having been over- heated, and all of these points must be attended to before the boiler can be considered again ready for proper service. (3) Bridge-wall The bridge-wall is liable to be found more or less burnt out and dilapidated, while on the front side clinker and bits of brick may be found fused together in irregular masses. All of this must be removed and the bridges built up again with fresh bricks to the proper height as referred to in Sec. 38 [i]. OPERATION, MANAGEMENT AND REPAIR. 3 2 9 (4) Tubes. The tubes will, of course, be swept and properly cleaned on the fire side. The existence of small leaks must be carefully looked for, the evidence being the presence of soot and scale burned to the metal where the water has come through and evaporated. The back and front tube sheets and the inside of the tubes must be carefully examined for any such evidence. Signs of especial wear should also be looked for at the back ends of the tubes, and if ferrules are used some will probably be found so worn and burned out as to require renewing. In water-tube boilers any special warping or change in the shape or curvature of the tubes should be carefully noted, as it may indicate overheating due to faulty circulation caused by a clogging of the tube by scale and sediment. A split or badly ruptured tube will, of course, show itself by the resulting leak, but in a water-tube boiler such leak may be very difficult to locate without the removal of several of the tubes in the vicinity of the one giving the trouble. These points depend entirely on the type and style of construction, and no general rule can be given for definitely and immediately locating such a tube in a water-tube boiler. (5) Joints and Seams. The joints and seams throughout the boiler, both in the combustion chamber and on the outside, should be carefully examined for small leaks, either between the plates or about the rivets. If the leakage is not serious, caulking will serve as a sufficient remedy. In other cases, however, the removal of old rivets and the insertion of new ones may be found necessary. (6) Front Connections and Uptakes. The front connections, uptakes and fittings should be examined to make sure that the plates are not warped or broken from their fastenings, and that the dampers and their operating gear are in proper condition. (7) Fittings. The valves and cocks are likely to be found more or less worn on their seats and leaky in consequence. These will require regrinding and refitting, or replacing by new where necessary. The operating gear, such as valve spindles, wheels, levers, chains, gear-wheels, etc., should be examined for any breakage or derangement of parts. The various joints and fittings about the steam and water pipes must also be examined for signs of leaks, distress, corrosion, or other derangement. (8) Bracing. The manhole plates will, of course, have been removed to facilitate examination of the interior. 330 PRACTICAL MARINE ENGINEERING. The braces, especially where pin joints and like connections are used, should be carefully examined for defects in the con- nections and fittings, and also for any symptoms of buckling or distress in the braces themselves. (9) Scale. The scale present in the boiler should be ex- amined as to its amount, distribution and character whether hard or soft, greasy or otherwise, closely adhering or readily cracked off. Accumulation of scale between the tubes or screw stays, and of scale and sludge in the bottom of the boiler must also be looked for and noted. In some cases an oily or greasy coating with little or no mineral matter and forming a coating over the scale and on the heating surfaces may be observed. This will indicate large quantities of oil in the boiler, and insuffi- cient use of the surface blow. (10) Corrosion. It is, of course, of the highest importance to examine carefully for signs of corrosion and pitting through- out the interior of the boiler. The following locations, however, are those in which it is most apt to be found : On the sheets at and near the water line. Occasionally also severe corrosion is found in the steam spaces. On the braces near the water line. On the tubes and combustion chamber tops. On the furnaces near the grate level. The nature and distribution of this corrosion must be care- fully noted, in order that the most suitable steps may be taken for its arrest and prevention in the future. When they can be gotten at, corroded spots may be scraped and scrubbed clean with water made alkaline by the addition of soda or weak lye, and if not on a heating surface, a redistribution of the zincs may prove of service, while in general a more careful attention to the various means suggested in Sec. 40 may be recommended. The zincs and their fittings., as discussed in Sec. 40, must also be carefully looked after. Many of the zincs will probably be found to have wasted away to only a small part of their original size, and to have become changed in physical structure to a blackish or brownish crumbly or brittle mass. In some cases remnants of the slabs may be found lodged between the tubes and screw stays, and often more or less covered or imbedded in deposits of scale. On the exterior of the boiler the points most liable to corrosion are on the fronts about the bottom where damp ashes OPERATION, MANAGEMENT AND REPAIR. 33 1 may have lain, or about the saddles and on the under side where dampness and water are liable to be formed. Thorough clean- ing, followed by a coat of paint, asphaltum varnish, or other like material, is the usual remedy in such cases, at least where its application is practicable. Before the application of any such coating, the plates should be thoroughly dried, else it will be of little use. The presence of moisture on the plates causes the especial difficulty connected with the effective application of paint in such places, and where convenient the use of a portable sheet-iron drying stove contain- ing burning charcoal or coke may be found of use. This may be placed under the surfaces to be covered so as to furnish an ascending current of warm air, thus aiding in keeping them dry during the application of the paint. For the structural material in bilges and bunkers a coating of Stockholm tar put on hot and then sprinkled with Portland cement is highly recommended by some engineers. (n) Manholes and Covers. The faces on which the manhole cover joints are made should be examined for corrosion or scale, or anything which may affect their evenness, or make difficult the fitting of a tight joint. (12) Drill Test. Where the boiler has seen long service, or where there are evidences of serious corrosion, or doubt exists as to the thickness or quality of the plates, they must be drilled at such points as may be selected. In this way the thickness of the remaining good metal may be ascertained, and the safe pressure to be carried may be fixed in accordance with the evi- dence thus found. (13) Hydraulic Test. When the boiler has been overhauled and put in proper condition, at least as far as anything which may affect its strength is concerned, the hydraulic test may be applied. To this end the boiler is filled full of water and pres- sure is put on, usually by means of a special pump connected for the purpose. The test pressure is usually one and one-half times the working pressure desired. It is considered that this pressure is not sufficient to seriously try or injure the boiler should it be properly constructed, and of suitable factor of safety throughout, while at the same time it will be sufficient to de- velop small leaks, and should the boiler be unduly weak at any point, the bulging or yielding or distress at such point should become apparent. If no such evidences appear, then it is con- 33 2 PRACTICAL MARINE ENGINEERING. sidered that the boiler is abundantly strong for the working pressure as desired. To prepare the boiler for the test the springs should be withdrawn from the safety valves and lengths of pipe of suitable size substituted, so that the valves may be screwed down fast. All stop valves and gauge glass connections should then be tightly closed, as well as the connection to any pressure gauge which will not indicate up to the test pressure. While the test is under way the boiler is subjected to the most careful examination, both inside and out. The furnaces, combustion chambers and back tube-sheets are examined from the inside, and the shell and its various joints and seams from the outside. Small leaks are watched for and stopped by caulk- ing, if possible, or if about the tube ends, by re-expanding. Es- pecial care must also be had in watching for any signs of bulging, buckling or other deformation or distress. Where the test is to be carried out with especial care, ex- tension and compression gauges are provided in the furnaces and combustion chambers, and at other points, as may be de- sired. These serve to indicate and to measure the actual amount of distortion which results from the gradually increasing pres- sure. If the distortion or bulging at any point should become abnormal, the pressure should be relieved by letting off a little water, in order to see if any permanent set has been made. The continuance of the test should then be made to depend upon the behavior of the part showing this relative weakness. For a thoroughly satisfactory test, all gauges should return to the original setting when the pressure is removed, showing no permanent set at these points.* It will usually be found very difficult to so tighten the vari- ous valves that there will be no leakage. An idea of the amount of leakage may be obtained by watching the rapidity with which the pointer on the pressure gauge moves backward when the pump is stopped, as well as by the amount of pumping required to maintain the pressure at its full value. The pressure gauge pointer will also frequently indicate by its more or less sudden movement backward, the sudden development of leaks about the riveted joints or tube ends. It has sometimes been urged against the hydraulic test that it may severely strain some part of the boiler where the yield or distress is difficult to observe, and thus so weaken it that a OPERATION, MANAGEMENT AND REPAIR. 333 further yield or rupture may occur under a much smaller, load at a later time. The hydraulic test is, however, very generally employed both in the naval and mercantile marines, and if care- fully conducted and with a pressure not exceeding one and one- half times the working pressure, it is not likely that harm will result, while the test will develop the small leaks and minor defects, and may be the means of exposing serious faults of workmanship or design. The same test is, of course, applied to new boilers as a final preliminary to the getting up of steam. In some cases the water test has been carried out by filling the boiler and then lighting wood fires within the furnaces. The expansion of the water will furnish the increase of pressure de- sired, which may be eased by the safety or stop valve, as neces- sary. It has been claimed that the boiler being in this way heated, was more nearly in its regular service condition. While this may be so to a slight extent, the boiler is, nevertheless, far from regular service condition, and the method has the serious disadvantage that it does not allow examination of the furnaces, combustion chambers and back tube sheets while it is under way. It is also under less ready control than the pump method, and is now but rarely employed. BOILER REPAIRS. In the following suggestions regarding boiler repairs we shall refer more especially to such as may become necessary at sea or under emergency conditions, rather than to those which may result in the course of a thorough overhauling in port. i (2) leakage from the Joints of Boiler Mountings. Such leakage by soaking through the lagging and keeping the plates wet may give rise to surface corrosion on the boiler shell. The first care must be to stop the leakage by screwing down, re-caulking or re-making the joints, as may be necessary. If there is reason to suspect corrosion of the boiler as well, the lagging should be removed and the corroded surfaces scraped clean and painted with good metal paint or other suit- able covering. (3) Leakage About Shell Joints. Usually caulking will be sufficient to stop any ordinary small leak in these joints. If it is serious and caulking gives 334 PRACTICAL MARINE ENGINEERING. but Jittle improvement, it may indicate a loose rivet or one with the head gone. In such case leakage about the rivet will usually be present also, and will thus serve to locate the trouble. Such rivet must, of course, be replaced, in order to effectually stop the leak. Where a rivet has blown out and a quick repair is desired, the hole may be drilled or reamed true and then tapped out. Then fit a bolt with corresponding thread and cut it partly through near the root with a hack saw. Screw this in, knock off the projecting end, rivet down the remainder and the job is complete. In some cases instead of replacing loose or broken rivets, or where for other reasons caulking seems to be inefficient in stopping the leak, it may be considered desirable to put a patch over the seam, rivets and all. In such case a so-called "soft- patch" is applied. This is illustrated in Fig. 204. The patch is flanged and made with a recess of suitable size and form to accommodate the rivet points. It is then filled with a stiff putty TUT Fig. 204. Patch for Leaky Joint. of red lead and secured by bolts as shown. Such an application is really a red-lead poultice, kept in place by a suitably formed steel cover, and secured to the shell, as explained. It is un- necessary to make such a patch of metal more than 3-16 or J4 inch thick, since it is not intended to add strength to the shell, but simply to keep the red-lead putty in place, and thus stop the jet of leaking steam or water. The chief difficulty with leaks in the shell seams and with the outside of boilers in general arises from the trouble in sub- jecting them to the proper examination due to the presence of the lagging. As usually fitted, this covering is difficult of re- moval, and small leaks thus covered in may continue for long periods of time, keeping the outer surfaces wet and causing rust and corrosion where its existence may not be expected. A form of boiler lagging admitting of ready renewal and re- placement in sections is much to be desired, and if full advantage were taken of such a form of covering to keep closer watch of all OPERATION, MANAGEMENT AND REPAIR. 335 joints on the outer surface, much trouble might be avoided by taking the first appearances of trouble in time. (41 I/eakage at Internal Joints. The internal joints, on the whole, give more trouble than those on the outside. This is only to be expected due to the thinner plates, the enormous range of temperature differences which exist, and the resultant expansions and contractions. The difference in expansion between the furnaces and tubes is es- pecially liable to give trouble with the joints connecting the furnace to the combustion chamber, and several varieties of joint have been proposed to reduce this trouble to a minimum. With a joint such as shown in Fig. 43, the greater expansion of the furnace tends directly to open up the joint, while with that shown in Fig. 9 the result is a shear on the rivets but no direct tendency to open the plates. In the latter case, however, the Soft Patch. Locomotive Patch. Hard Patch. Fig. 205. Different Forms of Patches. rivets are more directly exposed to the fire than in the former, and thus the points between the two joints are very nearly balanced. The joint of Fig. 9, however, allows a more ready re- moval of the furnace, and on this account it is often selected rather than that of Fig. 43. Leaky joints on the combustion chamber should be first carefully re-caulked. This operation, however, cannot be car- ried on indefinitely, for after caulking to a certain extent, the edge must be chipped off to get a fresh caulking edge. This, if repeated, will leave the metal between the rivets and edge too narrow for safety. If careful and judicious caulking does not remedy leaks in these seams, it is evident that the rivets need renewal, and in carrying this out especial care should be taken to see that the holes are fair in the two plates, and that the rivets fill them completely. 336 PRACTICAL MARINE ENGINEERING. (5) Patches. We may now turn more especially to the patching of boilers and to the different kinds of patches employed. We must first remember as a general principle that any thickening of metal on the heating surfaces is undesirable and to be avoided as far as possible, or reduced to the lowest possible extent. If, therefore, a patch on a heating surface is to be considered as a permanent fixture, the faulty metal should be cut out, thus doubling the thickness only over the necessary width for the fastenings. A patch put on in this way with rivets headed up as in regular boiler work is known as a hard patch, and is illustrated in Fig. 205. In some cases the patch must be put on from one side only, or is more temporary in character. In such case either the locomotive or the soft patch is used. The former is a patch put on with tap bolts, as illustrated in Fig. 205, and usually without cutting out the metal. The soft patch has been already referred to. In its more usual form, as shown in Fig. 205, it is made by lipping down a plate of steel so as to contain and hold in place a coating or layer of red-lead putty. It is more suitable for temporary repairs, or where the sur- faces are so rough and uneven that a patch of the other forms could not be fitted. The soft patch is sometimes secured with tap bolts, and sometimes with through bolts and nuts, as may be most convenient with the case in hand. As to whether a patch should be put on the water or fire side, much will depend on location and convenience. Where it is possible the water side may be chosen so that the steam pressure will tend to keep the patch in place. Usually, however, the fire side of the plate is more easily gotten at, and in many cases there is no choice but to put the patch upon this side. In any event with either the hard or locomotive patches, the edge will require careful caulking as the final closure and making of the joint. With the soft patch, caulking the edge is not neces- sary, as the putty is depended upon to stop the leak, and the office of the patch is merely to hold it in place. (6) Cracks and Holes. A small crack is usually treated by drilling a hole at each end to prevent its extension, and then covering with a patch, according to location and convenience. Very small cracks are sometimes drilled and tapped out as close together as the holes OPERATION, MANAGEMENT AND REPAIR. 337 will stand, and then filled with soft iron or steel bolts, riveted down so as to overlap and thus completely close the crack. Small isolated holes not accompanied by a general thinning of the metal may be treated in a similar fashion by drilling and tapping out the hole and riveting in a bit of soft iron or steel bolt. Larger holes, or where many are located near each other, or where they are accompanied by pronounced thinning of the metal must be treated by patching. In general it may be noted that plugging as above de- scribed, is only suitable for the mere stopping of a leak, and that it adds nothing whatever to the strength of the plate. If, then, the conditions are such as to make additional strength de- sirable, a patch must be fitted. Where a crack is found in a tube sheet it usually extends from tube to tube. Such a crack may be covered by a patch ex- Fig. 206. Patch for Boiler Tube Sheet. tending over the crack and taking enough good metal to obtain a secure hold. The patch must have holes cut in it, of course, to correspond to the tube ends as shown in Fig. 206. [7] Blisters and Laminations. With modern boiler material these defects are happily rare. In former years, and especially with iron plates, they were only too frequently met with as referred to in Sec. 5. The chief dan- ger from these defects is due to the weakening of the plates and the liability of overheating, due to poorer conductivity for heat. Such defects if very small are often left undisturbed, with care- ful watching and measurement from time to time. If small and the metal quite thin on one side, the thinner part was cut away, leaving the thicker side to do duty for both. In some cases also a dog and supporting bolt was fitted to support the remaining metal. For some serious cases, however, it was usually con- 338 PRACTICAL MARINE ENGINEERING. sidered preferable to cut out the metal thus affected, and cover the hole with a patch. In all cases where patches are put on, or in general where new material is put into the boiler, it is well, if convenient, to select it of stock as nearly like the boiler as possible in physical and chemical constitution. This will tend to decrease the pos- sible sources of electro-chemical action as discussed in Sec. 40. [8] Tubes. The repairs to boiler tubes comprise re-expanding, plug- ging, and renewal. Expanding has been explained in Sec. 16, and a repetition of the process may be required from time to time, to keep the tube ends tight. The immediate cause of the leakage of boiler tubes is often the accumulation of dirt and scale about the tube ends and on the tube sheet. These points should therefore be carefully looked after, or the re-expanding will be of little use. Care must be taken that the operation of re-expanding is not repeated too often, or the metal of the tube end may become so thinned and hardened that there will be danger of weakness or brittleness at this point. For stopping a tube which has split or in any way de- veloped a serious leak, a tube stopper or plug is used. Tem- porary stoppers of pine wood are often employed. Such a plug closely fitting the tube and twelve or fifteen inches long may be forced in from the front end to a point where it covers a split or hole, and thus provides a temporary repair. The swelling of such a plug caused by the action of the water and steam will cause it to stick closely in place and thus more effectually stop the leak than would a metal plug in the same location. For more permanently plugging a tube, tapered cast iron plugs are used, one at each end, driven in to a tight fit and held in place by a rod passing through them from one end of the tube to the other and set up with thread and nut. The plugs and nuts should be faced so that when set up with a copper washer or turn of cop- per wire underneath, a steam tight joint between the plug and nut may be made. To plug a tube in this manner the fire must, of course, be drawn and the back connection entered in order to insert the back plug in place and adjust the rod and nut. When a tube is to be renewed the old one must first be drawn. To this end the back end is closed down so as to readilv OPERATION, MANAGEMENT AND REPAIR. 339 pass through the hole in the tube sheet. A rod is then passed through the tube and a nut and washer are fitted to the back end, the washer being of such size that it will bear on the tube end and at the same time will pass through the hole in the tube sheet. The front end of the rod passes freely through a dog or strong-back whose feet rest on the tube sheet, and is provided with a nut bearing on the face of the dog. The nut being then forced down, the rod is withdrawn and with it the tube. To facilitate withdrawal the front end of the tube is usually made of slightly larger diameter than the back end, and the tube once started is readily withdrawn the remainder of the way. Before inserting the new tube the metal of the tube sheets about the holes should be carefully examined to see that the holes are smooth and fair and that no reason exists why the expansion of the new tube may not make a steam tight joint. The new tube may then be inserted, the ends expanded, beaded over at the back end or at the front and back ends if no stay tubes are fitted, and the operation is complete. [9] Leakage About Stays and Braces. Leakage at these points may be due to corrosion about the joint, or to loosening due to repeated expansion and contraction, or to bending or distortion of the plate or stay caused by bulging or partial collapse of the plate. If the leak is not serious, setting up on the nut, or caulking about the joint between stay and plate may prove sufficient. If not it will usually be neces- sary to remove and refit the stay. For screw-stay bolts this will usually require the reaming out and retapping of the holes for the next larger size. For braces fitted with nuts or nuts and' washers, the same size can usually be replaced, but especial care should be taken to insure the proper smoothness and fair- ness of surface about the holes, as well as the proper fit and ad- justment of the nuts and washers, so that the usual fitting will provide tightness of joint. [10] Bulging or Partial Collapse of Furnace or Combustion Chamber Plates. We have already discussed in Sec. 38 the causes of bulging or collapse, and the steps most suitable to insure immediate safety. When the time comes for examination and repair the following steps may be taken. If the bulge is quite small it may be decided to leave it un- 340 PRACTICAL MARINE ENGINEERING. disturbed, assuming that its strength is practically as great as before. In such case, however, a template should be fitted to the bulge, and this should be applied from time to time in order to detect any signs of further yielding at this point. In other cases special girder or through braces may be fitted to support the bulged portion, the details of the arrangement depending, of course, wholly on the circumstances of the injury. In other cases the bulged part may be more or less com- pletely forced back into place. This, however, is an operation requiring both skill and care, and should not be undertaken without making the preparations necessary to carry it out in the proper manner. A portable grate or furnace for burning coke or charcoal is first provided of such shape and with such arrangements that the burning fuel may be brought close up to the bulged surface. An artificial draft may be provided by means of a blower from a hand forge fitted with a suitable conduit, or otherwise as may be most convenient. In the meantime a cast-iron former block should be provided, shaped on its face to correspond to the sur- face of the plate when forced back into position. A hydraulic jack or other like appliance must next be provided, taking es- pecial care to arrange for the distribution of the load on the base over a considerable area of plate so that no harm may be done by the reaction from the head. To this end a support of heavy timbers is usually the most convenient to arrange. These various appliances being in readiness the bulged plate is heated to a low red, the former-block and jack are adjusted in position, and the plate is carefully forced back into shape. Several ap- plications of the heat and of the jack may become necessary before the plate is restored to its original form. It is thought by many that the partial heating of a steel plate in this way with no later opportunity for general annealing is liable to injure its homogeneity and toughness, especially if the operations are carried on at too low a temperature, or ap- proaching what is known as blue heat. This was undoubtedly true for much of the earlier products of the steel makers, and there is no doubt that the homogeneity of the metal is thus somewhat disturbed. With the latest and best grades of boiler plate, however, little danger as regards strength at least, need be feared on this score, and but little hesitation is now felt in reducing to shape a bulge of moderate depth. OPERATION, MANAGEMENT AND REPAIR. 341 [n] Split in Feed-Pipe. A small split in the feed-pipe may sometimes be temporarily repaired by wrapping with heavy canvas and marline, or copper wire, it is, however, difficult to make a tight joint with hand wrapping, especially with modern high pressures, and a more effective plan is to form up a patch of sheet copper and secure it in place by bolted strap clamps, with a sheet of good elastic packing, or a thin layer of stiff putty between the patch and the pipe to make the joint. A small hole in the feed-pipe may, if the metal is thick enough, be stopped by drilling and tapping out and riveting in a small screw plug. Soft solder when applied with skill may also be used to stop pin-holes, or to aid in securing a suitable plug in a larger hole. If, however, the hole is of any consider- able size, or if the metal is thin about its edges, some form of patch, as described above, must be made use of. All such repairs are, of course, only temporary, and at the earliest convenient opportunity the damaged length of pipe should be replaced with new. In some cases with copper pipes, however, where the neces- sary materials and skill are available, it may be desired to under- take a more permanent repair by brazing a patch over the hole or split. To this end the metal about the defective spot is first cleaned with file, emery cloth and acid. The patch similarly cleaned is cut from sheet copper of about the same thickness as that of the pipe, formed to fit over the defective spot and wired in place. A clear coke or charcoal fire is then prepared on a forge and the pipe placed in position. The spelter or hard solder, mixed with borax as the flux, is then placed in position on the inside of the pipe and the whole carefully heated. At the proper temperature the spelter will melt and run in between the patch and pipe, thus forming a joint between the two. Care must be exercised in this operation in order to avoid danger of overheating or "burning" the copper. The resulting loss of strength has been referred to in Section 3. Sec. 43. ENGINE OVERHAULING, ADJUSTMENT AND REPAIRS. We shall undertake in this section only a few hints regard- ing the more common operations involved in the overhauling, adjustment and repair of marine machinery. 342 PRACTICAL MARINE ENGINEERING. [i] Cylinders. First, in the main engine, the cylinder covers must be re- moved at proper intervals, and attention given to the condition of the wearing surfaces and of the piston springs. The troubles most liable to be found are cutting and scoring of these sur- faces, and derangement or breakage of the springs. The nuts of the follower studs and all other forms of screwed fastenings should also be examined, in order that any tendency toward loosening up or backing off may be noted and checked. To examine the condition of the piston the follower plate is lifted and the springs and packing rings removed. The latter, if wearing properly, will be of uniform thickness around the en- tire circumference, and of uniform polish on the outer surface. If the piston-rod is bent or cylinder bore not quite in line with the motion of the rod, the ring will wear wedge-shaped in cross section. In replacing, care should be taken to note the degree of tightness of the ring when set out with its springs. This should be such as to support the ring anywhere along the bore, but not so much that the ring cannot be pushed along by hand, using moderate force. In closing up the cylinder or valve-chests, especial care should be taken to see that all nuts, split pins, etc., are properly secured in place, and that no tools, waste or other foreign substance are left within. Neglect of this latter point has often been the cause of serious trouble, resulting in broken cylinder-heads, bent piston-rods, broken valves, port metal, etc. To test the tightness of the joints of the cylinder liners, the cylinder being open, steam is admitted to the jacket and the joints are carefully examined top and bottom. Where there is no manhole on the lower head, as is common with small cylin- ders, a leak of any significance will become evident by opening the lower indicator cock. In order to test the tightness of the piston under steam, the cylinder-head being in place, we may proceed as follows : Put the engine and links in such position that a little steam can be admitted on top of the piston and then open the bottom indicator cock. Then admit the steam, usually through the starting valve, and if it blows through the lower cock the piston is thus shown to be leaky. For a thorough test it will be well to try the leakage in both directions; that is, from top to bottom, as above, and similarly, from bottom to top. OPERATION, MANAGEMENT ./.YD REPAIR. 343 [2] Pin Joints and Bearings. The various pin joints and cylindrical bearings will need attention according to the special circumstances of the case. The manner in which a joint or bearing has been working, both as to noise and temperature, will often serve as a guide to those which the most require attention. To examine the crosshead bearings the main points of the operation may be outlined as follows : (1) The crosshead with piston-rod and piston must be se- cured near or at the top of the stroke. This is sometimes done by inserting pins or bolts in the upper edge of the slide through the holes for securing the slipper, and allowing such to project over the top of the guide. Or otherwise it may be done by shoring in such way as may best be suited to the details of the case in hand. (2) The outer caps and brasses are removed. (3) A wooden chock lashed to the connecting rod is fitted between its upper end and the guide. This will serve to support the upper end when free from the crosshead. (4) The connecting rod sloping in such way as will bring the support of its upper end upon the chock, the turning engine is used to revolve the crank down until the parts are sufficiently clear to admit of the examination desired. To remove the crank-pin brasses the main points of the operation may be outlined as follows : (1) Starting with crank near its lower position the bottom cap is removed and landed on a bed suitably prepared for it. (2) The turning engine is then used to carry the crank up nearly or quite to the top of the stroke, where the crosshead is secured by hanging up or shoring as described above. (3) The upper brass is then secured and the crank is rotated down until the parts are sufficiently clear for the purpose in view. For like examinations of other parts, similar means will readily suggest themselves. For removing the lower brass of the main pillow-block bearings where it is in the form of a half cylindrical shell, it needs simply to be rotated out as noted already in Sec. 21 [ii]. A method sometimes used for this purpose is to clamp to the crank-arm a bar of steel carrying a projecting pin or bolt so placed that it will engage with the top face of the brass when 3 4 4 PRACTICAL MARINE ENGINEERING. rotated around. The upper cap and brass being then removed, the shaft is rotated carefully by means of the turning engine, and in this way the lower brass is forced around and up until free from its bed. Bearings and journals of this character may simply require readjustment, or refitting and adjustment as well. When the wear has been considerable, the liners or chock pieces between the brasses will need thinning, in order to reduce the clearance between the journal and the bearing to the propor amount. In order to measure the clearance under any given adjustment, a piece of lead wire is employed, of somewhat greater diameter than the clearance is to be. This wire is placed on the journal and the cap is screwed down hard, thus compressing it between the journal and the brass. The cap is then removed, and from the resulting thickness of the wire the clearance at any point between the journal and the brass may be readily measured. Such an operation is called taking a lead. Several leads, if de- sired, may be taken at once from a bearing, and will thus serve to map out quite satisfactorily the distribution of clearance, and thus to show when the proper adjustment has been made. The proper amount of clearance in any given case is somewhat a matter of judgment, and will, of course, vary with the size of the journal. In ordinary cases it may be made about .002 of the diamater. If time is limited the adjustment may be effected without the taking of leads, as follows : The chock pieces or liners are taken out and the nuts are tightened up till the brasses bear full on the journal. Their positions are then marked, and they are then backed off an amount determined by judgment or ex- perience with the particular circumstances of the case, and the liners are stripped to fit this adjustment. While this method is not as satisfactory as with leads, it is much quicker, and with experience good results may be obtained. In connection with the marking of the nuts for such pur- poses it may be recommended as a good plan to mark per- manently with a line and a numeral i, 2, 3, 4, 5, 6, the faces of all the large nuts likely to be used in making adjustments. An adjacent reference line on the bolt or on the metal of the bearing caps will then furnish means for making a record of each adjust- ment, or if no permanent record is desired, such me^ns will greatly facilitate making the adjustment in any given case. OPERATION, MANAGEMENT AND REPAIR. 345 The refitting of bearings and journals on shipboard does not usually extend beyond removing or smoothing rough spots caused by overheating and scoring. This may be done by filing followed by "lapping" with oil stone powder or dressing with an oil stone. In some cases emery is used, but great care is then necessary in order to remove all particles, as if allowed to re- main they will give trouble by continued cutting and grinding in the bearings. The brasses are similarly redressed, usually by scraping. The nature of the contact between the brass and the journal is tested by lightly smearing the latter with red lead and then applying the brass in place and lightly rotating : and forth. The high spots will then be shown by the red lead and may be further dressed down till a satisfactory fit is obtained. It may be noted that where brasses are thus fitted up each one may show a satisfactory fit when tried separately and with- out external constraint, and yet when in place they may be unable to come to the same relative positions on the journal and make satisfactory contact with it. For this reason it is prefer- able to test the contact with the brasses together and regularly secured in place. This is not always possible, however, by reason of the additional time required, and judgment in all such cases must be used, having in view the various circumstances of the case in hand. [3] Cross Head Guides. The main guides and cross head slides must receive atten- tion, both as regards cutting or uneven wear, and as regards the question of adjustment. The result of wear is to throw a cross-breaking stress on the piston-rod at each stroke, as the cross head is forced over by the oblique action of the connecting rod to a bearing on the guides. Care must therefore be taken that when the engine is turned without a load, the guide surface remains in full contact with the face of the slide, and therefore in a condition to support and guide the lower end of the piston- rod in a path consistent with the movement of the rod in the axis of the cylinder. If this condition is not fulfilled the neces- sary adjustments must be made in the manner be*t suited to' the structural arrangements of the case in hand. To remove the slipper or bearing piece for examination or refitting, screw eyes may be screwed into holes in its upper edge made for the purpose, and from these the slipper may be supported by means of wire rope or stout wire wound around 346 PRACTICAL MARINE ENGINEERING. a bar suitably supported and secured above the slipper. The bolts holding the slipper to the crosshead are then removed and the crosshead forced over by screw or hydraulic jack or other convenient means, sufficient to ease the pressure between the slipper and the guide. The slipper may then be lowered by using the bar as an axle and the rope or wire will readily follow down between the crosshead and guide surface. [4] Crosshead Marks. In connection with the adjustment of the moving parts of the engine it is well to have a mark on the crosshead and cor- responding marks on the guide, showing the extreme positions of the piston when in contact with the cylinder heads, top and bottom; also two marks placed slightly within the latter and showing the ends of the natural stroke, and a mark placed mid- way between the two latter, showing the location of the piston when in midstroke. The distance from the extreme marks to those showing the ends of the stroke, shows the amount of clearance proper between the piston and the cylinder heads when the former is at the ends of the stroke. This will vary with the size of the engine and character of the workmanship, but it is usually found between y and ^ or 24 inches, being a little more at the bottom than at the top, to allow for the general tendency of the parts to lower rather than to rise through the effect of wear. To determine these points a convenient reference mark is first placed on the crosshead. The connecting rod may then be disconnected and the parts hoisted up as far as they will go, or until there is contact between piston and head. A mark is then made on the guide corresponding to that on the crosshead. The parts are then lowered down as far as they will go, or until there is contact between the piston and the lower head, and anothef mark is made on the guide corresponding to that on the crosshead. The distance between these is then taken, and from it is subtracted the length of stroke. The remainder is then divided between the two clearances, top and bottom. Midway between the two inner points a point may be placed to indicate the location for mid or half stroke. Thus, if the stroke is 36 inches and the distance found as above is 37 inches, the I inch difference is to be divided between the two clearances, giving to the upper, say, 7-16, and to the OPERATION, MANAGEMENT AND REPAIR. 34? lower 9-16 inch. These differences are then laid off within the outside marks, and the points thus given will serve at any time as a guide for the adjustment regarding clearance proper, while the movement of the piston may be readily brought to conform to these limits by suitable adjustment of the liners or chock pieces in the joints and bearings of the connecting rod and crank-shaft. The 36 inches may then be divided equally and the mark placed to show mid stroke, such a point being some- times of use in connection with the setting of the valve. Another method of determining the clearance which is avail- able when the cylinders have manholes is as follows : The man- holes are removed and a number of balls of stiff red lead or other putty and faced with plumbago are distributed on the top of the piston and on the inside of the lower head. The engine is then given a revolution by means of the turning engine and the balls are collected. This method serves to show just how the clearance is distributed, and is therefore a valuable test for a bent piston-rod, a condition which will throw the piston out of position and give greater clearance on one side than on the other. [5] I/ining Up. An important feature, both of the original setting up of ma- chinery and of its overhauling and adjustment, is the determina- tion or correction of the alignment of the various moving parts. It is clear, of course, what the condition of proper alignment is. For a marine engine it may be briefly stated as follows : (1) The centers or axes of the main pillow block bearings should all be in one straight line, which will coincide with the crank-shaft axis, and which we will take as a standard or line of reference. (2) The axes or center lines of the cylinders should all be in the same vertical plane containing the center line of (i), and they must also be at right angles to this line. (3) The same vertical plane should also contain the axes or center lines of all the crosshead pins. (4) The axes or center lines of the crank-pins or crank-pin bearings in the connecting rods must also be parallel to the center line in (i). (fO The surfaces of the main guides must be parallel to the plane in (2). (6) The line shaft must be in line with itself, and unless a 348 PRACTICAL MARINE ENGINEERING. flexible coupling is provided between this and the crank-shaft it must also be in line with the crank-shaft, as determined by the line in (i). The same general principles, of course, control the align- ment of the valve gear and the various other moving parts, such as the starting, handling and drain gear, attached pumps, etc., but into these we need not go in further detail. The implements used in establishing the relation between these various lines and planes will naturally vary with the circum- stances, but are usually found among the following: The level, plumb line and square. The straight edge. The stretched wire or cord. Provision for using a line of sight. A straight line, such as that for a line of shafting, may be determined by either of the latter. The sag in a piano wire of known size and length and stretched with a known weight over a pulley is a matter which may be found by a computation, into which we cannot enter here, or, better still, it may be deter- mined in the open air by the aid of a surveying instrument with the usual cross hairs. A table giving the sag at various points between the ends for known lengths and for a known stretching weight will then give a leady means of establishing a straight line on board ship, by stretching the wire under the same con- ditions, and then setting upward at the various points the amount of the sag. A series of levels may thus be found which will give a true, straight line within the limit of the error in measure- ment. When a line of sight is used the following method may be employed : A board is fitted to the bearings at the extreme ends of the line to be run, a hole of some considerable size being made in the board at about the center. This hole is then covered with a piece of thin sheet metal having a small hole, say, 1-16 to % inch in diameter. These sheets of metal are adjusted by measurement until the small hole, as accurately as may be, is brought to the center of the bearing. Similar boards are then prepared for the other bearings or points at which it is desired to establish the line. A light is then placed at one end beyond the further hole, and the eye at the other end. An assistant then adjusts the intermediate pieces of sheet metal until the light reaches the eye through the entire series of holes. The centers OPERATION, MANAGEMENT AND REPAIR. 349 of these holes will then serve to establish a series of levels which may be marked on the pedestals, bulkheads or other convenient points, and which will serve to establish the line as desired. In lining up and adjusting the engine itself so that the various conditions (i)-(5) above are fulfilled, very much will depend on the accuracy and care with which the various pans have been machined in the shops. The gaps in the bed plate, which receive the main bearing boxes, should be planed out so that they are all in line. This is a matter which may be tested by a straight edge, or by measurements from a stretched wire. If the bottom brasses are then adjusted, all to the same thick- ness, they will evidently support the crank-shaft in line: This may also be further tested by reference to a line of levels, each of which is obtained by measuring the same distance upward from the bottom of each gap, and locating on the bed plate at any convenient point the level thus determined. This adjustment, it may be noted, will bring the axis of the crank-shaft parallel with the bottom of the gaps. Passing now to the columns, the seatings for their feet should have been planed at the same time as the gaps. This will bring the bottom of the feet in a plane parallel with the bottom of the gaps, and hence parallel with the axis of the crank-shaft. The columns and cylinders may now be erected and temporarily secured in place. The center line for each set of moving parts may be next determined as follows : A piece of board is placed across the top of the cylinder and secured at each end and ovei one or more stud bolts. Then, by caretul measurement or the use of a beam compass, the center of the bore at the top of the cylinder is located on the board. A small hole is then bored at this point and a fine wire is passed through and attached to a little frame, which will allow a few inches of the wire to show above the board. The lower end of the wire is then located in the crank-shaft axis by suitable measurement from the faces of the bed plate. The wire is then stretched between the two points, and the adjustment of the upper end verified by renewed measurement. If these parts come accurately to place we shall find that the wire will be truly central relative to the opening left in the lower head for the stuffing box, and hence it may be taken as the true center line for the cylinder as a whole. We shall also find the wire at ,-i constant distance from the guid^ sur- face on the column, thus proving the latter parallel to the center 350 PRACTICAL MARINE^ ENGINEERING. line, as required by (5) above. We shall also find the wire at right angles to the crank-shaft axis, as required by (2) above, and, of course, in a general way, at right angles to the bed plate transversely. Supposing these various conditions fulfilled for each center line separately, then we must see if they are all in the same fore and aft plane as referred to in (2) above. To examine this point we may try to look the wires "out of wind," as the ex- pression is, by standing aft or forward and trying, by sighting fore and aft, to bring all the wires accurately behind the nearest one. If these various conditions, for each wire separately and for all collectively, are not fulfilled, then the necessary adjust- ments must be made until they are brought into the required relations, as above specified. As a further adjustment to be made at this time, a wire may be stretched fore and aft along or near the guide surfaces, and at the same horizontal distance from each vertical center line. This will serve to show whether the guide surfaces stand in the right direction fore and aft, and hence, whether the plane of each is parallel to the central plane defined in (2) above. In setting up attached auxiliaries, such as air, circulating or feed-pumps, the principles used will be similar to those al- ready discussed, while the methods used will depend upon the particular circumstances of the case. If the seatings are located on the bed plate they will probably be planed at the same time as the main bearing gaps, and if the pump bases are faced at the same time they are bored, their axes will come at right angles to the seatings, and hence parallel to the axes of the main cylinders, and thus properly in line. In order to test the line of the crosshead pins the connecting rod may be hung from the upper end and allowed to swing partially free at the bottom. Then, by turning the engine into various positions in the revolution and measuring the fore and aft clearance between the crank webs and the faces of the lower end of the rod when thus relieved of constraint, the accuracy of the adjustment can be determined. This operation may be car- ried out in the following manner: Assuming that it is desired to test the adjustment in the case of an engine completely set tip, the cap on the lower end of the connecting rod is removed and the cross head is shored up in any convenient manner. The engine is then turned slightly by hydraulic jack or turning en- OPERATION, MANAGEMENT AND REPAIR. 351 gine in such direction as to carry the crank-pin away from the rod and thus leave the latter free in a fore and aft direction, so far as direct contact with the pin is concerned. Measurements are then taken, and the engine is next moved around so as to bring" the pin against its bearing again, and then on to a new position. Here the crosshead is again shored, the pin backed off measurements taken as before, and so on. In this way the piston, crosshead and connecting rod are carried around by resting on the crank-pin, and then in each position the connecting rod is freed by shoring the crosshead and backing off the crank-pin. In case the clearance between the crank-pin brass and the faces of the webs is too small to allow a possible irregularity of move- ments to show itself, the regular brass may be taken out and a dummy brass or wooden block, with sufficient clearance for all possible motion, may be fitted in its place. In locating a line shaft, a wire or line of sight may be used in the general manner above described. After locating the center of the stern tube at the stern post, the line is run to the after end of the crank-shaft or on through to the forward end, as may be desired, such point being located by measurement accord- ing to the drawings of the ship, engine seating and bed plate. In twin screw ships the centers at the after struts are located by measuring at the proper height the necessary distance out- ward from the center line of the stern post, at the same time squaring from this center line so as to bring both centers at the same height above the keel. The two lines are then set at the forward end at equal distances from the keel at the proper height, in accordance with the drawings. In most cases the shafts are not parallel with the keel, either in a vertical or horizontal direc- tion, usually inclining outward from forward aft and either up- ward or downward, according to the size of the ship and other circumstances of the case. In the examination of the adjustment of machinery which has been already in operation, as in the routine care of marine engines, it is not to be supposed that the preceding operations in all their details will be necessary. Judgment must be used, having in view the particular points to be examined, and the best means of effecting such examination in acordance with the general principles above discussed. Thus the fairness of the line shafting must be tested occa- sionally, lest, as time goes on, wear in the bearings or changes in 352 PRACTICAL MARINE ENGINEERING. the structure of the ship may throw it seriously out of line. For this purpose the following method may be used : Three or more laths or battens are provided with a straight edge on one side. These are then placed across the shaft on the upper side, as nearly horizontal as judgment may indicate, being located at successive points along the line of shafting to be examined. A line of sight is then taken along the projecting lower edges of the battens and by adjustment they are brought parallel to each other. Then, if they can all be brought into one line the shaft itself is in line. If not, the shaft is out of line in the vertical direction, and, by blocking or other similar adjustment, until the battens are all brought into one line the amount by which the shaft is out at one point relative to two others is readily de- termined. In a similar manner the line in the horizontal direction may be tested by holding the battens vertical against the side of the shafting. This method presupposes, of course, that the shafting throughout the part tested is all of the same size. Instead of placing the battens on the shafting they may be placed on the couplings quite as well, supposing, of course, that the latter are all of the same size. Another test which is sometimes used consists in slacking the coupling bolts at a coupling near which it is suspected that the shaft is not in line, and noting whether there is any tendency for the two parts of the coupling to open out on one side or another. Such an opening out then shows an unfairness in the line in one way or another, according to the side on which it appears. [6] Valve Gear. In the routine examination of the valve gear the points to be looked after are wear and lost motion in the excentrics and excentric straps, in the link block brasses of the Stephenson link, or in like parts of other forms of valve gear, in the various pin joints and connections, and abrasion or uneven wear in the valve faces or seats. In the case of the excentrics and straps and various pin joints, the wear may be taken up by the adjustments usually provided and in the general manner already outlined for other similar parts. Excessive or irregular wear in a flat slide valve or seat may require either resurfacing or renewal, accord- ing to the circumstances of the case. With piston valves, es- pecially if not fitted with rings, excessive wear in either valve OPERATION, MANAGEMENT AND REPAIR. 353 or seat will mean a serious steam leak, and will usually call for new parts, either for valve or seat or both. [7] Thrust Bearings. The most common trouble with thrust bearings is scoring or irregular wear of the bearing surfaces, or a general wear which may allow the thrust shaft to move forward sufficiently to put a pronounced thrust on the line and crank-shafts. This will result in heating and wear, and may throw the crank-shaft bearings out of line. A little clearance is usually allowed in the shaft couplings and in the fitting-up of the crank-shaft and crank- pin bearings, so as to insure freedom from end thrust for the crank-shaft as a whole. If the wear at the thrust collars should exceed this, then a part of the thrust would be transmitted to the crank-shaft, with effects as above noted. With adjustable or horse-shoe collars this trouble is readily adjusted by moving the collars back by means of the adjusting nuts provided. With the plain type of thrust bearing as in Fig. 149 the bearing as a whole must be moved slightly aft by means of the screws provided for the purpose. [8] Circulating Pump. The engines for operating such pumps require the care necessary in all machinery of such type, the principles of which have been already discussed. The runner simply needs examina- tion from time to time to make sure that it is running freely, but without undue clearance on either side in its casing. Trouble is often met with in the maintenance of circulating pumps by the choking of the inlet passage, valve or strainer by marine growth of one form or another. To aid in freeing the strainer and inlet passage a connection is often made with the delivery of one of the fire or other auxiliary pumps by means of which they may often be cleared without the need of regular over- hauling. [9] Condensers. The chief troubles to be expected with condensers are as follows : (1) Leakage about the tube ends through the packings from the salt water to the steam side. (2) Corrosion and pitting of the tubes, resulting ultimately in the development of holes or the breaking of the tubes and similar leakage, as in (i). 354 PRACTICAL MARINE ENGINEERING. (3) Fouling of the tubes with oil deposit on the condensing surface, thus decreasing the heat conductivity of the metal and the efficiency of condensation. The condenser heads or bonnets must therefore be taken off from time to time and the condition of the tube ends and pack- ings examined with reference to the matter of leakage and general condition. To test the condenser for leakage the main inlet and out- board valves should be tightly closed, and the connections to the low pressure cylinder and air pump closed by blank flanges. The condenser heads may then be taken off and the steam side filled with water while a watch is kept for leaks on the tube sheets at each end. It is also desirable to be able to put, by means of a hand-pump or otherwise, a pressure of 15 or 20 pounds per square inch on the contained water, thus making the development of the leak more certain. It is sometimes desirable to be able to identify both ends of the same tube. This may be readily done by passing a wire through from one end to the other. In some cases a lamp held at one end will serve the same purpose. When provided with bonnets for the purpose, the steam side of the condenser must also be occasionally opened and the tubes and interior surfaces examined, with reference to grease coating and general condition. Where there may be any doubt as to the condition of the tubes in the interior, a few should be drawn when the heads or head bonnets are removed, and their condition determined. So far as the accumulation of grease is concerned, the con- denser may be cleaned by the use of hot soda or lye water, care being taken to wash it out thoroughly so as to remove any excess of the alkali. When soda is used for the boilers it is some- times introduced into the condenser, there entering the feed water and then passing on to the boiler. It may be questioned, however, whether this is the best plan, as accumulations of grease only partly converted to soap may thus be carried into the boiler, there giving trouble, as already referred to under that head. Zinc plates are often used on the salt water side in condenser heads to protect against corrosion, in a similar manner as ex- plained for boilers in Sec. 40. The condition of these plates and of their attachment to the shell should be carefully noted when OPERATION, MANAGEMENT AND REPAIR. 355 the condenser is opened, and such repairs made as may be required. [loj Air Pumps. The head, foot and bucket valves require the most frequent and careful examination. They often tend to become coated by an accumulation of a black, greasy paste formed from the cylin- der oil and the material of the wasted zinc plates, if such are used. This accumulation may prevent their proper working, and they should be carefully cleaned as occasion may offer. With air pumps attached to the main engine, and where the number of strokes is usually greater than with the independent pump, the valves sometimes give trouble by severe pounding against their seats and guards. This is due to their inertia, and is likely to be more severe as the valves are heavier and have more litt. Light metal valves of sufficient number and size to allow of moderate lift are therefore to be preferred for all such purposes. (See Figs. 185, 186). [n] Pumps in General. The chief troubles to be expected in the operation of the various forms of independent pumps found on shipboard are as follows : (1) In the water end the plunger rings or packing or the barrel may become worn, thus allowing considerable leakage or "slip," especially under high pressure, as in boiler feed pumps. (2) The water valves, either inflow or delivery, may become worn or deranged, and thus fail to hold the water as they should, so preventing the proper operation of the pump. (3) In the steam end the piston rings or cylinder barrel may be.-ome worn, allowing steam to blow from one side to the other and decreasing the effective steam load on the piston. (4) The main steam valve or more often some part of the auxiliary steam operating gear may become worn or deranged so that the pump can no longer properly operate under steam. These various troubles must be guarded against by periodi- cal examination of the points mentioned with a view to wear or derangement of any kind whatever. [12] Piping. Steam piping of copper if properly constrained may become brittle and weakened in spots by long continued expansion and contraction. An indication of this mav often be found in the 356 PRACTICAL MARINE ENGINEERING. wavy or irregular condition of the surface. Such pipe should, of course, be replaced at the first opportunity. A repair may, however, be made by banding with screw clamps made of strap iro-i or steel and closely spaced over the suspected part. Small holes which may sometimes develop may be treated with a soft patch held in place by a screw clamp, by filling with solder, or by a patch as in Sec. 42 [2] (10), according to the cir- cumstances of the case. Leakage and like trouble with steel piping may be treated by the same general means as for boilers, and as discussed in the preceding section. Sec. 44- SPARE PARTS. In order to provide for the results of regular wear, and for the possibilities of accident it is customary to carry a certain number of spare parts, especially of those most likely to require replacement either as the result of wear or accident. The pieces carried and their number will depend entirely of course on the extent to which it may be necessary or desirable to fit out the ship with provision for such wear and emergency. No attempt will therefore be made to give any complete list of such parts, but among those more commonly carried the following may be mentioned : Grate bars, bearers and dead-plates, furnace and ash- pit doors, boiler tubes, manhole and handhole plates with fit- tings, safety valve springs, boiler gauge cocks, fittings for boiler water gauges, feed check valves, bottom blow valve, surface blow valve, piston and pump rods for the various pumps, valves, valve guards and springs for the various pumps, follower bolts, nuts and springs for the various steam pistons, brasses for the various bearings, horseshoes for the thrust bearing, propeller blades, valve stems, metallic packing for the various stuffing "boxes where it is used, shaft coupling bolts, emergency shaft coupling, condenser tubes and glands, evaporator and distiller tubes, evaporator coils, one section of crank-shaft, if made in sections. Sec. 45. LAYING UP MARINE MACHINERY. The chief dangers to marine machinery when not in use arise from the likelihood of rust and corrosion. Fundamental prin- ciples relating to these chemical changes have been discussed in Sec. 40, and by reference to that point it will be seen that the chief points to be attended to relate to the protection of the sur- face from moisture and corroding acids. Where applicable a OPERATION, MANAGEMENT AND REPAIR. 357 good metallic paint well laid on will be found the most efficient and satisfactory. In such case the surfaces must be dry and well cleaned in accordance with the principles discussed in Sec. 42 [i] (10). For finished surfaces or bright work generally, where paint would not be suitable, a coating of heavy cylinder or other like oil may be used, or perhaps even more commonly a mixture of white lead and tallow in about equal proportions. Either of these will efficiently protect the surfaces and will remain for a long period of time without becoming too hard to admit of ready removal, especially with the aid of a little kerosene or other light oil. One of the most important features connected with the lay- ing up of marine machinery is the getting rid of water contained in the various cylinders, pipes, bends, valve chambers, etc. The draining off of the water is, of course, of importance relative to the question of rust and corrosion, but it may be of even still greater importance relative to the question of freezing and possible rupture of the chamber, casing, or pipe containing the water. Many a cracked cylinder or valve chest or globe valve chamber, or split in pipe elbow or bend, or in boiler or condenser tube, etc., has been due to incomplete drainage of water and subsequent freezing. In laying up marine machinery, therefore, where there is any liability of freezing, a systematic study must be made of the piping systems, pockets, etc., where water might collect and by freezing result in damage. These remarks apply especially to piping and fittings, to small auxiliaries, to the con- denser, and to water-tube boilers. If the proper drains are not fitted and the water cannot be gotten out in any other way, then the necessary joints should be broken and the water removed in this manner. 358 PRACTICAL MARINE ENGINEERING. CHAPTER VII. VALVES AND VALVE GEARS. Sec. 46. SI/IDB VAI/7ES. [ij Simple Slide Valve. In Fig. 207 VW represents a simple slide valve, supposed to be surrounded by live steam in the steam chest C C. P and Q c Fig. 207 Plain Slide Valve, Mid Position. are the^ ports leading to opposite ends of the cylinder as shown, while E is the exhaust port or passage leading to the condenser or to the air, as the engine is condensing or non-condensing. It is the business of the valve, as we shall explain later, to move Fig. 208. Plain Slide Valve, Position for End of Stroke. back and forth, thus alternately uncovering the ports P and Q and admitting steam from the chest to the ends of the cylinder. While the steam is thus being admitted at one end of the cylin- der, it must be allowed to escape from the other to the exhaust VALVES AND VALVE GEARS. 359 passage E, and thus the piston is moved to and fro in the cylin- der and the operation of the engine becomes continuous. If we suppose in Fig. 207 that the valve is in the middle of its travel back and forth, or in mid posi- tion as it is commonly called, then the distance A B by which the edge of the valve on the steam side extends over the edge of the port is called the steam lap. Similarly the distance CD by which the edge of the valve ex- tends over the port on the exhaust side is called the exhaust lap. In Fig. 208 let the piston be at the end of the stroke and the valve in the position shown. Then the distance A B by which the port is uncovered to steam is called the steam lead, while the distance CD by which the other port is uncov- ered for exhaust is called the exhaust lead. In gen- eral, therefore, lead is the amount by which the valve is open when the piston is at the end of the stroke. In Fig. 209 are shown a series of corre- sponding positions for valve and piston during a single stroke of the latter. The position a is the same as that of Fig. 208 and the port is open for the 36o PRACTICAL MARINE ENGINEERING. .admission of steam on I he left and for exhaust on the right. The piston is at the end of the stroke and just about to begin the stroke to the right. In b the piston has advanced about 10 per cent, of the stroke, and the valve has moved so that the port is nearly wide open. Up to this point the piston and valve have been moving in the same direction. In c the piston has advanced to about 60 per cent, of the stroke, while the valve has come back and has just closed the port to the entrance of steam. This is called the point of cut-off. Between b and c the piston has been moving on, but the valve has been moving back in the opposite direction. In d the piston has moved still further on while the valve is still moving to the left, and has just reached the point where the exhaust opening on the right is closed. This is called the point of exhaust closure, and the operation of com- pressing the steam in the end of the cylinder from this point to the end of the stroke is called compression or cushion. In e the piston is still nearer the end of the stroke on the right, while the valve has moved farther to the left, and is just about to open the port on the left for exhaust, thus allowing the escape of the steam which entered during the early part of the stroke. In f the piston has nearly reached the end of the stroke. The exhaust opening on the left is open still wider, while the port on the right is just about to open for steam. In g the piston is at the end of the stroke, the valve has moved so as to make the steam and exhaust openings still wider, and the return stroke is about to begin. This completes the history of the stroke, and the next or return stroke follows after it with like series of events, and so on con- tinuously. [2] Double Ported Slide Valve. The valve shown in the above diagrams is called single ported because it covers but one set of ports or openings. A double ported. valve is shown in Fig. 210. This is a form of valve within a valve. Thus taking one end of the valve we have at AB one set of edges respectively for steam and exhaust, and at A! Bj another like set. Steam surrounds the outside of the valve and is therefore ready to enter the port P past the edge A when the valve moves suffi- ciently to the left. Steam likewise enters freely at the side into the passage S, and is therefore ready to enter the port P l past the edge A Jt as the valve moves to the left. Similarly as the valve moves to the right the ports P and P! are open to exhaust past the edges B and B 1? respectively. The passage E t leads VALVES AND VALVE GEARS. 361 over the transverse passage S, and thus the entire exhaust finds its way into E the outlet passage. With a double ported valve the area of the port opening required may be obtained with a travel of valve only one-half that for a single ported valve, or with the same valve travel, twice the area of port opening may be obtained. It is this feature which often leads to the use of a double ported valve where it is desired to obtain a relatively large opening with small travel of valve. [3] Piston Valve. The face of the valves in the types so far noted is a plane, or in other words, they are flat slide valves. If now we can imagine such a valve wrapped up so as to form a cylinder with the valve ? B LONGITUDINAL SECTION. CROSS SECTION AND END VTEW. Fig. 210. Double Ported Valve. stem for axis, we shall have a cylindrical or piston valve as shown in Figs. 211, 214, 215. This consists essentially of two heads connected by an intermediate body, as shown. The steam enters past the outside edges, for example, and exhausts past the inside edges to the exhaust passage, in a manner entirely similar to that for the plain slide valve as above described. Otherwise the steam may enter past the inside edges and exhaust past the out- side as described below for the inside valve. The steam port and passage consists of an annular channel surrounding the valve and connecting with a passage leading to the end of the cylinder in the manner shown. The valve is placed somewhat out of center with reference to this annular passage, so that it is quite shallow on the side opposite the cylinder, and gradually increases in depth toward the side nearest the cylinder. This arrangement, 362 PRACTICAL MARINE ENGINEERING. which is shown in Fig. 212, gives a cross-sectional area of pas- sage varying in proportion to the amount of steam flowing through it, as may be seen by noting in the figure the natural direction of flow of the steam, radially outward through the Marine Engineering' \> Fig 211. Piston Valve. port opening, and then curving around to flow toward the cylinder. Comparing the two forms of valve it is readily seen that in the piston valve the outer circumference represents the active VALVES AND VALVE GEARS. 363 part of the valve, and corresponds to the plate AB of the flat slide, as shown in Fig. 210. The great advantage of the piston valve lies in the fact that it is perfectly balanced as regards the steam pressures which act upon it. It is readily seen that the flat slide valve is forced against its seat by the excess of the pressure on its back over that on its face, which excess will in the usual case be large, and will give rise to a heavy frictional load to be overcome by the excentric acting through the valve stem. The piston valve, on the contrary, is forced equally in all directions, and hence moves Fig. 212. Section Through Valve Chest and Cylinder. freely so far as the steam forces are concerned, and with only such frictional resistance as may be necessary to insure tight- ness against steam leaks. In order to keep the heads of the valve steam tight they have been very commonly provided with one or more packing rings of similar character to those used on the main piston, but usually without auxiliary steel springs to force them outward. Such an arrangement is shown in Fig. 215. In the latest prac- tice, however, especially for quick-moving engines, the special rings are very commonly omitted entirely, dependence being 364 PRACTICAL MARINE ENGINEERING. placed on a good working fit at the start and on the rapid re- versals of motion, to reduce the leakage to a negligible amount. Such arrangements are shown in Figs. 211 and 214. In the latter a solid working ring is fitted as shown, in such manner that it may be readily removed and replaced with a new one as occasion may require. The valve seat is usually a separate piece of hard and fine grained cast-iron, fitted as shown in Fig. 211. The ports in this seat instead of being continuous all around, thus dividing the seat into separate parts, are usually bridged over at several points distributed about the circle. The head of the valve is thus car- ried across from one side to the other, and is prevented from catching or jamming, as would very likely occur without such bridging. Where valve packing rings are used it is especially necessary to provide such bridging in order to prevent the ring from springing out into the port opening, and thus jamming the valve, or causing other damage. In Fig. 213 is seen the de- velopment or lay-out of the port for the valve shown in Fig. 215. J/ai*in< Engineering Fig. 213. Development of Piston Valve Port. The bridges are placed on the slant so as to distribute as much as possible the wear on the valve rings. In the case of wear on the valve seat or rings, they may be replaced with new. When rings are not used the wear is usually less rapid, thus furnishing a further reason for their omission. The valve itself, however, will slowly wear, and as necessity may require a new head or new valve entire may be fitted. In some cases where a piston valve takes steam on the out- side, it is desired to lead the steam to the chest at one end only, and then to pass it down to the other end through the inside of the valve. In such case as shown in Fig. 215 the body of the valve is made hollow and as large as possible, thus connecting the steam chest at top and bottom as desired. The valve stem passes through the center of the valve and is usually secured with nuts at top and bottom, as shown in the figures. In case the valve is hollow for the passage of steam VALVES AND VALVE GEARS. 365 between the two ends, the stem must be carried in bosses sup- ported by radial arms connected with the valve heads, and as small as possible in order to present the least resistance to the flow in either direction. Figs. 214, 215. Piston Valves. [4] Equilibrium Piston. The work of moving the valve up and down which is thrown on the excentric may be much decreased by fitting an equilibrium piston as shown in Fig. 215 The cylinder in which this is fitted is open at the bottom to the valve chest, and hence the full 3 66 PRACTICAL MARINE ENGINEERING. pressure of the chest acts constantly on the lower side of the piston. This may be so proportioned as to carry practically about all the direct weight of the valve, which thus floats on the steam, requiring comparatively small effort on the part of the excentric. to move it back and forth. Fig. 216. Joy Assistant Cylinder. [5] Joy's Assistant Cylinder. A further development of the equilibrium piston is found in Joy's assistant cylinder, as shown in Fig. 216. The purpose of this fitting is to more perfectly carry the weight of the valve uric! relieve the excentric and valve gear of the work required to VALVES AND VALVE GEARS. 367 move the valve. The cylinder is provided with steam and ex- haust ports, and in fact with its piston forms a small steam en- gine. The form of the piston as shown is such that it forms its own valve, thus simplifying the number of parts required. Power for assisting the main valve gear is thus obtained by the ad- mission of live steam to the assistant cylinder, and the ports are so arranged that cushioning at the ends of the stroke in this cylinder absorbs the forces due to inertia. An important ad- vantage claimed for such types of assistant cylinder over the ordinary equilibrium piston as in Fig. 215 is a considerable de- crease in weight, the greater efficiency of the apparatus for the purpose in view allowing of the use of smaller sizes. Such forms of equilibrium piston may, of course, be fitted to advantage with either the flat slide or piston forms of valve. [6] Equilibrium Rings. With a flat slide valve as in Fig. 210 the full steam chest pressure acts constantly on the back of the valve, while a much decreased pressure will act on a part only of the other side. In Fig. 211. Section Through Equilibrium Ring. consequence, the valve is forced with strong pressure against the seat and the frictional force thus developed must be over- come by the excentric. (See Sec. 73). With large valves and where the lubrication is scanty this may become excessive, 3 6S PRACTICAL MARINE ENGINEERING. causing the valve and seat to cut, and throwing a great deal of unnecessary work on the excentric. To relieve this condition, equilibrium or balance rings are often fitted on the back of the valve. Such an arrangement is shown in Fig. 217. The inner face of the valve chest carries a ring of metal within which is cut a groove as shown. Within this groove is a ring which is forced against the back of the valve by springs and screw ad- justment as shown. The back of the valve is faced off and thus a joint is made between the two, while the space within the ring and between the back of the valve and face of the cover is shut off from the steam within the valve chest, and hence this part of the valve is relieved from the pressure of the steam. In addi- tion to this, the space is sometimes connected by piping to the steam side of the condenser, thus bringing on this part of the back of the valve only the pressure in the condenser. In this way the load on the back of the valve and the resultant load on the excentric may be much decreased, and the opera- tion of the valves will be correspondingly smoother, and less work will be thrown on the excentrics and valve gear in general. There are several methods varying in detail for the fitting of the ring in such an arrangement, and in the formation of the joint between the ring and valve chest cover, but the principle is the same in all, and is sufficiently illustrated by the arrange- ment of Fig. 217. [7] Outside and Inside Valves. In the preceding figures for valves the steam enters past the outside edges and exhausts past the inside edges. Such is known as an outside valve. In some cases, However, it is con- Fig. 218. Inside Valve. venient to have this relation reversed, and to take steam past the inside edges, and exhaust past the outside edges. Such a valve is shown in Fig. 218, and is known as an inside valve. Live steam fills the space A and enters the port P past the VALVES AND VALVE GEARS. 369 edge C, while exhaust occurs past the edge F. The valve as here shown is in midposition and therefore C D is the steam lap and E F the exhaust lap. The only difference in the two forms of valve is in the relative amounts of outside and inside lap. In each case, for reasons which will appear later, it is seen that the steam lap is greater than the exhaust, being in one case on the outside and in the other case on the inside. It is also clear that the outside valve moves with the piston at the beginning of the stroke, and opposite to it during the latter part, while with an inside valve it moves opposite to the piston at the beginning, and with it during the latter part of the stroke. Sec. 47. MOTION DUE TO SIMPLE EXCENTRIC AND ITS REPRESENTATION BY VAI,VE DIAGRAMS. [i] Simple Excentric. We must now inquire by what means the valve can be given the motion necessary for the proper distribution of the steam as above described. The simplest of such means is the plain excentric as shown in Fig. 219. This consists of a cir- cular disc with center A set on the shaft excentric or out of the center. The distance between the two centers is seen to be OA. This is called the eccentricity or throw of the excentric." About the excentric is a strap ST, and attached to this is a rod RR. db Fig. 219. Plain Excentric, Skeleton of Motion. As the shaft turns, the excentric turns with it, and thus gives to the rod a to and fro movement exactly as though it were a connecting rod attached to a crank OA. This principle of the equivalence between an excentric and a crank of equal throw is very important, and the motion should be studied until it is quite clear that the operation of an excentric is exactly the same as that of a small crank of throw equal to that of the excentric. or to the distance from the center of the excentric to the center of *Some writers understand by tlie term throw * twice the above distance. In the present work we understand the term to refer to the distance OA as stated. 37 o PRACTICAL MARINE ENGINEERING, the shaft. For purposes of illustration therefore we may rep- resent the excentric by a crank of equal throw. With this understanding let us again examine Fig. 209, on the left, when it is readily seen that the series of movements de- sired is exactly such as would be given by a small crank located at an angle somewhat more than 90 degrees ahead of the main crank. Or, in other words, with the valve stem attached to such a small crank or excentric, the valve will be so moved' that the piston will be forced to and fro in the manner described in Sec. 46 [i], and the main crank will follow the motion of the excentric. This is what is meant by saying that with a slide valve connected as in the diagrams, the excentric leads the crank. In regard to the angle between the crank and excentric it is clear from the diagram of Figs. 207, 209, that starting with the valve in mid position, it must move a distance equal to the lap before the port will begin to open. Hence when the piston is at the end of the stroke the valve must already have moved from its mid position by an amount equal to the lap plus the lead. Suppose now that the excentric is loose on the shaft and may be adjusted as desired. In Fig. 220 let C denote the crank on the center. Then suppose the excentric first located 90 ahead of O C as shown at O A, where O A=O B= excentric throw. Then neg- lecting the slight effect due to the obliquity of the excentric rod, the valve will be in its mid position, as shown in Fig. 207. Next, move the excentric ahead until the valve has moved a distance equal to the lap plus the lead as in Figs. 208, 220. This gives the final location of the excentric for the proper operation of the valve, as already described. The angle AOB through which it is thus necessary to move the excentric in order to affect this move- ment of the valve from its mid position, or more exactly the angle between the excentric and the line at right angles with the crank we shall term the angular advance. This term is sometimes used in reference to the entire angle between crank and excentric, but we shall prefer to understand by the term the angle as defined above. The angular advance is usually denoted by the letter tf. With the arrangement of gear shown in Fig. 220 the angle be- tween crank and excentric will therefore be 90+^ In regard to the direction of motion of the crank, it is clear that when the piston is at the end of the stroke and the crank on the center, the latter must start off in such direction as will in- crease rather than decrease the opening of the port for steam. VALVES AND VALVE GEARS. 37i IfJ the connections and arrangements of a valve gear are known no matter how complicated, this principle will always furnish an answer to the question as to the direction in which the engine will turn. Thus in the direct connected gear, as in Fig. 220, with the piston at the end of the stroke, the crank moves in the same di- rection as the excentric, or follows it, simply because that is the direction which opens the port still wider for steam admission. Fig. 220. Diagram Showing Connections for Simple Valve Gear. With an inside valve the excentric is set 180 behind or directly opposite the position for an outside valve, as shown in Fig. 221, or at OBj, Fig". 220. In such case the angle between the crank and excentric is 90 d or the angle $ is set off toward the crank from the 90 position. It is readily seen that this will bring the valve slightly open when the piston is at the end of the stroke, and that the crank will move leading the excentric because this is Fig. 221. Inside Valve and Location of Excentric. the direction which opens the port wider for steam admission. It is also seen that to fulfil the same purpose the piston and valve at the end of the stroke must move in opposite directions. In some cases the valve-rod instead of being directly con- nected to the excentric rod is worked through a rocker-arm, which reverses the motion as compared with the direct connected gear. See Fig. 222. This provides a second mode of variation 372 PRACTICAL MARINE ENGINEERING. VACVE STEM Marine Engin.ef.nnj Fig. 222. Diagram for Valve Connections Through a Rocker Arm. which may affect the arrangement of a valve gear, giving in all four combinations, as shown in the following table : Valve. Connection. Outside Inside Outside Inside Direct Direct Rocker Rocker Angle Between Crank and Excentric. 90 + A 90 c 90 (J 90 -f 6 Which Leads. Excentric Leads Crank Leads Crank Leads Excentric Leads [a] Oval Valve Diagram. We will now proceed to an examination of the effects due to varying the steam and exhaust laps, and the angle of advance [i]. This may be done most conveniently by the aid of a dia- gram. In Fig. 223 let AB represent to any convenient scale the path of the piston. Then from the various points of AB corre- sponding to a series of successive piston positions, let the dis- tance of the valve above or below its mid position be laid off, and the points thus found be joined by a continuous line. For a revolution or double stroke the result will be found somewhat as represented by the curved line of the diagram. Thus at the lower end of the stroke, say at B, the valve will be at a distance BT above mid position. When the piston has gone on to S it will be at a distance SJ,at R a distance RK, at P a distance PL, at N it will be in mid position, and will then pass below] and reach a distance AV at the end of the stroke A. On the return stroke the valve will pass through a similar series of locations deter- mined by the distances from AB downward to the curve. With this arrangement of diagram the movement of the valve above mid position is laid off above the line AB and vice versa. With an outside valve this shows above the line AB the events for the ///> stroke and below the line the events for the down stroke. VALVES AND VALVE GEARS. 373 With an inside valve the relation is reversed, the events for the up stroke being shown below the line and for the down stroke above the line. We have already seen that starting from mid position the valve must move a distance equal to the steam lap before the port begins to open for steam. Suppose then, that BF is laid off equal to the steam lap on the lower end of the valve, and a line FL drawn parallel to BA. Then it is clear that the remaining distances from FL upward to the curve ZTKL give the dis- : /x s Fig. 223. Oval Valve Diagram. tances which the edge of the valve travels beyond the first edge of the port, and hence if the port is sufficiently wide, the actual widths of port opening. At R the farthest distance is reached, and the edge of the valve is at a distance OK beyond the first" edge of the port. It is clear that the distance RK is the throw of the excentric, and that this is equal to the lap plus the greatest width available for port opening. If the width of port is equal to or greater than OK, then the total movement OK can be utilized for opening -and will be its greatest value, while the vari- 374 PRACTICAL MARINE ENGINEERING. ous distances from FL to ZTKGL will give the entire history of the width of port opening for corresponding positions of the piston. Very often, however, the width of port is less than the distance OK. In such case draw a line IJ parallel to LF and at a distance from it equal to the width of the port. Then it is clear that the widths of port opening will be given by the distances from FL to the lines ZTJIL. Full opening is reached at J or with piston at S. This continues to I, or until the piston reaches Q. The port closes at L or when the piston reaches P. This is known as the point of cut off or steam closure. Similarly the port opens at Z just before the end of the stroke, and at the end is open a distance FT, which therefore represents the steam lead. Having thus obtained a general idea of the nature of this diagram let us examine by its aid the effects of a change in the steam lap. This corresponds to raising or lowering the line FL, and it is readily seen that the results of an increase, for ex- ample, are as follows : earlier cut-off, steam opening nearer the end of stroke, decreased lead, decreased port opening all the way through. The results of a decrease of lap are of course in the opposite direction respectively. In a similar manner we may examine the influence of a change in the exhaust lap. This is illustrated in the same figure where M Y is the lap line laid off at a distance B D from the center line, equal to the exhaust lap on the upper end of the valve; that is, on the end which opens the port to exhaust by moving above the mid position. It is thus seen that the valve opens to exhaust at Y with the piston a distance Y D from the end of the stroke, while at the end of the stroke it is open a dis- tance D T the exhaust lead. Then during the following stroke the distance of the exhaust edge of the valve from the corre- sponding edge of the port is given by the distance from D M to the curve T K L M. At M the port closes, and for M C, the remainder of the stroke, the steam undergoes compression in the cylinder. Usually the width of port is somewhat less than the total distance available, so that the full movement of the valve cannot be utilized for actual opening. In such case draw a line G H parallel to M Y and distant from it an amount equal to the width of port. Then full opening is reached at H with piston at W and continues to G with piston at U, the openings for the remaining portions of the stroke being given by the distance from M D to Y T H and G M. VALVES AND VALVE GEARS. 375 An increase of exhaust lap is thus seen to produce the fol- lowing results : earlier exhaust closure and longer compression, exhaust opening or release later or nearer the end of the stroke, decreased exhaust lead, decreased port openings or decreased time during which the port is wide open. A decrease of exhaust lap will of course, produce results in the opposite direction. We have thus far been concerned with the influence of an increase or decrease in the steam or exhaust lap. It remains to examine the influence due to a change in the angle 3 the angular advance. If this angle is increased and the new series of valve movements plotted as in Fig. 223, it will be found that the oval becomes narrower and touches the boundary lines nearer the Fig. 224. Oval Valve Diagrams. corners, as shown in Fig. 224. Similarly with a smaller value of d the valve oval will become wider or rounder, and will touch the boundary lines farther from the corners, likewise in the figure as shown. Remembering this and comparing Figs. 223 and 224 it is readily seen with the same values of the lap that changes in the various quantities will take place as shown in the tabular ar- rangement below. This table shows at a glance the variation in the various events due to change in the three items above the double line, as explained in the foregoing. 3 7 6 PRACTICAL MARINE ENGINEERING. Attention may also be called at this point to the diagram of Pig. 225, in which the various quantities for an outside valve are lettered and named in position. A careful study of this figure in connection with the valve positions of Fig. 209 will be of great aid in acquiring a good understanding of the operation of a slide valve, and of its representation by means of such a diagram. If the measurements for the diagram are taken from an actual engine or from a properly constructed model, it will be found that for the down stroke the curve is more humped or Angular Advance Increase Decrease Steam Lap Increase Decrease Exhaust Lap Increase Decrease Steam Opening Earlier Later Later Earlier Steam Closure Earlier Later Earlier Later Steam Lead Increase Decrease Decrease Increase Exhaust Opening Earlier Later Later Earlier Exhaust Closure Earlier Later Earlier Later Exhaust Lead Increase Decrease Decrease Increase Greatest Port Opening Same Same Decrease Increase rounded than for the up stroke, as shown in the figures above. That is, for the same relative positions of piston the valve will be farther from the center line on the down than on the up stroke. This is an effect due to the angularity of the connecting rod of the engine, and it results that the various points of opening and closure, and the values of lap, lead and port opening cannot be made the same for both strokes. As is shown by the diagram the cut-off is usually later on the down than on the up stroke, and it cannot be equalized without a serious derangement of the VALVES 4ND VALVE GEARS. 377 other events. Instead of attempting to equalize any two feat- ures such as steam lead, cut-off or port-opening, it is usually bet- ter to so adjust the steam and exhaust laps above and below that the resulting combination of events shall represent the best com- promise possible under the circumstances. If it were not for the effect due to the angularity of the connecting rod, the curve would be an ellipse, and the distribution of the events for both strokes could be made the same. see EOT EOB SOT SCT S O B=Steam Opening Bottom. E O T= Exhaust Opening Top. E C B=Exhaust Closure Bottom. S C T= Steam Closure Top. .'/urine Enginttring S C B= Steam Closure Bottom. E C T= Exhaust Closure Top. EO B= Exhaust Opening Bottom. S O T Steam Opening Top. Fig. 225. Oval Valve Diagram. [3] Bilgram Valve Diagram. In Fig. 226 let a circle be described with OP as radius equal to the throw of the excentric. Then draw the radius OP at an angle 6 (the angular advance) with the horizontal or line AB. Then draw CD above AB at a distance LM equal to the lead. Then from the point P as center and with PQ as radius describe a 378 PRACTICAL MARINE ENGINEERING. circle tangent to CD. Also on OP as a diameter describe a circle as shown. Then let A x be any position of the crank. Draw the radius AjO and extend it back to cut the circle on OP at E. Then the properties of this diagram are such that the movement of the valve from mid position is given by the distance PE, while the port opening will be less than this by PQ or PF the radius of the circle about P as center. This radius equals the steam lap, and the circle is for that reason known as the lap circle. It follows that EF is the port opening, or at least the travel of the edge of the valve beyond the edge of the port. The same con- struction holds for all other crank positions, so that we have here a means of representing by straight lines and circles the move- Fig. 226. Bilgram Valve Diagram. ment of the valve, and of thus determining the various events of the revolution. It must be understood, however, that while this construction shows with fair accuracy the relation between the movement of the valve and of the crank, it does not, without a further special construction, connect the movement of the valve with that of the piston. It is the special property of the oval diagram of [2] to show this latter relation for an actually constructed gear or for a model, where both sets of measurements may be actually made. It is the special property of the Bilgram diagram, and others VALVES AND VALVE GEARS. 379 composed of straight lines and circles, to connect together with- out actual measurement the movement of the valve and crank for the ideal case when there is no angularity of excentric-rod. The error here involved is usually small, and since the diagram is so easily constructed, it may be preferred for many purposes of initial design. It thus appears that the distances of the edge of the valve be- yond the edge of the port are given by the intercepts (shown by the shaded part of the diagram in Fig. 226), between the two cir- cles, one on OP as diameter and the other, the lap circle, about P as center. In case the width of the port is less than the dis- tance G O, an arc RS is drawn from P as center, such that the distance HS equals the width of port. The widths of opening are then given by the intercepts between J K S R L and the lap circle with P as center. It is seen that the port opens for steam at J with crank at A 2 and closes at L with crank at A 3 , while full opening holds from S to R. An entirely similar construction throughout with the ex- haust lap circle as shown by the small circle about P will give the various features of the movement on the exhaust side. The results of a change in the steam or exhaust lap, or in the angular advance d are readily examined by the aid of this diagram, and will be found to agree with the statements of the table in [2] . [4] etiner Valve Diagram. In Fig. 227 let ABCD be a circle described with radius OA equal to the throw of the excentric. Let A denote the angular position of the crank at the end of the stroke, and let OB be drawn perpendicular to AC. Draw OP at the angle <5 (the angu- lar advance) with OB, and on OP as diameter describe a circle as shown. Draw also an arc of a circle with OL equal to the steam lap, as radius. Let OA n be any position of the crank. Then the properties of this diagram are such that the travel of the valve from mid position is given by the distance OG, while the port opening will of course be given by EG the intercept between this circle and the lap circle MN. A similar construction holds for other locations of the crank, and it thus appears that steam opening will occur at N with the crank in the position ON while closure or cut-off will occur at M with the crank in the po- sition OM. By describing a circle with center at O and with radius equal to the exhaust lap, a similar construction gives the 380 PRACTICAL MARINE ENGINEERING. various features of the movement on the exhaust side of the valve. The history of the port opening for steam is thus given ~by the intercepts between MN and the circle on OP, as shown by the shaded part of the diagram. In case the width of port is less than the distance LP an arc RQ is drawn from O as center such that the radial distance be- tween MN and RQ equals the width of port. The history of the port opening is then given in the same way as for the corre- sponding case in Fig. 226, as there explained. The results of a change in the steam or exhaust lap, or in the angular advance #, are readily examined by the aid of this Fig. 227. Zeuner Valve Diagram. diagram, and will be found in accord with the statement of the table in [2] . Sec. 48. STEPHENSON I/INK VAIfVE GEAR. We have thus far examined in some detail the operation of a slide valve operated by a single excentric. In the course of the discussion it has appeared that with such a gear the direction of motion of the crank relative to the excentric depends on whether the valve takes steam on the inside or outside, and on the nature of the connection between the excentric rod and valve stem. With any one arrangement, however, motion in one direction only is possible ; and it is therefore clear that to enable VALVES AND VALVE GEARS. 381 the engine to reverse a fundamental requirement of all marine valve gears some additional features will be necessary. The general problem of a reversing valve gear is one which has been solved in a great variety of ways, both with and with- out the use of excentrics, as we shall see later. With the use of excentrics the simplest solution is furnished by the well-known Stephenson link. This is illustrated geometrically in Fig. 228. C represents the crank on the center. A denotes one excentric at an angle COA on one side of the crank and B another at the same or approximately the same angle COB on the other side. AD and BE denote two excentric rods connected by a link DE curved to an arc whose radius is the length of the rod AD or BE. To a block in this link is attached the valve stem DG. For the structural details of this -gear reference may be made to Sec. 53. Marine Engineering Fig. 228. Skeleton of Stephenson Link. Now it will be readily seen that with the arrangement of the diagram the valve is under the control of the excentric A alone. The excentric B simply pulls the link DE back and forth, causing it to swing about D, but in no way affecting the movement of the valve. Hence the engine will move entirely under the con- trol of the excentric A, and with an outside valve direct con- nected, the direction of rotation will be right-handed, or from C toward A. Now to effect the reverse, it is only necessary to move the link over so that E comes to the center line and the valve and engine pass under the control of the excentric B alone. For the reasons already noted in Sec. 47 [i] the motion will now be reversed and the rotation will be left-handed or from C toward B. 382 PRACTICAL MARINE ENGINEERING. We have next to tequire regarding the motion of the valve stem when the link is only part way over, as shown by the broken lines in the diagram. In such case it is readily seen that the motion of the valve will be derived partly from the excentric A and partly from B, the former giving the principal part ot the motion, and the latter exercising a modifying influence. Now without taking up the examination of this question in detail, it will be sufficient to state that within a very small error the result- ant motion will be the same as though it were given by a single excentric of somewhat decreased throw ,and increased angular advance as compared with A or B. A simple construction will serve to determine the throw and angular advance of this equiva- lent single excentric. This may be carried out as follows : (1) In Fig. 229 lay off the two excentric throws OA and OB, with the proper angular advance as shown, and draw the line AB. (2) Divide the length of the link DE Fig. 228 by twice the excentric rod AD and multiply the quotient by the length AC Fig r ' 229. (3) Lay off the result from C to D, and through the three points A D B pass the arc of a circle, as shown. Then the arc ADB may be considered as representing the link, and to find the throw and angular advance of the equivalent excentric for any given position of the link-block as F on D l E l . Fig. 228, we have only to take a corresponding point F on the arc ADB, and draw the radius OF. The throw is then repre- sented by OF and the angular advance fi by the angle POF. That is, if the link be put into the position shown by broken lines in Fig. 228 the movement of the valve will be, within a small error, the same as though it were operated by a single excentric of throw OF, Fig. 229 and angular advance POF determined in the manner described. It is readily seen, therefore, that as the link is so moved as to bring the block from the end nearer and nearer the center, the corresponding point F Fig. 229 will move from A nearer and nearer to D, and the throw of the equivalent excentric will continually decrease while the angular advance will increase. As the link passes the center and the block approaches the other end the corresponding point F moves on from D toward B, and the throw again increases, while the angular advance changes to the other side and gradually de- creases as B is approached. With the link in full gear at either end, the corresponding point F comes to either A or B, and the VALVES AND VALVE GEARS. 383 equivalent excentric becomes the same as the real excentric, with its throw and angular advance as constructed. In some cases, especally with the double-bar form (see Sec. 53) the link may be put over so as to bring the block even be- yond the points of attachment of the excentric rods. See Fig. 243. In such case the throw and angular advance of an equi- valent excentric will be given by extending the arc beyond A and B as shown in Fig. 229, and by then taking a point F cor- responding to the relative location of the block and link. In such case it is seen that the throw is increased and the angular ad- vance decreased. The details of the motion for any given position of the link- block may, of course, be determined by the use of any of the Fig. 229. Construction for Equivalent Excentric Stephenson Link. methods given above for the case of a single excentric. It is simply necessary to take the equivalent throw and angular ad- vance determined as in Fig. 229, and use them according to the methods described in Sec. 47. In this way it may be found that as the gear is linked up, or the block approaches the middle, the valve^ travel and port openings decrease, the lead increases, and the cut-off becomes earlier. This is further illustrated by the two oval diagrams" of Fig. 230. These are constructed as explained in Sec. 47 [2], and represent the effect of linking up. The larger diagram represents the movement for full gear position as shown by the full lines of Fig. 228, while the smaller and narrower one represents that for a linked up position as shown by the broken lines of the same diagram. 384 PRACTICAL MARINE ENGINEERING. A gear arranged as in Fig. 228 is known as an open gear or gear with open rods. That is when the crank is turned away from the cylinder the rods are open as shown. If instead of this the rods are crossed as shown in Fig. 231, then it is called a gear with crossed rods. It will be noted that with the open gear the rods become crossed when the crank is turned toward the cylinder, while in the same position the rods in the crossed gear become open. It is therefore necessary to note the character of the gear by the appearance of the rods when the crank is turned away from the cylinder as stated above. It must now be remembered that the construction given in Fig. 229 and the Fig. 230. Oval Valve Diagrams for Stephenson Link. conclusions drawn from it apply to the gear with open rods only. For the crossed rod gear, however, a similar construc- tion applies as shown in Fig. 232. The distance CD is here laid off toward the center and a like arc is passed through the three points ADB as shown. The diagram thus constructed is used in the same manner as with Fig. 229. It is thus seen as the link- block approaches the center of the link and the corresponding point F approaches D, that the equivalent angular advance in- creases, the equivalent throw, valve travel and port openings decrease, even more rapidly than with the open gear, while the lead decreases and the cut-off is earlier and earlier. The principal characteristics of these two types of Stephen- son link valve gear with regard to the effect on the various events, etc., due to linking the gear up may be conveniently pre- sented in the following tabular form : VALVES AND VALVE GEARS. 385 STEPHENSON LINK. EFFECT OF LINKING UP. Type of Gear. Open Rods. Crossed Rods. Equivalent Excentric Throw Decreased Angular Advance Increased Valve Travel Decreased Port Opening Decreased Lead Increased Cut-Off Earlier Decreased Increased Decreased Decreased Decreased Earlier Fig. 231. Skeleton of Stephenson Link, Crossed Rods. Fig. 232. Construction for Equivalent Excentric with gear of Fig. 231. The chief point of difference is seen to be in the lead, which increases with open rods and decreases with crossed rods as the gear is linked up. While both types of gear are met with, the open rod gear is more frequently employed. This is due to the fact that as the cut-off is made earlier by linking up, an increase 3 86 PRACTICAL MARINE ENGINEERING. of lead may be preferred to a decrease, and also to the fact that the width of port opening is decreased less rapidly by the open than by the crossed gear. Sec. 49. BRAEMME-MARSHAI,!, GEAR. The Stephenson link is by no means the only form of valve gear which will allow of reversal and which will give variable cut-off. Among the other arrangements are several known as "radial valve gears," and of these the more important may be briefly described. In Fig. 233 let C denote the position of the crank and E the position of a single excentric located directly opposite the crank. Let FD be a slide pivoted on the horizontal line OX, and EB a rod attached to the excentric at E and fitted with a pin joint and block at P so that the block may move in or A on the slide FD. Then as the excentric moves around O the end E of the rod describes a circle, the point P describes a straight line FD back and forth, and other points between P and E describe paths intermediate between these two. For a point such as Q this is found to be an inclined oval as shown in the diagram. For points beyond P such as Q', for example, the path is found to be a somewhat similar oval as shown. Now it is found that the proper motion for a valve can be derived from a point moving as Q or Q' and that it is simply necessary to connect such point by a proper link to the valve stem as shown for Q. Instead of placing the excentric at 180 degrees from the crank it may be placed with the crank, in which case in Fig. 233 we should consider the crank at C'. There are thus four arrange- ments of the gear according as the excentric is with or opposite the crank, and as the point Q is between P and E or beyond P. In all cases the gear must be so adjusted that when the crank is on either center as C, the point P is on OX, or at the pivotal point of FD. It is readily seen that if this condition is fulfilled for one center it will be likewise for the other. With regard to the kind of valve to be used (inside or out- side) and the direction in which the engine will run for any given arrangement of gear, the same principles may be applied as in the case of the single excentric. Thus it is easily seen from the symmetry of the motion that Q will go as far above the center line as below, and hence that OX contains the middle of its VALVES AND VALVE GEARS. 387 vertical motion. Hence in the arrangement of the figure with the crank on the top center the valve is below its mid position by the distance from Q to the center line OX. Hence to take steam on the top of the piston an outside valve must be em- ployed, and the engine will go in the direction which will open Fig. 233. Braemme Marshall Radial Valve Gear. the valve still wider. This must be that which ^will lower the valve, and hence that which will lower P, and hence that which will carry E to the left, or right-hand rotation. If, on the other hand the motion were derived from Q', the valve will be above 3 88 PRACTICAL MARINE ENGINEERING. its mid position, and hence to take steam on top it must be an inside valve. The engine in this case will turn in the direction which will raise Q' still further. This requires E to move to the right, and hence the rotation will be left-handed. If FD be inclined in the other direction, as shown by the dotted line, it will be readily seen by the same rule that the direction of rotation in each case will be reversed. It is also found that as the direction of FD approaches the horizontal or OX, the cut-off becomes earlier and earlier, and it is readily seen that the valve travel and hence the port opening will de- crease. We have here therefore an entirely similar action to that which takes place in linking up with the Stephenson link. The means for changing the cut-off and for reversal are there- fore furnished by providing a means for changing or reversing the obliquity of the slide FD, and for retaining it in any position desired. Since the point P comes to the center of the slide or pivot point when the engine is on the center, it follows that in this position the line EB, the point Q and the valve will have exactly the same location no matter what the position of FD, and hence no matter what the point of cut-off. Hence the lead of the valve will be the same for all points of cut-off, or in other words, the lead is not affected by the change in cut-off. This is a feature which, as we shall see, is possessed by the various forms of radial valve gear. With the Stephenson link the lead is vari- able with the cut-off as described in Sec. 48. As noted above there are four arrangements of this gear depending on the location of the point Q, and the angle between the excentric and the crank. Location of Q. Valve. o Inside P Inside. 180 Inside P Outside. o Outside P Outside. 1 80 Outside P Inside. These four arrangements are shown in the above table with the appropriate form of valve. The direction of rotation in each case will depend of course upon the direction of obli- quity of the slide FD. VALVES AND VALVE GEARS. 389 The arrangement of Fig. 233 shows the earlier form of the gear. Another and later form is shown in Fig. 234 in which the slide FD Fig. 233 is replaced by an arm Pl\ pivoted at T l9 and attached by a wrist pin to the rod EB. In this way the point P is caused to move in the arc of a circle F l D l inclined to the Fig. 234. Braemme Marshall Radial Valve Gear. horizontal OX as shown. In such case the motion of the valve is very nearly the same as if the point P moved in the line of the tangent F D, and except for secondary modifications it is there- fore equivalent to the motion of Fig. 233. The change of cut-off and the reversal are brought about by swinging the pivot T x 390 PRACTICAL MARINE ENGINEERING. about a center S, the intersection of FD with OX. In this way Tj is brought to a new position T 2 and the line of motion is brought to F 2 D 2 , thus reversing the direction of rotation ac- cording to the same principles as applied in the preceding case. ; I ,r\ N \ i 1 \ \ i 1 \ 1 1 1 U-a Fig. 235. Joy Radial Valve Gear. We may evidently have here the same four arrangements as in the other form of the gear, with the same relation between ex- centric angles and type of valve as given in the table above. VALVES AND VALVE GEARS. 29' Sec. 50. JOY VAI,VE GEAR. In this form of radial valve gear no excentric whatever is required. As shown in Fig. 235 F is a point on the connecting rod to which a link DF is attached pivoted to a swinging or sus- pension bar DK. The point F moves in an oval path as shown. The point D moves in the arc of a circle as shown. An inter- mediate point as E will move in a path somewhat as shown. From this point on, the gear is similar 1 to a Braemme-Marshall. Thus EP is a link pivoted at E and with the point P carried by a suspension bar PR exactly the same as PT of Fig. 234. The motion for the valve is similarly taken from a point Q as shown. It is thus clear that the Joy gear as here shown is the gear of Fig. 234 in which, however, the point E instead of moving in a circular path derives its motion from the connections shown in Fig- 235 and moves in a distorted oval path as there shown. It is clear that there will be the same two varieties of gear ac- cording as the point Q is taken between E and P or beyond P. The reversal is also effected in the same fashion by swinging PR, or the straight slide may be used as in the gear shown in Fig- 233. Sec. 51. WAI,SCHAERT VAI,VE GEAR. In this gear as shown in outline in Fig. 236, one excentric E is used. MGK is a curved link pivoted at G. H is a block sliding on or in the link and connected by a radius arm to the valve lever AF. The end F of this lever is connected by a pin joint to the valve rod, and the other end A by a short link to the main crosshead as shown. The valve is thus seen to de- rive its motion in part from the main crosshead and in part from the excentric. The former part comes through the valve lever which pivots about D and thus communicates motion from C to F. The latter part comes from the curved link which is operated by the excentric, causing it to swing about G and thus through the radius arm and valve lever the motion of the excentric is communicated to the valve rod. The combination of these two motions is found to be such as to give a suitable movement to the valve. The linking up and reversal are accomplished by swinging the block H and radius rod from one side to the other of the mid-position or pivot G. As the block H is brought nearer to G the cut-off becomo* earlier while the valve travel and port-open- 392 PRACTICAL MARINE ENGINEERING. ing are decreased the same as with the Stephenson link above described. In order that this gear may operate properly, certain ad- justments are required as follows: The radius of the curved link MGK must equal the radius- rod HD. Place the crank on say the top center, and bring the link Fig. 236. Walschaert Valve Gear. MGK into line with an arc struck from D as center with DH as radius. Then M should be so taken that the angle OMG is a right angle. Also the excentric E is placed at a right angle from OM as shown. Then in this position the block H may be drawn to and fro along the link without moving the valve. It is also clear that after the crank has gone 180 degrees the excentric will be at E, and MG will be again in the same position VALVES AND VALVE GEARS. 393 and the block H may be drawn along the link without giving motion to the valve. It follows that the position of the valve when the crank is on the centers will be the same no matter where the block H may be located, and hence that the lead of the valve will be the same for all points of cut-off. It is clear that the arrangement of Figs. 233-236 will bring the valve chest on the side of the cylinder transversely instead of fore and aft. The cylinders may therefore, so far as valve chests are concerned, be placed nearer together than with the Stephenson link, in which case the valve chests are forward or aft of the cylinders. The length of the engine as a whole may therefore be made somewhat less with the radial types of gear than with the Stephenson link, and it is this feature which gives to them their best claim of advantage. Such gears possess also, as we have seen, the property of giving the same lead for all points of cut-off, while with the Stephenson link the lead varies with the cut-off. With proper design, however, the varia- tion in the latter case is not sufficient to constitute a feature of any importance, and the difference on this point can hardly be considered as forming any noteworthy advantage for the radial gears. The general character of the valve movement and the distribution of events in all cases is best studied by the aid of a diagram such as that of Fig. 223. It will thus be found that the results for these various cases will be quite similar, and that such differences as appear are of relatively small importance. Speaking broadly, it is perhaps fair to say that there is not suffi- cient difference in the operation of the valve itself to furnish any pronounced claim of advantage for the usual cases arising in marine practice. The choice must therefore be made rather by reason of structural considerations, such as the shortening up of the engine referred to above, or the details of construction of the gear as affecting the questions of breakage, wear and tear, readiness of repair, readjustment, etc. On the whole, the Stephenson link seems to be usually preferred as the best ful- filling the all around requirements for the marine valve gear, and it may be fairly considered as the representative gear in present-day marine practice. Sec. 52- CRANK VAI,VE GEAR. As we have seen in Sec. 47 [i] the action of an excentric is equivalent to that of a simple crank of throw equal to the 394 PRACTICAL MARINE ENGINEERING. excentric and set at a corresponding angle with the main crank. It is evident then that a series of cranks will operate a valve and gear in a manner identical with a corresponding series of excentrics. Such cranks, however, on account of their small throw cannot readily be located or formed on the main crank- shaft, and hence where used for operating the valves, are neces- sarily placed on a special or auxiliary shaft. In Fig. 237 is shown the usual way of arranging the parts of this gear. S is the center of the main crank-shaft, and ST the main crank. A, B, and C are gear wheels, A attached to the crank- shaft, B an idler, and C attached to the valve shaft. O is the center of this shaft and OP represents the throw and angulai location of the small crank for operating the valve. The valve Fig. 237. Crank Valve Gear. shaft will then turn in the same direction as the main shaft, and as may be readily seen, will operate the valve precisely in the same manner as an ordinary excentric of the same throw and angular location. For reversing with this gear the usual plan is to have but one crank and valve-connecting-rod correspond- ing to one excentric rod. The angular location of the crank must then be changed from a position such as OP in the figure to OPj. By comparing this with Sec. 47 [i] it is seen that such a change in the location of the crank will necessarily cause the engine to move in the opposite direction. To bring about this change in the location of the valve crank relative to the main crank, various mechanical devices may be used. Thus it may be seen that if after the engine has stopped VALVES AND VALVE GEARS. 395 the gear C were slipped out of the mesh with B, turned around through the angle POP l and then slipped back into mesh again, the crank would be brought to OP l and if the engine were started again it would go in the opposite direction. This, of course, is not a practicable form of reverse, since it cannot be carried out quickly enough, nor when the engine is in motion. It does, however, serve to illustrate the necessary change to be made in the angular location of OP. In the usual mode of operation, some form of spiral cam is employed, as illustrated in Fig. 238. C is the gear wheel car- ried on a sleeve AB and connected to it by a key way and feather so that the sleeve may be moved back and forth axially and still remain coupled to the gear C so far as rotary motion is concerned. The gear C is also prevented by suitable stops from being carried out of mesh with the gear B, Fig. 237. This sleeve is carried on the shaft D to which is attached the valve crank, Fig. 238. Crank Valve Gear, Reversing Arrangement. and is loose on D and only connected with it by a pin P which projects through a spiral groove RS cut in the metal of the sleeve. At E there is a circumferential groove in the sleeve, in which is fitted the end of a controlling lever F, by means of which the sleeve may be moved back and forth longitudinally. In the figure the sleeve is shown pushed in so that the pin is at one extremity of its travel in the spiral groove, and the valve- crank will therefore be in a corresponding position with refer- ence to the gear C and main crank, which we will suppose to be for full gear ahead. If now the sleeve be pulled longitudinally until the other end of the groove contains the pin, it is clear that we shall have changed the angular location of the pin rela- tive to the gear and hence of the valve-crank relative to the main shaft. If then the spiral groove be of suitable extent and location, such a change will serve to move the crank OP, Fig. 396 PRACTICAL MARINE ENGINEERING. 237, from its position for full gear ahead, to OP^ its position for full gear astern. Instead of one pin and spiral groove, two on opposite sides may be used, and other details may vary in many ways, but the arrangement will serve to illustrate the principles involved. While this form of valve gear is thus efficient for reversing, it is much less suitable for linking up or varying the cut-off than the other forms of gear discussed above. Referring to Sec. 48 it was there shown how to find the equivalent simple excentric for any adjustment of the Stephenson link, as shown by the line A D B, Fig. 229, for an open rod gear. Now it is readily seen that the form of reverse just considered is equivalent to taking the excentric O A and carrying it around from OA to OB, so that for the varying intermediate positions the virtual excentric would be. given by drawing a line from O to the arc A B with OA as radius. From the principles discussed in Sec. 47 [2] it is readily seen that the effect on the valve will be as follows : Linking up will produce : Earlier cut-off. Earlier steam opening. Greatly increased lead. Earlier exhaust opening. Earlier and greater compression. The same valve travel and opening. While therefore the port opening is not decreased by link- ing up, the lead and compression may become excessive, and re- strict the practicable range of variable cut-off to narrow limits. In Fig. 237 we have referred to one cylinder and valve op- erating crank only, but the same arrangement may be applied, of course, to a series of cylinders for a multiple expansion engine. In such case the valve operating shaft has a series of cranks, one for each cylinder, and set at the proper angle from the corre- sponding main crank. Then with a reverse gear similar to that described in Fig. 238 all the cranks are moved together and are brought into the proper relation with their main cranks to oper- ate the engine in the reverse direction. It is also to be noted that this arrangement brings the valve chests at the sides of the cylinders and that on this account it has the same effect in shortening up the engine as the use of a radial valve gear. This type of gear has been used to some extent on launch, yacht and torpedo boat engines, but has not VALVES AND VALVE GEARS. 397 found favor for larger or slower running engines as used in ordi- nary mercantile and naval practice. Sec. 53. DETAILS OF STEPHENSON LINK VALVE GEAR. In the present section we shall give a brief description of the more important details of the Stephenson Link valve gear as a representative gear, and including as it does most of the ele- ments of other forms of gear as described in Sec. 49-52. fi] Excentric and Strap and Excentric Rod. The general construction of this part of the gear is shown in Figs. 239-242. The excentric consists of a disc or sheave of .. ! Fig. Excentric, Detail of Construction and Fitting. circular form, and placed on the shaft excentric or with its cen- ter set out from the center of the shaft. As shown in the figure the sheave is made in two unequal halves which join on the cen- ter line of the shaft, and are secured by bolts as shown. This brings the center of the disc at the point shown, the distance AB between this and the center of the shaft being the excentric throw as defined in Sec. 47. 'Once adjusted the excentric is keyed in place and in addition set screws or binding bolts may be fitted, as shown. In the excentric of Fig. 239 the larger part of the sheave is lightened out to save weight. In excentrics of moderate size this is not usually done, and the bolts connecting 39 8 PRACTICAL MARINE ENGINEERING. the two parts are tapped into the larger part and hold the other portion in place by means of a countersunk head. The material of the excentric is either cast-iron or steel, or if small in size, ^brass is sometimes employed. The strap which surrounds the excentric as shown in Fig. 240 is also made in two parts bolted together, and the excentric rod is attached by a flanged foot to the upper half as shown in the figure. There are several ways of fitting the surfaces of the strap and excentric together, as shown in Fig. 241. In modern Fig. 240. Excentric Strap, Detail of Construction and Fitting. practice the strap is usually of cast-steel or brass, lined with white metal for a bearing surface as shown at a and described in Sec. 21 [n]. With this arrangement of excentric sheave and strap, it is readily seen that as the former turns with the shaft the center of the sheave turns about the center of the shaft ; also that the center line of the excentric rod which will always pass through the center of the sheave, will therefore move exactly as though it were a connecting rod with the distance A B between the two VALVES AND VALVE GEARS. 399 centers as a crank arm. Hence as noted in Sec. 47 [i] the mo- tion communicated to the rod will be exactly the same as would be given by a crank and connecting rod the former of throw equal to that of the excentric. The other excentric strap and rod are Fig. 241.' Different Methods of Fitting Excentric Strap. fitted up in the same manner and the two rods connect with the ends of the link in the manner shown in Fig. 242. In this figure is shown on the left the lower end of the excentric rod with flange for securing to the upper strap as in Fig. 240. On the Fig. 242. Excentric Rods, Fittings at Ends. right is shown the upper end of the rod sometimes known as the excentric rod fork. The form is more properly that of a U, the two sides being fitted with bearing brasses and cap to pro- vide a bearing for the pins by means of which the connection is made with the link. 400 PRACTICAL MARINE ENGINEERING. [2] In Fig. 243 is shown the usual form of double bar link as ft is termed. It consists of a pair of bars curved in the arc of a circle of radius equal to the geometrical length of excentric rod ; that is, equal to the distance from the center line of the link to the center of the excentric sheave. These bars are connected at the ends by bolts and by a block between so as to main- tain the desired distance between them. Near the ends are fitted the pins A, B, C, D, which serve for connecting with the excen- rrn A n c ( TTI 1 o O 1 i i r g [ r ; ! '4 O fo)) O JZ 1 t="-~-4 LiJ Fig. 243. Stephenson Double Bar Link. trie rods by means of the bearings in the upper ends, as shown in Fig. 242. Another pair of pins E, F, is fitted, either at the center as shown or as an extension of the pairs at the ends, or at some intermediate point. To these are attached a pair of bars or links usually known as side or bridle rods as shown in Fig. 244. These lead to the rock or weigh shaft, and serve to control the gear when linking up or reversing, and to hold it in any desired position. The rock-shaft or weigh-shaft is usually carried in bearings on the outside of the columns near the top, and is provided with VALVES AND VALVE GEARS. 401 arms, one each for the several links, and one for the connection to the reverse cylinder by means of which it is operated as de- sired. This is sufficiently illustrated in Figs. 100, 116, 247. In order to provide an independent adjustment for the valve Marine Eiiyineering Fig. 244. Side or Bridle Rods. gear of the different cylinders, the weigh shaft arm as shown in Fig. 245 may be provided with a slot within which moves a block under the control of a hand-wheel and screw as shown. The bridle rods are attached to pins on the sides of this block Fig. 245. Independent Adjustment for Cut Off with Stephenson Link. as shown on the right, and by this means without moving the weigh shaft at all, the links may be given an adjustment within the limits of the motion of the block in the slot. It is custom- ary to so adjust the line of motion of this block that when the 402 PRACTICAL MARINE ENGINEERING. g:ear is in the ex>-ahead position, it shall lie nearly in the line of the bridle rods so that any movement of the block will be com- municated to the link without loss. In the backing position on the other hand, the line of movement of the block will lie across the line of the bridle rods at a considerable angle, and movement of the block back and forth will give but slight motion to the link. See also Figs. 100, 247. This arrangement is often of use in adjusting the points of cut-off in the separate cylinders so as to divide as equally as pos- sible the power among the different cylinders. See also Sec. =55 [43. [3] I/ink Block and Valve Stem. The connection between the link and the valve stem is made by means of a link-block as shown in Figs. 243, 246. This 1 r Hi J!; ill h S .--<.. cP 1 ' ,-.-t~. \ i 3Si2i L qS ] ; - '3s ij \ : \ ! J! A T ' T I i Jfari'K Enyineering\ Fig. 246. Link Block for Stephenson Double Bar Link. consists of a central pin with wing pieces at the ends, as shown in the figure, the latter being fitted with bearing surfaces for connecting with the bars of the link, and permitting sliding mo- tion between the two. The pin is connected with the lower end of the valve stem, which is formed in the usual manner with brasses and cap. See also Fig. 248. The valve stem is usually guided by means of a special guide or bearing as shown in Figs. 100, 247, which sup- ports it against side stress, especially at the stuffing-box just above. In good practice the valve-rod stuffing-box is usually packed with some form of metallic packing, and is of the same VALVES AND VALVE GEARS. 403 general form and arrangement as the piston-rod stuffing-box described in Sec. 24 [7]. Passing through the stuffing-box the valve-stem is attached to the valve, and thus the chain of con- nections between the excentric and the valve is completed. The assemblage of these various parts of a Stephenson valve gear is further illustrated in Fig. 247, showing the upper ends of the excentric rods, the link, link block, valve-sttm and guide, bridle rods, rock-shaft arm and brackets for supporting the shaft, and independent cut off control in rock-shaft arm. Marine Engineering Fig. 247. Arrangement of Stephenson Link and Rock Shaft Connections. Reference should also be made to Figs. 97, 99, 100 for further general illustrations of this gear. When two piston valves are driven side by side as is very commonly the case on the L. P. or I. P. cylinders, the two valve- stems are connected across by a yoke as shown in Fig. 248, which in turn is connected to the link block by a form of bearing similar to that for the single stem. In such case the guide is very commonly attached tp the yoke, the arrangement consist- 404 PRACTICAL MARINE ENGINEERING. ing of a dovetailed or gibbed slide and guide, the first formed on the yoke, and the second by a vertical plate or bar projecting SCALE OF FEET Vi # 1 2 3 4 5 Fig. 248. Yoke and Guide for Driving Double Piston Valves. downward from the bottom of the cylinder head as shown in the figure. VALVES AND VALVE GEARS. 405 Sec. 54- VAI,VE SETTING. [i] Putting an Engine on the Center. One of the important features of valve setting is the placing of the engine on the centers or dead-points in order to deter- mine the lead. In a rough way this may be done by turning the engine and watching the cross-head slide as it approaches the dead-points. The slide will move along the guide, more and more slowly, and will finally stop and begin to return. Just as the far- thest point is reached, the crank is on the dead-point. By mov- ing the engine back and forth and watching carefully the move- ment of the slide relative to a light mark or score on the guide, the desired point may be determined with fair accuracy for pur- poses of valve setting. The difficulty in making an accurate determination by this method lies in the fact that when near the center the crank mav Marine Engi Fig. 249. Putting an Engine on the Center. be moved to and fro through a sensible angle with hardly a no- ticeable movement of the slide. Hence while it is possible to determine to a nicety the point on the slide which corresponds to the highest or lowest position of the piston, it is less easy to know just where to set the crank so as to have it accurately correspond to the same location. For more accurate setting the following method may be used. The engine is placed with the cross-head slide at a sma'll distance from the lowest or highest position. A mark A is then made on the slide and "a corresponding mark B on the guide. The distance which the cross-head should be placed from the center when these marks are made depends of course on the size of the engine, but I or 2 inches or say 1-20 to i-io the stroke 4 o6 PRACTICAL MARINE ENGINEERING. will be a suitable distance. See Fig. 249. Another pair of marks P, Q, is next made on the forward end of the shaft and the adjacent brass, or on one of the coupling flanges and an ad- jacent block or bar set up for the purpose. The object is sim- ply to have two pairs of marks, one on the cross-head slide and its guide, and one on the shaft and its support or guide or an ad- jacent and fixed object. The engine is then moved around con- tinuously in one direction past the center till the cross-head slide moves back and the mark A again comes opposite B. The point P on the shaft in the meantime will have moved on to a new location, and a corresponding mark R is made on the bear- ing or stationary part of the engine on which the first mark Q was placed. The angle between these two marks Q R, on the shaft or coupling corresponds to the movement of the cross-head from the position of the first pair on to the end of the stroke and back again an equal distance. A mark S midway between Q and R, will give the proper location for the mark P when the cross-head is at the end of the stroke and the crank on its dead point. In this way by moving the shaft till P is brought oppo- site S the location of the crank for each dead point may be quite accurately found. [2] Setting the Valve. To return to the setting of the valve we first note that the distribution of the steam to a cylinder by means of a slide valve depends on four chief items : (1) The throw of the excentric. (2) The angular location of the excentric relative to the crank. (3) The length of the valve stem. (4) The steam and exhaust laps. Now let us assume that the parts of the valve gear are made, and that it simply remains to connect them up and make the proper adjustments. It is seen that we have but two items which may be varied, or which may enter into the question of the setting of the valve. These are (2) and (3) above. We should first adjust for (3) and then for (2). Referring to Sec. 55 [2] (9) it appears that an incorrect length of valve-rod will give an improper balancing up of the events for the top and bottom of the cylinder. Hence the vari- VALVES AND VALVE GEARS. 407 ous events for both ends must be examined and compared. To this end the entire gear is connected up according to judgment, the link being placed in the position intended for normal running ahead, and the necessary arrangements made for observing the movement of the valve. If the valve is a flat slide the valve chest cover is left off for this purpose. With piston valves, however, it is necessary to observe the movement of the valve by means of peep holes through the shell of the chest, such holes being fitted with screw plugs or covered by caps when the en- gine is closed up and ready for operation. In this manner the lead is observed while the engine is on fHe centers, and the points of cut-off and other items are observed for each end of the cylinder. The location of the valve on the stem is then varied until a fair balance between the two ends is obtained. It will be found that with anything like equal leads the cut-off will be later on the down than on the up stroke, or with an attempt to even the points of cut-off the lead and port opening on top will be- come too small and the lead on the bottom excessive. It will often be found that with something approaching equal leads on top and bottom, the points of cut-off will vary in the two ends by nearly or quite 10 per cent, or even more. It is readily seen that similar derangements will result from an attempt to balance the exhaust items. In general it is far better not to attempt to exactly balance any one item in the two ends, but simply to aim for the best all around combination of events which can be obtained in the given case. When a fair balance is thus obtained, the question of the point of average cut-off, steam-opening, release and compression may be taken up. Changes in these items require a change in the angular location of the excentric relative to the shaft, and it may be shifted according to the relations shown in the table of Sec. 47 [2] until the general character of the various items is made satisfactory. It thus appears that of the two items, length of valve-rod and location of excentric, the latter really fixes the general character of the various items, while the former makes it possible to ap- proximately even up or balance the various items between the two ends, according to what seems the most desirable average distribution. If the excentric is shifted through any considerable an.rle from its first location it will be necessary to again examine the 4 oS PRACTICAL MARINE ENGINEERING. question of balance between the two ends, and to again adjust the length of valve-rod. If by the adjustment of both valve-rod and excentric, the desired events, openings, etc., cannot be obtained, it means that the trouble lies with one or both of the other items, throw of ex- centric and steam or exhaust lap, and steps must be taken to modify these features as the conditions may require. The following table gives an illustration of the balancing up of the various items in the two ends of the cylinder. TOP. BOTTOM. Steam opening .7 per cent, before end of stroke .4 per cent, before end of stroke Steam closure or cut-off 68 per cent. 59 per cent. Exhaust opening 90 per cent. 91 per cent. Exhaust closure 85 per cent. 84 per cent. Steam lap 2.44 in. 2.40 in. Exhaust lap .12 in. + .68 in. Steam lead .60 in. .52 in. Port opening for steam 2.08 in. 2.12 in. Angle of advance 33 degrees Throw of excentric> 4 15-16 in. The setting of the valve may of course be examined or re- adjusted at any time, as desired, by the use of the same general method. [3] Valve Setting from the Indicator Card. The indicator cards interpreted in accordance with the re- lations given below in Sec. 55 [2] furnish most valuable evidence as to the adjustment of the valve gear, and its suitability for operation under steam. In attempting a readjustment or re- setting by the aid of the indications given by the cards, the question of balance between the two ends as affected by the length of valve-rod should be taken first, next the items depend- ing on the angular location of the excentric, and last the ques- tion of lap and excentric throw. If the cards are pushed over to one side or show differences in the two ends as in Fig. 260 it is evidence that the valve stem is not of the right length, and it must be changed accordingly. VALVES AND VALVE GEARS. 409 This is done first, cards being taken after each change until the two ends are fairly well balanced up. Attention is next given to the location of the excentric. The points of cut-off, re- lease and compression will show whether the angular advance is too large or too small, and the readjustment is made accordingly. A change in the angle of the excentric for the purpose of adjust- ing any one item is moreover liable to disturb other items in such way as to require a readjustment of the lap, and is there- fore to be avoided unless considered necessary. Thus if the cut-off is too late, for example, and the excentric is turned so as to increase the angular advance, the cut-off will be made earlier and the exhaust and compression as well, while the lead will be increased. If the change necessary to adjust the cut-off produces too great a disturbance in the exhaust and com- pression, or if in general a suitable and satisfactory arrange- ment of events cannot be reached by adjustment of the excentric and valve rod only, it means that the lap is at fault or perhaps the throw of excentric. Change in the lap can of course, only be effected by removing the valves and cutting them down if it is to be decreased, or fitting a new valve or head if it is to be increased. Similarly change in the throw of the excentric can only be effected by a removal of the old and fitting a new one of proper throw. 4io PRACTICAL MARINE ENGINEERING. CHAPTER VIII. STEAM ENGINE INDICATORS AND INDICATOR CARDS. Sec. 55- INDICATOR CARDS. [i] Descriptive. An indicator card is a diagram showing for each point of the stroke in both directions the steam pressure on the piston. Thus Fig. 250 represents an indicator card showing the steam pressure above the piston, say, for both the down and up strokes. RS is the line of zero pressure from which all pressures are measured upward according to the scale of the diagram. This is called the absolute pressure line. A is the beginning oi the down stroke, B the point of cut-off, C the point of exhaust Fig. 250. Indicator Card. opening, and D the end of the stroke. The line AB is called the steam line and shows the steam pressure on the upper side of the piston from the beginning of the stroke to cut-off. The line BC is called the expansion line and shows the decreasing values of the pressure during that part of the stroke. At C the exhaust opens and the pressure drops suddenly as shown by CD. For the return or up stroke, D is the beginning, E the point of exhaust closure or beginning of compression above the piston, and F the INDICATORS AND INDICATOR CARDS. 4'i point of steam opening just before the beginning of the next down stroke. CDE is the exhaust line and shows the nearly con- stant pressure during this period. EF is the compression line and shows the increasing pressures on the return stroke after the closure of the exhaust valve. FA is the admission line and shows the sharp jump upward as the steam is opened again just before the beginning of the next down stroke. The line PQ drawn when the space below the indicator piston is shut off from the engine cylinder and connected to the air is called the atmospheric line. The distance PR between RS and PQ thus represents the pressure of the atmosphere, 14.7 pounds per square inch, its length depending of course on the scale of the diagram. Thus for the down stroke the varying pressures on the top of the piston are shown by the varying distances from RS to ABCD, while for the up stroke the pressures on the Fig. 251. Pair of Indicator Cards. same side of the piston are shown by the distances from RS to DEFA. There will be, of course, a similar diagram for .the head end of the cylinder showing the pressures below the piston for both the up and down strokes in the same manner as for the diagram described. Such a pair of diagrams taken from actual practice is shown in Fig. 251. Let us now compare the cards of Figs. 250, 251 with Fig. 252, the latter showing a so-called ideal card ; that is, a card which would be given if the valves opened and closed instantaneously, if when closed they were tight against all leakage, if there were no loss of pressure due to friction of steam in the passage, and if the expansion and compression lines were equilateral hyper- bolas. Instead of these conditions the valves open and close gradually, even when closed there may be some leakage, there is always some loss of pressure due to friction or resistance to the flow of steam, especially through a gradually closing or 412 PRACTICAL MARINE ENGINEERING. opening port and the expansion and compression lines are not true hyperbolas. Added to these we have the inertia of the indi- cator piston which prevents it from following with absolute ex- actness all the variations of pressure as they occur. As a result of these various causes the actual engine and in- dicator give us the diagrams of Figs. 250 and 251 rather than such as Fig. 252. The gradual opening and closure of the valve rounds off the various corners, while the steam line instead of being horizontal, droops somewhat, due to the loss of pressure through the ports and passages. The piston, of course, moves faster as it approaches mid-stroke and hence the steam must flow in at an increasing velocity to fill up the space behind the advancing piston. The higher the velocity the greater the loss of pressure, and hence there is a continual slope down from the beginning of the stroke as shown in Fig. 251 and often to a far Fig. 252. Ideal Indicator Card. more pronounced degree. The actual point of cut-off is also not always easy to locate, rounded off as it is by the gradual closure of the valve. We may, however, properly consider that the point of actual final closure is where the curve changes di- rection of curvature, that is, from convex to concave, as at or near P. Fig. 251. It is sometimes considered that the point of equivalent cut-off is more nearly obtained by continuing the curve back as shown by the dotted line to Q and supposing a sharp cut-off at this point. The result would then be an ex- pansion line from Q similar to that which is obtained by the gradual closure in the actual case. The steam engine indicator diagram is valuable for two chief purposes. (a) It enables us to judge of the operation of the valve by noting the various events, steam opening and closure, the loca- INDICATORS AND INDICATOR CARDS. 413 tion relative to that of the piston, the resulting piston pressure, and to answer various questions relative to the general problem of the distribution of steam to the cylinder. (b) It enables us to answer all questions which depend on the amount and distribution of steam pressure on the piston and thus to determine the mean pressure, and knowing the revolu- tions to find the indicated horse power; also the turning effort at the various points of the revolution, and the mean effort for the entire revolution. [a] The Indicator Card and the Operation of the Valve Gear. We will now consider briefly the more important derange- ments which may be met with in the valve gear, and the re- sults as shown by the indicator card. Fig. 253. Indicator Cards with Angular Advance too large. (i) E.vcentric too far from a line at right angles to the crank ; that is, angular advance d too large (Sec. 47 [i]). Results: Cut-off too early, steam-lead large, exhaust open- ing and closure early. In short, the whole round of events is ahead of time. See Fig. 253. Fig. 254. Indicator Card with Angular Advance too small. (2) E.vcentric too near a line at right angles to the crank ; that is, angular advance d too small (Sec. 47 [i]). Results: Cut-off late, steam lead small or even negative, compression small, steam opening late, exhaust opening and closure late. In short, the whole round of events is behind time. See Fig. 254. 4i4 PRACTICAL MARINE ENGINEERING. (3) Steam lap too large. Results: Cut-off early, steam opening late and lead small or even negative, port opening small with a probable wire draw- ing of the steam, and drop of pressure on steam line. See Fig. 255- Fig. 255. Indicator Card with Steam Lao too large. Fig. 256. Indicator Card with Steam Lap too small. (4) Steam lap too small. Results: Cut-off late, steam opening early and lead large, port opening large. See Fig. 256. (5) Exhaust lap too large. Results: Exhaust closure early and compression large, ex- haust opening late and exhaust lead small. See Fig. 257. Fig. 257. Indicator Card with Exhaust Lap too large. Fig. 258. Indicator Card with Exhaust Lap too small. (6) Exhaust lap too small. Results: Exhaust closure late and compression small, ex- haust opening early. See Fig. 258. INDICATORS AND INDICATOR CARDS. 45 (7) Compression excessive. Results: The pressure in the cylinder may be carried above that in the valve chest before the steam valve opens, thus form- ing a loop as shown in Fig. 253. This may be due to either (i) or (5) above. (8) Expansion Excessive. Results: The pressure in the cylinder may fall below that in the next receiver or exhaust space beyond, thus forming a loop as shown in Fig. 259. Fig. 259. Indicator Card with Excessive Expansion. (9) Valve Stem too long. Results: This means that the middle of the stroke of the valve is placed too high relative to the ports. The results for an outside valve will be to give too much steam-lap on top and exhaust lap on the bottom, and too little steam lap on the bot- tom and exhaust lap on top. Hence we shall have : Steam opening in top late and small and cut off early. Steam opening on bottom early and full, and cut off late. Exhaust opening on top early and full and closure late. Exhaust opening on bottom late and small and closure early. See Fig. 260. Fig. 260. Indicator Card with Valve Stem too long or too short. (10) Valve Stem too short. Results: Similar to those for (9) but oppositely related to the ends of the cylinder. 416 PRACTICAL MARINE ENGINEERING. To these we may also add the following. (n) Leaky piston or piston rod stuffing-box. Results: The expansion line will be steeper than it should be. The compression line may also flatten off somewhat near the top. (12) Port openings or Passages too small. Results: Wire drawing or loss of pressure on the steam line and rise of pressure on the exhaust line. See Figs. 251, 255. It will be noted in the above that different causes may pro- duce similar results, so that in interpreting a given set of cards caution must be used in working back from result to probable cause and remedy. This operation may be aided by the follow- ing general hints. It will be noted that the general effect of a valve-stem too long or too short is to effect the two ends of the cylinder in op- Fig. 261. Indicator Card Showing Combination Effect. posite directions, thus giving the cards the appearance of hav- ing been pushed over in one direction or the other as in Fig. 260. On the other hand, if the valve-stem is of proper length but the excentric is- improperly set the results will be of the same kind in both ends of the cylinder as shown in Fig. 253. Various com- binations of these may exist in the same engine. Thus a pair of cards as shown in Fig. 261 indicates an incorrect length of valve-stem, an incorrect adjustment of the laps, with perhaps too large an angular advance. The combination nearly corrects certain difficulties and makes others still worse. Various special features may combine to make the so-called "freak" cards, but we shall not examine this part of the subject further as such freaks are of rare occurrence, and a careful study of the results of the various single derangements as given above in (i) to (12) will usually be sufficient to show the nature of the trouble. INDICATORS AND INDICATOR CARDS. 47 [3] Working Up Indicator Cards for Power. From the principles of mechanics we know that work is the result of a force or effort acting through a distance, and is measured by the product of the force in pounds by the distance in feet. This gives the measure of the work in foot-pounds. Power measures the capacity to perform a certain amount of work in a given time. The common unit is the horse power, which is 33,000 foot-pounds of work done in one minute of time. Hence to find the power of an engine we have two chief steps : (1) To find the foot-pounds of work done per minute. (2) To reduce this to horse power by dividing by 33,000. It may be noted here that the term Indicated Horse Power means simply the horse power as: determined from the indicator cards. Now by definition the foot pounds per minute for the steam engine will be the product of the acting force multiplied by the distance through which it acts in one minute. The acting force equals the mean load on the piston, and this equals th^ mean effective pressure per square inch multiplied by the area in square inches. The distance acted through per minute must be measured in feet, and equals twice the stroke multiplied by the number of revolutions per minute. Let p = mean effective pressure in pounds per square inch ; A = area of piston in square inches ; L = length of stroke in feet ; N = revolutions per minute. Then pA acting force or mean total load on the piston measured in pounds, and 2LN distance moved per minute in feet = piston speed. Hence foot-pounds of work per minute equals product (pA) X (2LN) or what is the same thing 2pLAN. Hence we have the formula : 2 pLAN Horse power = - 33000 This is the usual formula for finding the indicated horse power, and is commonly employed for working up indicator cards for this purpose. The reasons for measuring L in feet and A in square inches will be readily seen from the following considerations. Work is composed of two factors, the force factor and the distance factor. The first must be measured in pounds and the second in feet. The product pA is the force factor, and since / is usually measured in pounds per square inch, A must be measured 4 i8 PRACTICAL MARINE ENGINEERING. in square inches in order that pA may be the total mean load in pounds. The product 2LN is the distance factor, and hence 2.L the distance traveled per revolution must be measured in feet, in order that 2.LN may be the distance traveled per minute measured in feet. The product (pA) X (2ZJV) or 2pLAN will then give the work measured in foot-pounds as we have seen above. We will now give by rule the operations necessary to find the indicated horse power, as expressed by the formula above. Rule Multiply together the mean effective pressure in pounds per square inch by the length of the stroke in feet, and this product by the area of the piston in square inches, anrl this product by the number of revolutions per minute, and this product by 2, and then divide the final product by 33,000. The quotient will give the indicated horse power. Fig. 262. Mean Effective Pressure from Indicator Card. Now the various factors which enter into either the formula or rule for horse power, the length of stroke and area of the piston come from the dimensions of the engine, and the revolu- tions per minute from the counter, or by actually counting them, watch in hand. There remains the mean effective pressure p which must be found from the indicator cards, and to this part of the operation we now turn. The mean pressure for a single card such as Fig. 262 gives simply the mean of the pressure in one end of the cylinder, say the top. To obtain this mean pressure we may proceed in a number of different ways. Fundamentally the mean of such a series of pressures as given by the indicator card, is found by dividing the area of the card by the length. This gives the side of a rectangle which would have the same area as the card. Thus in Fig. 262 if the rectangle ABCD has the same area as the card, then the side A D of the rectangle is the. mean height of the card, and to the proper scale INDICATORS AND INDICATOR CARDS. 419 will give the mean pressure desired. Hence any method which will give the area of the card may be used for rinding a mean height, and hence a mean pressure. In Part II., Sec. 9 [15] are given various rules and methods for finding the measure of an irregular area, illustrated by the ex- ample of an indicator card, and any of these may be used as there explained. The method most commonly used is to meas- ure the ordinates on the dotted lines as in the figure there shown, take their sum, and divide by their number, 10. This multiplied by the scale of the indicator spring will give the mean pressure desired. The simplest method of locating the intervals for these dotted ordinates is that explained in Part II., Sec. 10 [4]. To carry this out we proceed as follows : Let the card be represented in Fig. 263, then draw the lines at the ends as shown, perpendicular to the atmospheric line OA Fig. 263. Subdivision of Indicator Card for Obtaining Mean Ordinate. and tangent to the card, thus fixing its length. Then lay off the line OB at an angle and on OB lay off first a half divi- sion Oi, then nine whole divisions, and then a half division as shown. The divisions may be taken from y to y 2 inch in ac- cordance with the length of the card. Then drawing a line from B to A and other parallel lines from the points of division on OB to OA, the locations for the ordinates are determined, and they may be drawn as shown. Where a large number of cards are to be worked up in this way, time will be saved by the use of a form of template or pattern for locating these points. Such an implement is shown in Fig. 264 and consists of a piece of hard wood with small steel points set in to the edge, spaced according to the lay out of points along OB Fig. 263. The distance between the extreme points is somewhat greater than the length of the longest card likely to be met with. Instead of 420 PRACTICAL MARINE ENGINEERING. steel points set in a block of wood, a thin plate of steel may be cut out and filed up so as to leave the points projecting at the desired intervals. In using this device it is simply necessary to draw lines tangent to the ends of the card as shown, and then to place one end of the template on one boundary line PR at any convenient point as P, and swing it to such an angle as will just bring the other end Q to the other line QS. The template is then pressed down so as to mark the paper with the points, and lines parallel to those at the ends are drawn through the points thus marked, as shown by the lines of the figure. In this way the ordinates spaced in the manner desired may be rapidly laid out and drawn in. For summing the ordinates the method by the use of a strip of paper as explained in Part II., Sec. 9 [15] may be recom- \ i i Fig. 264. Subdivision of Indicator Card for Obtaining Mean Ordinate. mended as the simplest, quickest and most satisfactory available for the purpose. Having thus in one way or another found the mean effective pressure for one card, the other one of the pair is taken in like manner, thus giving tlie mean effective for the other end of the cylinder or other stroke. These two values may then be averaged, and the result taken as the mean effective pressure for the revolution, thus furnishing the final factor p required in the formula or rule for horse power. It must be noted that this operation is slightly in error by reason of the difference in area between the upper and lower sides of the piston. On the upper side the entire area is effective INDICATORS AND INDICATOR CARDS. 4*' while on the lower side the piston rod takes out a small area in the center. To take account of this, we may compute the I.H.P. for each end of the cylinder separately. To this end we take each card by itself, say the head end first, and find the mean. effective pressure which we may denote by / x . Let the entire piston area he A l . Then as before the mean load or average acting force is the product of the two, />, A r The distance acted through is L for each down stroke, and the number of down strokes per minute is equal to the number of revolutions A r . Hence the distance per minute for the down strokes is LN and the I.H.P. for this end of the cylinder will be: i 33000 33000 In a similar manner we then find the mean effective pres- sure for the bottom or crank end of the cylinder which we may call pi. Then taking from Ai the area of the piston rod, we have the effective area of the bottom of the piston which we may call At. Then similarly as in the head end we have for the I.H.P. in the crank end, H --- P* A LX ^P~- LA - N 33000 33030 The total I.H.P. will then be the sum of these for the two strokes up and down, or : IH.P. ^ H,-\ H,= For illustration see example (7) below. Mean Effective Pressure by the Aid of the Planimctcr. The planimeter, an instrument for measuring areas, is also frequently used for working up indicator cards, and where the number is large will be found of great service. Such instru- ments may be. obtained of most makers of indicators or of dealers in mathematical instruments. General directions for their use will accompany them. The following hints may be given for their use with indicator cards. Where the instrument has an adjustable bar it should be sel so ns to read the area in square inches. \Yhere the bar is not adjustable the instrument is usually already set to read in terms of this unit.- The order of procedure is then as follows : (i) Draw lines at the ends of the card at right angles to the atmospheric line so as to be able to determine its length. 422 PRACTICAL MARINE ENGINEERING. (2) Place the instrument and card in a suitable position, and read the record wheel, putting down the result, say 3.26 as below : Readings. Differences. Average. First 3.26 Second 7.08 3.82 Third 10.92 3.84 3.83 (3) Then trace around the contour, usually in the direction with the hands of a watch for a second reading greater than the first, and come back carefully to the starting point. Then read again and set down the result, say 7.08 below the first as shown. (4) Then repeat, tracing around as before, read and set down the result, say 10.92, below the others as shown. In mak- ing the last reading it will be noted that on the instrument itself we might be able to read only 0.92, but the increase upward from 3 to 7 shows that the wheel has passed the starting point and begun again, so that we must add the ten and write 10/12. (5) We then take the difference of the readings, the first from the second and the second from the third and set down as shown, and then average these two numbers, thus finding in the present case 3.83 for the area in square inches. The reason for going around the area twice is to have two measurements, so that each will give a check on the other. If they differ widely an error somewhere is certain, and they must be repeated, while if nearly the same, as in the case given above, the error is no more than must be expected with such means, and the average may be taken as the value of the area desired. (6) We next divide the area by the length of the card. Thus suppose in the case in hand that the length is 4.2 inches. Then 3.83 -r- 4.2 = .912 inches. This is the mean ordinate or mean height of the card in inches. (7) We next multiply by the scale of the indicator spring and thus find the mean effective pressure desired. Thus sup- pose the spring to be 60 pounds to the inch. Then 60 X .912 = 54.72 pounds. This is then the mean effective pressure for the stroke as given by the card thus measured. We then proceed similarly with the other card, and use the results for the determination of horse power in the manner al- ready explained. INDICATORS AND INDICATOR CARDS. 4*3 Illustrative Examples. (1) The area of an indicator card is 2.87 sq. in. and its length is 3.8 in. What is the mean height? Solution: 2.87 -4- 3.8 = .755 in. (2) The scale of the indicator spring is 40 Ibs. per inch. What is the m.e.p.l* Solution: .755 X 40 = 30.2 Ibs. (3) The ordinates measured in inches taken from an indi- cator card divided up as in Fig. 263 are as follows : .91, 1.30, 1.44, 1.40, 1.35, 1.20, .95, .80, .70, .25, and the scale of the indicator spring is 60 Ibs. per inch. Find the m.e.p. Solution : Adding the lengths as given, we have for the sum 10.40. Hence dividing by 10 we have for the mean ordinate 10.40 -f- 10 1.04. Hence the m.c.p. is 60 X 1.04 = 62.4 Ib. (4) The total length between marks on a strip of paper used to measure the ordinates as described in Part II., Sec. 9 [15] is found to be 6.3 in. The scale of the spring is 20 Ib. Find the m.c.p. Solution: 6.3 -f- 10 = .63 in. = mean height, and .63 X 20 = 13.6 Ib. = m.e.p. (5) Given an indicator card with ordinates spaced as in Fig. 263. The pressures measured by a scale corresponding to the indicator spring are as follows : 18, 26, 28.4, 27.8, 27, 24.2, 19, 16, 14.3, 7.2. Find the m.e.p. Solution: We add the pressures and find the sum 207.9. Divide this by 10 and we have 20.79 or 2o -8 Ib. as the value of the m.e.p. (6) From the two cards of a pair the values of the m.e.p. are found to be 28.6 for one end and 32.2 for the other. The piston area is 1,213 sc l- m -> the stroke 39 in. and the revolutions 102. Find the I.H.P. neglecting the effect due to the area of piston rod. Solution: The m.e.p. for the whole revolution is the mean of the values for the two ends or m.c.p. (28.6 X 32.2) -f- 2 = 304- Then stroke in feet = 39 -^ 12 = 3.25. Then I.H.'p. : = 2 X 3 ' 4 X 3 ' 25 x I213 X I02 33000 * This abbreviation is often used for the term mean effective pressure. 4 2 4 PRACTICAL MARINE ENGINEERING. Multiplying out the factors of the numerator and dividing by the denominator we find I.H.P. = 741 Ans. (7) Given the following : Diam. of cylinder = 24 in. . Diam. of piston rod = 5 in. m.e.p. from head end or pi = 63.4 Ib. m.e.p. from crank end or p* = 58.8 Ib. Stroke = 36 in. Revolutions no. Find the I.H.P. both with and without the allowance for the area of piston rod. Solution: Area of 24 inch piston or Ai = 452.4 sq. in. Area of 5 inch piston rod or a = 19.6 sq. in. Effective area of lower side of piston = difference, or A* = 432.8 sq. in. Then neglecting the effect of the rod we should say : m.e.p. = (63.4 + 58.8) -r- 2 = 61.1 2 X 61.1 X 3 X 45 2 -4 X no 33000 Working this out we find: I.H.P. = 552.8. Taking account of the piston rod area we have for the head end: H = 6 3-4 X 3 X 452.4 X no =2g6 g 33000 For the crank end : = 58.8x3^433-8X110 = 33000 Adding we have : H = 541.3. There is thus seen to be in this case a difference of 11.5 horse power, constituting an error by the first method of some considerable amount. It is readily seen that this error will be relatively less the larger the cylinder, especially in the cylinders of a multiple expansion engine. Thus in the case given which was for the H.P. cylinder of a triple expansion engine the error is 11.5 horse power, or about 2 per cent. For the I. P. cylinder the error would be not far from 4.5 horse power or about .8 per cent., while for the L.P. cylinder it would be perhaps two horse power or about .3 per cent. This would give a resultant error and J.H.P = /'X6..ix 3 X45'.4Xiiox V 33000 / INDICATORS AND INDICATOR CARDS. 425 of about i per cent, for the engine as a whole. While these figures would vary with particular circumstances, they will serve to illustrate the nature of the error, and the methods given show how to avoid it when so desired. [4] Combined Indicator Cards. The cards taken from the various cylinders of a multiple expansion engine, as for example those of Fig. 265, may be HIGH PRESSURE ATMOSPHERIC LINE ATMOSPHERIC LINE Fig. 265. Set of Indicator Cards from Triple Expansion Engine. combined in such a manner as to show very instructively the continuous history of the expansion of the steam, that is the continuous relation between volume and pressure as the steam 4*6 PRACTICAL MARINE ENGINEERING. passes through the engine. To effect this combination it is necessary to lay down the various cards in one diagram and all to the same scale of volume and pressure. The details of the operation may be sketched out in the following steps : (1) In Fig. 266 take the two lines at right angles, OX and OY, the former as an axis of volume and the latter as an axis of pressure. (2) Determine in cubic feet for each of the cylinders the volume of the/ clearance (Sec. 67), and the volume swept by the piston. (3) Lay off the lines AB, CD, EF at such distances from OY as to represent respectively the clearance volume in the Marine Engineering Q X. Fig. 266. Combined Cards from Triple Expansion Engine. H.P., I. P., and L.P. cylinders, taking care to select the scale of volume such that the L.P. volume plus its clearance as measured between the lines OY and GK will come within the desired limits of the diagram. (4) Lay off on each card the line of zero pressure or the perfect vacuum line, as shown by OX in the small diagram A. (5) Take next the H.P. card as at A for example, and select any point such as P. Measure in any convenient units the dis- tances MP and MN : multiply the volume of the cylinder by the former and divide by the latter. This will give the volume INDICATORS AND INDICATOR CARDS. 427 swept in the H.P. cylinder from the beginning of the stroke to the point P. (6) The corresponding point P of the combined diagram is then found by measuring from AB a distance HP representing this volume, and from OX a distance JP representing the pres- sure PO on the card. This will give the point P, and other points are found in a similar manner, as many as may be needed to determine the form of the card as shown. It is to be especially noted that the H.P. card of the combined set is the same as that at \ but drawn simply with different scales, and therefore more or less distorted in appearance. (7) The points necessary to determine the other cards of the combination ae found in a precisely similar manner, re- membering that in each case volume is measured from the clear- ance line CD or EF, while the pressure must be measured from the line of zero pressure for the card and laid off from the cor- responding line OX of the combined set. This diagram shows the general manner in which the steam expands on its way through the engine. An expansion line PQ shows the general law of expansion as a continuous operation. PR is an ideal expansion line laid down as a hyperbola, all points in the curve corresponding to the condition that the product of volume by pressure shall be constant, or in symbols, pv Constant. This shows the result of the so-called true hyperbolic expansion law, and as appears from the diagram, the actual expansion line is somewhat below this ideal line. The equation to the actual expansion line may be expressed in the form pv" = Constant, where n is an exponent having values usually lying between 1.15 and 1.2. The equation pv 1 - 18 may be taken as very commonly representing this line in good average practice. The extent to which the area bounded by the line PR and the clearance lines on the left is well filled in. is an indication of the degree to which the performance of the actual engine approaches that of an engine having true hyper- bolic expansion and with indicator cards as shown in Fig. 252. The relation between the actual engine and such an ideal case is usually expressed by a percentage factor known as the "card factor." For good practice with triple expansion engines, this factor will be found from .60 to .70. With quadruple expansion engines representative values are found from .55 to .60. 428 PRACTICAL MARINE ENGINEERING. The diagrams of figures 265 are reproduced from an actual case and may be considered as representing good modern practice in general character and form. At this point reference may be made to the effect on the distribution of power in a compound or multiple expansion engine, of linking up or cutting off earlier in the intermediate or low pressure cylinders. Taking first the case of a compound, linking up or shortening the cut-off on the L. P. cylinder will increase the power in this cylinder and decrease it in the high. This result at first sight seems contradictory to common ex- perience, because in a single cylinder we are accustomed to associate an earlier cut-off with decrease of power. In the case of the compound, however, cutting off earlier in the L.P. cylin- der gives a higher back pressure in the H.P. cylinder and a consequently higher initial pressure in the L.P. cylinder, and thus results in an actual addition to the L.P. indicator card area instead of a decrease as in the case of a single cylinder. At the same time the area of the H.P. card will be reduced and the power developed in this cylinder will be decreased correspond- ingly. Similarly for a multiple expansion engine and in general, cutting off earlier in any of the cylinders beyond the first or H.P. will result in an increased back pressure for the next pre- ceding cylinder, and in a higher initial pressure for the cylinder itself, and thus in an actual addition to the area of the indicator card and a corresponding subtraction from the area of the card for the cylinder preceding. Thus in Fig. 266, cutting off earlier in the L.P. cylinder will result in raising the upper line of the L.P. and lower line of the I. P. cards, and thus in increasing the area of the former and decreasing that of the latter. In like manner cutting off earlier in the intermediate cylinder will result in raising the upper line of the I. P. and lower line of the H.P. cards and thus in increasing the area of the former and decreasing that of the latter. In like manner cutting off later in any cylinder be- yond the H.P. will result in similar changes but in the opposite direction. Thus a later cut-off in the I. P. cylinder will decrease the power developed in that cylinder, and increase the power developed in the H.P. cylinder. It thus results that a combi- nation of changes such as a later cut-off in the I. P. cylinder and earlier cut-off in the L.P. will both tend to decrease the power developed in the I. P. ; while an earlier cut-off in the L.P. cylinder INDICATORS AND INDICATOR CARDS. 4*9 and a later cut-off in the H.P. will both tend toward an increase of power developed in the I. P. Sec. 56. STEAM ENGINE INDICATORS. [i] Descriptive. The indicator card has already been described in Sec. 55. It is the purpose of the indicator to draw this card. It must therefore provide for the proper combination of these move- ments, (i) A movement in step with the piston and propor- tional to it in amount so that all horizontal distances on the card shall bear a constant proportion to the corresponding parts of the stroke. (2) A movement at right angles to that in (i) and in direct proportion to the pressure per square inch on the pis- ton in the end of the cylinder to which the indicator is con- nected. The combination of these movements will then result in a diagram such as those shown in Sec. 55, and giving at each point of the stroke the pressure on the piston as desired, the upper line showing the pressure which urges the piston for- ward on one stroke and the lower line the pressure which re- sists its movement backward on, the return stroke. In Fig. 267 a modern indicator is shown. A is a drum to which the paper is attached by means of the clips as shown. This drum is given a motion back and forth about its axis by means of a connection with the crosshead through the so-called "reducing motion." By this means the drum is given a motion of some three to five inches in extent, just in step with the motion of the piston and proportional to it in amount. B is the indicator cylinder or barrel connecting with the end of the engine cylinder from which the card is to be taken. Within the cylinder, as shown, is a piston with a coiled steel spring above, resisting pressure from below the piston upward. To the piston rod is attached a linkage carrying at the end of the arm P the pencil point which is to trace the diagram upon the paper carried by the drum. The connection between the linkage and the piston rod is such that the former may be swung freely about the cylinder upon a ring to which it is attached. The pencil may thus be brought into contact with the paper on the drum or withdrawn from it as desired. An adjustable screw stop is provided, and so arranged as to arrest the movement 43 PRACTICAL MARINE ENGINEERING. of the pencil motion when swung around by the hand, and thus allow only light contact between the pencil point and the paper. In some cases a brass point is used instead of a pencil, the cards being of paper specially prepared so that the brass will leave a black mark upon it. Such points are strong and require no sharpening except at long intervals. The object of the linkage which, forms the pencil motion is to magnify the movement of the indicator piston, and thus Marine Engineering Fig. 267. Steam Engine Indicator. to allow the use of stiff springs with a corresponding small movement of spring and piston. With high revolutions es- pecially, this is found necessary in order to reduce as far as possible the disturbance in the diagram due to the inertia of the moving parts of the indicator. The linkage is thus a form of multiplying motion, or a reducing motion reversed, and it INDICATORS AND INDICATOR CARDS. 43 1 should give to the pencil a movement exactly proportional to that of the piston, but 3 to 5 times greater as may be desired. The relation between the pressure per square inch and the actual movement at the pencil point fixes the so-called scale of the spring. This depends also on the actual area of the indi- cator piston, which is, however, usually about one-half square inch. Thus a 40 pound spring means a spring such that a pres- sure of 40 pounds per square inch on the indicator piston, or say an actual load of 20 pounds, will produce a movement of one inch at the pencil point. By means then of the piston, spring and linkage, the second of the necessary movements as mentioned above is thus pro- duced. Returning to the drum the first of the motions above noted is obtained by some form of reducing motion as described be- low. The connection between the drum and the reducing mo- tion is usually made by means of a cord C wrapped around a groove in the base as shown. The cord thus serves to pull the drum around in one direction while the return stroke is made by means of a coiled spring in tfie base. This spring op- poses the motion given by the cord, and is therefore coiled up during the forward stroke. As soon, however, as the pull of the cord ceases the spring takes charge and uncoiling carries the drum in the reverse direction as fast as the cord will allow, thus keeping the latter taut and insuring the motion of the drum in step with the main piston in both directions as accurately as the form of reducing motion may determine. A separate indicator may be provided for each end of the cylinder, or by suitable pipe connections and a three way cock, one indicator may be made to serve for both ends. In any case the cock which shuts off the indicator must be so arranged that when shut off from the cylinder the space below the piston will be connected to the outside air. The piston with equal air pressure on both sides will then come to a position of equilib- rium, and the atmospheric line may be drawn. [2] Reducing Motions. The purpose of the reducing motion has already been stated. There are many different ways in which the desired movement may be given to the drum, some of them accurate in geometrical principle and some only approximate. 432 PRACTICAL MARINE ENGINEERIXG. One of the most common is by means of links, levers and bell-cranks. The simplest of such forms is shown in Fig. 268. A is a pin attached to the crosshead. AB is a short link con- necting the crosshead to a lever BD pivoted at C. The point D will then move in step and nearly in constant proportion to the piston, and from D the motion for the drum may be taken, either by a cord direct, or from the end E of a rod DE moving as shown. In such cases the cord should run in continuation of the line DE and not off at an angle as EF or DH. As a general rule in all such cases, the reducing motion should be so adjusted that the cord part should not undergo changes of angular direction, or at least such changes should be made as small as possible. Thus in Fig. 269 suppose the point from Fig. 268. Reducing Motion. V B" Marine n gineering Fig. 269. Reducing Motion. which the. motion is taken to move through a path AB, and the indicator guide pulley to be at P. Then at one extreme the cord will be represented by PA, and at the other by PB. Such a change in the angular direction of the cord relative to the line of motion AB will result in error, and should be avoided by bringing P over AB or AB under P. It is not necessary that the motion of the point E Fig. 268 should be vertical so long as the gear is so arranged as to reduce to a minimum all angu- lar changes in cords and connecting links. Thus the arrange- ment of Fig. 270, while containing a large number of joints and parts, may be as nearly correct as the simpler form of Fig. 268. Instead of taking the motion direct from D a link DG con- nects this point with a bell-crank GHI pivoted at H. Then a INDICATORS AND INDICATOR CARDS. 4:3 second link 1J connects this to a second bell-crank JKL and a rod LE guided at M gives a point E from which the motion- may be taken, or if more convenient the rod LE may be dis- pensed with and the motion taken from L direct. Such a com- plication of gear is of course not desirable, and the arrangement is shown simply as an illustration of a combination of links and bell-cranks which would still give the motion required. A - 4- Fig. 270. Reducing Motion. All such forms of reducing motion are approximate and not geometrically exact. The error is, however, in most cases small and is usually neglected, though if desired its nature and extent may be investigated by a suitable geometrical analysis of the gear. Instead of taking the motion from the crosshead by means of a short link as AB Fig. 268, a lever BD Fig. 271 is some- times provided, having a forked end and pivoted at C or D. A pin on the crosshead working in the slot or forked end gives the to and fro motion to the lever, while from D or C the desired motion is taken. Fig. 271. Reducing Motion. Instead of attaching the cord direct to C for example, a sector of wood PQD with center at D is attached to the arm, and the string is led off from the face of the sector. Such a sector may also be employed with the arrangements shown in Figs. 268 and 270. None of these motions is geometrically exact. A form of pantograph consisting of jointed rods as shown in Fig. 272, may sometimes be used when there is room for it 434 PRACTICAL MARINE ENGINEERING. to work freely. A is attached to the crosshead and D or E is the fixed pivot. Then the other point E or D will provide a motion for the indicator drttm which is geometrically exact. Here again however, the string should be so led that its angu- larity will not vary. Instead of this arrangement of links the so-called lazy-tongs as shown in Fig. 273 is sometimes employed. This is also geometrically exact, and is in fact an equivalent to the panto- graph in Fig. 272, without requiring quite as much room. Various combinations of pulleys may also be used, as illus- trated in Fig. 274. AB is an arm projecting from the crosshead and moving with it. To the end B of this arm is attached a cord wrapping around a light pulley P. Q is a smaller pulley on Marine UnjiMerinj Fig. 272. Pantograph Reducing Motion. Fig. 273. Lazy Tongs Reducing Motion. the same axis and moving with P. Wrapped on this is a cord CD, which may be led off in various directions to the indicator as shown by CD, CD^ CD L> . This gear is geometrically exact. Various other forms of reducing motion are also to be met with, but those described will be suffcient to show the forms most commonly available for marine practice. [3] Taking an Indicator Card. The instrument should first be examined and put into proper condition and adjustment. This should include the following points : (i) The joints should all work freely, but without lost motion. INDICATORS AND INDICATOR CARDS. 435 (2) The piston should not bind nor should it be so loosely fitted as to allow serious leakage. A slight leakage is, however, better than too snug a fit. (3) The working surfaces of the barrel and piston should be carefully wiped and oiled. This should be repeated from time to time when a series of cards is being taken. The joints of the Fig. 274. Reducing Motion. pencil motion should also be lubricated with clock oil as often as may be required. (4) The pencil points should be sharpened and the screw stop so adjusted that the point can rest only lightly on the paper. The operation of taking the card itself is briefly as follows : The indicator is attached to the cock, a blank card is placed on the drum and the cord connection is adjusted so that the drum will have the proper stroke without coming against the Fig. 275. Putting on an Indicator Card. stop at either end. In attaching the blank card the most con- venient way will be to bend the sheet of paper around and grasp both edges between the thumb and forefinger as at AB in Fig. 275a. Then slip over the drum and under the clips so that the latter will come outside the paper as shown at PQ, b. Then slip the paper down into place, pull and adjust so that it fits snug- 43 6 PRACTICAL MARINE ENGINEERING. ly, and bend the edges back as in c. The cord is then hooked on to the reducing motion and the drum takes up its movement with the main piston. The cock is then opened to the end of the cylinder from which the diagram is desired, and the pencil immediately takes up its motion corresponding to the varying pressures of the steam. The indicator piston should be allowed to work in this way for a few strokes, or until everything is warmed up into working condition. When everything is in readiness the pencil motion is moved up against the stop so that the pencil resting lightly on the paper will trace its path for a complete revolution or longer if de- sired. Then remove and shut off the indicator from the cylinder. This will connect it with the air, the indicator piston will come to equilibrium under atmospheric pressure, and the atmospheric line may then be drawn. The drum connection is then un- hooked, the paper removed, a fresh one replaced, and the next card taken when desired. If one indicator is used for both ends of the cylinder, both cards should be taken on the same paper with as small an interval between as possible. The cock is swung over for one end and the card taken, and then imme- diately swung over for the other end and the second card taken without loss of time. The cock is then closed off connecting the indicator with the air, and the atmospheric line is then drawn. Each card as it is removed from the indicator should be marked with sufficient data to identify it, and make possible its use for the purpose intended. This should include at least the following items : (1) Cylinder. (2) End from which card is taken. (3) Revolutions. (4) Scale of spring. (5) If a series of cards is being taken the time and serial number should also be set down. The various other items usually printed on the back of the card may be filled in at a later time as may be convenient. When cards from both ends are taken on one paper, we must be able to assign each to its proper end of the cylinder. The most cer- tain way of determining this is to shut off the connection to one INDICATORS AND INDICATOR CARDS. 437 end of the cylinder entirely, and then take the card from the other end. It will thus appear how the card from this end lies on the paper, whether with admission line to the right or left, and this will show how to mark the entire series of cards taken with the same arrangement of reducing gear, etc. 438 PRACTICAL MARINE ENGINEERING. CHAPTER IX. SPECIAL TOPICS AND PROBLEMS. Sec. 57. HEAT AND THE FORMATION OP STEAM. [i] Constitution of Matter. For the purpose of explaining or discussing the relations be- tween matter and the forces of nature, all substances are sup- posed to be composed of enormously large numbers of in- definitely small parts called molecules, each one of which is supposed to be, in fact, the smallest portion of the substance which can exhibit its various properties. These molecules are furthermore not at rest, but are supposed to be in a state of more or less violent agitation or motion. If the motion of each molecule is about a fixed center so that they all retain their average positions fixed in the body, it is said to be a solid or in the solid state. If the motion of the molecules is about centers which themselves are free to move about in any direction, so that the average position of the molecules is not fixed and the body readily changes its form, it is said to be a liquid or in the liquid state. If the motion of the molecules is in straight lines hither and thither, bound to no center or location, but ever striving to fly as far apart as possible, the substance is said to be a gas or in the gaseous state. In the solid and liquid states the molecules are bound to- gether by forces of molecular attraction, so that they tend to maintain about the same average distance apart, and thus to fill the same volume. Any attempt to change this average distance between the molecules and thus to make the volume larger or smaller, must deal with these molecular forces. The only prac- ticable way of doing this is through the agency of heat, as we shall see in the next section. In a gas the forces binding the molecules together have been overcome, and the molecules have SPECIAL TOPICS AND PROBLEMS. 439 been separated so much further apart that all traces of these attractive forces have disappeared, and instead we now have a repulsive force acting between the molecules and urging them as far apart as the limits of the volume which contains them will allow. Due to this property a gas will expand and fill any volume, no matter how large, the repulsive force or force of ex- pansion, however, becoming weaker as the volume increases and the average distance between the molecules becomes greater and greater. [2] Heat. (i) Heat and Its Relation to Matter. We know energy as the capacity for doing work. Also the energy of motion is called kinetic energy, while the energy of position or location relative to a given force, is called potential energy. Heat is one of the many forms of energy. It is, in fact, the energy of the molecule, and the heat in a body means therefore simply the amount of such molecular energy which the body possesses. This energy of the molecule is partly kinetic or due to its motion, and partly potential due to its position relative to the molecular forces which act upon it. The addition of heat to a body or its subtraction from a body means therefore the addition or subtraction from the energy of its molecule, and hence the addition to or subtraction from its store of molecular energy. This addition or subtraction of heat is always accom- panied by a series of changes in the state or condition of the body. Thus if heat be added to a lump of ice at the melting point or 32 Fah. it first melts or changes from a solid to a liquid, remaining at the constant temperature of 32 and slightly con- tracting in volume meanwhile. If heat is still farther added the water grows warmer to the touch and as shown by the ther- mometer. At the same time it continues to contract slightly till it reaches a temperature of about 39 Fah. and then slowly ex- pands. If under atmospheric pressure the increase of tempera- ture and volume will continue with the addition of heat until the thermometer marks a temperature of 212 Fah. Then the further addition of heat occasions no further elevation of tem- perature, but instead, a new change of state. The water now passes into the state of vapor or steam, the temperature of both the water and the vapor formed from it remaining meanwhile 440 PRACTICAL MARINE ENGINEERING. constantly at the fixed temperature of 212. After the water is completely vaporized, if the vapor be inclosed in a chamber of fixed volume and heat still further added, it will then be found that the pressure and temperature will continue to increase so long as additional heat is supplied. If instead the pressure is kept constant, the volume and temperature will increase as heat is added. If the temperature is kept constant, the pressure will fall as the volume is increased. From the start then, as more and more heat has been added, the water has exhibited successively the three states of matter. As ice it is a solid; in its usual state or between 32 and 212 under atmospheric pressure, it is a liquid; and after it is com- pletely vaporized and heat is still further added so as to carry the conditions considerably beyond those at which the vapor was formed, it becomes a gas. We must here explain the difference which may be implied in the words gas and vapor. When a substance first changes from the liquid to the gaseous state, or while the pressure, volume and temperature are near those corresponding to such a change, the substance is more strictly called a vapor, or is said to be in the vaporous condition. If the substance is in the gaseous state but with pressure, volume and temperature conditions far removed from those corresponding to the change of state, the substance is more generally called a gas. There is no sharp line of difference between a vapor and a gas. The former means simply a substance in the gaseous state, but at or near the con- ditions corresponding to the process of change from one state to the other, while the latter means likewise a substance in the gaseous state, not far removed from the conditions correspond- ing to the process of change of state. There are thus two chief kinds of change which the applica- tion of heat may produce. (a) It may change the temperature of a substance accom- panied by a change of pressure or volume or both, but without change of state. (b) It may produce a change of state as from solid to liquid or liquid to vapor, accompanied usually by a change of volume, but without change of temperature. If, however, the pressure varies during the change of state, then the temperature at which the change occurs will also vary, but there will be no change of temperature directly accompanying the change of state. In SPECIAL TOPICS AND PROBLEMS. 441 consequence, during the change from solid to liquid or vice versa, the temperatures of both are the same, and similarly during the change from liquid to vapor or vice versa, the temperatures of both are the same. It must be understood when changes are referred to as depending on the addition of heat, that the subtraction of heat will produce changes in exactly the opposite direction. Thus if the addition of heat causes a body to expand, the subtraction will cause it to contract : if the addition causes an increase of pressure the subtraction will cause a decrease : if the addition causes a change of the state from liquid to vapor, the subtrac- tion will cause a change from vapor to liquid, etc. (2) Sensible and Latent Heat. Heat which causes a change of temperature in a body, as when water is heated and becomes hotter to the touch or to the thermometer, is called sensible heat. This corresponds to a change in the kinetic energy of the molecule, so that increase of velocity of the molecule and in- crease of its kinetic energy correspond within the substance to the growing hotter to the touch and to increase of temperature as observed on the outside. Heat which is involved in a change of state but which pro- duces no effect on the temperature of the substance (as in the melting of ice at 32 or the boiling of water at 212) is called latent heat. This corresponds to a change in the potential energy of the molecule so that an increase in the average distance between the molecules (acquired in opposition to the molecular forces acting), and a consequent increase in their potential energy corresponds within the substance, to the change of state at constant temperature as observed on the outside. It must be understood that there is really but one kind of heat, and that this division into sensible and latent is only a matter of convenience in order to signify the particular energy change which is effected within the body. The heat required to raise the temperature of a body or to increase its sensible heat is thus expended in increasing the velocity of the molecules of the body, and hence in increasing their kinetic energy. The heat required to effect a change of state, or to increase the potential energy is expended, on the other hand, in increasing the average distance between the molecules, and in increasing the volume, of the body against whatever external forces may exist. The gradual expansion of a body with increase of tempera- 442 PRACTICAL MARINE ENGINEERING. ture is accounted for by assuming that as the velocity of the molecules is increased, their average path is increased also, and hence their average distance apart, and hence the volume of the body. (3) Temperature. We have seen above that temperature refers to the condition of a body as regards its sensible heat, or the kinetic energy of its molecules. Two bodies are said to be at the same temperature when there is no tendency for heat (that is, molecular energy) to flow from one to the other. This con- dition is measured by the thermometer, an instrument too well known to require particular description. The Fahrenheit scale which is commonly used by engineers in the United States is graduated as follows : The temperature of melting ice is called 32 and that of boiling water 212. The interval between the two is then evenly divided into 180 parts, and the same divisions are extended above and below as far as may be desired. On the Centigrade scale the temperature of melting ice is called o and that of 'boiling water 100. The interval is then evenly divided into 100 parts, and the divisions extended above and below as may be desired. For transforming temperatures from one scale to the other we have the following equations : F == 9/5 C + 32 C == 5/9 (F -- 32) where F and C denote respectively the temperatures on the Fahrenheit and Centigrade scales. Examples: Transform 20 C into Fah. Operation : F =: 9 x 20 -^ 5 + 32 = 36 + 32 = 68. Transform 20 Fah. to C. Operation: C =5 /9 (20 32) 5/9 ( 12) - -6 2/3 or 6 2/3 below zero. Transform 77 Fah. into C. Operation : C =5/9 (77 32) = = 5/9 x 45 = = 2 5 Transform 22 Fah. into C. Operation : C == 5/9 ( 22 32) == 5/9 ( 54) - - 30 (4) Heat Unit. Care must be taken to distinguish between quantity of heat and temperature. The first refers to the total amount of heat energy present in the substance, the second to the kinetic energy of a molecule. A large cup of warm water and SPECIAL TOPICS AND PROBLEMS. 443 a small cup of hot water may both have the same quantity of heat, but not the same temperature. A cup of hot water and a barrel full of hot water may have the same temperature, but the quantities of heat will be very different. For measuring quantities of heat, use is made of a heat unit defined as the amount or quantity of heat required to raise one pound of water one degree in temperature. Inasmuch, further- more, as the amount thus required would vary slightly at different temperatures, it is necessary to fix the temperature at which the unit is to be defined. The temperature thus taken for the definition of the heat unit has sometimes been at the freezing point, or again at the point of maximum density of water which is about 39 Fah., or again at about 62, or from 62 to 63. It is very difficult to determine the amount of heat required to raise water one degree at or near the freezing point, while between 60 and 70, or at about an average atmospheric tem- perature, the measurements are most readily made. For this reason a temperature within this range is to be preferred for definition of the heat unit. . The heat unit thus defined is often known as the British Thermal Unit, the name being usually abbreviated to B. T. U. (5) Joule's Equivalent. Since heat is but a form of energy it follows that it should be possible to transform heat into me- chanical work, and vice versa. It is for the first purpose that the steam engine is used, while instances of the latter transforma- tion are constantly before our eyes, as in the heat developed by the friction of a bearing, or in turning a chip from a bar of steel, etc. It therefore becomes of importance to know the ratio of transformation, or how much mechanical work measured in foot-pounds corresponds to one heat unit as above defined. This has been made the subject of careful experiment extending over the past one hundred years, and the latest and most reliable results seem to give for this ratio the value 778. That is, one B. T. U. is equivalent to 778 foot pounds of mechanical work. This means that when in a steam or other heat engine heat is transformed into mechanical work, for every B. T. U. so trans- formed and disappearing as heat, 778 foot pounds of work will be obtained ; or again when mechanical work is transformed into heat, for every 778 foot pounds so transformed and disappear- ing as work, one B. T. U. of heat will appear. 444 PRACTICAL MARINE ENGINEERING. This number or ratio, 778, is known as the mechanical equivalent of heat, or frequently as Joule's equivalent, though its value as determined by Joule was somewhat smaller than the value given above. (6) Transfer of Heat. Heat may be transferred from one body or place to another in three different ways : by radiation, by conduction, and by convection. By radiation we mean the transfer of heat through space in straight lines, as from the sun to the earth, or from a furnace fire to the face when the door is opened. By conduction we mean the transfer of heat along a body from one molecule to the next, as when a slice bar becomes warm at one end if red-hot at the other. By convection we mean the transfer of heat from one point of a liquid or gas to another by means of currents set up in the liquid or gas and carrying the heated molecules from one place to another, as in the circulation set up within a Scotch boiler. Two other operations are also concerned in the transfer of heat from one substance to another. These are emission and absorption. By emission we mean the giving off or transfer of heat from the molecules of one body to those of another. By absorption we mean the converse of this, the receiving of heat by the molecules of one body from those of another. The heating of water in a boiler is due, at least in part, to all of these processes. The fire in the furnace radiates heat to the crown sheet ; convection and draft currents convey the hot gas to the heating surface ; there is emission from the hot gases and absorption by the metal of the heating surfaces; there is conduction through the metal from the fire to the water side ; there is emission from the metal and absorption by the water; and finally there are convection currents developed in the water by means of which the temperature is more or less uniformly raised. [3] Steam. Steam or the vapor of water is the substance almost univer- sally used as the medium through which the heat set free by the coal is transformed into the mechanical work of the engine or pump. Its properties are therefore of great importance for the engineer, and we may properly study briefly the more im- portant at this point. SPECIAL TOPICS AND PROBLEMS. 445 (i) Formation of Steam. Let AB in Fig. 276 be a very tall vessel open at the top and having an inside cross-section of one square inch. Let us suppose at the start that there is in the bot- tom of this vessel one cubic inch of water at say 60 temperature. On top of the water let there be a piston as shown which we may suppose to move without friction, and to be without weight. In other words we wish simply, something to separate the water from the air. Then on the surface of the water there will be just the atmospheric pressure of say 14.7 pounds per square inch. Now let heat be applied at the bottom of the chamber. The first 11 Fig. 276. The Formation of Steam. result will be a transfer of heat through into the water, and a resultant rise in temperature of the water near the heating sur- face. In consequence of this the water will expand somewhat and thus become lighter than the other water above and farther from these surfaces. The heated water will thus tend to rise to the top and so displace the cooler water there, which will in conse- quence sink and thus in turn be brought into contact with the heating surfaces. There is set up in this way a general ascend- ing current of warmer water and a corresponding descending current of cooler water by means of which the whole mass is gradually raised in temperature. In this manner are formed the convection currents referred 446 PRACTICAL MARINE ENGINEERING. to in the preceding section, and to their formation in a steam boiler is due the circulation of the water, especially in those of the fire-tube or tank type. In this way then the temperature of the water will gradually rise until it reaches 212. The temperature then ceases to rise and steam begins to form, rapidly increasing the volume below r the piston and thus forcing it upward. The steam formed is of the same temperature, 212, as the water of which it is formed, the only changes being the increase of volume and the change of state. If we continue to supply heat at the bottom and pre- vent its escape from the sides of the tube or chamber, the water will thus gradually be all converted into steam, just balancing by its own pressure the atmospheric pressure on the top of the piston. The volume of steam thus formed would be 1,663 cubic inches, or in other words the tube would have to be 1,663 inches or 138.6 feet high to allow of the operation as we have supposed it to take place. Suppose now that at the beginning the piston is loaded down with a weight so that the total load on the water is 20 pounds instead of 14.7. Then let heat be supplied as before. A like series of changes will follow, but the water instead of beginning to change state from liquid to vapor at 212 must be heated to 228 before the change begins, while the final volume will be only 1,244 cubic inches. If the initial pressure were 100 pounds then the temperature at which the change of state would begin would be 328, and the final volume would be only 275 cubic inches. Similarly for 200 pounds pressure, the figures are 382 and 144 cubic inches. On the other hand, if by means of an air pump the pressure on the water were decreased below that of the atmosphere the temperature of change would become lower, and the volume greater. Thus if the pressure is 10 pounds the figures are 193 and 2,385 cubic inches, and if 5 pounds they are 162 and 4,576 cubic inches. Similarly, to boil water at 32, or the freezing point, it would be necessary to reduce the pressure to .089 pounds, while the volume of vapor formed would be about 21,170 cubic inches. In general we thus find that as the pressure is increased or decreased there is a corresponding rise or fall in the tempera- ture at which the formation of vapor begins, and that it re- mains fixed at this temperature during the process of change of SPECIAL TOPICS AND PROBLEMS. 447 state, and that the temperature of the vapor formed is also the same as that of the water from which it is formed. It thus appears that steam is simply the vapor of water, or water in the vaporous state, as defined in [2]. The process of steam formation as above described is known as boiling or ebullition, or sometimes in the general sense as vapor- ization. The temperature at which the change of state occurs is known as the boiling point or point of ebullition. At lower temperatures there is always a certain amount of slow vaporization going on, the pressure of the vapor formed being limited to that corresponding to the temperature of the water. It is by means of such slow vaporization that water is carried up for the formation of rain clouds from the surfaces of rivers, lakes and oceans, or that mud dries up in the roads, or clothes when hung out to dry. Thus if the temperature is 100 the maximum vapor pressure is about one pound. Considerable vapor will thus be formed, which will gradually find its way up- ward into the air, at least so long as the air is not saturated ; i.e., already charged with vapor of the full pressure corresponding to the temperature. This is, however, a branch of the subject that we cannot here pursue further. When, however, the temperature is such that the vapor pressure is sufficient to just balance the entire pressure on the surface of the liquid, then the vapor is formed with freedom, and more or less from the body of the liquid, producing the agitation and other conditions which constitute boiling or ebullition as re- ferred to above. We have thus examined in some detail the formation of steam at constant pressure. Let us next examine briefly its for- mation at constant volume, the case which corresponds to its generation in a steam boiler. The boiler being first open to the air through the safety valve, the water is subject simply to atmospheric pressure. The heating of the water and first formation of steam proceed accord- ing to the process as described above. The air is thus displaced from the boiler and driven out through the safety valve or other escape. The safety valve or escape is then closed and in con- sequence the steam which is formed tends to increase the pres- sure, and as this rises the temperature of the boiling point will rise also. In this way as heat is added, a part of it is used in raising the temperature of the water and steam up to the ever- 448 PRACTICAL MARINE ENGINEERING. rising boiling point, while the remainder goes for the vaporiza- tion of a fresh portion of steam. In this way the volume of vapor remains practically constant, but the pressure and temperature rise together according to the regular law which relates the one to the other, while the increase of vapor is accommodated in the constant volume by the increase in density, or decrease in volume required per pound as the pressure rises. It is thus seen that the temperature and volume of steam are closely dependent on the pressure to which it is subjected. For engineering purposes pressure may be measured from two different starting points. The true or so-called absolute pressure is measured from the zero or no-pressure condition, and is the true or total pressure exerted by the gas or vapor in ques- tion. The ordinary steam gauge, however, as described in Sec. 17 [7] does not measure the absolute pressure, but simply the difference between this and the pressure of the atmosphere. This is due to the fact that the gauge is subjected to the pressure of the steam on one side of the tube and to that of the atmosphere on the other side. It thus measures simply the difference be- tween the two. This is commonly called "gauge pressure." The absolute pressure is greater than the gauge pressure therefore, by the pressure of the atmosphere. This varies with the altitude and with other circumstances affecting the barometer. For en- gineering purposes it is very commonly taken at 15 pounds per square inch. A more correct average for the sea level is, how- ever, 14.7, as noted above. It results therefore that having given the gauge pressure we may find the absolute pressure by adding 15 or 14.7, as we may choose, according to the degree of ac- curacy needed in the case in hand. (2) Saturated and Superheated. Steam. When steam and water are present in the same vessel together and there is no tendency for the water to change into steam or the steam into water except as heat is added or taken away, the water and the steam are said to be in thermal equilibrium. When steam is thus in equilibrium in contact with water, it is said to be saturated. Thus during the entire process of steam formation illustrated in Fig. 276, the steam is saturated. When there is no moisture or water in the liquid condition suspended in or mixed with the vapor, the steam is said to be 'dry. When there is moisture or water suspended in or mixed with the vapor, the steam is said to be moist or wet. In such case SPECIAL TOPICS AND PROBLEMS. 449 the steam or vapor part of the mixture must itself be in the saturated condition as defined above, so that wet steam is simply a mixture of saturated water vapor and liquid water. When steam is free from all suspended moisture, but is still in the saturated condition as determined by its pressure, tem- perature and volume, it is called dry and saturated. Thus the condition of the steam in the vessel of Fig. 276, just as the last bit of vapor is formed, is dry and saturated. During the opera- tion the vapor would be dry and saturated provided it contained no suspended moisture. Practically this is a condition difficult to realize. The greater or less violence of the ebullition is apt to carry up a certain amount of water in the shape of fine mist into the steam space, from which it settles back only slowly, and so is liable to be carried over into the engine. The steam fur- nished by the average boiler under good conditions contains usually not less than from I to 2, per cent, of moisture, while under poor conditions the amount may rise to 5 per cent, and more. Suppose now, referring to Fig. 276, that after the last bit of water has been vaporized, heat is still further applied, the pres- sure on the piston remaining the same. The temperature which during the process of vaporization has remained stationary, will now begin to rise, accompanied also by an increase of volume. If we now recall the three stages which the water has passed through, all at constant pressure, it appears that during the first stage there was a rise in temperature of the water at nearly con- stant volume : during the second stage (that of steam formation) there was an increase of volume at constant temperature : during the third stage, as just described, there is increase of both volume and temperature. If in this last operation instead of keeping the pressure con- stant the piston were held fast, thus keeping the volume con- stant, we should find with the addition of heat that both the tem- perature and the pressure would increase. Steam in the condition resulting from these operations is said to be superheated. As compared with saturated steam its temperature and volume are greater for the same pressure, or its temperature and pressure are greater for the same volume, or its volume is greater and pressure less at the same temperature. It is clear that superheated steam cannot be in contact with water and remain superheated. It cannot therefore be moist. 450 PRACTICAL MARINE ENGINEERING. If it were brought into contact with water it would lose its super- heat and become saturated, forming by the heat given up, a little more vapor from the water present. We may also put the relation between saturated and super- heated steam into the following form : Saturated steam contains only as much heat as absolutely necessary for its maintenance as steam at the given pressure. Superheated steam at the same pressure contains more heat than saturated. The temperature and volume per pound for saturated steam correspond with the pressure as in the process of vaporization, and are respectively the lowest temperature and smallest volume at which steam of the given pressure can exist. The temperature and volume per pound lor superheated steam are both larger for the same pressure than for saturated steam. [4] Xotal Heat in a Substance. (i) Total Heat of Steam. The total heat of a body in a given condition is the total amount of heat required to produce this condition, reckoning from some starting point agreed upon. For steam this point is usually taken as 32 Fah., or the freezing point of water. The total heat per pound of steam at a given pressure and temperature, means then the total amount of heat, both sensible and latent, required to produce one pound of steam of the given pressure and temperature, from water at 32. These quantities of heat are used in the solution of problems relating to the heat required for evaporation, boiler efficiency, gain by feed-water heating, etc. The value of the total heat in terms of the temperature is very closely given by the following approxi- mate equation : H = 1082 + .3* while the latent heat is similarly given by the equation : L = 1114 .ft. In these equations, H denotes the total heat, L the latent heat, and t the temperature. Instead of using these or other similar equations, the values are more conveniently taken from tables prepared so as to give the various quantities for regularly varying values of the pres- sure. Thus from the Table it appears that at 14.7 pounds pressure absolute, or at the pressure of the atmosphere, it requires 180.9 B. T. U. to heat the water from 32 to the boil- SPECIAL TOPICS AND PROBLEMS. 451 ing point 212, and then 965.7 B. T. U. to completely vaporize it at this point. The great excess of the latter or latent heat over the former or sensible heat may thus be noted. It is also seen that according to the table the heat required to raise the water from 32 to 212 is not exactly measured by the difference in degrees which is 180. The excess is due to the fact that the B. T. U. is defined for i rise from 62 to 63, while the amount required to make i difference at other temperatures is slight- ly different, increasing on the whole for higher tempera- tures, so that between 32 and 212 the average is slightly greater than from 62 to 63. It thus results that the sensible heat per pound of water involved in a temperature change is' slightly greater than the number of degrees which measures such change. This difference is, however, so small that for most engineering purposes it may be neglected if more convenient, and the number of heat units per pound of water may be taken equal to the number of degrees difference in temperature. (2) Total Heat of a Mixture of Steam and Water. Steam as actually used is usually moist ; that is, it contains a small fraction of water. To find how much heat is required to produce one pound of such a mixture of steam and water, a given fraction being steam and the remainder water, we have simply to re- member that all of the water must be raised to the temperature of boiling, while only the given fraction is vaporized. If there- fore S denotes the sensible heat and L the latent heat, while x is the fraction which Is steam, or the quality of the steam as it is called, then the heat H required to produce one pound of the mixture will be : H S -f- xL. The quality ,r -is usually expressed on the percentage basis. The following examples will illustrate the use of the steam tables : (1) Find the sensible heat, the latent heat and the total heat in one pound of steam at 120 pounds gauge pressure.* Ans. from the table, 322.1, 866.6, 1188.7. (2) Find the heat in i pound of feed water at a temperature of 110. Ans. no 32 = 78. * For present purposes, and in the following problems, it will be suffi- ciently accurate to take the pressure of the atmosphere as 15 pounds per square inch. The absolute pressure is therefore found from the gauge pressure by simply adding 15. 452 PRACTICAL MARINE ENGINEERING. (3) How much heat would be required to produce the steam in example (i) from the feed water in (2)? Ans. The difference between the two or 1110.7. Remark: These three examples show how we may find the heat necessary to produce a pound of steam of given pressure from feed water of any given temperature. (4) How much heat is required to make i pound of steam at 150 pounds gauge pressure from feed water at 130? Ans. 1095.5. (5) How much heat is required to produce i pound of moist steam of 92 per cent, quality at 150 pounds gauge pressure from feed water at 120? Solution : The sensible heat per pound of steam is. ... 338.4 The sensible heat per pound of feed is 88.0 The difference is 250.4 The latent heat for one pound is 855.1. But since only 92 per cent, is vaporized, only .92 of this will be required. We have therefore : H = 5 + xL 250.4 + .92 X 855.1 = 1037. Ans. (6) One engine requires per I.H.P. per hour, 16 pounds of steam of 96 per cent, quality at 150 pounds gauge pressure, the feed being at a temperature of 140. Another engine requires 20 pounds of steam of 90 per cent, quality at no pounds gauge pressure, the feed being at a temperature of 110. Find the amounts of heat required per hour in the two en- gines, and hence their real comparison as heat engines. By the methods illustrated above we find as follows : For the first engine 16821 B. T. U. per hour. For the second engine 20436 B. T. U. per hour. The second engine requires therefore 3615 B. T. U. per hour more than the first, and in consequence is about 21.5 per cent, more expensive in terms of the heat required. Further illustrations of these principles will be found in Sec. 58. [5] I/atent Heat in Passing from Ice to Water. We have seen in [2] (i) that a certain amount of heat is absorbed in the melting of ice at the constant temperature of 32. It is thus rendered latent or is taken up in effecting the change of state in the same general manner that heat is rendered latent SPECIAL TOPICS AND PROBLEMS. -45* in passing from liquid to vapor. It may be of value to note here the quantity of heat thus rendered latent. This amounts to about 143 heat units, or B. T. U., per pound of ice melted from 32 into water at the same temperature. Sec. 58. STAM BOH,ER ECONOMY. [i] General Principles. There may be several different bases for boiler economy ac- cording to the particular feature held in especial prominence. The output of the boiler is estimated in terms of the steam pro- duced, and we may have the following kinds of economy : (1) Economy in coal consumption, increasing with the out- put of steam per pound of coal burned. (2) Economy in weight of boiler, increasing with the output of steam per pound of boiler. (3) Economy in first cost, increasing with the output of steam per dollar invested in the boilers. (4) Economy of maintenance or total life, increasing as the life .of the boiler is longer and the amount necessary for repairs is smaller. It is never possible to fulfil in the highest degree the condi- tions for these various kinds of economy, and a compromise must always be made among them, though usually (i) or (2) will take the first place in the order of importance. Without special note, however, the term economy is under- stood to refer to (i), though the considerations relating to the others should always be kept in mind. In some cases, as in tor- pedo boat and like practice, (2) may assume first place in the order of importance, and, perhaps, require some sacrifice relative to the others. We will now consider more especially the econ- omy referred to under (i). From the standpoint of coal economy or efficiency, the boiler is charged with all the coal that is thrown through the furnace doors, and is credited with the steam which it sends to the engine. Or to state the matter more definitely, it is charged with all the heat which could be gotten from this coal by perfect and complete combustion, and is credited with the heat which is transferred through and actually used in the formation of steam. If the efficiency were perfect, or if there were no loss, these two amounts of heat would be equal. Actually there are many losses, large and small, and, in consequence, the latter is considerably 454 PRACTICAL MARINE ENGINEERING. less than the former. The ratio of the two is known as the boiler efficiency. In practice its value varies from 50 to 75 or 80 per cent. Following are the more important sources of loss which occasion this drop in efficiency. In,, jthe first place, a little of the fuel may fall unburned through the grate into the ash pit. Again, a little in the form of dust and small bits may be carried by a strong draft, either un- burnt gr only partially burnt, through into the tubes, uptakes or funnel. Still another small portion may escape as srnoke, which consists almost entirely of very fine particles of unburnt carbon formed from the gases which are distilled away from the coal in the process of combustion. Still another portion of these gases may escape unchanged and unconsumed. Again, there may be an incomplete combustion of the carbon forming carbon monoxide, and giving only about 4,450 heat units per pound, instead of 14,500 which result from the complete combustion into carbon dioxide. Hence, whatever carbon escapes in the form of carbon monoxide is only partly burned, and may be considered as car- rying away over two-thirds of the heat which would be liberated by complete combustion. These losses all occur in the furnace, and are due to poor firing and to imperfect combustion. To reduce them to the lowest limit, the fireman must know his business, and be willing to attend to it with ceaseless care and diligence. In addition, there must be provided, by proper design, the necessary supply of air both above and below the grate, together with such arrangements as experience may show are needed for good combustion with the fuel in hand. At best this loss may be reduced to perhaps 2 or 3 per cent., while with carelessness or poor design, or both, it may easily reach values from 10 to 20 per cent. The heat being thus more or less perfectly liberated- in the furnace, is then passed on to the boiler heating surface, whose duty it is to transfer it through into the water on the other side. The energy is still to exist as heat, but it is to be transferred from the hot gas to the water, thus converting- the latter into steam. This, however, cannot be perfectly accomplished, and thus arises a further loss. A part of the heat, instead of passing through the heating surface, goes up the funnel carried bv the escaping gases, and so gets away into the outside air. Another and smaller part escapes by radiation into the fire room. These losses it is im- possible wholly to avoid. It would be necessary to avoid all loss SPECIAL TOPICS AND PROBLEMS. 455 of heat by radiation, and to reduce the temperature of the pro- ducts of combustion in the funnel to that of the outside air. The latter, especially, cannot be done for the best of reasons. In the first place, the temperature cannot be reduced below that of the steam and water in the boiler, because heat always flows naturally from a hot body to a cooler one, and it will, therefore, flow from the gas to the water only so long as the latter is the cooler of the two. The actual temperature of the escaping gases must be considerably higher than that of the steam, because in the first place sufficient heating surface to reduce them to nearly the same temperature could hardly be allowed ; and, again, aside from blowers, the strength of draft is dependent on the tempera- ture of the hot gas in the funnel, and for a satisfactory rate of combustion it is necessary to discharge the products of combus- tion at temperatures not less than 500 to 600 degrees. This loss is one therefore which exists in the nature of things, and cannot be reduced below some 20 or 30 per cent. On the whole, then, the entire losses under the best condi- tions can hardly be reduced much below 25 per cent., while wi h poor conditions they may aggregate 40 to 50 per cent. The 're- maining fraction, or the 50 to 75 or 80 per cent., represents then the efficiency of the boiler as defined above. Since a pound of average good coal has available sor-e 13,000 to 14,000 heat units, it follows that the heat actually utilized per pound of coal is usually found between say 7,000 and 11,000 units. In general the conditions favorable- to high efficiency are the following: (1) A free burning coal of good quality, with suitable fur- naces and air supply for complete combustion. (2) Moderate draft. (3) Abundant heating surface. Or, as a combination of (2) and (3), we may put : (2) Moderate evaporation required per square foot of heat- ing surface. The opposite of these conditions will cause necessarily a loss in efficiency more or less pronounced according to circumstances. [2] Evaporation Per Pound of Coal. The efficiency of a boiler is often roughly estimated by the number of pounds of water evaporated into steam per pound of 456 PRACTICAL MARINE ENGINEERING. coal burned on the grates. This, according to conditions, may vary from 6 or 7 to perhaps n. Remembering that it usually requires rather more than 1,000 heat units per pound of steam, the general agreement between these figures and those above foi the heat utilized per pound of coal is readily seen. In fact, the figures for the heat utilized are derived really from a measure- ment of the pounds of steam evaporated per pound of coal, together with a knowledge of the heat required per pound of steam, the latter being derived, of course, from the conditions of the evaporation. When we remember the great difference in the amount of heat required per pound of steam, depending on the temperature of the feed, the temperature of the steam, and whether the steam is moist or dry, it is clear that for any fair measure of boiler per- formance in terms of steam formed per pound of coal, these differences must be allowed for, especially in comparisons be- tween boilers -working under different conditions. To this end it is customary to reduce the number of pounds evaporated to what it would be if the steam were dry and the temperature of both feed and steam were 212 degrees. In such case it would require to make one pound of steam simply the latent heat at 212 degrees, or 966 B. T. U. (British thermal units). This is known as the reduced evaporation, or the equivalent evaporation from and at 212 degrees. It is really the number of pounds of steam which would be formed if each required 966 B. T. U., and is, therefore, simply a measure of the B. T. U. put into the steam per pound of coal. The ratio between the number of B. T. U. actually required and the 966 is known as the factor of evaporation. These factors are often arranged in tabular form, assuming dry steam in each case, but with temperature of feed water and steam varying over the usual rano-e. The annli cation of these various principles relating to boiler economy will be better understood by the solution of the follow- ing illustrative problems. In these problems we shall still for convenience consider the pressure of the atmosphere as 15 pounds per square inch, and the absolute pressure therefore as 15 pounds greater than the gauge pressure. (i) Temperature of feed 110, steam pressure 150 pounds, gauge. Thermal value of the coal 14,000 thermal units per SPECIAL TOPICS AND PROBLEMS. 457 pound. Efficiency of boiler .64. Find the pounds of water evap- orated into dry steam per pound of coal. Operation : From the steam tables : Heat in the water at boiling point 3384 Heat in the feed = 1 10 32 = 78 Difference 260.4 Latent heat 855.1 Heat required per pound of dry steam IIT 5-5 Heat available per pound of coal = .64 X 14,000 = 8,960. Hence pounds of steam evaporated = 8960 -f- 1115.5 8.03 Ans. (2) Temperature of feed 140. Steam pressure 200 pounds, gauge. Quality of steam 96 per cent. Thermal value of coal 14,400 thermal units per pound. Efficiency of boiler .70. Find the pounds of water evaporated per pound of coal into steam of the given quality. Operation : Heat in the water at boiling point 361.3 Heat in the feed = 140 32 108 Difference 253.3 Latent heat per pound = 838.9. Take .96 of this 805.3 Heat required per pound of moist steam , . . . 1058.6 Heat available per pound of coal = .70 X 14,400 10,080. Hence pounds of steam evaporated = 10,080 ~ 1058.6 9-52. (3) Temperature of feed 100. Steam pressure 120 pounds, gauge. Evaporation 8 pounds per pound coal. Assuming dry steam, what is the evaporation from and at 212, and what is the factor of evaporation? Operation : Heat in the water at boiling point 322.1 Heat in the feed = 100 32 = 68.0 Difference 254.1 458 PRACTICAL MARINE ENGINEERING. Latent heat per pound 866.6 Heat required per pound of dry steam 1 120.7 Heat utilized per pound of coal = 8 X 1120.7 8965.6. Evaporation from and at 212 = 8965.7 966 = 9.28. Factor of evaporation = 1120.7 -f- 966 = 1.16. Evidently also Equivalent evaporation 8 X 1.16 = 9.28. (4) Same as in example (3) but assuming the steam of 95 per cent quality, what are the results? Operation : Heat in the water at boiling point 322.1 Heat in the feed = 100 32 = 68.0 Difference 254.1 Latent heat per pound = 866.6. Take .95 of this 823.3 Heat required per pound of moist steam IO774 Factor of evaporation = 1077.4 -r- 966 = 1.115. Equivalent evaporation = 8 X 1.11$ = 8.92. (5) Temperature of feed 160. Steam pressure 200 pounds, gauge. Quality of steam 97 per cent. Evaporation 8.8 pounds steam per pound coal. What is the equivalent evaporation from and at 212, and what is the factor of evaporation? Operation : Heat in the water at boiling point 361.3 Heat in the feed = 160 32 = 128.0 Difference 233.3 Latent heat per pound = 838.9. Take .97 of this 813.7 Heat required per pound of moist steam 1047.0 Factor of evaporation = 1047.0 -r- 966 = 1.084. Equivalent evaporation = 8.8 X 1.084 9-54- (6) Compare the economy in (3) and (5). Ans. in the ratio 9.28 : 9.54 or i : 1.028. (7) Which is the more economical of the following cases : (a) Coal at $4.00 per ton, 9.2 pounds of steam per pound of SPECIAL TOPICS AND PROBLEMS. 459 coal ; quality of steam 98 per cent. ; steam pressure 150 pounds, gauge; temperature of feed 110. (b) Coal at $3.20 per ton; 8.0 pounds of steam per pound of coal ; quality of steam 96 per cent. ; steam pressure 135 pounds, gauge ; temperature of feed 120. By the methods of the preceding examples we find that the equivalent evaporations in the two cases are as follows : (a) : 10.46. (b) : "8.85. The cost of steam in the two cases will therefore be in the compound ratio. (See Part II., Sec. 6 [2]) : (a) : (b) : : 4.00 : 3.20. : : 8.85 : 10.46. or (a) : (b) : : 4.00 X 8.85 : 10.46 X 3-2O. Whence (a) : (b) : : 1.058 : I or case (a) is nearly 6 per cent, more expensive than (b). NOTE. In solving the above examples the heat in the water at boiling point has been taken from the tables. Somewhat more quickly such problems may be solved by taking the heat in the water at boiling point as measured simply by the difference in temperatures, as explained in Sec. 57 [4] (i). The difference is small and is very commonly neglected. In the above examples, however, we have preferred to use the more exact values. The simpler form of solution will be illustrated by solving example (5) in this way, and the result will serve to show the nature of the difference between the two. We have thus : Temperature of steam 387.7 Temperature of feed 160 To raise one pound feed to boiling point 227.7 Latent heat for one pound = 839.9. Take .97 of this 813.7 Heat required per pound moist steam 1041.4 Factor of evaporation 1041.4 -^ q.66 1.077. Equivalent evaporation = 1.078 X 8.8 = 9.49. [3] Evaporation Per Pound of Combustible. In discussing further the details of stenm boiler perform- ance, it is often desirable to make the necessary allowance for the ash in the coal, or for the ash and moisture, so as to obtain 460 PRACTICAL MARINE ENGINEERING. the evaporation per pound of actual combustible matter. To this end it is only necessary to divide the evaporation per pound of coal determined as above by the fraction of the coal which is combustible, or what is the same thing, we may increase the result per pound of coal in the ratio in which the coal is greater than the combustible. The result will be the evaporation per pound of coal exclusive of ash or of ash and moisture. This result may relate, of course, either to the actual evaporation under the given conditions, or to the equivalent from and at 212. This will be illustrated by the following examples : (8) In example (5) Suppose the ash to be 12 per cent., what are the actual and equivalent evaporations per pound of moist combustible? Ans : Actual evaporation = 8.8 -- .88 = 10 Ibs. Equivalent evaporation = 9.54 -i- .88 = 10.84 Ibs. (9) Under the same conditions suppose the ash and mois- ture to be 15 per cent., what are the evaporations per pound of dry combustible? Ans: Actual evaporation = 8.8 -f- .85 = 10.35. Equivalent evaporation = 9.54 -r- .85 = 11.22. Sec. 59- STEAM ENGINE ECONOMY. [i] General Principles. In the following discussion it will be assumed that the reader has a general knowledge of the chief properties of steam and of its relation to the heat which it contains. We will then take up in an elementary way a discussion of the principles governing its economical use in a steam engine. At the very outset it must be clearly understood that we derive the work of the engine from the heat which the steam contains, and not from the steam in itself. The steam is simply a carrier for the heat and the operation of the engine is simply a means for transforming into useful work a fraction of the heat which comes into the engine, and then rejecting the remainder with the steam which is its carrier. The larger the fraction of the heat which can be transformed into useful work the better the efficiency of the engine, and the constant aim is therefore to turn into useful work the largest possible fraction of the heat which enters with the steam. It may be asked, why not turn all the heat into work, and so realize a perfect efficiency? Unfortunately a series of natural SPECIAL TOPICS AND PROBLEMS. 461 laws and limitations seems to prevent all hope of realizing such an ideal, and actually we must be content with turning into useful work a comparatively small fraction of the total heat supplied. First and foremost among the causes of this reduction in effi- ciency is a principle or law sometimes known as the second law of thermodynamics. This law fixes a limit on the fraction of heat which can be transformed into useful work, such limit de- pending on the extreme temperatures between which the sub- stance is worked in the engine. Thus if U is the temperature of the steam at admission and t* that at exhaust, so that h and t* are the two temperatures between which the steam is worked, and (/i fr) is the range, then the law asserts that no engine, no matter how perfect, can transform into useful work a fraction of the entering heat greater than (fr -- fc) -f- (h + 461). As another way of stating this relation, the temperature may be supposed to be measured from a point 461, or more accurately 460.7 degrees, below the ordinary zero of the Fah. scale. This is called the absolute zero, and temperature measured from this zero is called absolute temperature. The difference of the tem- peratures would be the same no matter whether measured from the ordinary of absolute zero. The numerator of the above frac- tion is therefore the difference or range of temperature, while the denominator is the absolute temperature of the entering steam. The fraction of heat converted into useful work can therefore never exceed the temperature range divided by the absolute tem- perature of the entering steam. Thus to illustrate, suppose that h = 370 and ts = 140. Then the fraction becomes (370 140) -4- (370 -f- 461 or 230 -i- 831 = .277 or slightly over one-quarter. These figures represent the limits for steam of about 160 pounds gauge pressure, and it therefore appears that for engines operating between these limits this law steps in, and at one stroke reduces the ideal efficiency from one to about one-quar- ter ; or in other words we are forced, due to the operation of this law, to throw away about three-quarters of the total heat, and at the very best with the most ideally perfect engine could only transform into useful work the remaining one-quarter. Such then is the very best that could be done by a so-called ideal engine. The working substance in the simplest form of such an engine must be carried through a series of changes or operations, four in number, and specified as follows : (i) The first operation must consist of an expansion at con- 462 PRACTICAL MARINE ENGINEERING. stant temperature, and all heat received from the source of sup- ply must be received during this operation. (2) The second operation must consist of an expansion with decrease of temperature during which, however, no heat as such is allowed to either enter or leave the substance. (3) The third operation must consist of a compression during which the temperature remains constant and all heat re- moved from the body must be removed during this operation. (4) The fourth operation must consist of a compression with increase of temperature, during which, however, no heat as such is allowed to either enter or leave the substance, and at the end of which the substance must find itself in the same condition as at the beginning of number (i). Work is done by the substance during operations (i) and (2) and work must be done on the substance during (3) and (4). The difference between the work done by and on the substance will be the net work obtained from the heat in the substance, and the ratio of this to the total heat supplied during number (i) or the efficiency of the engine will be exactly measured by the difference between the temperatures of operations (i) and (3) di- vided by the larger increased by 461 ; or in symbols : ; 'i *. efficiency = - - - t t + 461 This is then the cycle and the efficiency of an ideal engine in the simplest form. There may be certain related variations in the operations (2) and (4) making a more complicated cycle, but with the same efficiency. This ideal marks, then, the highest possible limit of efficiency for any and all engines working be- tween the given temperature limits ft and ft. In the table are shown the values of this limiting efficiency for engines with gauge pressure as indicated, all condensing and supposed to have a back pressure of 2.8 pounds absolute, or a lower temperature, ft, of 140. An examination of this table shows that with the ideal con- ditions which correspond to the operation of this engine, the fraction of heat utilized with modern boiler pressures would range from 25 to 30 per cent. These conditions, however, are far from those which actually exist in practice. Every one of the conditions specified above is violated in greater or less degree, and the result is that with the operation of the engine under the best conditions obtainable in actual practice, the frac- SPECIAL TOPICS AND PROBLEMS. 463 tion realized will be only some 60 to 80 per cent, of the figures for the ideal case as given in the table below. These figures, 60 to 80 per cent, in the best practice, really measure the efficiency of the engine so far as the engineer is responsible. That is, nothing which he can do will serve to avoid the loss which re- duces the limiting efficiency down to that for the ideal engine as given in the table above. His efforts are therefore limited to approaching as nearly as possible to the conditions of the ideal engine, and the figures 60 to 80 per cent, measure the de- gree of approach which modern engineering practice has made TABLE. Gauge Pressure at Engine. Limiting Efficiency IOO 248 IIO 253 1 2O 259 130 264 140 269 ISO 273 160 2 7 8 170 28l 180 285 190 289 200 292 210 295 22O ,299 230 301 24O 304 25O 307 to this ideal. Thus, for illustration, if the ideal engine could transform 25 per cent, of the heat into useful work, a good actual engine working between the same temperature limits will be able to transform from 15 to 20 per cent., and similarly for other conditions. To put the matter a little differently, any and all engines fail to transform into work all of the heat supplied to them. In the ideal engine as specified above, the part not transformed but rejected as heat is the least possible for all engines working be- tween the same limits of temperature /< and h. In any actual engine the amount not transformed into work but rejected as 4 6 4 PRACTICAL MARINE ENGINEERING. heat is greater than in the ideal case. Such additional amounts of heat rejected and not transformed into work are called wastes or losses. That is ; all differences between the performances of the ideal and actual engines are considered to be due to these so- called wastes or losses. These various wastes may be classified as follows : (a) Radiation and Conduction Waste. This consists of heat which is radiated away from the hot surfaces of the cylinder, or conducted away through the columns and bed plate. The heat thus escaping avoids transformation into work and is therefore counted as a heat waste, or as an ex- pense from which no corresponding return is received. (b) Initial Condensation. At the instant the steam valve opens, the steam rushes into the cylinder to find itself in contact with surfaces which have but recently been exposed to the influence of the condenser or ex- ternal air. They are, therefore, at a temperature much lower than the steam, and in consequence a part of the heat is absorbed and a corresponding part of the steam is condensed. The heat thus absorbed by the surfaces of the cylinder and piston will be given up later during the exhaust period of the revolution, and thus communicated to the condenser. It thus appears that a thin skin of metal on the inside of the cylinder and on the faces of the cylinder head and piston may be considered in a sense as a place of hiding into which a portion of the heat slips on the entrance of the steam, and from which it escapes to the con- denser or air without having taken part in the cycle of the en- gine, and hence without having contributed its part to the usefu) work done. The heat so escaping appears thus as an expense, but without any corresponding return in work, and therefore con- stitutes a heat waste. (c) Irregularities of the Cycle. We have specified above the four fundamental operations of the ideal engine cycle in its simplest form. In the actual engine none of these is realized, and the variations are all such as to count against the efficiency. Into the details of these points we cannot here enter, and the broad statement must suffice that with but few exceptions, the variations from the routine specified above for the ideal engine will count against the efficiency and occasion a heat waste greater or smaller as the circumstances mav determine. SPECIAL TOPICS AND PROBLEMS. 4^5 The Improvement of the Steam Engine. From the preceding section it follows that there are two fundamental methods open for the improvement of the steam engine from the standpoint of economy. (1) An increase in the temperature range and thus an in- crease in the ideal or limiting efficiency. (2) The saving of some of the various wastes as noted above. The first raises the ideal efficiency and hence with a given proportion of wastes will raise the actual efficiency as well. The second raises the actual efficiency by carrying it a little nearer to the ideal. The temperature range may be increased in two ways, the initial temperature can be raised, and< the final temperature can be lowerd. The continually advancing pressures in modern practice means a constant rise in the upper temperature, a constant in- crease in the ideal efficiency, and with the same proportion of losses, a corresponding rise in the actual efficiency. This is then the real significance of high pressures in modern practice so far as they are related to the question of economy. Again by decreasing the back pressure from say 18 pounds for a non-condensing engine to say 3 pounds for a condensing engine, a very considerable decrease in the final temperature is obtained, a corresponding increase in the temperature range, and a resultant increase in actual efficiency. This is likewise the real significance of the influence of the condenser on the econ- omy of the engine. In general then, the proportion of heat wastes being the same, the economy will be better as the initial pressure is higher, and the back pressure is lower; or in general, as the range of pressure and temperature worked through is the greater. We may turn next to the problem of reducing the wastes of the actual engine, as specified under the three heads above. The waste due to radiation and conduction cannot be wholly avoided, but the former, which is by far the larger of the two, may be much reduced by suitable lagging or non-conducting covering. With such provision the loss under this head is usually very small compared with the other losses mentioned. The waste due to the so-called initial condensation is one which may be reduced, but not wholly avoided. Before discuss- 4 66 PRACTICAL MARINE ENGINEERING. ing the means suitable to this end some further explanation of the nature of the loss will be required. As already pointed out, the action of the metal walls in pro- ducing this loss depends on their capacity when at a lower tem- perature, for absorbing heat from the steam (as during admis- sion) and for giving it up when at a higher temperature (as dur- ing exhaust). The action depends, then, on the range of tem- perature between admission and exhaust, and on the particular readiness with which the walls absorb and reject heat according as they are cooler or hotter than their surroundings. There are therefore two distinct features to be considered the range of temperature, and the readiness with which the iron absorbs and rejects heat under the conditions mentioned. Now it is found that if the expansion through the entire temperature range is split up into a series of steps, each carried out in a cylinder by itself, the loss under consideration is less than if the entire expansion should take place in one cylinder. Carrying out this principle we have, of course, the multiple ex- pansion engine with its total range of operation divided among several cylinders in series. This, then, is the real significance of the multiple expansion (compound, triple, quadruple, etc.) engine, so far as its relation to economy is concerned the splitting of the total expansion or of the total temperature range into a series of steps is, found to reduce considerably one of the wastes, and so raise the actual efficiency of the engine. Next turning to the other controlling feature of this loss, the readiness of absorption and emission it seems to be the case that once the internal surfaces become wetted or covered with a film of moisture, the absorption and emission of heat into and from the metal proceed with much greater readiness than when they are dry. In other words the passage of heat between metal with a moistened surface and moist steam is much more rapid than between the same metal with a dry surface and dry or superheated steam. In the ordinary steam engine we have, therefore, an action of the walls due to the range of temperature employed, and to the natural capacity of cast-iron or steel to absorb and emit heat from and to the steam. This is further greatly aug- mented by the presence of a more or less complete film or layer of water over the surface, which arises from SPECIAL TOPICS AND PROBLEMS. 467 the condensation of the first entering saturated steam. The use of superheaters, reheaters and jackets is found in a general way to decrease the readiness with which heat ex- changes occur between the metal and the steam, and thus to decrease the amount of waste due to their actions. Thus in an engine using moderately superheated steam we should have the same general tendencies as noted above for the operation with saturated steam, but less augmented because of the smaller amount of moisture formed. In an engine using steam super- heated to such an extent as to remain above the point of satura- tion during its entire passage through the cylinders, no moisture is formed and the action of the surfaces is limited to that which can take place between their dry surfaces and the dry super- heated steam. The office of superheating is then simply to re- duce the readiness with which the exchange of the heat between the metal surfaces and the steam is effected. The results show that in such case the reduction is real and productive of a con- siderable increase in economy. Regarding the use of reheaters it seems likely that their bene- ficial action will be well marked in proportion as they are able to superheat the steam passing through them, and thus act as a superheater in stages, each for the cylinder next beyond. The beneficial results gained by the use of steam jackets are in large measure due to action of the same character. The jacket containing steam at a temperature higher than that in the cylinder transfers heat into the inner surface of the cylinder walls and thus tends to keep it dry and to reduce the amount of heat exchange, and hence the corresponding waste. The steam jacket acts also to some extent to modify the character of the cycle as noted below, but most of its useful action may probably be put down to the hindering of heat exchanges between the walls and the steam in the cylinder. It must not be forgotten, however, that whatever gain is thus effected within the cylinder is obtained at the expense of the heat drawn from the jacket, and the whole operation is there- fore an attempt to reduce one loss by introducing another. If the latter is less than the saving in the cylinder, the net result will be a gain equal to their difference. If the latter is the greater of the two, the net result will be a loss, and if they are equal the net result will be no change in the economy of the engine. These re- lations account for the varying experience with jackets, but it 468 PRACTICAL MARINE ENGINEERING. now seems well assured that when properly fitted and operated, the result will show a gain of from 5 to 10 per cent, over similar conditions unjacketed. We come now to the last principal division of the wastes of the actual steam engine, those due to irregularities in the cycle, or in other words to variations from the routine of operations which would give the efficiency of the ideal engine as discussed above. In this respect but little can be done to improve matters. The use of jackets and reheaters may possibly affect the routine in such a way as to bring it somewhat closer to the ideal condi- tions, but this is by no means certain, and the benefit due to these appliances comes mostly from the decrease in cylinder con- densation as explained above. There are methods, however, of modifying the cycle of the engine by the use of a series feed water heater, in such way as to bring it somewhat nearer to the ideal cycle. Such a feed heater for a quadruple expansion engine may consist of say three chambers or heaters through which the feed passes in series. In the first it is heated by steam drawn from the L.P. receiver. It then passes on to the second chamber, where it is heated by steam drawn from the second I. P. receiver, and then goes on to the third chamber, where it meets with steam drawn from the first I. P. receiver. As the feed water thus becomes hotter and hotter it meets with steam of higher and higher temperature drawn from the successive higher receivers in the engine, and it is thus brought nearly to the temperature of the water in the boiler. The exhaust from pumps may also be turned into the first chamber, thus making it a means of taking heat from their exhaust and of returning it with the feed to the boiler. In some cases also live steam of full boiler pressure has been used in a last chamber to still further raise the temperature of the feed. Various modifications may be worked out in the details of the operation of such feed heaters, but in all cases their significance lies in the fact that the cycle of operations as a whole may in this way be brought a step nearer to the ideal cycle than would other- wise be the case. All such changes, if made in accordance with the proper principles, may therefore result in a saving of heat and in a gain in the economy of the engine, and in this fact lies the chief significance of the feed-water heater as a feature of modern engineering practice. See also Section 30 with reference to the same subject. SPECIAL TOPICS AND PROBLEMS. 469 [2] Relation of Expansion to Economy. The question of the expansion of steam and its influence on engine economy has long held an important place as perhaps the chief factor in engine economy, and it may therefore be well to refer to this feature in somewhat further detail. From the stand- point of the preceding discussion of the question we should say that the expansion of steam is favorable to economy because it brings the cycle of operations nearer to that for the ideal engine. These points may, however, be treated differently and in a more elementary manner, and we therefore proceed to discuss the question by the actual comparison of the two indicator diagrams given by an engine working with and without expansion. Consider the two cards C D I H and C D E F H of Fig. 277. The first is the card that would be given by using the steam in an engine with stroke C D following to the extreme end, and then exhausting along D I H. The second card is such as would C G Fig. 277. The Expansion of Steam. >* be given by the same steam used expansively cut-off taking place at D and the stroke continuing expansively to E. The back pressure in each case is represented by the line H F. The area C D I H represents the work in one case and the area C D E F H in the other, so that the difference or D E F I represents the gain by expansive working. In other words, if we use the steam full pressure up to D and then exhaust it, we throw away an amount of work measured by D E F I which might be saved by expansive working. It is likewise true that the exhaust open- ing at E causes a loss of work E J F which might be saved by continuing the expansion down until the forward pressure falls to the back pressure as at J. It is rare, however, that we can afford cylinders of sufficient size to carry the expansion to sucfi a point, and, as may be seen, the amount thus lost is smaller 470 PRACTICAL MARINE ENGINEERING. and smaller as the final pressure E G is nearer the back pres- sure F G. To illustrate the gain by expansive working let us suppose the initial pressure L C = 100 pounds, the back pressure L H = 3 pounds, and that the cut-off is at a series of points .1 .2 .3, etc. Then neglecting the effect due to clearance, the number of expansions will be as 10, 5, 3.3, etc., and the ratio of saving will be as given in the following table. The numbers in the column headed e give values of the ratio DEFI-i-CDIH, or the ratio of the amount saved by expansion to the amount done before expansion begins. Point of Cut-off. Expansion Ratio. e. .1 10. 2. II 2 5- 1-55 3 3-30 I.I8 4 2.50 .91 .5 2.00 .69 .6 1.66 .51 7 143 -36 .8 1.25 .23 .9 i. ii .11 .10 i.oo .00 It will be understood that the figures of the above table refer to indicator cards such as those of the diagram in which there is no allowance for clearance, compression, rounding off of cor- ners, etc. These conditions are of course taken in order to simplify the necessary computations. The nature of the results would, however, be the same in the actual case, and these figures may therefore be taken as a sufficiently close indication for il- lustrative purposes. It thus appears that the gain is proportionately greater the larger the number of expansions, and for the highest efficiency we should therefore carry the expansion to the highest limit. Practically there are two considerations which fix an early limit to this extension of the expansion range. The first is the limit of size. The greater the number of expansions the larger the engine and hence, especially for marine engines, we can seldom afford weight enough to give the number of expansions which other considerations might warrant. The second limitation comes from the increase of internal or cylinder condensation SPECIAL TOPICS AND PROBLEMS. 471 which increases with the number of expansions until finally the resulting waste would off-set the gain due to the increase in ideal efficiency. This loss is decreased by the compounding of engines, so called, or by the splitting up of the total expansion into a series of steps in separate cylinders. Hence with multiple expansion engines we are able to employ higher rates of expansion without corresponding losses from cylinder condensation than with a single cylinder; and this, as we have seen in [i], is the real sig- nificance of the use of multiple expansion rather than simple engines. [3] Economy of the Actual Engine. We have already seen that the highest possible efficiency of an ideal engine under usual conditions will be found between 25 and 30 per cent., while the actual engine at the best will realize only some 60 or 70 per cent, of these figures, or an efficiency of say 15 to 20 per cent, in good practice. Now one horse power is 33,006 foot-pounds of work per minute, and from the value of the work equivalent of heat this is equal to 33,000 -r- 778 = 42.42 heat units per minute. Hence one horse power means the transformation of 42.42 heat units per minute into mechanical work. It follows that the heat which must be supplied to the en- gine in order to provide for one horse power will be given by di- viding the number 42.42 by the efficiency at which the transforma- tion is effected. But 42.42 -f- 15 = 283. + and 42.42 -f- 20 = 212. -J-. Hence, placing the limits a little more broadly, it ap- pears that in good practice we shall require from say 200 to 300 heat units per minute for each horse power developed in the en- gine. This corresponds to a range of 12,000 to 18,000 heat units per hour. Now remembering that each pound of steam brings to the engine roughly 1,000 heat units, it is clear that this will cor- respond to a range of steam consumption of say 12 to 18 pounds per I. H. P. per hour. These figures may be taken as covering the range of good practice from about the best at present attain- able to a value only moderately fair for modern triple expan- sion engines, or good for the usual type of compounds. Again each pound of coal burned may be expected to fur- nish under good conditions some 9,000 or 10,000 heat units to the water in the boiler, or to transform some 9 or 10 pounds of water into steam. Hence the coal required per I. H. P. per hour will be given by dividing the heat units or the pounds of 472 PRACTICAL MARINE ENGINEERING. steam required by the amount of either which may be expected from one pound of coal. This will give a coal consumption of from about 1.2 to 1.8 pounds per I. H. P. per hour, which may also be considered as representing the upper part of the range of good practice for triple and quadruple expansion engines under from moderately good to the best conditions at present attainable. In a few exceptional cases by the use of feed heaters, superheated steam and all means favorable to economy the con- sumption has been reduced to i.o pound coal per I. H. P. per hour. For compound and simple condensing engines under good to moderate conditions the steam consumption will rise to from 20 to 30 pounds of steam, corresponding roughly to from 2 to 3 pounds of coal with good boiler economy, and to perhaps 2.5 to 3.5 pounds with poor boiler economy. Farther along the line will come engines perhaps non-con- densing ; and of still lower efficiency, such for example as electric light, centrifugal pump, blower, winch, and steering engines. The steam required for them may rise to from 40 to 60 pounds or more per I. H. P. per hour, corresponding to a coal consump- tion of from perhaps 4 to 8 pounds, according to the boiler efficiency. Still lower in the scale of economy we find the ordinary direct acting pump. Such pumps operate in the steam cylinder with almost no steam expansion, and the piston speed is very low, thus giving full time for the transfers of heat which cause cylinder condensation. Due to these and other less important causes the steam consumption may rise to 200 pounds and more per I. H. P. per hour, while rarely can it be brought as low as 100 pounds. This corresponds to a coal consumption from say 10 to 25 pounds, depending somewhat on the efficiency of the boiler. In terms of absolute efficiency these figures correspond to from about I to 3 per cent., the values thus ranging down- ward from the 15 to 20 per cent, given above as the highest values at present attainable. Sec. 60. COAly CONSUMPTION AND RELATED PROBLEMS. As we have already seen in Sec. 59 the coal required per I. H. P. per hour in good practice is usually found between say 1.5 and 2.0 pounds. Where especial attention is given to econ- SPECIAL TOPICS AND PROBLEMS. 473 omy the figure may be reduced below the lower value down even to i pound per I. H. P. per hour, while by the neglect of due attention, or in cases where the conditions are such that econ- omy must be sacrificed, the value may rise above the higher limit. Let : c denote the pounds of coal per I. H. P. per hour. H denote the I. H. P. Then cH = pounds of coal per hour, cH -i- 2,240 = tons of coal per hour, , 24 cH 3 cH cH and - or - - or - - = tons of coal per day. 2240 280 93.3 As a thumb rule for a quick estimate, we may remember that at a coal consumption of 1.86 pounds per I. H. P. per hour (a figure only moderately good), the coal required per day will be 20 tons per 1,000 I. H. P. The use of the above formulae may be illustrated by the following examples : (i) With a coal consumption of 1.78, how much coal will be required in the bunkers of a ship making a seven-day trip, the I. H. P. being 2,400 and a margin of 10 per cent, being allowed for emergencies? ^ * 3x1.78x2400 Coal per day = - - = 45.75 tons. 28O Coal for 7 days = 7 X 45-75 = 320.25, say 320 tons. Margin 32 tons. Coal in bunkers = 352 tons. (2) Which will require the more coal per day, a ship with 9,800 I. H. P. at 1.82 Ib. per I. H. P. per hour, or two ships each of 4,000 I. H. P. at 2.20 Ib. per I. H. P. per hour? For the first : 3X 1.82X9800 280 For the second : 3X 2.20x8000 = 191 tons per day. = 188.5 tons per day. 280 Difference 2.5 tons. (3) How long time can a vessel steam on 213 tons of coal and how far on a speed of 12 knots, the I. H. P. being 3,600 and the coal consumption being 1.68? 474 PRACTICAL MARINE ENGINEERING. 1.68X3600 Coal per hour = - -==2.7 tons. 2240 Time 213 -4- 2.7 = 78.9 hours. Distance = 78.9 X 12 = 947 miles. (4) A vessel's log shows 420 tons of coal used in a period of 9 days, 16 hours. The average I. H. P. was 2,120. What was the coal consumption per I. H. P. per hour? Number of hours 9 X 24 -\- 16 = 232. Amount used per hour = 4055 Ib. 3 Coal consumption = ^5- = I.QI Ib. 2120 As a further development of the same problem we may often wish to find the coal burned per mile, or per ton-mile of displace- ment, or per ton-mile of cargo. These we may illustrate by the following examples : (5) Given: Displacement... = 9,486 tons. I. H. P = 12,000 Speed = 18 knots. Coal consump- tion = i .8 Ib. per I. H. P. per hour. Cargo = 2,000 tons. Then: Coal per hour = 1.8 X 12,000 = 21,600 Ib. Coal per mile = 21,600 -f- 18 = 1,200 Ib. Coal per ton-mile of disp. = 1,200 -4- 9,486 = .127 Ib. Coal per ton-mile of cargo = 1,200 -4- 2,000 = .6 Ib. (6) If the same ship were to be driven at but half the speed, only about one-eighth the I. H. P. would be required, or say 1,500 I. H. P., while the cargo might be increased to say 5,000 tons. With the same engine economy we should then require : Coal per hour 1.8 X 1,500 = 2,700 Ib. Coal per mile = 2,700 -f- 9 = 300 Ib. Coal per ton-mile of displacement 300 -4- 9,486 = .316 Ib. Coal per ton-mile of cargo = 300 -f- 5,000 = .06 Ib. (7) Again a case similar to one of the large modern ocean freighters : Displacement = 27,000 tons. Speed = 13 knots. SPECIAL TOPICS AND PROBLEMS. 475 I. H. P. = 6,600. Cargo = 15,000 tons. Coal consumption =1.3 lb. per I. H. P. per hour. Then: Coal per hour = 1.3 X 6,600 = 8,580 lb. Coal per mile = 8,580 -i- 13 = 660 lb. Coal per ton-mile of disp. = 660 -f- 27,000 = .0244 lb. Coal per ton-mile of cargo = 660 -4- 15,000 = .044 lb. At the other extreme take a torpedo-boat of the destroyer type as follows : Displacement = 310 tons. I. H. P. = 6,200. Speed = 31 knots. Coal consumption = 2.2 lb. per I. H. P. per hour. Then : Coal per hour = 2.2 X 6,200 = 13,640 lb. Coal per mile = 13,640 -f- 31 = 440 lb. Coal per ton-mile of disp. = 440 -j- 310 = 1.42 lb. These examples illustrate the principle that per ton-mile, less coal is burned as the ship is larger and goes slower, while more is burned as she is smaller and goes faster. This is the re- sult of the two facts. (1) As the ship increases in size the power required per ton of displacement for a given speed decreases, and accordingly the larger 1 the ship the less the coal required per ton at a given speed. (2) For a given ship, as the speed increases, the power and hence the coal required increase nearly as the cube of the speed ratio, while the time for a mile or for a given voyage is reduced only in the simple ratio of the speeds. Thus to illustrate : If the speed is increased 10 per cent., or say from 10 knots to n knots, then the power will be increased nearly in the ratio (n -i- io) 3 =3 (i.i) 3 = 1.331, while the time on the mile or on a given voyage will be decreased in the ratio io -i- u. Hence the coal will be changed in the compound ratio -- x --- or 1.21 to i. Hence it appears that in such case the increase of speed in the ratio i.i to i will increase the coal per mile or per voyage in the ratio 1.21 to i. Or briefly an increase of io per cent, in the speed will mean an increase of about 20 per cent, in the total coal required. Similarly, of course, a decrease of io per cent in 476 PRACTICAL MARINE ENGINEERING. the speed would mean a decrease of about 20 per cent, in the total coal required.- If there were no other principle involved, it would follow that the slower a given vessel goes the more cheaply could she make a given voyage. This would be true if we could consider only the power in the main engine, and assume for it a constant coal economy. This cannot be done, however, in the case of a single ship going at different speeds, because as the power in the main engines is decreased below its normal amount the coal required per I. H. P. increases continuously. Furthermore the power required for the various auxiliaries never decreases in the same ratio as the power of the main engines, and for cer- tain auxiliaries the power is hardly affected by the change in the main engine. The coal required for the auxiliaries becomes therefore greater and greater relative to that required for the main engine. Due to these facts it follows that as the speed is decreased a point will be reached below which the saving in the total coal required per hour will be more than offset by the in- crease in the time required, so that for a given voyage the total coal expense will begin to increase rather than decrease. This point is known as the "most economical speed" and is the speed at which a given voyage can be made with the least expenditure of coal. Its value will depend largely on the amount and char- acter of the auxiliary machinery in operation, but is often found at a speed somewhat above half the full power speed. In the mercantile marine it is rare that ships are operated at speeds other than those corresponding to normal full power conditions, so that the determination of a most economical speed is not of great importance in such cases. In the naval service, however, where economy may be of more importance than the reduction of time required for a voyage, ships are often operated at or about the most economical speed, and its determination and the principles fixing its location are of importance in such cases. Sec. 61. THE I/EVER SAFETY VALVE AND THE SAFETY VALVE PROBLEM. The spring loaded safety valve as described in Sec. 17 [i] is used almost exclusively in modern practice. The ability to solve problems relating to the weighted arm safety valve (see also the same section), is, however, required of all candidates for U. S. Engineer's Licenses, so that it is of importance to SPECIAL TOPICS AND PROBLEMS. 477 thoroughly understand the method of solving the various prob- lems which may arise in this connection. These problems are all special cases of the general problem in mechanics which has to deal with the equilibrium of a body under the action of a system of forces, and for a clear understanding of the matter the principles discussed and explained in Part II., Sec 12, must be kept well in mind. The arrangement of a weighted arm safety valve is shown in skeleton in Fig. 278. The steam presses upward on the lower face of the valve V, and is opposed by three forces tending to keep the valve on its seat as follows : (1) The weight of valve and spindle direct. (2) The weight of the lever with center of gravity at some point N and pivoted at the fulcrum O. (3) The weight proper at M acting with a leverage or arm equal to MO. Now just as the valve is about to open, these two sets of M ? 1 t ^ T W Fig. 278. The Safety Valve Problem. forces, the one acting upward and the other acting downward, will balance. It is furthermore a principle of mechanics that when such forces are just on a balance, the product of the forces by their arms or leverages must make the same sum in each direction. Thus in the present case the up force at S may be considered as tending to cause motion of the lever about the fulcrum O, in the direction of the hands of a watch, while the down forces at B and W tend to cause motion about the same fulcrum in the opposite direction. We therefore measure the arms from the fulcrum point O. Now if A is the area of the valve in square inches and /> the steam pressure in pounds per square inch by the gauge, the total steam load on the valve will be the product pA. This acts directly upward, and, as noted above, is directly opposed, as far as it goes, by the weight of the valve and spindle. Denote this weight by V. Then the difference (pA-V) is the actual or net force transmitted from the valve to the lever at S, and tending, as noted above, to turn the lever about O from left to right. Let 478 PRACTICAL MARINE ENGINEERING. a denote the arm for this force, or the distance SO from the center of the spindle to the center of the fulcrum. Then (pA-V)a is the product of force by arm for the upward forces. Let us save this and turn next to the remaining or downward forces. Let W denote the amount of weight at M, and / the arm or dis- tance MO from the center of gravity of the weight to the iui- crum. Also let B denote the weight of the lever, and c the arm or distance NO, from the center of gravity of the lever to the fulcrum. Then (Wl + Be) is the sum of the products for the downward forces. By condition these are equal when the two sets balance and the valve may be considered as on the point of opening. Hence as an equation we shall have : Wl + Be = (pA-y)a or Wl + Bc= p'Aa-Va. From this equation we can find the value of any one quan j tity which we may wish, provided we know all the others. Thus suppose we know all but W. Then we have : l[7 _pAa - VaBc ( , 7 ............. V 1 ; Similarly if we know all but / we have : pAa- Va Bc ~W~ and if we know all but f( the pressure per square inch at which the valve will open with a given weight and location, we have : We may readily express by rules the operations represented by these equations as follows : Rule (i) To find the weight knowing the other quantities. Multiply together the pressure per square inch, the area of the valve in square inches, and the distance from the center of the valve spindle to the center of the fulcrum. From this subtract the product of the weight of the valve and spindle by the same arm SO, and also the product of the weight of the lever by its arm NO. Divide the remainder by the weight arm MO, and the quotient will be the weight desired. Rule (2) To find the location of the weight or length of the arm MO knowing the other quantities. Find the same difference as in rule (i) and divide by the weight W ' . The quotient will be the length of the arm MO. SPECIAL TOPICS AND PROBLEMS. 479 Rule (3) To find the pressure at which a given valve and weight will lift. Multiply the weight W by its arm MO ; also the weight of the lever by its arm NO, and the weight of the valve and spindle by its arm SO. Add these three products and divide the sum by the product of the area of the valve times the arm SO. The quotient will be the pressure desired. Example : Let MO or / = 28 in. Let NO or c = 12 in. Let SO or a = 4 in. Let diameter of valve = 3^ in. Then area of valve or A = 9.62 sq. in. Let weight of lever or B = 5^2 lb. Let weight of valve or V = 4 lb. Let steam pressure or p 80 per lb. per sq. in. Then, pAa = 80 X 9.62 X 4 = 3078.4. Va = 4 X 4 = 16. Bc=$y 2 X 12 = 66. Then 3078.4 16-66 = 2996.4 and W = 2996.4 -f- 28 = 107 lb. in round numbers. Or if W were known and / required, we should find the same numerator 2996.4, and then have : / = 2996.4 -7- 107 = 28 inches in round numbers. Or if p is desired we should have : Wl = 107 X 28 = 2996 Be = $y 2 X 12 = 66 Va = 4X4 = 16 Sum Aa = 9.62 X 4 = 38.48- We then have : p =3078 -r- 38.48 = 80 lb. in round numbers. General Remarks on the Problems. The arm / is to be meas- ured from the center of gravity of the weight W to the fulcrum or turning point O. Usually the weight is of regular form, cir- cular or rectangular in elevation, so that its center ot gravity is readily found. If the lever turns about a pin, then the arm / must be measured to the center of the pin. If it is provided with 48o PRACTICAL MARINE ENGINEERING. a link and knife edge bearing as in Fig. 78 then / is measured to the bearing edge. If the center of gravity of the weight W and the fulcrum O are not on the same horizontal line, then the arm / must be measured as the horizontal distance between ver- ticals drawn through these points. The center of gravity of the lever arm must be obtained practically either by measurement or by balancing on an edge in the familiar manner. If it is practically a uniform straight bar the method of measurement will be quite accurate ; if it is taper- ing or irregular the method by balancing may be preferred. In any event, with usual proportions, as seen in the example above, the influence of the lever is relatively small, so that a slight error in the values relating to its weight or center of gravity would be of much less importance than a like proportional error in the weight W or its arm /. The area of the valve, A, should be that, of course, of the lower face, or more accurately, of the opening at the lower edge of the seat. The weights of the various parts are of course obtained by weighing. If this is not practicable, a fair approximation may be made by computation based on careful measurement. In such case the volumes are found by the most appropriate means ac- cording to the shape of the figure (see Sec. 77) and then by the use of the known weights of the substances per unit volume, (see p. 30) the weights may be. found. The general U. S. regulations relating to safety valves will be found among the extracts from the Rules of the U. S. Board of Supervising Inspectors given in Sec. 19. Sec. 62. THE BOILER BRACE As we have seen in Sec. 16 all flat surfaces of any consider- able size, in a boiler, require some support in addition to that which can be furnished by their own strength. In fact the whole idea of bracing is to subdivide by the braces a large flat sur- face into a sufficient number of smaller surfaces, each of which shall be self-supporting between the points where the braces are connected to the plate. The braces are then designed so as to be able to carry the entire load as a whole, and the parts of the plate between the braces are simply required to support, without undue change of form, the part of the load which comes upon them. SPECIAL TOPICS AND PROBLEMS. 481 To illustrate by a diagram let Fig. 279 represent a part of a boiler head requiring bracing. Now imagine the plate entirely cut out around the dotted line, and then fitted in so exactly as to make a steam tight joint. The part thus cut out is therefore entirely separated from the remainder of the head, and without some especial support would be blown out immediately when steam was raised. Now suppose the braces to be so designed that they may be safely depended on to carry the entire load on the plate, and thus keep it securely in place in the head. It simply remains then for the parts of the plate between the braces to support themselves without losing their proper shape, and the support is thus made complete. In the actual boiler head, or in all cases where a flat surface has to resist pressure, the design of the braces is worked out exactly along these lines, and no / Aooooooooo / / ooooooooo I /oooooooooo 1 / oooooooooo I / OOOOOOOOOO l_i_opoooopppo 0000000 ooooooo ooooooo ooooooo ooooooo ooooooo 000000000\ ooooooooo \ ooooooooooX oooooooooo \ oooooooooo \ 00000000_QOJ Fig. 279. Boiler Bracing. account is taken of the strength of the plate for the general sup- port of the load as a whole. In designing boiler braces we have to consider two things : (1) The total load to be supported and number of braces, or simply the load upon one brace as determined by their spac- ing and the steam pressure. (2) The safe load per square inch of section of brace. The total load depends on the area to be supported and on the gauge pressure. In figuring out the area, as in Fig. 279, it is customary to consider that a narrow strip of metal around the outside will be well supported by the shell or by the tubes. The width of such strip is usually taken as 2 or 3 inches, though there seems to be no good reason why it should not be taken as half the spacing or pitch of the braces. This amounts to con- 482 PRACTICAL MARINE ENGINEERING. sidering the shell and tubes as effective bracing or support lor that part of the plate near them, in the same manner and to the same extent as for the braces themselves. If the area thus found is multiplied by the gauge pressure, the total load results. The spacing of the braces must then be taken in accordance with the principles and rules given in Sec. 19. The total number of braces is thus determined, and the average load per brace may be found by dividing the total load by the number. Or otherwise, after the spacing is decided upon, the load on each brace may be found by multiplying the area which it supports by the pressure per square inch. Thus in Fig. 28oa the surface supported by the brace is considered as the dotted square, and the spacing being the same both ways, its area equals the square of the pitch. In some cases the spacing is not the same in both directions, as in Fig. 28ob. In such case the Marint Engineering Fig. 280. Boiler Bracing. supported area is found by multiplying together the two pitches. Sometimes, again, the braces are irregularly distributed, and the area supported by one brace may be roughly triangular or of other irregular shape. In such case the area which the brace may be fairly called upon to support must be taken by approxima- tion, using 1 the best judgment which can be brought to bear on the special circumstances. When the braces are arranged in rows and columns as in Fig. 279, it will usually be found that due to the necessary spac- ing about the edges, the average load is slightly less than that which would correspond to an entire square or rectangle, and in consequence it is usually safer to take the load as determined directly by the area supported. Thus in Fig. 28oa, let the side of the square be 7 inches : then the supported area is 49 square inches. Likewise in Fig. 28ob, let the pitch be 14 inches in one SPECIAL TOPICS AND PROBLEMS. 483 direction and 16 inches in the other: then the supported area equals 14 X 16 or 224 square inches. Again in Fig. 67, suppose that three braces are to be used to support the approximately triangular area on the back tube sheet. In such case we make a fair allowance for the support about the edges, sketch in the area which the braces may be called on to support, sketch in the braces so as to divide the area as evenly as possible, and either compute the area of the whole triangle and divide by 3, or com- pute the smaller areas separately. Turning now to the second chief question, the safe load to be allowed per square inch of section of brace, we find that the U. S. Rules provide that iron braces shall not be allowed more than 6,000 Ib. per square inch of section ; while for steel, if in- spected according to regulation, the allowance may be as fol- lows : From \y$ in. diameter to 2^2 in. diameter, not to exceed 8,000 Ib.; and above 2^/2 in. diameter, not to exceed 9,000 Ib., each per square inch of section. (See also Sec. 19). It must be noted that in all cases the diameter is measured at the root of the thread or at the smallest section. For this reason the threads are usually raised so that the diameter at the bottom is not less than that of the body of the brace. We have thus discussed the determination of two necessary items the load which the brace is to support, and the safe load per square inch of section. It is clear then that if we divide the latter into the former, the quotient will be the necessary cross sectional area of brace. Having found the area, we find the diameter by means of a table of diameters and areas, or by the proper rule or formula of mensuration. See Part II., Sec. 9 [10]. These various operations may be expressed in the form of a rule as follows : (1) Find the area to be supported by one brace, and multiply this by the gauge pressure per square inch. The product will be the load to be supported by the brace. (2) Take the safe load per square inch of section in accord- ance with the rule above given. (3) Divide the total load as found in (i) by the safe load as taken in (2) and the quotient will be the necessary area in square inches. (4) Find the corresponding diameter either by the help of a suitable table or by means of the proper formula or rule of men- suration. 484 PRACTICAL MARINE ENGINEERING. To illustrate the foregoing a few examples will be of aid. (1) In Fig. 279, suppose the total area to be supported is found by measurement to be 3,784 square inches, the steam pressure being 160 pounds gauge. Find the total load. Ans. Load = 3784 x 160 = 605,440. (2) In Fig. 28oa, suppose the braces spaced 14 inches each way, the steam pressure being the same as in (i). Determine the load on one brace. Ans. Load =: 14 x 14 x 160 = 31,360. (3) Suppose, instead, that we wished to space the braces 14 inches one way and 16 inches the other. Find the load on one brace. Ans. Load = 14 x i6x 160 = 35,840. (4) Suppose that we space screw staybolts 6 inches x 6 inches. Find the load on one brace. Ans. Load =6 x6x 160 5,760. (5) Suppose in (4) that the spacing were 7x6^. Find the load. Ans. Load = 7 x 6 l /> x 160 = 7,280. (6) What would be the area and diameter of a steel brace in (2), allowing 8,000 Ib. per square inch of section? Ans. Area = 31,360 -r- 8,000 = 3.92 square inches. Corresponding diameter = 2% inches nearly. (7) What would be the area and diameter of a steel brace in (3), allowing 8,000 Ib. per square inch of section? Ans. Area = 35,840 -i- 8,000 = 4.48 square inches. Corresponding diameter = 2 7-16 scant. Probably 2^ inches would be employed. (8) What would be the area and diameter of an iron stay in (4), allowing 6,000 Ib. per square inch of section? Ans. Area = 5,760 -h 6,000 = .96 square inches. Corresponding diameter = i 1-8 inches nearly. (9) What would be the area and diameter of an iron stay in (5), allowing 6,000 Ib. per square inch of section? Ans. Area = 7,280 -~ 6,000 = 1.213. Corresponding diameter = i*4 inches nearly. (10) Suppose that screw stay bolts are spaced 7x7 inches, the steam pressure being 200 Ib. gauge. Find the area and diam- eter of a steel stay, allowing 8,000 Ib. per square inch of section. Load = 7 x 7 x 200 = 9,800 Ib. Area = 9,800 -H 8,000 = 1.225 square inches. SPECIAL TOPICS AND PROBLEMS. 485 Corresponding diameter = i j4 inches nearly. Load on Oblique Braces. In case the brace is not at right angles to the surface to be supported, proper allowance must be made for the increase of load on the brace due to the angle of obliquity. This problem is explained in Part II., Sec. 12 [14] (14)- Load on Forked. Ends of a Brace. The load on the forked ends of a brace, as in Fig. 59, is greater than one-half the load on the brace, in a ratio depending on the angle of obliquity. This prob- lem is explained in Part II., Section 12 [14] (13). Sec. 63. STRENGTH O BOILERS. In order to examine the relation of the strength of a boiler shell to its diameter, thickness and the steam pressure, consider 3 F H D Uttriiie t^'iyiiuxrinff Fig. 281. The Stnt gth of Rollers. first a hollow chamber, as in Fig. 281, with parallel sides, AC and BD, a face AB perpendicular to these sides, and for the other end any other curved or irregular surface CD. Let this contain steam under pressure. Now it is a well-known fact of experience that under such circumstances the chamber will remain in equi- librium, and it will not move as a whole, and in particular will move neither to the right nor to the left. Hence the internal force acting to the right must equal that to the left. But the force acting to the right is the total resultant of all the forces act- ing on the curved surface CD, while the force acting to the left is the resultant of the parallel forces acting on the plane face AB. Hence numerically these two resultant* must be equal, nnd this will be the same, no matter what the shape of the surface on the right, as, for example, EF or GH. Now AB is called the pro- jected area of any curved surface, such as CD, EF or GH, the 486 PRACTICAL MARINE ENGINEERING. direction of projection being of course parallel to the sides AC and BD. Hence we may say that the total resultant force in any direction due to the pressure of steam or of any gas or vapor act- ing on the curved surface will equal the pressure of the projected area of such surface, the projection being taken in the direction of the resultant desired. This is a very general and very im- portant principle in mechanics, and has many applications, one of which is to the problem of the strength of a boiler, as we will pro- ceed to show. In Fig. 282 let ABCD denote a cross section of a cylindrical boiler with steam pressure acting on the curved surface, as de- noted by the arrows. Suppose a plane of division AB, and let us consider what it is which keeps the two halves from separating under the action of the steam pressure. The surface ACB is Q Marine Engineering Fig. 282. The Strength of Boilers. urged upward and the surface ADB is urged downward, while they are prevented from separating by the strength of the ma- terial at A and B. Now the force tending to thus separate the two parts is evi- dently measured by the force urging ACB upward or ADB down- ward. As we have just seen, this equals the force on the pro- jected area which is represented by AB. Suppose the axial length of the section which we are considering to be one unit, or one inch, and denote the diameter by d, the radius by r and the thickness of the shell by t. Then the area of AB equals 'd. square inches, and if p is the pressure per unit area the total load on AB is pd. But as we have seen this is numerically the same as the SPECIAL TOPICS AND PROBLEMS. 487 force which urges ACB upward and ADB downward, and which is opposed simply by the strength of the material at A arid B. The cross sectional area on each side will be t x i or / ; hence the total area of material will be 2t. Let 5 denote the stress de- veloped in the material per square inch of section. Then 2/5* is the total stress developed, and this must equal the load pd* Hence we have the equation 2tS = pd = 2/>r. (i) 2/5 tS and p = ~~d = 7 ^ 3) In these equations (3) gives the value of the steam pressure p, which would produce the stress S in the metal of thickness t. If, however, a shell, as in Fig. 282, were formed with riveted joints the strength of the metal in the joint would be less than that of the plate itself in the ratio given by the efficiency of the joint as discussed in section 15. Hence, if 5 is to be the safe working stress in the metal of the joint, and e is the efficiency, the working pressure p must be reduced in the ratio of the effi- ciency, or from p to ep, in order to keep the stress in the joint down to the value S. Also if T is the ultimate strength of the metal, we do not wish S to rise above a certain fraction of T. The number by which we divide T to find the safe stress S is called the factor of safety. Denote this factor by f. Then in (3) substituting for 5" its value T -f- f and allowing for the efficiency of the joint we have : 2etT etT P = ~j j r = - f (4) and , m (5) In a similar manner let us consider the strength of the boiler to withstand rupture around the shell. In this case the area of the head is nd 2 H- 4 and the load is/nv/ 2 -~ 4. The section of metal carrying this load is measured by the circumference multiplied by the thickness, or by xdt. Hence if 5 is the stress developed per unit area, the total stress in the metal carrying the above load is ndts. Equating the load and the total developed stress we have : 7T dtS = 4 4/5 2/5 or P ~ 438 PRACTICAL MARINE ENGINEERING. Comparing this with (3) it is seen that in the case of the shell without seam or joint the pressure necessary to produce rupture around the circumference will be just twice that required for rupture along the length ; or, in other words, the boiler is twice as strong for rupture around the circumference as for rup- ture along the length, and this is an important principle which should be borne in mind in dealing with questions relating to the strength of a cylinder against pressure from within. It also fol- lows that the longitudinal seams must be made with the greatest care and of the highest efficiency, while joints of lower efficiency, so long as they insure tightness against leagage of steam, will be sufficient for the circumferential seams. To take account of the factor of safety and of the efficiency of the joint we must in- troduce in (6) the factors / and' e, the same as in (3). This will give : 4 etT 2etT P = ~fd = 7~^ (?) and , = (8) For a bumped boiler head, as referred to in section 19, we consider that the head is a part of a sphere, and that all parts of such a surface are equally strong. Now for a sphere as a whole we have for the total load on a circumferential section the pres- sure p multiplied by the projected area of the hemisphere. But the latter is ^ 2 ~ 4, and therefore the load is ^pd^ -f- 4. The total section of metal is ndt, snd if 5 is the stress developed per unit area, then the total stress is ndtS. Hence we have : npd* = 7T dtS 4 4/J or p = But, as seen above, this is the same as the value for a cylin- drical shell for rupture around the circumference. Hence we have the principle that a sphere has the same strength in all di- rections as a cylinder of equal diameter for rupture around the circumference. It will be noted that this relates simply to the strength of a sphere or part of a sphere for pressure on the con- cave surface. For the strength of a head bumped inward or con- vex on the inside, there is no method of treatment by simple mechanics. For the mechanics involved in the computations relating to SPECIAL TOPICS AND PROBLEMS. 489 plain boiler bracing reference may be made to section 62 and to Part II., section 12. Sec. 64. JyOSS BY BLOWING OFF. In the days of the jet condenser, and when blowing off to reduce the density of the water in the boilers was the usual prac- tice, the loss of heat occasioned by this operation was necessarily the subject of consideration, and it became necessary to be able to compute this loss in any given case. This is most easily done by the simple application of algebraic methods. Let F denote the pounds of feed water in any given time, and f its density. Let B denote the pounds of water blown out in the same time and b its density. Then (F 5) = pounds of water evaporated into steam in the same time. Likewise fF represents the amount of solid matter brought into the boiler during the giveif time, and bB represents similarly the amount blown out in the same time. Since the density of the water in the boiler remains constant at b, the amount of solid matter in the water must remain constant, and hence as much must be blown out as comes in by the feed, or : fF = bB (i) From this we readily derive the following relations : F b B =? ^ ^B~ = "/" (3) Now let ti = temperature of feed, /a = temperature of steam, H = total heat in one pound of steam at given pressure. Then B (/-/) = heat blown out, and (F-B) [H-(t^2)] = heat put into the steam formed. Then (F B) (H + 32) + Bt* Fti = total heat. Hence ratio of loss e is given by : e = X (', f,} ^ By the aid of the ratios above, this expression is readily re- duced to the following form : ^? __ 490 PRACTICAL MARINE ENGINEERING. These algebraic operations may be expressed by the fol- lowing : Rule (i) Multiply the density of the feed water by the dif- ference between the temperatures of the steam and of the feed. (2) Subtract the density of the water blown out from the density of the feed. (3) Add 32 to the total heat of i Ib. steam. (4) Multiply together the results in (2) and (3). (5) Multiply the density of the feed by the temperature of the steam. (6) Multiply the density of the water blown out by the tem- perature of the feed. (7) Add the results in (4) an the volume as before and note the weight required. Then move the engine up to the center slowly, catching the water as it is forced out and weighing as be- fore. The amount forced out corresponds to i inch of piston dis- placement. Subtract this amount from the total, and the re- mainder represents the water in the clearance. Divide the latter by the amount representing one inch of piston travel, and the quotient is the number of inches corresponding to the clearance. This divided by the stroke will give the clearance percentage. As an illustration of the first mode of procedure, suppose diameter = 22 inches, stroke = 40 inches, weight of water to fill clearance = 85 pounds. The volume of clearance = 85 -f- 62.5 = 1.36 cubic feet. The volume of piston displacement = 3.1416 X ii X ii X 40 -^ 1728 = 8.8 cubic feet, nearly. Hence clear- ance percentage 1.36 -f- 8.8 = 15.45 per cent. For the second mode of procedure let the figures be as fol- lows : Total weight of water with engine i inch off center = 99 pounds. Weight of water forced out when engine is brought to center = 13.5 pounds. Difference = 85.5 pounds. Then 13.5 pounds represents i inch of piston travel, and 85.5 pounds the 49 6 PRACTICAL MARINE ENGINEERING. whole clearance. Hence 85.5 -f- 13.5 = 6.33 inches = number of inches of piston travel giving a volume equal to that in the clearance. Hence 6.33 -f- 40 inches = 15.8 per cent. = clearance percentage. Sec. 68. THE EFFECT OF CLEARANCE IN MODIFYING THE APPARENT EXPANSION RATIO AS GIVEN BY THE POINT OF CUT-OFF. As we have seen in Sec. 67, the clearance volume is defined as the volume or space between the piston when at the end oT the stroke and the face of the valve. It comprises the "clearance proper" or space between the piston when at the end of the stroke and the cylinder head, together with the volume of the ports or passages leading from the valve face to the cylinder. O A Marine *<,VnHn0 p Fig. 283. The Effect of Clearance on the Expansion Ratio. The volume of the clearance expressed as a fraction of the vol- ume swept by the piston is usually known as the clearance ratio or per cent., and is usually found in marine practice from .10 to .15, though in some cases it may rise as high as .20. The steam within this volume takes part, of course, in all expansions and compressions to which the steam in the cylinder as a whole is subjected, and its influence on the apparent expansion ratio must therefore be considered. If there were no clearance volume, then the expansion ratio would be given by dividing the total volume swept by the piston, by the volume up to the point of cut-off. But this would be the same as taking the reciprocal of the cut-off ratio. Thus, for example, if the cut-off were at 1/2 stroke the expansion ratio- would be 2 ; if at 1/3 stroke, 3; if, at 2/3 stroke, 3/2 or 1.5, etc. With a clearance volume, however, this is modified as shown by Fig. 283. Let AB denote the volume swept by the piston and OA the clearance volume to the same scale, or otherwise let AB SPECIAL TOPICS AND PROBLEMS. 49? denote the length of the stroke and OA the clearance volume re- duced to stroke by dividing the volume by the piston area. Then if cut-off is at some point X the actual volume of steam within the cylinder and ready to expand is denoted by OX rather than by AX. Again at the end of the stroke when the piston reaches B, the final volume of the steam is OB. Hence the real expan- sion ratio is OB/ OX and denoting its value by r we have : AB4-OA = AX+O A Now dividing both numerator and denominator of this frac- tion by AB we have : i + OA AB AX OA AB + AB Now AX -f- AB is the cut-off ratio, and OA -f- AB is the clearance ratio or per cent. Denote the first of these by a and the second by c. Then we have : i + c ~- ^m- Examples : (1) Cut-off at */2 stroke, clearance 10 per cent. Find the true expansion ratio. Operation : a = 3/2 = .50. c = 10 per cent. = .10. i. oo + .10 1. 10 Hence r - - ~ =1.83 Ans. .50 + .10 .60 (2) Cut-off at 60 per cent, clearance 15 per cent. Find the true expansion ratio. I. oo -f . i Z i. ic Operation: r = i 53 Ans. .60 + .15 .75 Sec. 69. ENGINE CONSTANT. As seen in Sec. 55 [3] we have for the horse power formula : 33,000 33,ooo Now the factors 2.LA -=- 33,000 are always the same for any one cylinder, while the other two (pN) will vary according to the conditions. We may therefore compute in advance the value of the factor (2.LA -f- 33,000) and then to find the H.P. we shall 498 PRACTICAL MARINE ENGINEERING. have simply to multiply these by the other two, of which one, p, is found from the cards, and the other, N, from the counter. This factor 2.LA -f- 33,000 is called the "engine constant," and is often thus computed as a matter of convenience, especially when large numbers of cards are to be worked up. For the power in one end of the cylinder only we have sim- ply to take the factors LA -r- 33,000 with N and the value of p found from the corresponding card. To allow for the area of the piston-rod on the lower side of the piston in the formula for the full power, we may use the average area top and bottom with the average mean effective pressure. When there is a difference in the values of the mean effective pressure top and bottom, this will not give quite the same result as if the two ends were taken separately. The difference, however, is in all ordinary cases quite unimportant. See also Sec. 55 [3] . Example : Given a cylinder of diam. = 36", stroke = 42", diam. of piston-rod = 5"- Find the constant neglecting the pis- ton-rod, and also allowing for it as above explained. Area of cylinder = 1017.9 sq. in. Stroke = 3.5 feet. Constant = (2 X 3-5 X 1017.9) -v- 33,000 = .2159. Next to allow for the piston-rod we have for its area 19.6 square inches. Taking this from 1017.9 we have 998.3 square inches as the area of the lower side of the piston. The mean of the upper and lower sides is then 1008.1. It may be noted that in all such cases the mean may be most easily obtained by taking from the upper area one-half the piston-rod area, or in this case, by taking 9,8 from 1017.9, giving 1008.1 as above. We then have: Constant = (2 X 3-5 X 1008.1) -=- 33>ooo = .2138. Sec. 70. INDICATED THRUST. The indicated thrust in pounds may be defined as the indi- cated power in foot pounds divided by the product of the pitch of the propeller multiplied by the revolutions per minute. Let: ;.j H = I. H. P. p = pitch of propeller. N = revolutions per minute. T indicated thrust. SPECIAL TOPICS AND PROBLEMS. 499 >rmula T in pounds = Then by formula : 33,000 // pN This may be reduced to tons by dividing by 2,240, and we T- 33)0oo H 14.73/7 have T in tons = - ^ , Dividing the above value of T in pounds by the value of the reduced mean effective pressure as given by equation (i) in Sec. 71, and we have : T 33,000 H iLNA 2 LA < An p 33>ooo p It thus appears that the ratio of the indicated thrust to the reduced mean effective pressure is measured by twice the stroke times the L.P. area divided by the pitch of the propeller. All of these are constants for any given engine, and it thus follows that the ratio between the indicated thrust and the reduced mean effective pressure is a constant, or in other words that the former is in a constant ratio to the latter. The indicated thrust which is often considered as a rather vague quantity is thus related to the reduced mean effective pressure, a much better known quantity. The indicated thrust may also be considered as the actual thrust which would be exerted if the propeller worked without slip, and if all the power developed in the cylinders were used in driving the ship forward at the speed thus produced. Actually a part of the power is lost in the friction of the engine and in the water due to the operation of the propeller, while the latter does not operate without slip. In consequence the actual thrust ex- erted on the thrust block is usually found somewhere about two- thirds the indicated thrust, computed as above. Example: The I. H. P. is 1,640, the pitch 13 feet, and revolutions 148. Find the indicated thrust in pounds and in tons : , . 33,000 X 1.640 7 in pounds = - - 28,130 13 X 148 T in tons = 28,130 -f- 2,240 = 12.56. Sec. 71. REDUCED MEAN EFFECTIVE PRESSURE. In the multiple expansion engine the power, as we know, is developed in the various cylinders, as equally as the designer is able to bring about. The reduced mean effective pressure may be defined as the mean effective pressure which, acting; in the low 500 PRACTICAL MARINE ENGINEERING. pressure cylinder alone with the same piston speed, would pro- duce the same power as the actual engine with its series of cyl- inders. , . Taking the usual formula for power, as in Sec. 55 [3] we have : 33,000 and solving for p we have 33,000 H 3^ * 2 LrtN '- (2 LA/) A Hence if the entire power were to be developed in the L. P. cylinder the necessary mean effective pressure would be found by the operations indicated by this equation, and such would be the reduced mean/ effective pressure, or the mean effective pres- sure reduced to the L.P. cylinder. The operations indicated by the above equation may be expressed by a rule as follows : Rule: (1) Multiply the indicated horse power by 33,000. (2) Multiply twice the length of the stroke in feet by the revolutions (giving piston speed) and this by the area of the low pressure piston in square inches. (3) Divide the result found in (i) by that found in (2) and the quotient is the reduced mean effective pressure desired. To obtain a somewhat different expression for the reduced mean effective pressure denote the areas of the three pistons H.P., I.P. and L.P. of a triple expansion engine, for example, by Ai, As, A*, and the corresponding values of the mean effective pressure in these cylinders by {H, p*, p*. Then the total power H of the formula (i) above may be expressed as follows : H _. (2LN)frA* + (*LN)pJ 9 +(2LN)fJ 3 33,000 According to (i) this value of H is to be multiplied by 33,000 and divided by 2 LN times A* the L.P. piston area. This will give the following as the value of the reduced mean effective pressure : According to this formula the procedure for finding the re- duced mean effective would be as follows : (i) Divide the mean effective for the H.P. cylinder by the ratio between the L.P. and H.P. piston areas. This reduces tEe SPECIAL TOPICS AND PROBLEMS. 501 H.P. mean effective to the L. P. piston. (2) Divide the mean effective for the I. P. cylinder by the ratio between the 1 L.P. and I. P. piston areas. This reduces the I.P. mean effective to the L.P. piston. (3) Add together the results found in (i) and (2) and the mean effective for the L. P. The sum will be the total mean ef- fective reduced to the L.P. piston. Example: Given for a triple expansion engine the following: Diam. H.P. cylinder = 24" I.P. = 38" L.P. " = 60" Length of stroke = 42" Revolutions = 106 From sets of indicator cards suppose the mean effective pressures found as follows : For the H.P. /* = 61.9 " " I.P. p> = 30.2 " " L.P. p* 13.8 Find the total I. H. P. and the reduced mean effective pres- sure. For the piston areas we have from a table of areas of circles : A l = 452.4 A a =: 1134.1 A 3 = 2827.4 Then finding the I H. P. in each cylinder we have as follows : I. H. P. in H. P. cylinder = ........ 629.6 I. H. P. in I. P. cylinder = ......... 770.2 I. H. P. in L. P. cylinder = ......... 877.2 Total I. H. P. ................ 2277.0 Then according to rule (i) for the reduced mean effective : 33,000 x 2277 g2 1 7 X 106 X 2827.4 = According to rule (2) for the same we should have as follows : . 1134.1 = 6l '9 >' + 30.* ! -~- + 13.8 or/ = 9.9 + 12.12 + 13.8 = 35.82. So* PRACTICAL MARINE ENGINEERING. The results are of course the same, since the two operations are simply two methods of computing the same quantity. If the I.H.P., revolutions, length of stroke and L.P. piston area are given, then the first method would be used. If the mean effec- tives in the various cylinders are given, together with the revo- lutions, length of stroke, and piston areas, then the second method may be used without necessarily finding the I. H. P. at all. Problems : (1) Given I. H. P. = 5,120. L. P. area = 5,612. Stroke 48". Revolutions = 112. Find the reduced mean effective pressure. Ans. 33.6. (2) From a pair of H. P. indicator cards the mean effective pressure is found to be 72.6 Ib. The diameters of the H. P. and L. P. are respectively 18 and 48 inches. Find the high pressure mean effective reduced to the L. P. piston. Ans. 10.2. (3) In the same engine as in (2) the mean effective pressure for the I. P. cylinder is found to be 33.2 Ib., and the L. P. diam. is 29 inches. Find the I. P. mean effective reduced to the L. P. piston. Ans. 12.1. (4) In the same engine as in (2) the L. P. mean effective pressure is 14.1 Ib. Find the entire reduced mean effective pres- sure. Ans. 36.4. Sec. 72. PRESSURE ON MAIN GUIDES. The load on the crosshead guides comes from the load on the connecting rod and the obliquity of its line of action. The mechanics of this problem is considered in Part II., Sec. 12 [14] (15) and the maximum value of the load, which is found when the crank is at right angles to the center line, is readily computed in the manner there shown. It thus appears that the maximum load on the guide will bear the same relation to the load on the piston that the length of crank does to the connecting rod. This method of computing the load will be illustrated by an example. (i) At about mid stroke given the pressure on the top of the piston 180 Ib. per square inch and on the bottom 88 Ib. per square inch. The ratio of connecting rod to crank is 4.5 to i. The area of the piston is 404 square inches. Required the maxi- mum load on the guide. SPECIAL TOPICS AND PROBLEMS. 505 Net pressure on the piston =. 180 88 = 92 Ib. per square inch. Net load on the piston = 92 X 404 = 37,i68 Ibs. Maximum load on guide 37,168 H- 4.5 = 8,260 Ibs. The safe load on guides is usually taken at from 50 to 70 Ibs. per square inch. In this case therefore taking 60 Ibs. as a safe load per square inch we should have : Area needed = 8,260 ~ 60 138 square inches. Sec. 73. FORCE REQUIRED TO MOVE A SI,IDE VAI/VE. The net load on a slide valve is the difference between the steam loads on the two sides. On the back we have a load clue to the full steam pressure in the steam chest. On the inside we have a more variable load due partly to the pressure in the steam chest or cylinder, and partly to the exhaust pressure. For the low pressure cylinder exhausting into the condenser the exhaust pressure is small and is usually neglected. The area of the face subjected to pressure from the cylinder is also relatively small, and for the purposes we have now in view is usually omitted. The load on such a valve is therefore taken simply as the load on the back, the pressure per square inch, multiplied by the area in square inches. Denote the pressure by p and the area by A. Then the total load will be pA. The resistance to the motion of the valve which must be overcome by the valve rod will be the load pA multiplied by the coefficient of the fric- tion between the valve and its seat. Let f denote this coefficient, and F the force necessary to move the valve. Then we have : F=fpA. The values of f will depend on the condition of the surfaces and on the lubrication. With well fitted and lubricated surfaces its value should not exceed .01 to .02. With dry surfaces, es- pecially if they should begin to abrade, its value may rise to .10 and more. Example: Given a low pressure slide valve with dimensions 50 inches by 60 inches : average excess of pressure in valve chest over condenser, 26 Ibs. Coefficient of friction .02. Find load on valve stem. Area = A 50 X 60 = 3,000 square inches. Load = pA = 26 X 3,000 = 78,000. Load on valve stem = fpA = .02 X 78,000 = 1,560 Ib. 504 PRACTICAL MARINE ENGINEERING. In designing a valve stem relative to such a load it must be given a large factor of safety in order to provide for starting the valve from rest or where partly stuck to the seat, and also for extra stresses due to the effects of inertia. For a flat slide valve on a high or intermediate cylinder, an estimate must be made of the load on each side and the differ- ence taken. Without serious error the net pressure may be taken as the difference between the average pressure in the valve chest and in the next following receiver. If then pi and />* are these pressures, (pi p*) will be the difference, and (pi />*) A the average load on the valve. The remainder of the operation is, of course, the same as explained above for the low pressure valve. Sec. 74. AMOUNT OF CONDENSING WATER REQUIRED. In Sec. 57 we have seen how to find the amount of heat required to formv one pound of steam of given temperature and pressure from a pound of feed-water of given temperature. To condense the steam and reduce it back to the condition of the feed-water will require the subtraction of the same amount of heat. Hence we may find the heat to be taken from each pound of steam in the condenser in exactly the same manner as in Sec. 57. Now suppose the condensing water as it comes in to have a temperature of ft, and as it is discharged, a temperature of t*. Then the temperature of each pound will be raised (t* fi) de- grees. This means that it will absorb (t* h) units of heat. Then if we divide this into the number of heat units which must be taken from each pound of steam, it will give the number of pounds of condensing water which must be provided to con- dense one pound of steam. Then if we know the amount of steam to be condensed, the total amount of condensing water is readily found. This may be illustrated by the following example : Pressure of steam at exhaust = 3.5 pounds, absolute. Corresponding temperature = 148. Temperature of condensed water = 130. Temperature of condensing water at entrance or h == 62. Temperature of condensing water at discharge or t* 98. Then from the steam tables we find that 1,029 heat units per pound must be subtracted in order to condense the steam and reduce it to the condition of the water in the condenser. SPECIAL TOPICS AND PROBLEMS. 505 We have also t* U = 98 62 = 36 = number of heat units absorbed per pound of condensing water. Then 1,029 -f- 36 = 28.6 = number of pounds of condensing water per pound of steam. Let us suppose an engine of 2,000 I. H. P. requiring 16 Ibs. of steam per I. H. P. per hour to be condensed under these con- ditions. Then for the total weight of water W we have : W = 2,000 X 16 X 28.6 = 915,200 pounds per hour. And 915,200 -.- 60 = Ibs. per mt. = 15,253. Then 15,253 -f- 64 = cu. ft. sea water per mt. = 238. In all ordinary cases the number of heat units to be sub- tracted will not differ much from 1,000, and for a rough estimate this number is often taken without detailed computation from the steam tables. Then, varying with the season of the year and the locality, we may expect that each pound of condensing water will absorb from say 25 to 50 heat units, and hence that the condensing water required per pound of steam will vary from 40 to 20. Sec/75. WORK DONE BY PUMPS. It is sometimes desired to find the net work done by a pump in handling a certain amount of water. This may be computed closely if we know the conditions under which the pump op- erates. It is shown in mechanics that work may be divided into a volume factor and a pressure per unit area factor, and this form of the expression for work is usually most convenient for use in such cases. Let us take first the case of a boiler feed pump feeding against a gauge pressure of 160 pounds and supplying 16 pounds water per I. H. P. per hour for 2,100 I. H. P. Then the amount of water supplied will be 2,100 X 16 = 33,6oo pounds per hour. This equals 33,600 -f- 60 = 560 pounds per minute. Taking 62.5 pounds per cu. ft. this will occupy a volume of 560 -:- 62.5 = 8.96 cu. ft. This volume of water is pushed into the boiler against a total pressure of 160 + 14.7 or say 175 pounds per square inch or 175 X 144 = 25,200 pounds per square foot. Hence we have: Work per minute = 25,200 X 8.96 = 225,792 ft. Ibs. Reducing this to horse power we have : H.P. = 225,792 -f- 33,000 = 6.84. This is the net work, and assuming that there is no leakage or loss of steam. Actually there will be such a loss, raising the amount of water which the pump must deliver by from 5 to 10 per cent or more. 506 PRACTICAL MARINE ENGINEERING. Now between the steam cylinder where the total work is developed and the net delivered work as above determined, there is a series of losses. These may be classified as follows : (1) Loss due to the friction of the water in the pipes and to the inertia or resistance of the valves. These items form an extra resistance which must be overcome in addition to the regular pressure in the boiler. (2) Loss due to the friction of the pump itself. This like- wise forms an extra resistance as in (i). (3) Loss due to the slip of the pump. The pump plunger and valves are rarely tight and a certain amount of "slippage" to the water is sure to occur. It results that the volume displaced by the pump plunger will be greater than the volume delivered to the feed pipe, and the work to be done in the water cylinder will be increased in about the same ratio. The slip is quite a variable feature, being quite small with good workmanship and careful attention, and large under contrary conditions. With the usual run of boiler feed pumps, however, it will rarely be less than 5 per cent., and with lack of care may readily rise to from 10 to 20 per cent. The sum of losses (i) and (2) will be found usually between 15 and 20 per cent., and hence the sum of the total losses may be expected to vary between perhaps 20 or 25 and 40 per cent. In the present case, for illustration, assume the loss by leak- age of steam at joints, etc., as. 6 per cent. Then the water ac- tually delivered to the boiler will require a net work of 6.84 -'- .94 = 7.28. Assume the total losses between steam cylinder and feed pipes to be 33 per cent. Then the I. H. P. in the steam end will be 7.28 -f- .67 = 10.87, an d we should therefore expect that under moderate to fair conditions such a pump would require from 10 to ii I. H. P. With the pump plunger and valves leak- ing badly, stiff working parts and generally poor conditions, the amount will, of course, rise far above these figures. The full capacity of the feed pump would also be, of course, consider- ably above these values. We are here simply concerned with an estimate of the power actually required and the net power delivered under a given set of conditions. Again consider the case of a centrifugal pump for the same engine handling we will say 30 pounds condensing water per pound of steam condensed. Then the total amount of water handled per hour will be 2,100 X 16 X 30 = 1,008,000 pounds. SPECIAL TOPICS AND PROBLEMS. 507 In this case the resistance to be overcome is due chiefly to forcing the water through the condenser tubes. In some cases also the discharge outlet is slightly above the surface of the water and this additional lift increases the work to be done. The most convenient method of computation in this case is to estimate the total head equivalent to the resistance occasioned by the condenser tubes, and the lift of the water above the sur- face. This will be the total height of water which would pro- duce the same pressure as must be overcome by the pump at the tips of the vanes. In usual cases we may assume the head corresponding to the resistance in the condenser tubes at from 4 to 5 feet. If the water is discharged at or below the water level this will then be the total head against which the pump works. In case, however, the pump draws from the bilge as when used for freeing the ship of water, then the total head will be the total lift plus the head due to the condenser tubes, and its value may rise in such cases to 20 feet and more. In such cases the work done is the product of the weight of water handled as the force or resistance factor, multiplied by the head as the distance factor. In the present case, assuming a total head of 6 feet we have : Work per mt. = 16,800 X 6 = 100,800 ft. Ibs. or H. P. = 100,800 -f- 33,000 = 3.05. The efficiency of such pumps is usually found between .30 and .50. That is, between 50 and 70 per cent of the power de- veloped in the steam engine operating the pumps is lost, chiefly in the slip of the pump. Hence under fair conditions we may assume that 'this 3.05 H. P. will be about 40 per cent, of the I. H. P. of the engine. Hence the latter will be greater than 3.05 in the ratio of 100 to 40 or 2^2 times. Hence we have : I. H. P. required = about 2*/ 2 X 3.05 = about 7.5. These examples will serve to show the methods to be used in working such problems, and if the principles involved are kept clearly in view they may be similarly applied to the solution of many problems likely to present themselves in engineering work. Sec. 76. DISCHARGE OF STEAM THROUGH AN ORIFICE. It may be sometimes convenient to be able to compute ap- proximately the amount of steam which will escape into the atmosphere from a chamber under a given pressure through an aperture of given area. 5 ofc PRACTICAL MARINE ENGINEERING. Let p be the pressure, supposed to be not less than 25 Ibs., absolute. Let A = area of aperture in square inches, and W = weight discharged in pounds per second. Then Napier's rule for the approximate value of W is as follows : w~& 70 Thus given A = .5 sq. in. and p = 140 we have : W = I4 X ' = i lb. per second. 7 X 2 Take the following problem : What weight of steam would be discharged per hour through a small hole or crack of area .005 sq. in. under a pressure of 200 pounds per sq. in.? Using the formula we have : TJ _ 200 x -005 x 3600 - , W = - - - 51.4 pounds per hour. 7 We may thus realize the importance of small leaks. Sec. 77. COMPUTING WEIGHTS OF PARTS OP MACHINERY. The determination of the weights of various parts of marine engines and boilers is often necessary as a part of an estimate of costs for repairs or for other purposes. Such determinations are usually made by numerical computation, and consist in find- ing first the volume of the piece in question, and then its weight by the use of factors such as those given in the Table on p. 30. The chief part of the computation is therefore mensuration, the principles of which are given in Part II., Sec. 9. We will here add some general suggestions regarding the application of these rules, with some additional methods which may be used in special cases. [i] Units to be Used. The dimensions will usually be taken either from a drawing or directly from the piece in question. It may be recommended as a general rule to reduce all dimensions to inches as the unit rather than feet or feet and inches, the latter requiring the use of duo-decimal notation and methods as explained in Part II., Sec. 4 [5]. Where the pieces are small and fractions of an inch are to be dealt with, it will usually be most convenient to re- duce them to decimal form rather than to express them as com- mon fractions. In brief the inch as the unit and numbers ex- pressed decimally are recommended as a general rule in such SPECIAL TOPICS AND PROBLEMS. 509 computations. The factors for reducing cubic inches to pounds are then used as given in the Table on p. 30, and the weight is readily found. [2] Approximations and Short Cuts. In computations of this character absolute accuracy does not exist. In fact with no physical measurement can absolute accuracy be attained. In practical life we wish simply an ap- proximation, a value sufficiently near for the purposes in view; a value so near that the error is not of commercial or financial importance. All engineering measurements and computations recognize this principle, and of the acquirements which may come to the engineer with experience, none is of greater value than that which enables him to know where to stop his compu- tations, how far to carry his measurements and approximations, what error will be of importance, and what insignificant. Thus if we are to measure the dimensions of a coal bunker in order to compute its volume, it is evidently absurd to note the figures to the fraction of an inch. We can be by no means sure that the length, for example, is uniform within any such limit, and the difference due to a variation of ^4 r Y^ inch either way will be insignificant for the purpose in view. On the other hand, if we are to measure a journal in order to make a new one which shall fit in the same bearing, the admissible error is only a few thousandths of an inch, and the utmost attainable accuracy will be in order. So likewise if we are finding the weight of a sheet of boiler plate . an error of l /% inch in the length or breadth will introduce no significant error in the final result, while such an error in the thickness would cause a most serious error in the result. The former would make a difference of perhaps one part in 1,000 or so, while the latter might cause an error of one part in 8 or 10. Another point which may also be remembered is that a large relative or percentage error is more permissible in some small part of the whole than in a large part. Thus in a boiler an error of 10 per cent in the weight of the tubes may be of less importance than one of i per cent in the weight of the shell and heads, while an error of 50 per cent in the high pressure cylinder cover, for example, might make less difference than one of 10 per cent in the low pressure cover. Of course there should be no excuse for making any 50 or 10 per cent errors, but the principle may be 5 ro PRACTICAL MARINE ENGINEERING. borne in mind as a legitimate means of saving time when a roughly approximate value must be determined. The most common approximations are those which make the computation of volume simpler by substituting for the actual body some other of simpler form, and with such dimensions as Fig. 284. Approximate Area of Segment of Circle. Marine Enyintering Fig. 285. Approximate Area of Boiler Plate. to be of equal volume so far as judgment may be able to deter- mine. Such substitutions are often employed, but they must be used with judgment and care in order that the possible error in- troduced may not be larger than permissible. No general rules SPECIAL TOPICS AND PROBLEMS. 5" can be given for such approximations, but the most common consist in substituting a rectangle or triangle or sometimes a cir- cle, for a more irregular area ; or a cylinder or regular prism or plate for some irregular volume. Thus in Fig. 284, if we wish to find quickly an approximate value of the segment of the circle ABC, we may sketch in a tri- angle ADC, so taking the sides that the area left out shall be judged equal to that taken in, and hence the area of the triangle may be taken as an approximation to that of the segment. This area is then readily found by the usual rule for a triangle. Again, in computing the area of a front boiler tube sheet, as shown in Fig. 285, we may for a first approximation substitute by judgment for the actual contour a rectangle ABCD, and thus quickly obtain a value which may be sufficiently close for the purpose in hand. Again we may often add by judgment something to one of the dimensions of a piece in order to provide for additional or irregular parts which would not be included in the regular geo- metrical figures dealt with. Thus in finding quickly the approxi- mate weight of a cylinder casting, provision may be made for the flanges by adding by judgment an appropriate amoilnt to the length of the casting; or similarly for a piece of shafting with flanged couplings at the ends. It is often necessary to divide a more or less complicated piece into several parts, each of which may be of some relatively sim- ple form. In some cases the volume of one simple form may be subtracted from that of another, thus giving as the remainder the volume of a more or less irregular form. Thus, to find the volume of a pair of brasses with square backs and sides, we may find the volume from the outside dimensions as though the block were solid, and then the volume of the cylindrical hole, and take the one from the other. Many such little devices will suggest themselves in connec- tion with the details of the work ; but it will be unnecessary to here enter further into the subject. In connection with the rule of Pappus, Part II., Sec. 9 [30], we may note the following method of applying it to the deter- mination of the weight of such forms as a piston, cylinder head, etc. The operations are as follows : (1) The cross sectional drawing is supposed to be at hand. (2) A copy of the half cross section, as shown for a piston 512 PRACTICAL MARINE ENGINEERING. in Fig. 286, is prepared on thick, uniform paper, and then cut carefully out with a sharp-pointed penknife. (3) This is weighed on delicate scales, and also balanced on the knife edge, the line AB containing the center of gravity be- ing thus found. (4) A square of the paper containing any convenient num- ber, say 100 square inches of area, is also cut out and weighed. This divided by the area will give the weight of the paper per square inch. (5) The weight of the paper half section is divided by that Fig. 286. Volume of Piston by Rule of Pappus. of the square inch. The quotient will be the area of the paper half section in square inches. (6) This area is multiplied by the square of the scale ratio of the drawing. Thus if the drawing is to a scale I inch = I foot, it is in the ratio i : 12 with the original, and we multiply by 12 X 12 or 144. If the scale is i^ inches = i foot it is i : 8, and we multiply by 64. If to a scale of 3 inches = i foot it is i : 4 and we multiply by 16. The result thus found will be the area of the actual full-sized half section in square inches. (7) We then multiply the distance AG scaled off according to the scale of the drawing and expressed in inches, by 6.2832, and the product by the area as found in (6). The result will be the volume in cubic inches. SPECIAL TOPICS AND PROBLEMS. 513 Instead of the preceding, we may less accurately find the area by taking it in parts and using substituted simpler forms, as above explained. We may then by judgment assume the loca- tion of G and then proceed as above in (7). Thus, for example, suppose we find as follows : Scale of drawing i l / 2 inches = i foot. Weight of paper section 240 grains. Weight of paper per square inch 36 grains. Arm AG 1.7 inches on the paper or 13.6, as scaled from the drawing. Then area =. 240 -=- 36 = 6.67 inches. This multiplied by 64 gives 426.7 square inches as the area of the actual half section. Then volume 13.6 X 6.2832 X 426.7 = 36462 cubic inches. 514 PRACTICAL MARINE ENGINEERING. CHAPTER X. PROPULSION AND POWERING. Sec. 78. MEASURE OF For measuring the speed of steamships the customary unit is the knot. While this term is often used as a distance, it is really a speed or velocity. As adopted by the United States Navy Department, it is a speed of 6080.27 ft. per hr. The Brit- ish Admiralty knot is a speed of 6080 ft. per hr. For all ordi- nary purposes the United States and British knots may be con- sidered the same. It is often necessary to reduce knots to feet per minute or vice versa. To this end we divide 6080 by 60 and find 101.33 ft. per minute as the equivalent of one knot. Hence the following rules : To reduce knots to feet per minute multiply by 101.33. To reduce feet per minute to knots, divide by 101.33. In the inland waters of the United States, and to some ex- tent on the coast for tugs, yachts, launches, etc., the mile per hour is used as the unit, instead of the knot. A statute mile consists of 5,280 feet. Hence one mile per hour equals 5,280 -r- 60, or 88 feet per minute. Hence : To reduce miles per hour to feet per minute, multiply by 88. To reduce feet per minute to miles per hour, divide by 88. Also: To reduce miles per hour to knots, divide the former by I5. To reduce knots to miles per hour, multiply the former by Sec. 79. PROPULSION. To propel a ship through the water some kind of a propul- sive thrust must be obtained. This is the fundamental problem of propulsion. Thus when a boat is poled along a shallow creek PROPULSION AND POWERING. 515 the thrust is obtained as a reaction from the bed of the creek against the end of the pole and thence to the man who is pushing it, and thence to the boat. In the usual case, however, there is no bottom to be reached, and the only thing outside the ship which can be gotten hold of for the purpose of gaining a reaction is the air or the water. For all cases with which the engineer is concerned it comes to the latter, and so the problem is to get from the water a reaction or force directed forward by means of which the ship maybe pushed through the water. To understand how this is possible we must remember the property of inertia, one of the fundamental properties of matter. It is this property which en- ables all matter to resist any effort made to change its condition bf rest or relative motion, and to react back on the means by which such a change is effected. Thus a push of the hand may serve to set in motion a weight hanging by a rope, but while the condition of rest is being overcome the weight will react back on the hand with a force equal and opposite to that which the hand exerts upon the weight. Similarly, when a shot is fired from a gun, the inertia of the shot causes it to react back against the as and so to the gun, causing the well known recoil. From the fundamental principles of mechanics it follows that to obtain a thrust or reaction forward it is only necessary to produce in a certain mass of water an increase in velocity, such increase being directed from forward aft, or at least having a component in that direction. There will then be a reaction directed from aft forward, or having a component in that direc- tion, and such reaction exerted on the means used to produce the change of velocity may be utilized as a propulsive thrust. This is carried out in practice by either a screw propeller or paddle wheel, and remembering the principles above stated, it appears that the immediate purpose of the propeller or paddle wheel is simply to produce an increase in the velocity of the water directed from forward aft. In consequence of this the water will exert a forward reaction on the propeller or paddle wheel, and thus produce the thrust required to propel the ship through the water. It may be added that this increase of ve- locity from forward aft, referred to above, may be obtained either by taking hold of water at rest and giving it a motion stern ward, by taking hold of water already moving stermvard and giving it a still higher velocity in the same direction, or by taking hold of PRACTICAL MARINE ENGINEERING. PROPULSION AND POWERING. 5*7 water moving forward and decreasing such forward motion, stopping it and leaving it at rest, or reversing it to a sternward motion. In all cases it is the change of velocity which is of im- portance. Thus a change from rest to 5 feet per second aft, or from 3 feet per second aft to 8 feet per second aft, or from 5 feet per second forward to rest, or from 2 feet per second forward to 3 feet per second aft, will each give the same forward thrust. We shall not go further into the theory of propulsion, but in the next section will give certain definitions relating to screw propellers and the solution of a few simple problems. Sec. 80. SCREW [i] Definitions. A screw propeller as shown in the frontispiece and in Figs. 287, 288, consists of a hub and a certain number of blades, usually two, three or four. The blades have on their rear or driving side an approximately helical surface that is, a surface similar to that which forms the faces of an ordinary screw thread. In this view a two-bladed screw propeller may be considered as a small part of a double-threaded bolt, the threads being cut very deep, and all portions being cut away down to the hub except the parts retained for blades. Similarly a three or four-bladed propeller may be considered as a small part of a triple or quad- ruple-threaded bolt similarly cut away except for the parts re- tained for blades. The hub or boss is the central portion to which the blades are attached, and through which they receive their motion of rota- tion in a transverse plane relative to the ship. A propeller is said to be right hand or left hand, according as it turns with or against the hands of a watch when looked at from aft and driving the ship ahead. The face or driving face of a blade is to the rear. It is that face which acts on the water and so receives the forward thrust. The back of a blade is therefore on the forward side. Care must be taken not to confuse these terms. The leading and following edges of a blade are respectively the forward and after edges. The diameter of a propeller is the diameter of the circle swept by the tips of the blades. The pitch of a propeller is the same as the pitch of the screw thread, of which it may be considered as forming a small part 518 PRACTICAL MARINE ENGINEERING. that is, it is the longitudinal distance between the successive turns of the helical surface. This definition will hold, however, only when the pitch is the same over the entire face of the blade. In many cases the pitch varies from one point to another, and we must therefore understand the term as relating, in such cases, to a small element of the driving face only. From this view the pitch may be defined as the longitudinal distance which the ship would be driven for one revolution were this element to work Fig. 288. Screw Propeller,, Detachable Blades. on a smooth, unyielding surface, as, for example, the cor- responding surface of a fixed nut. The pitch thus defined will depend on the location and inclination of the surface at the point or element considered, and its value may thus vary from one point to another over the entire face of the blade. The pitch is thus said to be uniform or variable, as its value remains the same or changes from point to point over the driving face. If it in- creases as we go from the hub to the tip of the blade it is said to PROPULSION AND POWERING. 519 increase radially. If it is greater on the following than on the leading edge, it is said to increase axially. The latter is usually implied by the simple term increasing or expanding pitch. The pitch ratio is the pitch divided by the diameter, or the ratio of pitch to diameter. The area, developed area or helicoidal area of a blade is the actual surface of the driving face. For the propeller as a whole it is the sum of the areas of all the blades. The projected area is likewise the area of the projection on a transverse plane, of one blade or of all the blades collectively. The disk area is the area of the circle swept by the tips of the blades. The pitch has been defined as the distance which the pro- peller in one revolution would drive the ship if it worked on a smooth, unyielding surface. Instead of working on such a sur- face, however, the propeller works on the water, a yielding me- dium, and in consequence the water recedes somewhat under the action of the propeller and the ship moves forward per revolu- tion a distance less than the pitch. The difference between the pitch and the distance the ship actually moves per revolution is called the slip, or, more concisely, the slip per revolution. The ratio of this slip to the pitch is called the slip ratio, or simply the slip stated in per cent as a slip of 20 per cent, 30 per cent, etc. Let p denote the pitch of the propeller in feet. N " " revolutions per minute. u " ' velocity of the ship in knots. ^ " " slip ratio. Then 101.3 -r- AT is the distance traveled by the ship per revolution, and p (101.3 w N) is the slip per revolution. Hence for the slip ratio we have : 101.3 " Multiplying both terms of the fraction by ^V we have: AY- ""-a K ,. ~~pN~ The term pN is the distance the ship would go per minute if there were no slip, while 101.3 is the distance which is actually made good. The difference or pN 101.3 u may therefore be called the slip per minute, and the quotient of this by /\Y is the 520 PRACTICAL MARINE ENGINEERING. slip ratio. This latter equation for ^ is the one by means of which its value is usually computed. It may be well to note at this point that while slip implies a certain loss of effectiveness in the propeller, it is a loss which is necessary in the very nature of the case. We have already seen that to obtain a propulsive thrust we must give to a certain body of water an increased velocity sternward. This means that the water must yield under the action of the propeller, and it is this yielding or falling sternward which thus gives rise at the same time to both the slip and the propulsive thrust. We cannot therefore have the thrust without the slip: we must accept the latter to obtain the former. We must now introduce a further consideration. We have defined slip as the difference between the pitch on the driving face and the advance per revolution. The latter admits of being defined in two ways according as we take for our point of refer- ence a point in the outlying still water, or a point in the water about the stern of the ship and in which the propeller works. So far as we are concerned with the movement of the ship through the water as a whole, the former is the natural point of reference. For various considerations connected with the operation of the propeller itself, however, the latter is the more important. Let us note briefly the condition of the water close about the stern of the ship and in which the propeller works. The ship in moving through the water will throw into for- ward motion a skin of water extending from the surface of the ship for several inches outward. Very near the surface of the ship this will move with nearly the velocity of the ship, while as the distance from the surface is increased the velocity will rap- idly decrease and soon become insensible. The water thus given forward motion by the skin of the ship will finally be found at the stern, where, still further influenced by wave and stream line motion, it forms the so-called "wake." The forward velocity in the wake at different points in a transverse plane at the stern is quite irregular, rising as high as 50 to 75 per cent of that of the ship at points near the surface and near the stern post, and de- creasing irregularly and gradually to nothing at the outlying still water. For single screw ships the average value in that part of the wake directly influenced by the screw is usually from 10 to 20 per cent of the speed of the ship. For twin screws located somewhat aside from the strongest part of the wake the values PROPULSION AND POWERING. 521 are usually found between 6 and 12 per cent of the speed of the ship. Now with reference to the propeller, it is evident that so far as it is concerned individually and as an appliance for developing thrust, it should be judged relative to the water immediately about it and in which it works rather than relative to an outly- ing body of undisturbed water upon which it has no direct influ- ence. The slip which is given by taking the speed relative to the wake is therefore called the true slip, while that given by taking the speed relative to the outlying still water (the speed as usually considered) is called the apparent slip. To show the relation between the true and apparent slips let v denote the forward velocity of the wake and u that of the ship as before, both measured in knots and relative to the outlying still water. Then (u v) is the speed of the advance of the pro- peller through or relative to the wake. Also using the same no- tation as above, p N 101.3 (u v) is the true slip per minute, while, as before, 'p N 101.3 u is the apparent slip per minute. Denoting the lat- ter by 5"i, and the former 5"*, we have : Si = p N 101.3 u. S* = p N 101.3 (u v) = 5"i + 101.3 v. It thus appears that the difference between the two slips in feet per minute is simply the wake velocity, as we should expect. To reduce to slip ratio we use pN as the divisor in each case, and denoting the resulting ratios by si and s* we have : pN 101.3 u . s t = - - as before, and: pN fNi6i*3(u v) 101.3 v ~pN~ = S * + pjy Where the term slip is used without special definition, the apparent slip is usually intended. In the preceding discussion of slip we have used the term pitch as though it were of constant value over the entire surface of the blade. If such is not the case, then the term must be un- derstood as referring to a mean or average value. Such an aver- age value of the pitch of a propeller might be defined in a variety of ways, but engineers are not as yet agreed upon the method most suitable. This point, however, is one which cannot be fur- ther developed in the present work. 522 PRACTICAL MARINE ENGINEERING. Problems. (1) To find the apparent slip. From the preceding value of the apparent slip ratio s we may derive the following : Rule : (i) Multiply the pitch by the revolutions per minute. (2) Multiply the speed in knots by 101.3. (3) Subtract the result in (2) from that in (i) and divide the difference by the result in (i). The quotient will be the slip ratio. Example : Given speed of ship, 1 1 knots ; pitch, 20 feet ; revolutions, 72. Find the apparent slip. Operation : 20 X 72 = 1440. ii X 101.3=1114.3. 1440 1114-3 -i- 1440 = 3 2 57 -=- J 440 = 22.6 per cent, ans. (2) To find the speed, having given the other items. From the preceding equation we derive the following value for u: u . >" (' - '> (,) 101.3 Whence the following : Rule: (i) Multiply the pitch by the revolutions. (2) Subtract the slip per cent from i .00. (3) Multiply the result in (i) by that in (2). (4) Divide the result in (3) by 101.3. The quotient will be the speed in knots. Example: Given pitch, 18 feet; revolutions, no; apparent slip, 18 per cent. Find the speed. Operation : 18 X no = 1980. i.oo .18 = .82. .82 X 1980 = 1624. 1624 -T- 101.3 = 16.03 knots, ans. (3) To find the revolutions, having given the other items. From the preceding equation we derive the following value for N: ,, 101.^ U * ' The use of this formula will be illustrated by the following example : Given speed, 22 knots; pitch, 26 feet; apparent slip, 16 per cent. Find revolutions. PROPULSION AND POWERING. ' 523, Operation : 101.3 X 22 = 2228.6 (1.00 .16) X 28 = 23.52 2228.6 -f- 23.52 = 94.8 revolutions per minute, ans. (4) To find the pitch, having given the other items. From the preceding equation we derive the following value for p. 101.3 if P - -N(is) < 4 > The use of this formula will be illustrated by the following example : Given speed, 28 knots; apparent slip, 21 per cent; revolu- tions, 380. Find the corresponding pitch. Operation : 101.3 X 28 = 2836.4 380 X (i.oo .21) = 300.2 2836.4 -4- 300.2 = 9.45 feet, ans. [3] Varieties of Propellers. Screw propellers are found in the greatest variety according to the number, shape, style and arrangement of blades. In mod- ern practice the number of blades is usually either three or four, the former being perhaps more commonly met with in twin screws and the latter in single screws. The shape of the blades may be oval or elliptical, as in Figs. 287, 288, or broadening somewhat toward the tip with rounded corners, or of any intermediate or similar form which may be desired. The oval or generally rounded form of blade is most commonly met with in modern practice. The blades may also be bent or curved in various ways. Thus in propellers for small boats the blades are often bent back, as in Fig. 287, so as to throw them somewhat farther from the stern post. They are also sometimes curved in the plane of rotation so that the en- tering edge is well rounded as it enters the water in going- ahead. Combined with these there may be various modifications of pitch, as above referred to. The normal or standard pro- peller in modern practice may, however, be considered as one having plain blades of uniform pitch, of oval or elliptical form, and standing at right angles to the axis, as in Fig. 288. Most of the variations from this type are based on fancy rather than on definite engineering reasons. So far as is known at present, the simple normal type, as specified above, is the equal of any of those of variable pitch or of special form or shape of blade. 524 PRACTICAL MARINE ENGINEERING. and while it may be that some special combination of pitch, shape and form of blade may give a higher efficiency than can be obtained from the normal type, yet up to the present time such results have not been proven. Small propellers are usually made complete or in one cast- ing, as in Fig. 287. Large propellers are made either in one casting or with separate or sectional blades, as in Fig. 288. In the latter case the root of the blade carries a circular flange fit- ting into a corresponding recess in the hub. This serves to se- cure the blade to the hub by stud-bolts passing through the flange and fitted with nuts countersunk below its outer face. The general details of this arrangement are shown in the figure. The holes in the flanges are usually made slightly oblong, thus providing for a slight change in the pitch by turning the flange back and forth, and thus changing the average obliquity of the blade to the axis of the propeller. Once adjusted as desired the holes are filled by packing pieces so that no further change can result from the accidental slipping of the flange under the nuts. In this connection it may be noted that the change of pitch re- sulting from such a twisting of the blade is not the same for all parts of the blade, but varies from root to tip. It follows, if the blade is made of uniform pitch, that it will remain so only sa long as it is set at the corresponding angle, and that if it is twisted to and fro the pitch will be increased and decreased, but not uniformly ; so that in all positions but this one the pitch will no longer be uniform, but variable. For a moderate angle of twist, however, the change from uniformity is but slight, and changes of average pitch up to perhaps 10 to 15 per cent may be made without serious departure from the average. The chief advantages of the separate blades lie in the possi- bility of varying or adjusting the pitch as just described, and in the readiness with which repairs may be executed. A separate blade broken or defective may be .readily removed and replaced with a new one, this operation in small vessels being sometimes accomplished without placing the vessel in dry dock. One or two blades may also be carried as spare parts or shipped by rail, or otherwise, much more readily than an entire propeller. The attachment of the propeller to the shaft is shown by the figures. The taper is usually about I inch in the diameter per foot. The propeller is prevented from turning on the shaft by one or more keys fitted, as shown. The after end of the shaft PROPULSION AND POWERING. 525 is fitted with a nut which serves to hold the propeller against any tendency to slip off when backing, and this is often covered with a conical tail piece, as shown, in order to reduce the eddy formation just aft of the boss. It may be noted that for a right- hand propeller the nut is usually left hand, and vice versa, it be- ing considered that this arrangement reduces the liability of loosening or backing off. If water is allowed to come into contact with the taper of the shaft on which the propeller boss is secured it may give rise to considerable corrosion, and this may set the boss so firmly on the shaft that great difficulty will be experienced in its removal. In order to prevent the contact of water with the taper, various means may be employed. In one method the brass liner on the shaft is carried along nearly to the forward end of the taper, and a rubber ring is placed just forward of the boss or in a counter- bore. As the boss is forced on, the rubber ring is compressed between the boss and the liner, and thus a water-tight joint is made. See Fig. 288. In other cases the liner is carried into a counterbore in the boss and a red lead joint is made between the two. For the examination or repair of the stern bearing it may become necessary to remove the propeller and withdraw the tail shaft forward into the ship. This is of course an operation re- quiring the docking of the ship. For the removal of the pro- peller the first attempt may be made with steel wedges between the forward face of the boss and the stern post, or after end of the stern bearing. The space between the two is made up with the metal blocking necessary, and the wedges are then inserted and driven one from either side. In this way a tremendous strain can be exerted and the boss will be started unless seriously corroded or jammed unduly tight. In the latter cases recourse must be had to hydraulic jacks, or to a heavy ram or to heating the boss in order to expand it in size and break the connection with the shaft. Once the boss is started the weight of the pro- peller may be taken by chain hoists suspended from the counter, and the shaft may then be drawn forward into the tunnel. In the case of twin screw ships with the common form of strut, the same general means may be employed, except that it should be remembered that the strain set up is carried on the strut, and the means taken should not go so far as to endanger its rupture or the undue straining of its fastenings. 526 PRACTICAL MARINE ENGINEERING. [3] Materials. Cast iron, cast steel, brass, gun metal and the various bronzes are the materials used for screw propellers. Cast iron is the cheapest, but is relatively weak and brittle, and the blades must necessarily be thicker and less efficient than if made of steel or bronze. Cast steel is stronger than cast iron, and the sections may be accordingly decreased with a resultant gain in efficiency. The surface of cast steel is naturally not as smooth as with cast Iron, but with improved methods of production the difference is not important. Brass and the various bronzes have naturally a smoother surface, and seem furthermore to have a lower co- efficient of skin resistance. This, added to their strength and good casting qualities, makes possible a smooth and relatively thin blade with sharp edges, all of which are features favorable to good efficiency. With the best bronzes the ultimate strength may vary from 50,000 to 60,000 pounds per square inch of sec- tion. With cast steel the ultimate strength will reach still higher, or, say, to 65,000 pounds per square inch. With gun metal an ultimate strength of 25,000 to 35,000 pounds may be expected, while with common brass and cast iron not more than 20,000 to 25,000 pounds can be depended on. Of the various materials available, manganese bronze may perhaps be considered as possessing the best combination of desirable qualities, such as strength and stiffness, good casting qualities, resistance to corrosion, etc. Care is needed in the manipulation of the various bronzes in melting, pouring and cooling, in order to insure uniformity and the full realization of the valuable properties of the alloy. The greater cost of such bronzes restricts their use, however, to warships, yachts and launches, ocean liners and other cases where the importance of a saving in propulsive efficiency may be considered worth the in- creased cost of the propeller. The durability of propeller blades is usually in the order: bronze, cast iron, cast steel. The two latter usually suffer by general corrosion and local pitting, the average life being usually from five to ten years. The life of bronze blades is practically indefinite. [4] Measurement of Pitch. To determine the pitch of a given propeller three measure- ments are necessary. See Fig. 289. These are : (i) The radius OA at which the pitch is desired. PROPULSION AND POWERING. 527 (2) The angle or part of the complete circumference cor- responding to the distance on the blade between A and B, the two points between which the pitch is to be found. (3) The advance BC parallel to the line of the shaft, corre- sponding to this part of a complete revolution. In the figure, A and B are points on the face of the blade, and are at a constant distance OA from the shaft center line OO. AC is an arc of a circle which lies in a plane through A and per- pendicular to the shaft. The angle AOC is therefore the one re- ferred to in (2), and the distance BC is the corresponding ad- vance. Then BC is the same fraction of the entire pitch that AOC is of a complete circle, or the same fraction that the length Fig. 289. Measurement of Pitch. AC is of a complete circumference with OA as radius. This complete circumference will be 6.2832 X OA. Hence the pro- portion : AC : 6.2832 X OA : : BC : pitch. 6.2832 x OA x BC or pitch AC It is not, however, as easy to measure AC as AB, so that we may put for AC its equal j/ ^-g *_ p^.and we then have pitch == 1^3*_x.OAjLgC AB 2 - h'C 2 A brief outline of the operations is as follows : 5 2S PRACTICAL MARINE ENGINEERING. (1) Select the points A and B at and between which the pitch is desired, making sure that they are at equal distances from the shaft center line. This can be done by squaring down from a straight edge or other reference line PQ, PR, placed across the hub and at right angles with the shaft. Then measure the length AB. (2) The propeller being leveled up, measure the distance BC from a level through A vertically down to B. Or if the pro- peller cannot be leveled, measure from B in a direction parallel to the shaft out to a line through A in a plane at right angles to the shaft. Or measure from Q down to A and from R down to B and take their difference BC. (3) Multiply the distance OA or its equal PQ by 6.2832, and by the length BC all in the same units of measure. (4) Square the lengths AB and BC, subtract the square of the latter from that of the former and extract the square root of the difference. (5) Divide the result found in (3) by that found in (4) and the quotient will be the pitch desired. Thus, for example, suppose AB = 20 inches, BC = 13 inches and OA = 48 inches. Then 6.2832 X 48 X 13 39 2 Q-7 AlSO 1/400 169 - 1/237 =: 15.2. Then 3920.7 -f- 15.2 = 238 inches = 21 ft. 6 in. = pitch. If the pitch is variable instead of uniform, the operation is precisely the same, but the result found must be considered merely as the mean or average value of the pitch between the points A and B. For other parts of the blade a similar process will give the pitch at those points. When the propeller is in place on the ship it is sometimes more convenient to carry out the principles involved in this method of measuring pitch somewhat differently, as follows : Let the propeller be turned so as to bring one of the blades horizon- tal. Then select the place at which the pitch is desired, and hang over the blade at this point a cord with two weights, as shown in Fig. 290. Care must be taken that the two points A and B at which the cord touches the edges of the blade are at the same distance from the center. It is then readily seen that the points A and B of Fig. 290 correspond to the similar points of Fig. 289, except that in Fig. 290 they are of necessity taken on the ex- treme edges of the blade. We then level up a bar PQ and meas- PROPULSION AND POWERING. 529 ure the distances, AB and BC, as noted above, using them in the same way for finding the pitch. Or we may measure AC directly and use this with BC in the proportion above. As a rough and ready rule it may be remembered that the pitch of a propeller will equal the length of a circumference at the place on the blade where the slope of the face is 45, or where it is equally inclined to the shaft and to the transverse direction. Starting near the shaft, the inclination to the longitudinal is small, but increases toward the tip, passing at some point through the value 45. At this point let the radius be r. Then Marine Enyinefri*g Fig. 290. Measurement of Pitch. pitch = 2 TIT = 6.2832 r. In this way an approximate idea may often be quickly obtained of the pitch of a wheel by estimate without special measurement, except for the radius or diameter at which the blade has the slope of 45. The details of the above methods for finding pitch may vary considerably, but the description given will serve to show the principles involved, and with reasonable mechanical skill no trouble will be found in carrying out the measurements required. Sec. 81. PADDLE In addition to the screw propeller the paddle wheel is the other appliance used for ship propulsion. In Fig. 291 is shown in skeleton a common radial paddle wheel. In this type of wheel the paddles or floats are rigidly fixed to the arms, the lat- 530 PRACTICAL MARINE ENGINEERING. ter being connected at their inner ends to a hub, which is carried on the shaft. In this manner the motion of the shaft is transmit- ted to the floats, and these, acting on the water, drive it stern- ward and thus receive the forward thrust which is required for the propulsion of the vessel. In Fig. 292 is shown a feathering paddle wheel. In this ar- rangement the floats are hung on axes and are swung in such way that they enter and leave the water nearly in an edgewise direction. In this way there is less disturbance of the water and a smoother action of the wheel is obtained. Such arrangement is especially suitable for ships operating under widely varying conditions of draft, for the floats of a deeply immersed radial Fig. 291. Radial Paddle Wheel, Skeleton Diagram. wheel enter and leave the water at a great obliquity and there would be considerable loss by oblique action. There are two chief methods by which the proper motion may be given to feathering floats, depending on whether the pad- dle shaft has an outer or spring bearing on the outside of the paddle box or is overhung ; that is, provided simply with a bear- ing on the rail, the paddle wheel itself being then mounted on the overhung end of the shaft. In the former case the arrange- ment will be understood from the skeleton drawing of Fig. 293. The stationary excentric A has its center forward of the wheel center, as shown. To the excentric strap is attached a drive link HB, connected by pin joint to an arm BC, carrying a float DE. PROPULSION AND POWERING. 53i 532 PRACTICAL MARINE ENGINEERING. The other floats, mounted in a similar manner, are connected by pin joint links to the excentric strap, as shown. As the wheel turns the drive link HB carries the strap around the excentric sheave, and with it the series of connected links. This gives a see- saw motion to the ends of the arms BC and thus swings the floats in the manner desired. When the paddle shaft has no outer bearing, as in the ar- rangement shown in Fig. 292, the disc carrying the links may be mounted on a supporting pin carried on the outer side of the guard. It may then be given motion through a drive link and connections, as shown, giving a similar see-saw motion to the floats, as in the former case. In modern practice the arms of paddle wheels are made of Fig. .293. Paddle Wheel, Skeleton of Arrangement for Feathering Floats. steel, the hubs of cast iron or cast steel, and the floats of wood or boiler plate ; in the latter case often curved in cross section. In estimating the pitch of the paddle wheel or what corre- sponds to pitch in the screw propeller, we must consider it as the circumference of the circle traveled by the floats. Since, how- ever, a float as a whole is made up of a series of strips or ele- ments at varying distances from the center, each such element will have its own circumference and therefore its own pitch, arid will try to drive the ship at a speed corresponding to such pitch. The paddle wheel as a whole has therefore a varying pitch, in- creasing from the outer to the inner edge of the float. The re- PROPULSION AND POWERING. 533 sultant mean pitch is considered as the circumference traveled by a point called the center of effort. The proper basis for the deter- mination of this point, and hence of the true mean pitch of a pad- dle wheel is, however, not definitely known, and can only be de- termined by the aid of extended experimental investigation. In the absence of such definite basis it is sufficient for all practical purposes to take it at the center of the float radially, though its true location would lie somewhat outside this point. Counting the circumference through this point as the pitch, the actual dis- tance traveled by the boat per revolution is less by the amount of the slip, which is usually found from 15 to 25 or 30 per cent. The circle whose circumference is equal to the distance trav- eled per revolution is sometimes known as the rolling circle. It is so called from the fact that the speed of the boat is the same as though it were carried on wheels of this diameter, "which rolled on a supporting surface as wagon wheels along a smooth, level road. The solutions of problems relating to the revolutions, diam- eter and slip of paddle wheels are found in the same general man- ner as for the screw propeller, and the re-suiting equations are similar to those found in Sec. 80 [i], with the substitution for p of D, as defined below, and 88 for 101.3. Let D = diameter of rolling or pitch circle. i N = revolutions per minute. u = speed in miles per hour. ^ i= slip ratio. Then, as with the screw propeller, we have : DN - 88 u 88 u D - These may be illustrated by the following examples : (i) Given diameter of rolling circle, 36 feet; revolutions, 45 per minute ; speed, 14 miles per hour. Find the slip ratio. Operation : D N = 36 X 45 = 1620 88 u 88 X H = 1232 1620 1232 -i- 1620 = 388 -r- 1620 = 23.3 per cent. 534 PRACTICAL MARINE ENGINEERING. (2) Given diameter of rolling circle, 30 feet ; revolutions, 50 per minute, what speed can be made,, allowing a slip of 30 per cent? Operation : D N = 30 X 50 = J 5oo i s = i .30 = .70 .70 X 1500= 1050 1050 -r- 88 = 11.9 miles per hour = 10.35 knots. (3) Given a speed of 18 miles per hour, a slip of 24 per cent, and a wheel whose rolling circle has a diameter of 40 feet. Re- quired the number of revolutions per minute. Operation : 88 X = 88 X 18 = 1604 i ^ = i .24 = .76 D (i s) = 40 X 76 = 304 1604 -T- 30.4 = 52.8 revolutions per minute. (4) Given a speed of 14 miles per hour ; revolutions, 40 per minute ; slip, 28 per cent. Find the corresponding diameter of rolling circle. Operation : 88 X = 88 X 14 = 1232 i s= i .28 = .72 N (i s) 40 X -72 = 28.8 1232 28.8 = 42.8 feet. Sec. 82. POWERING SHIPS. The subject of the pow r ering of ships is one which can be here only referred to in a brief and elementary way. The usual prob- lems are to find the power required to drive a given ship at a pro- posed speed, or the probable speed for a given ship with a given power. Such problems require a knowledge of the relation be- tween power, speed and the ship. In the present state of our in- formation on this subject, such relation cannot be accurately ex- pressed by any ordinary formula or equation. Several approxi- mate formulae have, however, been employed for the solution of such problems, and among them none has perhaps been of wider general usefulness than the so-called Admiralty coefficient formula. Let/f= I.H.P. D = displacement in tons. v = speed in knots. K = a coefficient. PROPULSION AND POWERING. 535 Then according to this formula we have : H - * and solving for speed : 3 /~HK~ and solving for the coefficient : K = j^_ The whole point in the use of the formula is to properly se- lect the values of the coefficient K in accordance with the special features of the case, including the form and size of the ship, pro- posed speed, probable efficiency of propulsion, etc. The safest plan is to find values of K from the trial data of actual ships of about the same size, character of form and speed, as the pro- posed case, and to be guided by such values in the selection of the coefficient for the proposed case. There are other special methods for obtaining from the trial data of ships of similar form, by the so-called law of comparison, the suitable values for a proposed case, even when the sizes and speeds differ consider- ably from those of the proposed case. Into the details of these points, however, we cannot here enter. Some general sugges- tions regarding the value of K with a few illustrative examples must suffice. We find then by experience that in general the value of K is greater (and hence the I.H.P. relatively less) as the ship is larger, but more especially as she is longer, also as she is nar- rower in proportion of length to beam, and as she is finer in form, especially in the water lines. In the reverse cases the values of K will be smaller, and the I.H.P. relatively larger. The values of K are also smaller and the I.H.P. relatively larger as the speed is higher in proportion to the length, or, more exactly, as the speed is higher in propor- tion to the square root of the length. For small launches and such craft driven at speeds in miles or knots greater than ;/Z i n feet, the values of K will be quite small, ranging perhaps from 100 to 150. At lower speeds equal to or less than t/Z" the values will rise to perhaps 200 and more with fine form and^small pro- portion of beam to length. For yachts and craft of similar form, moderately fine and at fairly high speeds, values of 200 above 536 PRACTICAL MARINE ENGINEERING. and below will be found. For torpedo boats, with their narrow proportions and fine form, their excessive speeds carry them into a set of conditions where the coefficients are larger and the power required relatively less than we might expect. Varying with size and other conditions, values of 200 above and below are found for boats of this character. For mercantile vessels of moderate size, rather full form and moderate speed, the values will be usually found from perhaps 220 to 250. For larger mer- cantile vessels at moderate speeds or for those of moderate size under exceptionally good conditions the values may rise from 250 to 300. For fast passenger boats varying with size, and other conditions, values from 220 to 280 may be expected. For naval vessels, cruisers and battleships, from 200 to 250 is the usual range. These various values are not intended as marking definite limits, nor can they enable a person without individual judgment to properly select a suitable value for a given case. They are intended simply as general suggestions of the range of values commonly met with. We will now solve a few examples to illustrate the use of this formula. We may first note that D\ means the cube root of the square, or the square of the cube root of the displacement in tons, and hence with a table of squares and cubes or square and cube roots, the value desired may be readily found. In some hand books values of /> are given directly. (i) Given D = 3200,27 =12 and take K = 230. Required the power. From arable of squares we have (32)*= 1024, and hence (320o) 2 = 10,240,000. Looking in the column of cubes of num- bers of three figures we find that the nearest cube is 10,218,313, and that the number corresponding is 217. This will be suffi- ciently near for all practical purposes, and is therefore taken as the value of D\. We have also (12)' = 1728. Hence we have : = 1630 Ans. 230 (2) Given a yacht of displacement 366 tons, to be driven at a speed of 18 knots. Assume k = 200 and find the necessary power. In this case (366)' = 133,956 and the number corre- sponding to the nearest cube is 51.2. Also (i8) 3 = 5832. Hence PROPULSION AND POWERING. 537 H = 5I ' 2 X 5832 = 1493. 200 (3) Given D = 7243, v 16 and take K 240. Find the power. Without important error we may drop the last 3 tons so as to bring the number within the range of the usual tables of squares and cubes. We have then (724) 2 = 524,176, and hence (7240)2 = 52,417,600. The number corresponding to the nearest cube is 374. Also (i6) 3 = 4096. Hence : H = 374 X 4 9 6 240 (4) What speed may be expected from a liner of 15,400 tons displacement and 26,000 I.H.P.? Take, in this case, ^ = 250. Then (i54) 2 = 23716 and hence ( 1 5400)' = 237,160,000. The number corresponding to the nearest cube is 619. Then we have s / 26,000 x 2 5 ~- V 619 : F 10,500 = 21.9. (5) Given D = 8320, v = 13 and H = 3400. Required the value of K. We have (832)'= 692,224 and hence (8320)' = 69,222,400. The number corresponding to the nearest cube is 411. Also = Hence we have : K = 411 X 2197 3400 Sec. 83. REDUCTION OF POWER WHEN TOWING OR WHEN VESSEL IS FAST TO A DOCK. It is well known that the power developed by the engine when the ship is towing is less than when she is running free, the steam pressure and cut-off being the same ; also that at a dock trial (engines running, but ship fast to the dock) the power is considerably less than may be developed in free route under the same steam pressure and point of cut-off. To explain these results let us first assume that the ship, boilers, engine and propeller are all properly designed for a given speed. This means that with a given boiler pressure (say 180 Ibs.) the boilers will be able to supply steam enough to drive the engines at the designed revolutions (say ioo) and thus de- velop the designed power, while the propeller with a certain slip (say 20 per cent) will drive the ship at the designed speed (say 16 knots). Now it must first be noted that all of these conditions 538 PRACTICAL MARINE ENGINEERING. go together, and if any one of them is disturbed it will react on all the others. The next point is that a constant set of pressures throughout the engine means a constant reduced mean effective pressure, a constant turning moment on the shaft and a nearly constant thrust, and hence a nearly constant resistance over- come. Now at the regular speed, if the resistance is increased, as by taking up a tow, what will be the immediate result? Evi- dently the speed will decrease until at some reduced speed the nearly constant thrust will balance the resistance, and the mo- tion will become uniform again. The greater the increase in re- sistance at the regular speed that is, the larger the tow the lower the speed at which the nearly constant thrust will be able to balance the resistance and thus produce steady conditions. 19 15 13 12 11 CO fE 8 UJ ' LU C- 6 co 1 3 2 ( I/ l/ / / \ / / 7_ 1 i i I I j / ) 10 30 30 40 5'J JO ',o 80 90 iO REVOLUTIONS Fig. 294. Diagram Showing Relation Between Revolutions and Speed for Constant Turning Moment. The whole question as regards power developed now turns on the revolutions at this reduced speed. In other words, how do revolutions and speed vary for a constant turning moment, and a nearly constant thrust developed or resistance overcome? This is best answered by experimental data, which give us a re- lation similar to that shown in Fig. 294. Revolutions are laid off horizontally and speed vertically. If we suppose that 90 revolutions and 14 knots are the designed conditions, as indi- cated on the curve, then the diagram shows how the revolutions and speed vary for a constant thrust. In particular the curve shows, as the tow is increased in amount and the speed for a PROPULSION AND POWERING. 539 given thrust decreases more and more, so likewise do the revolu- tions decrease, though at a slower rate. Hence with the de- crease of speed the slip constantly increases. The relations as shown by this curve furnish the key for the solution of all ques- tions regarding the variation of the power. The work done by the engine is a product of the revolutions into other factors, and since these other factors include merely dimensions of the engine and mean effective pressure, and since by assumption all of these remain constant, it is evident that under the conditions assumed the power developed will vary directly with the revolutions. Hence the diagram shows the relative decrease of power with de- creasing speed, as well as the actual decrease in revolutions. If we should continue to add to the tow indefinitely we should at length reach a condition similar to that of a vessel tied to a dock ; that is, a condition where the speed has become re- duced to nothing and the revolutions reduced in quite marked degree. The exact relation between revolutions in free route and when fast to a dock will of course depend on the special cir- cumstances. The mean effective pressure remains the same, however, and the work done and power developed will therefore vary simply with the revolutions according to a law similar to that shown in the figure. To sum up the matter, therefore, the power falls off because the revolutions fall off, and the revolutions fall off because the speed falls off, and because at the reduced speed and increased slip the constant turning moment of the engine can no longer turn the propeller at the original. number of revolutions. The reason why of the facts expressed by the curve in Fig. 294, on which the whole matter turns, is to be found in the funda- mental relation between revolutions, slip, thrust, etc., a complete discussion of which is of course beyond our present purpose. Once these relations accepted as experimental truth, however, the desired explanation is seen to flow from them as a necessary consequence. Sec. 84. TRIAI, TRIPS. The general purpose of a trial is to determine the power or speed which may be maintained for a certain distance or time. In addition to these fundamental purposes, information relating to the general problem of resistance and propulsion may also be gained, as well as that bearing on other points which may be the object of special inquiry. We shall not here refer especially to 540 PRACTICAL MARINE ENGINEERING. the determination of power, as that has been already sufficiently treated in Sec. 55 [3], For the determination of speed alone it is sufficient to ob- tain observations of distance and time. The revolutions should, however, be also taken, in order that the slip of the propeller may be found. For speed trials we may use a long course, as, for example, from 20 to 100 miles or more, over which but one run, or, more commonly, one run in each direction is made ; or, on the other hand, a short course of I or 2 miles, over which as many runs may be made as desired. For marking off the course, buoys or ships at anchor are often used for the long course, while range marks on shore for the limits and buoys for the direction and location are commonly employed for the short course. At each end of the short course there should be plenty of room for making turns and gathering headway before entering the course for the return run. The free space available for this purpose should be not less than from one-half to one mile. To eliminate the error due to the tide on the long course run, tidal observations should be made from vessels anchored along the course by means of a patent log or equivalent device, and from the results the average tidal influence may be deter- mined. To eliminate the tidal error on short course trials the runs are made in both directions and an average is taken. This may be either a simple average or the result of a "continued average," as illustrated below. Suppose four runs made, two in each direction, and let the resulting speeds in order be those entered in the column on the left. North 17.2 . 17.00 South 16.8 17-075 17.15 17.10 North 17.5 I7- I2 5 17.10 South 16.7 An average is first made of Nos. i and 2, then of 2 and 3, and then of 3 and 4, and these are put in the second column. Then these are averaged in like manner and put in the third column, and these are again averaged for the final result, which, in the above case, is 17.10. With six runs the operation is car- PROPULSION AND POWERING. 541 ried out in the same way. While this is often considered as the only correct way of averaging such a series of runs, it may be shown that such is by no means the case, and, as a matter of fact, that under ordinary conditions the simple average .will give quite as probable a result as the more complex method. In the above case the simple average would give 17.05, as against 17.10, a difference of .05 knot, and the former value is quite as likely to be correct as the latter. In some cases it is desirable to make a complete speed trial riU 18 1G 14 6 z 12 x. z Q u) 10 m CL CO 8 4 2 ( ./ / / / f / / j / / / / ) 10 20 30 40 50 60 70 80 90 10 R EVOLUTIONS ^" n u in**ring Fig. 295. Diagram of Revolutions and Speed. and thus obtain a series of values of the power, revolutions and speed from full power conditions down. This may be done on the measured mile or short course by making runs in pairs, the conditions for each pair remaining as nearly constant as possible, while from one pair to another the conditions change over the complete range to be included in the trial. The average results in speed, power and revolutions are then used for plotting the curves showing the various relations desired. Such a curve showing the relation between revolutions and power is shown in 542 PRACTICAL MARINE ENGINEERING. Fig. 296, together with the spots which may represent the actual single observations. The curve may then be drawn through and among the spots as a method of getting a graphical average ; or otherwise the values may be averaged numerically and plotted as a series of averages, and the curve then drawn through them. As a somewhat shorter method, a series of runs may be taken in each direction, beginning at the highest, and at con- stantly decreasing revolutions., The results for speed and revo- lutions are then plotted, as shown in Fig. 295, and a fair curve drawn through and among the spots. This is then taken as the 1000 -10 20 30 40 50 60 70 80 90 REVOLUTIONS Marine JJn u i>, Fig. 296. Diagram of Revolutions and Horse Power. relation between revolutions and speed. The relation between revolutions and power is also plotted, as in Fig. 296. Then, by the aid of these two, the speed-power curve may be plotted, as shown in Fig. 297. We will now note briefly the computations arising in connection with such trials. The observations with which we are here concerned are simply time and revolutions. Let the course be a measured mile (marine or statute, as the case may be), and let the time on the course be t, expressed in minutes and decimals. This is usually determined by a stop- watch reading the half or quarter second. The value cannot, PROPULSION AND POWERING. 543 however, be depended on as accurate to much within i second. Then if v denotes the speed we have : v = 60 -f- t The revolutions will be obtained from the counter by sub- tracting the readings at the entrance and end of the course. This will give the number of revolutions for the course. Let this be denoted by R. Then r> % Revolutions per minute = 9000 SOOO roa coco X'5000 4000 3000 2000 1000 16 18 20 Marint Snginttnng Diagram of Speed and Horse Power. Also let p = pitch of propeller. Then assuming the course to be a nautical mile, we have : (pR -6080) = slip In feet, and pR ~ 6o8 = slip ratio. pR These computations may be illustrated by the following ex- ample : Let the course be a mile of 6,080 feet, and let the following data be taken : Counter at entrance. Counter at end. Time. Run north 106,248 106,654 4 m. 26 sec. Run south 107,112 107,542 4m. 33 sec. Pitch of propeller 18 feet. 544 PRACTICAL MARINE ENGINEERING. Required the mean speed and slip for the two runs. For the run north the revolutions are 106,654 106,- 248 = 406. For the run south the revolutions similarly found are 430. The average revolutions are then 418. The speed north is 60 -T- 4.433 = 13-53- The speed south is 60 -r- 4.55 = 13.19. The mean speed is then 13.36. The slip in feet = 418 X 18 6080 7524 6080 = 1444. The slip ratio = 4 = 19.2 per cent. 75 2 4 Sec. 85. SPECIAL CONDITIONS FOR SPEED TRIADS. In speed or power trials the purpose is often the develop- ment of the maximum speed or power, and in the present section we may note the more important points connected with the ful- filment of these purposes. Boilers. Where there is a record performance to be made there must be no loss of evaporative efficiency due to accumula- tions of soot and ashes on the fire side, or of oil, scale or mud on the water side. Hence especial care must be taken to see that the boilers are thoroughly clean on both fire and water sides. Fuel. If possible, the fuel should be of the highest grade and carefully selected with reference to clean, free burning qualities. Engines. The engines should be adjusted with the various joints sufficiently loose to avoid danger from heating, and at the same time not sufficiently loose to hammer seriously. Special attention must be paid to oiling gear, and also to the provision for supplying water in case the bearings tend to become hot. Ship. The ship should be lightened as much as possible that is, the displacement should be made as small as possible. This point must not be carried so far, however, as to decrease the draft or change the trim sufficiently to bring the tips of the propeller blades too near the surface of the water. In the latter case the propeller will fail to develop the necessary thrust and the highest speed cannot be attained. The bottom of the ship should also be thoroughly clean and fresh painted, or, if cop- pered, clean and polished, if not too large. The propeller should also be looked after, and if there is opportunity it should be cleaned and the edges sharpened. REFRIGERATION. 545 CHAPTER XI. REFRIGERATION. Sec. 86. GEKERAI, PRINCIPLES. In connection with the general principles of refrigeration reference should be made to Section 57, where the general nature of heat and its relation to matter is discussed. The fundamental problem of refrigeration is the abstraction of heat from some body or substance A, or the maintenance of such substance A at a temperature lower than that of the surrounding air. This is most conveniently brought about by bringing the substance A into relation with another cooling substance B at a lower tem- perature, such that heat may readily pass by conduction from one to the other. The heat then flows from A to B, and thus the end desired is brought about. It is clear, however, that unless there is a continuous renewal of the substance B, or some way of removing the heat which flows into it, then in the end the two substances A and B will come to the same temperature, and if this is lower than that of the surroundings, it will gradually rise until both A and B are in equilibrium with their general sur- roundings. Again it is seen that if the substance A is kept below the temperature of its surroundings there will be a constant flow of heat from these surroundings (structural material, earth, air, water, etc.) into it, and this heat must be as constantly removed by conduction into the substance B at still lower temperature, which again must be renewed in order to maintain its capacity for absorbing heat from A. Again we may have two different cases, according as the substance A is cooled by the conduction of its heat directly into B, or first into some intermediate sub- stance such as air and then into B. In other \Vords, the sub- 546 PRACTICAL MARINE ENGINEERING. stance B may affect A directly, or through the intermediate ac- tion of the air surrounding both of them. Thus in making artificial ice the water to be frozen is brought as directly as possible under the influence of the cooling substance, whatever it may be, while in certain systems for the refrigeration of meat, etc., in a refrigeration or cold storage room, the meat is kept cool by the action of the cold air of the room, which, in turn, is cooled by the action of the cooling sub- stance, usually conducted through coils of pipe about the walls of the room. In other systems of refrigeration or cold storage, air itself is made the cooling substance, and the cooled air is passed through the storage room, thus acting directly upon the substances stored therein. With the foregoing by way of a statement of general prin- ciples we come now to the production of the cooling substance. In other words, how shall we find or produce a substance whose temperature is far below the usual temperature of the air, and which may be made available for the purposes outlined above? To this end we have two general methods ; one involving a change of state, either physical or chemical or both, and the other the compression, cooling and expansion of an elastic gas such as air. Illustrations of these methods will be found in the systems of refrigeration described in the following sections. Sec. 87. REFRIGERATION BY FREEZING MIXTURES. If salt and ice are mixed there is a tendency for the mixture to pass into the liquid state. As to just why this is so we are not concerned, but simply with the fact. In answer to this ten- dency the two substances pass rapidly from the solid into the liquid state, thus forming a brine, or, more exactly, the ice passes from the solid to the liquid state and the salt dissolves in the liquid. Now ice cannot pass from a solid to a liquid state without absorbing heat. This point has been referred to in Sec. 57 t 1 ]* where it was also noted that the term latent heat is ap- plied to the heat which is thus involved in a change of physical state. Heat must therefore be supplied from somewhere in or- der that the change from ice to liquid may take place. Further- more, due to the physical and chemical forces at work, this change takes place faster than heat can be supplied from the general surroundings, and since it must come from somewhere it is drawn from the substances themselves, brine, salt and ice, RRFRJGERA TION. 547 which are thus reduced to a much lower temperature than they would have if separate. Thus a mixture of ice and salt forms a brine having a temperature of about 5 Fah.,or about 37 below the freezing point of ice. Such solutions or mixtures are known as freezing mixtures, and the brine thus formed may then be used as a cooling or freezing agent in whatever way may be most convenient. Thus in the ordinary manner of freezing ice-cream and ices the ice-salt mixture is commonly used, inclosed in a casing which surrounds an inner vessel containing the substance to be frozen. In the manner above described then the ice will be melted, a brine will be formed, and heat will be withdrawn first from the freezing mixture itself, and then from the substance in the inner vessel, which thus becomes cooled down to its freezing point. Next its own latent heat will be drawn upon, and thus finally the substance becomes frozen as desired. There are many such mixtures composed of various chemi- cals, and by means of which temperatures from o to 50 Fah. may be obtained. For the general purpose of refrigeration, how- ever, the use of such mixtures has not been found as efficient as other means, and it will not be necessary therefore to further refer to them in the present connection. Sec. 88. REFRIGERATION BY VAPORISATION AND EXPANSION. We will next consider the application of substances like ammonia or carbonic acid, which are gaseous at the usual tem- peratures, but may be liquified at low temperatures and under suitable pressures. Anhydrous ammonia (ammonia without water) has a boiling point under atmospheric pressure of 37 be- low zero. With higher pressures the boiling point rises. As we have already seen in Sec. 57, a liquid passing into the state of vapor absorbs a certain amount of heat, and this latent heat, as it is termed, will be drawn either from the surroundings or from 'the liquid itself, or from both, thus lowering their temperatures. In order to utilize these properties of ammonia the refrigerating apparatus consists of the following : (i) A series of expansion evaporating coils which are placed in the refrigerator room or space to be cooled, or which in other systems are surrounded by a liquid which is used as the imme- diate cooling agent in the coils of the refrigerator room. 548 PRACTICAL MARINE ENGINEERING. (2) A reservoir containing liquid ammonia which is allowed to flow as may be required into the expansion coils. (3) A pump which withdraws the vapor from the expansion coils and then compresses it back into the coils of a condenser, which are surrounded by cool water. Here, under the influence of the pressure and moderate temperature, the vapor becomes condensed to liquid and then flows to the reservoir from which it started. The two fundamental parts of the process are there- fore (i) evaporation and expansion, (2) compression and con- densation. In this manner the continuous operation of the pump insures the formation and continuous flow of ammonia vapor at low temperature through the cooling coils. The vapor is thus in condition to absorb heat through the metal of the coils from the surroundings, either air or liquid, and thus the refrigeration is effected. Where a liquid is employed as the immediate cooling agent it is usually a brine made with common salt, which, after having been cooled down by giving up its heat to enable the ammonia to evaporate, is then, circulated by a brine pump through the coils of the refrigeration room. It has been well said that the action of the ammonia in this round of operations is like a sponge. It vaporizes and expands in the expansion coils and absorbs or soaks in the heat from its surroundings. Then it is compressed and the heat is forced or "squeezed" out, and it is ready for a new round, thus acting as a carrier of heat away from the substance to be cooled. It may aid further in understanding the action of the liquid ammonia in the refrigerating coils to note that relative to the air or brine surrounding these coils the ammonia is situated some- what like the water in a water-tube boiler with hot gas on the fire side of the tubes. The furnace gases are hot relative to the water, and so heat tends to flow through the tubes into the water, thus forming steam. So is the temperature of the air or brine about the coils far above that at which ammonia would naturally exist in the liquid form under the pressure in the coils. In fact, the liquid ammonia when first admitted is itself far above this temperature, so that the first result is a tendency for the liquid to fly into vapor immediately, drawing on its own sensible heat to supply the necessary latent heat, and thus cooling the re- maining liquid and the vapor formed. Then the heat from the surrounding air or brine flows in and thus the vaporization is completed. We may thus say that the liquid ammonia is boiled REFR1GERA TION. 549 into vapor chiefly by the heat which it draws from the surround- ing air or brine. So likewise if we should set a jar of liquid am- monia into a snow bank, the latter would be warm relative to the boiling point of the ammonia under atmospheric pressure, and in consequence the snow would play the part of the fire in the usual case with water and supply the heat which would serve to vaporize the ammonia, the snow becoming thereby cooled by reason of its loss of heat. Having thus sketched the general outline of the process, the following additional points may be mentioned : The liquid ammonia is usually under a pressure of 125-175 Ibs. per square inch, corresponding to temperatures from about 70 to 90 degrees. By the action of the ammonia pump, which draws the vapor from the refrigerating coils, the pressure in the latter is maintained at from 30 to 60 Ibs., corresponding to tem- peratures from o to 30 Fah. The ammonia condensing coils are in some cases immersed in water, which is renewed in order to maintain the temperature as low as convenient, while in otlier cases the condensation is brought about by allowing a spray of water to fall over them from top to bottom. Except for details of the apparatus employed, the principles outlined above, as well as the leading features of the equipment, are the same for a variety of substances which may be used as refrigerating agents. Thus, sulphur dioxide, carbon dioxide, sulphuric ether, me- thylic ether and still more recently liquid air may be and have been used in the general manner above described. Sec. 89. PRINCIPAL FEATURES OF AMMONIA REFRIGERATING APPARATUS. In Fig. 298 is shown diagramatically the arrangement of ap- paratus in the De La Vergne system of ammonia refrigeration. In all such systems involving the compression of a gas it is most important that the compressed gas be as completely discharged as possible at Hie end of the stroke, else it will re-expand on the return stroke, thus preventing the inflow of a full charge of fresh gas and thus reducing the effective capacity of the machine. In the system illustrated in these figures this is accomplished by in- jecting into the compressor at each stroke a certain quantity of oil which fills all clearances and thus insures the delivery of prac- tically the entire charge of gas. This oil likewise acts to lubri- 550 PRACTICAL MARINE ENGINEERING. cate the moving parts and to seal the stuffing-box, piston and valves, and thus to prevent leakage,. It also acts to some extent to absorb the heat resulting from compression, thus to reduce the expenditure of work required. In Fig. 299 is shown the double acting compression cylinder used in this system. The two passages marked "Suction" and "Discharge," respectively, connect the compressor with the pipe system. On the up stroke gas flows through the lower suction valve into the space behind the moving piston, while the gas above the piston, after being compressed to the condenser pressure, is dis- charged through the upper valves (in the loose head) into the discharge passage. On the down stroke gas flows into the cylinder through the AMMONIABCONDENSER Fig. 298. Diagram Showing Arrangement of Ammonia Refrigerating Machinery. upper suction valve, and the gas below the piston is compressed and passes through the lower discharge valves into the discharge passage. The piston in its downward course closes successively the openings of these two discharge valves. When the lower is closed, however, the upper one communicates with the chamber in the piston, and the gas and oil still remaining below the piston are discharged through its valves into the chanfber and out by the upper discharge valve. The oil is injected directly into the compressor after the compression of the full cylinder of gas has commenced, and thus does not reduce the capacity of the machine. The compressed gas and oil thus delivered from the com- pressor cylinder pass on to the oil cooler. The cooled oil drops REFRIGERATION. 55i into the bottom of the tank, while the gas continues into the con- denser, where it is liquified and collected in a second tank. Two forms of condenser may be employed. In one form the con- densing coils are immersed in a tank of cold water, which, by suitable pumping arrangements, is continuously withdrawn and renewed in order to maintain as low a temperature as convenient. In the other form of condenser water is sprayed over the coils, falling from top to bottom, while the gas enters preferably at the Marine 'ngintcrin0 Fig. 299. Ammonia Compressor Cylinder. Fig. 300. Ammonia Compressor Cylinder. bottom and passes upward in a direction opposite to that of the water. The latter type of condenser is the more efficient of the two for the same amount of water, while it has the further ad- vantage that ammonia leaks are readily detected by the odor, while with the submerged condenser the escaping gas is ab- sorbed by the water, and its escape is not so readily noted. From the collecting tank the liquid ammonia passes through 552 PRACTICAL MARINE ENGINEERING. the expansion cock into the expansion coils. The latter may be located directly within the space to be refrigerated, or they may be surrounded by a brine, which in turn is pumped through the re- frigerating coils proper. The former method is the more efficient inasmuch as a loss always attends a multiplication of such pro- cesses. The chief objection to this method lies in the somewhat greater liability of ammonia leaks and the resulting presence of ammonia in places where it may be objectionable. The expan- sion cock must be capable of nice adjustment in order to make possible the proper control of the flow of liquid ammonia into the coils. In the system here shown this is accomplished by making the orifice on the delivery side of the cock m the shape of a very narrow wedge, the point of which is the first to open. Move- ment is then imparted to the plug by a worm and wheel, thus in- suring adjustment of the most delicate character. The point of chief importance in connection with the expan- sion coils, and, in fact, in connection with the entire piping sys- tem, is that of the joints. Screwed connections are far more lia- ble to leak under ammonia than under steam, and the utmost care is needed in regard to this feature. For the best results special joints are required. In a representative joint of this char- acter the thread into which the pipe screws does not reach en- tirely to the outside of the fitting, but instead a smooth annular space is provided around the pipe beyond the termination of the thread. This recess is filled with solder, the pipe and fitting be- ing well tinned, and thus a screwed and soldered joint is made which is found tight against ammonia under all pressures em- ployed. The cooling efficiency of the refrigerating coils is also much increased by clamping to the pipes thin disks of cast iron. These disks are made in halves, and are placed at intervals of 6 to 10 inches on the pipes. They effect an increase in the surface in contact with the air, and thus an increase in the heat, which can be withdrawn from the air and conducted to the cooling sub- stance within the pipe. In the Eclipse system of refrigerating machinery the same general principles are involved, but with some differences in the apparatus employed. The compressor, as shown in Fig. 300, is single acting, the gas being compressed on the upper side of the piston only. No oil is used to fill the clearance spaces, and the clearance is reduced to a negligible quantity by working the REFRJGERA TION. 553 piston almost metal and metal against the head. This is made practicable by making the pump head movable so that it may op- erate as a large valve the full size of the bore of the cylinder, and through the seat of which, if need be, the piston might pass without injury. Under normal conditions this entire head does not work as a valve, the discharge being through a small steel valve in the center of the head, as shown in the figure. The com- pressor cylinder is surrounded with the water jacket, which ab- sorbs a part of the heat generated by the compression of the gas. For controling the expansion in this system a special form of valve is used which provides for close adjustment of the opening and is fitted with an index and pointer so that the amount of opening may be ascertained and such adjustments made as have been by trial found to best suit each case. Sec. 90. REFRIGERATION BY THE EXPANSION OF A COMPRESSED GAS. We will next examine the principles involved in the use of air as a refrigerating agent through compression, cooling and expansion. If compressed air is allowed to expand against a resistance, thus doing work, while at the same time no heat is allowed to enter, the air will lose a part of its heat, the equivalent in amount of the work done. That is, the work is done at the expense of the heat in the air, which gives it up as called for and becomes cor- respondingly cooled in consequence. Thus, for example, if air at 100 pounds absolute pressure and at a temperature of 70 degrees were allowed to expand to 15 pounds pressure, and no heat be permitted to enter, the temperature would become reduced by about 220 degrees, or to about 150 degrees below zero. Actually the absorption of some heat could not be avoided, and hence the actual temperature reached would be higher than thus indicated. The equipment for utilizing these properties of air is substantially as follows : (i) A cylinder in which air is drawn from the atmosphere or from the refrigerating coils and compressed. The air thus be- comes heated and its temperature is raised. It is therefore sent next to (2), a cooling coil working after the manner of a surface condenser for steam, or for ammonia vapor, as above described. The difference here is, however, that no effort is made to con- dense the air, but simply to cool it down to somewhere about at- 554 PRACTICAL MARINE ENGINEERING. mospheric temperature. The air is next sent to (3), a cylinder in which the air expands and does work and becomes thereby cooled. From this cylinder the cooled air on the return stroke is forced out through the refrigerating coils, and thus the cooling action is brought about. The compression and expansion cylin- ders are connected to the same crank shaft in such manner that the work done by the expanding air will aid in effecting the com- pression of the incoming fresh charge. The difference in the work of compression and that furnished by expansion plus the friction of the machine must be made up by the motor operating the machine. Sec. 91. PRINCIPAL FEATURES OP COMPRESSED AIR REFRIGERATING APPARATUS. We will now briefly describe the leading features of the Allen dense-air refrigerating machine as illustrating this type of apparatus. Experiment has shown the advantage of using relatively high pressures throughout the apparatus. The air in the refriger- ating coils is therefore kept at about 60 Ibs. gauge pressure. From these coils the compressor cylinder draws its air, which is then compressed to 200 Ibs. or over, and this, after cool- ing, is again expanded back to 60 Ibs. and sent to the coils again, so rhat the same air is used over and over. To make up for leak- age a small air compressor is added, capable of delivering air at the lower pressure into the inflow pipe leading to the main com- pressor. Again the cold air on its way back from the coils at a temperature usually below freezing is used in a special cooler to further cool the compressed air at high pressure before it is sent to the expansion cylinder. Referring to Fig. 301, the following are features of the cyl- inder with their uses : (A) the steam cylinder which furnishes the power required. (B) The air compressor cylinder. This is usually sur- rounded by a water jacket to assist in cooling the air as it is compressed. (C) The cooling coil surrounded by water. Through this the air passes and thus becomes cooled nearly to the tempera- ture of the external air. (D) The return air cooler for still further cooling the com- pressed air by allowing it to give a part of its heat to the air re- REFRIGERATION. 555 turning from the refrigerating coils to the compressor inflow, as noted above. (E) The expansion cylinder. The cooled air is admitted to about one-third stroke and is then cut off. The charge is thus expanded to about three times its original volume, and is thus brought to about the same pressure as it had when entering the compressor cylinder, but at a much lower temperature. The air is then discharged through a pipe which leads it to the re- frigerating coils or to the point where its capacity for absorbing heat is to be utilized. (F) A trap through which the air passes after leaving the Fig. 301. Diagram Showing Arrangement of Compressed Air Refrigerating Machinery. expansion cylinder and in which are gathered the lubricating oil carried by the air from the compressor cylinder as well as the frost which results from the freezing of the moisture in the air. This leaves the air pure and dry and in the best possible condi- tion for carrying out the refrigeration in the coils beyond. (G) A pump for supplying water for the water jacket around the compressor cylinder, for the bath around the cooling coils (C), and for the trap (I). (H) A small air compressor for supplying the loss due to leakage. (I) A trap for taking the moisture from this supplementary air supply so as to have it enter the machine as dry as possible. 556 PRACTICAL MARINE ENGINEERING. Sec. 92. OPERATION AND CARE OF REFRIGERATING MACHINERY. Before starting refrigerating machinery, whether newly in- stalled or after any considerable period of disuse, all piping and joints should be tested for leaks. This may be done, no matter what the system be, using the compression pump to compress air into the piping up to whatever pressure may be considered suitable. The seriousness of the leakage may then be estimated by the rapidity with which the pressure is lost after allowing the pump to stop. The larger leaks may be determined by the noise made by the escaping air. For the smaller ones the joints are sometimes covered with soap-suds so that the escaping air may show itself by blowing a cluster of bubbles. After the points which may show leaks have received proper attention, the system should, for a considerable time, hold the pressure without sensible loss. In this connection, however, it must be remem- bered that the air as it leaves the compressor will be heated by the work of compression, and as it loses this excess heat in the coils there will tfe a corresponding loss cf pressure. After equality of temperature with the outside air has been reached, however, the further loss of pressure should not be appreciable. With an air refrigerating plant the presence of leaks is of course of less importance than with ammonia. In the former a leak may result in a slight decrease in the capacity of the machine, while in the latter the capacity of the machine is not only af- fected, but ammonia will be lost as well. With the air machine no further preliminaries are needed beyond the examination necessary to insure the proper mechanical condition of the compressor "and steam cylinders. With the ammonia machine, however, it is necessary next to exhaust the air from the entire system by working the pumps and discharging through valves provided for this purpose. When the gauges show the highest vacuum which can be maintained, the valves are closed and the system is ready for charging. The ammonia is usually provided in steel flasks containing a known weight of the liquid. To introduce the charge the flask is connected to the charging valve according to the directions which usually accompany them. In the meantime the machine is run at slow speed with the suction and discharge valves open and the condenser ready for operation. The expansion valve is then closed and the valve of the flask opened, thus allowing the REPRIGERA TION. 557 ammonia to be exhausted into the system. In this manner one flask after another is exhausted into the system until the liquid shows to a suitable height in the glass gauge of the receiver. The charging valve is then closed and the expansion valve opened and regulated until with the machine running at a nor- mal speed the pressure gauges steady down to the pressures usually maintained, as mentioned in Sec. 88, and a frosting of all parts of the expansion coils in contact with the air shows that the refrigerating action is in vigorous operation. The weight of ammonia in the flask being known, its complete dis- charge may be determined by weighing before and after con- nection with the machine. For the routine care of refrigerating machinery the same principles apply as for steam engines and pumping machinery in general, and they need not be here repeated in detail. A few special points may, however, be mentioned. In ammonia machinery, through leaky stuffing-boxes and in other ways, air may occasionaly find its way into the system. Its presence will decrease the efficiency of the machine, and it must therefore be removed as soon as possible. The most no- ticeable symptoms of such trouble will probably be a rise in the* condenser pressure. Purging valves are usually fitted on the condenser or elsewhere through which such air may be drawn off. To this end it is desirable to stop the machine for a time to allow the air to collect. It may be then drawn off through a rubber hose or other suitable means and discharged under water. The rise of bubbles will show that air is escaping, while on the other hand the presence of crackling or snapping sounds will indicate that the air is all exhausted and that ammonia is escaping and being absorbed by the water. Reference has been made to the importance of joints and piping. This part of the system must receive especial care both in the original installation and in the routine attention. For ammonia in particular, as already noted, special joints are usually required, and both ammonia and air will find smaller leaks than steam. It must also be remembered that the chemi- cal action between ammonia and copper renders impossible the use of copper, brass or bronze through all parts of the installa- tion with which the ammonia may come in contact. With compressed air refrigerating machinery it sometimes happens that the ports or passages through which the air first 558 PRACTICAL MARINE ENGINEERING. passes in its expansion become clogged with a deposit of snow or ice, due to the freezing out of the moisture contained in the air. In the Allen dense-air machinery, where the same air is used over and over again, additional moisture can only come from the small make up air supply, and most of this is removed by the trap provided for this purpose. In operation this trap should be watched in order to make sure that its action is efficient and that there is no danger of the passage of water over into the ex- pansion system. In routine operation it is usually desirable to clean the machine by heating it up and blowing out all the oil and ice deposits. To this end the valves in the main pipes lead- ing the air to and from the coils are closed, thus shutting off the machine from the remainder of the system. A by-pass is then opened, connecting the main expansion pipe beyond the oil and snow trap with the main return from the coils. Connections are then opened in the so-called hot air pipe leading from the compressor cylinder to the expander cylinder, and the expander inlet valve Is partly closed. Live steam is then let slowly into the jacket of the oil trap in order to thaw out all ice and hard- ened oil, and the machine is run moderately for a time, during which the blow off valves of the trap and expander cylinder are frequently opened until everything appears clean. Then the machine is readjusted to its normal condition and run as before. If it should be suspected that any considerable quantity of oil and water have gotten into the pipe system and are clog- ging the surfaces, the pipes may be cleaned by running hot air through them and drawing off the oil and water at the bottom of the manifolds of the refrigerating coils. ELECTRICITY ON SHIPBOARD. 5 59 CHAPTER XII. ELECTRICITY ON SHIPBOARD. Sec. 93. INTRODUCTORY. In the present chapter we shall discuss briefly and from the practical standpoint the application of electricity on board ship for lighting, and as a source of auxiliary power. The limitations of space prevent, of course, the development of the subject in detail, and we shall therefore give by way of introduction a few / / V \ t ,' / t Fig. 302. Simple Bar Magnet, Showing Lines of Force. statements and definitions which must be taken for granted by those not already familiar with the elements of electrical theory. (i)'We first suppose that the reader is familiar with a com- mon magnet and its more well-known properties. (2) The name magnetic field is applied to the space around a magnet and through which the magnetic forces act. Let PQ, Fig. 302, be a magnet, with one pole at E and one at A, and sup- 560 PRACTICAL MARINE ENGINEERING. pose the latter to correspond to the north end of a compass needle. It must be understood that the magnetic forces act really in closed paths, as indicated by the dotted lines in the figure. That is, if we should map out the direction in which the north end of a long, thin magnet would be urged, beginning with A, we should trace out a path ABCDE. That is, a! north magnet pole, if free to move by itself, would tend to move along the path from A around to E, in the direction of the arrow, and would so move unless prevented by some external force. Hence the magnetic force acts all along this line from one end to the other, thus mark- ing out what is called a line of force. Now, to complete the cir- cuit it is considered that the same force acts on through from E Marine Engineering Fig. 303. Horseshoe or Bent Magnet, Showing Lines of Force. to A inside the iron or steel, although we are not able to measure the actual force there in the ordinary way. The entire space around and within a magnet is thus occupied with these lines of force, and in its widest sense therefore the magnetic field, or field of force of a magnet, would include all space. As we move away from the immediate vicinity of the poles, however, the force be- comes weaker and weaker, and finally at no great distance be- comes very small. Practically, then, the field of force includes only that part of space within which the magnetic forces are measur- ably large in amount. By changing the form of the magnet, as in Fig. 303, the sensible part of the field becomes limited to the space between the two poles, as shown by the dotted lines, and it also becomes quite uniform in strength. ELECTRICITY ON SHIPBOARD. 561 (3) All the phenomena connected with what we call electric currents in wires or other conductors take place as though a cur. rent of something was flowing around the closed circuit. Scien- tists do not assume that there is in reality anything actually flow- ing within the wire. In fact, the nature of electricity and of the electric current are not satisfactorily known, and so in the ab- sence of more definite information we speak of the electric current simply as an aid in the discussion. (4) The fundamental principle which seems to connect mag- netism with electric currents is found in the following fact : A wire or conductor in which an electric current is flowing is surrounded by a field of magnetic force, as shown in Fig. 304. If the current is flowing away from the observer, or along the direction in which he looks, then the direction of the force is such that a free north magnetic pole would tend to go round and round the wire in circular paths in the direction shown by the dotted lines. ..>-._\Vv-//7 C^S .Marine Engineering Fig. 304. Lines of Force About a Wire Carrying an Electric Current. \ (5) If we bend the wire in w r hich the current is flowing into the form of a circle, as in Fig. 305, then these separate effects combine and we have a field of force just the same as though the wire circuit were a very short, flat magnet, the two poles being very close together. If we have many turns of wire on a spool then all these effects are added, and we have a magnetic field of still greater force and distributed almost exactly as though the core of the spool were a bar magnet. If, in fact, we put in a piece of soft iron for the core of the spool, then we shall find that the iron itself becomes magnetised, and adds its force to that of the current, thus producing a still stronger field of force. A rather more exact way of stating this is to say that the current which flows tends to produce a magnetic field, but that there is a certain resistance to the setting up of this force, and that this resistance depends on the substance through which it is to be set up. If there is no metal core, then the magnetic force must pass through 562 PRACTICAL MARINE ENGINEERING. air around the entire circuit. It so happens that the resistance to the setting up of magnetic forces is very much less in iron than in air, so that if an iron core is put in, the total resistance in the cir- cuit of the magnetic forces is very much reduced, and the same electric current can then set up a much stronger field than through air all the way. (6) We can now state the fundamental principle upon which the operation of the electric generator depends. If a wire is so moved as to cut across 1 the lines of magnetic force, then there will be generated a force tending to set up a current of electricity in the wire. This is known as the electro- motive force, and is usually abbreviated into E.M.F. If, then, the ends of the wire are connected so as to form a closed circuit, A Fig. 305. Lines of Force About a Coil Carrying an Electric Current. and the movement is such that the amount of magnetic force which passes through the circuit of the wire undergoes a change, either increase or decrease, then a current of electricity will be set np in the wire, and will continue as long" as such change is in progress. Thus, in Fig. 306, on the right, if the loop of wire should be moved from a strong to a weak field, as shown, then the amount of force passing through the circuit would decrease and a current would be set up, as shown, and lasting as long as the change was in progress. If, further, the coil should move on from the weak to a strong field, there being no change in the di- rection of the lines of force, then a current would be developed in the opposite direction to that developed by the movement from strong to weak. If, however, at the same time the direction ELECTRICITY ON SHIPBOARD. 563 of the lines of force should change, then the direction of the cur- rent would remain unchanged, as shown in the figure. If also, as shown on the left, the loop were to be turned sideways, so that a smaller amount of force could pass through, then also a current would be set up and would last as long as the change was in progress. In all such cases the direction in which the current will flow may be determined by the following rule : If we look at the loop along the lines of force in the direction in which a free north mag- netic pole would tend to move, and the change in the amount of force passing through the loop is a decrease, then the current will flow in the right-hand direction, or with the hands of a watch. If the change of force is an increase, the current will of course flow in the opposite direction. The generation of electricity in all forms of electric gener- 5^ 777 \ Fig. 3CKJ. Development of Electro-Motive Force by Moving a Coil of Wire in a Magnetic Field. ators, and its use in all forms of motors, depends fundamentally upon the few principles explained above. Electro-Motive Force. The force in answer to which the elec- tric current is set up and maintained is known as the electro-motive force. Relative to the electric current this force plays a part quite similar to that played by steam pressure, or a difference of steam pressures, in causing a flow of steam from one place to another. In fact, the term electric pressure, or difference of electric pres- sures, is now quite commonly used by engineers instead of elec- tro-motive force. The phrase electro-motive force is commonly abbreviated to E.M.F. The unit of E.M.F. is known as the volt. Resistance. The electric current, in flowing around the cir- cuit, meets with a certain resistance, and it is in fact this resist- ance which the E.M.F. must constantlv overcome. This resist- 5 6 4 PRACTICAL MARINE ENGINEERING. ance to the flow of the electric current may be likened to the resistance of a pipe to the flow of water within it. Electric resistance depends on the material of the circuit, on its length, and on its cross-sectional area. The greater the length the greater the resistance, and the greater the cross-sectional area the less the resistance, both in direct proportion. Substances are usually divided into conductors and non-conductors. There is no substance so good a conductor, however, but that it op- poses some resistance to the passage of a current, and there is no non-conductor so perfect that it will not allow the passage of minute currents, especially under very high pressures. The unit of resistance is called the Ohm, and is defined as the resistance which is opposed to the passage of an electric current by a tube of pure mercury of a certain size and length.* The result, then, of the action of electro-motive-force against electric resistance is to produce an electric current, and the unit of cur- rent thus produced is called the Ampere. This is defined as the current which will be produced by an E.M.F. of one Volt acting through a resistance of one Ohm. It signifies a certain rate of flow, just as if we should give a special name to a flow of say 20 gallons of water per minute through a pipe. Electric Power is represented by the product of E.M.F. and rate of flow, just as in the case of the flow of water in a pipe it is represented by the product of the pressure per square foot and the rate of flow expressed in cubic feet. The unit of electric power is called the Watt, and is the power required to maintain for a minute a flow of one ampere under a pressure of one volt. Similarly a current of 8 amperes under a pressure of 50 volts will require 400 watts. To connect electric with mechanical power it is found that in round numbers 746 watts equals one horse power. This must not be taken to mean that one indicated horse power in a steam engine will give 746 watts in a generator. There are losses be- tween the two due to the fact that the electric generator cannot transform all the mechanical energy it receives into electric en- ergy, and thus wastes a certain amount, which appears chiefly as heat. The number 746 gives the ratio which would exi^t if there were no losses of any description whatever. * Cross section of one millimeter square or about 1/25 inch, and length of 1063. millimeters or about 42. inches. ELECTRICITY ON SHIPBOARD. 565 The ordinary commercial unit of electric power is the kilo- watt, or 1,000 watts.. It is thus equivalent to about I 1-3 horse power of mechanical work. Ohms Law. We will now state the fundamental law which gives the relation between the current, the E.M.F. and the resist- ance. It is simply that the current in amperes equals the E.M.F in volts divided by the resistance in Ohms, or in symbols C = E -f- R or E = CR. Likewise, if we denote the electric power by P we have : P = CE = CR This measures the power which is required to maintain the cur- rent in the circuit. If no other effects are produced it is wholly expended in heating the circuit, and the heat thus developed will be measured by the power multiplied by the time or in symbols H=CRt. Now, without further discussion of the principles of electrical engineering, we will proceed to a brief description of the appar- atus more commonly met with on shipboard. Sec. 94. THE DYNAMO. We may consider the dynamo simply as an apparatus de- signed for the development of electric current, or for the trans- formation of mechanical into electrical energy. It consists essen- tially of two electro magnets, which we may call A and B. A is stationary, and between its poles B rotates, carrying its coils of wire through the field produced by A. The rotating magnet and its coils is known as the annaturc, and the fixed magnet and coils as the poles and field coils. In Fig. 307 is shown one of the rotating coils A of the armature, while its successive positions are shown by i, 2, 3, 4. The field of force due to the field coils and poles is also indicated by the arrows. In accordance with the principles above stated an E.M.F. is thus generated in the arma- ture coils. It may be likewise seen that the E.M.F. will act alter- nately in opposite directions in these coils, changing as their plane is about midway between the poles, or in the position shown at A. All these elementary forces thus generated in the separate coils of an actual armature are gathered together and produce the full pressure at the terminals. Electric generators are of two chief varieties, direct and alter- nating current. In the latter the E.M.F. generated is allowed to produce the current in the circuit back and forth, alternating in 566 PRACTICAL MARINE ENGINEERING. direction as the coils pass between the poles. The current may thus be likened to a series of surges to and fro, but without con- tinuous flow in either direction. In the former, or direct current machine, these impulses are so taken up by the commutator that they are all adjusted or turned in one direction, and we have, therefore, a continuous flow rather than a series of surges back and forth. It is found by experience that either form may be used for the development of light by either the incandescent or arc sys- tem, while also either, by the use of appropriate motors, may be used for the development of mechanical power. / / / / 3 v - \ \ \ \ V X \ 4 Q ~ > o \ \ Mariiie Engineering Fig. 307. Action of Single Coil of an Electric Generator. For use on board ship the direct current form is usually em- ployed. A discussion of the relative advantages and disadvant- ages of the two forms is beyond our present limits, but it may be said in a word that for lighting the limited space of a single ship the alternate current system does not possess the advantages which it may in the case of distribution over a wider area, and for the operation of motors its use would entail some disadvantages and complexity from which the direct current system is free. Restricting our attention therefore to direct current machin- ery, the simplest is found in the so-called series dynamo. In this ELECTRICITY ON SHIPBOARD. 567 type the circuit as a whole leads continuously around both the armature and the field coils, thence into the external circuit at one terminal, and around back to the machine at the other ter- minal. If instead of this arrangement the wires are lead as in Fig. 308, the current leaving the armature is divided, and one part flows around the field coils while the other goes through the external circuit. This constitutes the so-called shunt-wound dy- namo. In such case the field coils consist of many turns of fine wire, while in a series machine they consist of a few turns of larger wire. A combination of the series and shunt-windings constitutes the so-called compound wound machine. For the purpose of COMMUTATOR Marine En-ing Fig. 308. Shunt-Wound Electric Generator, Outline Diagram. delivering a constant potential or electric pressure the shunt- wound machine is usually employed, and it is this type which is commonly met with on shipboard. We will now pass immediately to a brief description of a modern electric generator applicable to marine purposes. According to size the typical marine generator is made with four or six poles, distributed uniformly around the circumference of the armature, which is of the ring type, as shown in Fig. 309. The machine is shunt wound according to the diagram of Fig. 308. The commutator, as shown in Fig. 310, consists of a series of bars of special bronze or copper formed into a cylinder or drum, 568 PRACTICAL MARINE ENGINEERING. and with mica or other insulating material between them. Each bar of the commutator is joined to the winding on the armature, and the connections are such that the E.M.F. generated in the Fig. 309. Ring Armature. Marine Enyineering Fig. '310. Commutator. entire series of coils is so directed as always to urge the current out through one of the brushes and in through the other. The brushes are usually in the form of a block of carbon, and are ELECTRICITY ON SHIPBOARD. 569 carried in metal holders, as shown in Fig. 311, and provided with means for holding them by adjustable spring pressure up to their contact with the commutator, while at the same time the frame which carries them may be rotated as a whole about the axis of the machine, thus bringing them to bear on different parts of the commutator for purposes of adjustment with varying load. With a four-pole machine the brushes are usually placed one nearly on top and one at about right angles. This makes them more accessible than if placed at opposite sides of the commuta- tor, as is necessary in two-pole machines. CLAMPING SCREW BRUSH PRESSURE SPRING \HARD ROLLED COPPER LEAVES ADJUSTING SCREW Fig. 311. Brush Holder. In the selection of such a generator special attention should be paid to points of mechanical excellence, especially in connec- tion with the bearings and balancing of the armature, the con- struction of the brush carriers, the binding posts, and other like points entering into the construction of the generator as a ma- chine. The capacity of the generator should be such that it will be able at its normal rating to supply the expected demand foi light and power. Generators are expected to be able to stand a certain amount of over load, and if of proper design and in a 570 PRACTICAL MARINE ENGINEERING. \ cool and well ventilated -room will run safely at far above their rated power. It must be remembered, however, that the dynamo room of a ship is rarely cool or well ventilated, and that the over- heating of armature and field coils is the chief limitation on the capacity of an electric generator. Hence in the unfavorable situ- ation in which such machines are usually installed, they should not be expected to carry any considerable over load. The typical marine generating set consists of a generator as above, together with engine set on one base and coupled direct together. The usual number of revolutions at which such sets are operated ranges from perhaps 300 to 500, according to size. The engine may be either a simple or compound, or even a triple- expansion, though the latter are but rarely employed in marine practice. In the design and construction of such an engine the chief points to be held in view are solidity and strength, espe- cially! in the running parts, but without undue excess of weight, generous bearing surfaces and provision for continuous and sure supply of lubricant. With such small high-speed engines the presence of water in the cylinder is likely to produce serious damage, and especial care should be taken in regard to the relief and drainage valves, both hand and automatic systems being preferably fitted. The governor provided with such engines is of the shaft au- tomatic type, and should control the revolutions within about 2 per cent, for change from full load to no load, or vice versa. In the care and operation of such engines no points are in- volved which have not already been discussed in connection with other engines, and it will not therefore be necessary to further consider these topics. MOTORS. Electric motors are coming into use on shipboard for a variety of purposes connected with the application of auxiliary power, but chiefly for running hoists and ventilating fans. It will be sufficient for our present purposes to note that a motor is es- sentially the same as a generator, and only differs in the manner of its use. With the latter we supply mechanical energy and with- draw electric energy. With the former we supply electric energy and withdraw mechanical energy. The motor contains the same parts as a generator, and similarly related, and differs only in being thus operated in the inverse manner to the generator. ELECTRICITY ON SHIPBOARD. 571 Sec. 95. WIRING AND THE DISTRIBUTION OF I/IGHT AND POWER. The conductors used for the distribution of electricity may be either of single copper wire, varying in size according to the current to be carried, or of several small wires made up into a cable and of corresponding capacity. The insulation must be of extra good quality in order to stand the severe conditions to which it may be subjected on shipboard. The materials available for the insulation of wire are rubber, either gum or vulcanized, gutta percha, and various special com- pounds, together with braided or wrapped coverings of cotton, linen or silk. Gutta percha is rarely used except for submarine cables and for other special purposes. It must be understood that none of these substances singly and no combination of them is a perfect non-conductor. There is always a small leakage through the insulation and air, and the purpose of the covering is to reduce this leakage to a safely negligible amount. For marine work it is especially necessary to protect the insulation against the effects of dampness and corrosion, as under these influences deterioration may set in, causing a breaking down of the resist- ance to the passage of the current and an increase in the leakage. The usual form of marine lighting wire is insulated with vul- canized rubber or other special compound, covered with braided cotton, the whole covered with a coating of waterproof and pre- servative material. For switchboards and mountings for fixtures and all attachments, slate, marble and porcelain are used. The conductors are run either in iron pipe or in double wooden mouldings. The former or the conduit system is to be preferred, as the conductors are thereby given the protection of the iron pipe. The conduit system is, however, much more ex- pensive than the moulding system, and the latter is therefore more commonly employed, except in warship work and where high first cost is not an objection. The chief point in either system is to give to the wires and to the various junctions and connections the greatest possible pro- tection from mechanical injury and from the action of dampness and water, and all parts of the distributing system exposed to the weather or to the sea should be made as nearly water-tight as the limitations of first cost will permit. The method to be adopted for the distribution of electricity depends somewhat on the purpose for which it is to be used. 572 PRACTICAL MARINE ENGINEERING. The most common use on board ship is for operating incan- descent lamps, where as nearly as may be the same pressure is required at each lamp. For this purpose the so-called dis- tribution in parallel is required. . This is illustrated by the dia- gram of Fig. 312, where G is the generator and // the lamps. It is seen that each lamp has its own bridge across from the two mains LL, and may thus be turned on or off independent of the operation of the others. In the early days of electric installations on shipboard the iron or steel hull was frequently made a part of the circuit, or, as it was sometimes stated, th^ return was made through the hull. To use the hull in this way it was simply necessary to connect one Marine Enyinee.riny Fig. 312. Distribution in Parallel. pole of the generator to the ship, and then connect one lead from each lamp to the hull likewise. Great difficulty, however, was experienced in making and keeping good contact between the conductors and the ship. Corrosion was especially active at these points, and they were found to be the source of constant trouble. The presence of stray current returning through the ship was also believed to be a factor in the corrosion and deterioration of parts of the ship's machinery. This system was therefore open to grave objections, and is now rarely met with. The modern practice is to employ a com- plete wire conductor for the external circuit, and to keep the cur- rent insulated entirely from the hull, as indicated in Fig. 312. Arc lamps are very commonly operated in series, as shown ELECTRICITY ON SHIPBOARD. 573 in Fig. 313, each lamp thus receiving the same current which flows around the entire circuit. On board ship the chief or only use of arc lamps is for the searchlight, and the number there- fore will usually not be greater than one or two, except for warships, where a larger number may be employed. We may also need current supplied at various special points for the operation of motors for running ventilators, hoists, etc. The entire distribution may therefore comprise various cir- cuits according to the use to be made of the current and the point at which it is to be delivered. It is furthermore found desirable to split up the incandescent lighting distribution into a series of circuits, each of which is led from a main distributing point. The entire distribution will thus comprise several main circuits, all of which, however, will be led from the central point. This distribution point is actually furnished by the sivitch- Fig. 313. Distribution in Series. board, a slate or marble slab, on which are mounted the various instruments, switches, circuit breakers and connections needful for safely carrying out the distribution in the various ways in which it may be required. We will now refer briefly to the more important items usu- ally grouped on the switchboard : Switch or Cut Out. The object of a switch or cut out is to break the circuit and thus stop the flow of current. With a single pole switch the circuit is broken at one point only. This is the usual form fitted in the sockets of electric lamps, etc. With a double pole switch the circuit is broken at two points. The switches mounted on the switchboard are usually of this type, and are to be preferred, since by this means the line is entirely cut off from connection with the generator. ^74 PRACTICAL MARINE ENGINEERING. Fuses. A fuse is a short piece of fusible alloy, so adapted to the proper current in the circuit that any marked increase in current strength will cause the fuse to melt, due to the increase in the heating effect. The result of this will be a break in the circuit and an interruption of the current. This is therefore an automatic device for preventing the rise of the current strength beyond a certain value. In the same manner as with switches, we may have single pole or double pole fuses. The latter are to be preferred, as they give a double chance of breaking the circuit, and hence a greater relative mar- gin of safety. Circuit Breakers. It is found that the ordinary fuse does not satisfactorily provide protection against momentary variations of current strength due to excessively rapid fluctuations in the gen- erator or in the outer circuit. To prevent possible damage from such cause a magnetic circuit breaker is often employed. This consists of an electro-magnet, through the coil of which the main current flows. Any sudden increase of current will correspond- ingly increase the magnet strength, and the armature is so ad- justed that in answer to this excess of pull it will move toward the magnet poles, thus breaking the circuit by the motion pro- duced, and interrupting the current as desired. Ammeter. This is an instrument through which the current is passed in order to measure or indicate its strength. The in- dication is shown by a finger moving over a dial, graduated usually so as to read the current in amperes. The Ammeter must be connected in series with the machine and main circuit. Volt Meter. This is an instrument which measures or in- dicates the E.M.F. or difference of electrical pressure between the two points to which its wires are attached. It serves a sim- ilar purpose as the steam gauge for the boiler. The indication is shown by a finger moving over a dial graduated usually so as to read the pressure in volts. It is usually connected with one wire to each pole of the generator so as to give the entire pressure in the external circuit. Rheostat. This is simply an arrangement for varying the total resistance of the external circuit, and thus of varying the pressure available for that part beyond the instrument. It con- sists essentially of a series of coils of wire, more or less of which can be brought in and made a part of the circuit by moving a handle across a series of contact points. ELECTRICITY ON SHIPBOARD. 575 Rheostats are often required in connection with the use of arc lights, or with the governing and control of shunt-wound generators and motors. The complete installation of instruments, switches, connec- tions, etc., thus brought together on the switchboard has as its object the possibility of shifting the load from one generator to another, of connecting the various circuits singly or in different combinations with any one or any combination of generators, and at the same time providing for safety and for the proper measurement of the pressure and current. Sec. 96. I/AMPS. Electricity is used on shipboard for operating incandescent or glow lamps for general lighting, for operating arc lamps for search-lights, and for operating motors. Incandescent Lamps. The usual style of incandescent lamp consists of a filament of carbon in; a glass bulb exhausted of its air and sealed air-tight. The carbon filament is connected to metal terminals, through which connection with the external cir- cuit is made. The resistance of the carbon filament is very high and the passage of the current gives therefore a heating effect, which is sufficient to raise it to the luminous point. If the air were not exhausted from the bulb the carbon would be imme- diately burned up or converted into carbon dioxide by union with the oxygen. Since, however, the oxygen is almost entirely removed such combustion is limited to the smallest fraction of the filament when the current is first turned on, and it then re- mains nearly unchanged for a period of time ranging from 600 to 1,000 hours. Gradually the filament seems to disintegrate or lose its strength, and finally fails by snapping in two, or the bulb becomes blackened by a deposit of carbon on its inner sur- face. The usual lamp for ship fitting is one of 16 candle power, requiring about no volts pressure, and taking about y 2 ampere of current. It thus follows that such a lamp will require about 55 watts of electrical energy. To supply this will require the equivalent of not far from 75 at the steam engine, or about i-io H.P. It follows, then, that we may expect to operate roughly about ten such lamps per I. H. P. at the engine. More powerful lamps, such as 32 or 50 candle power will require more current, and hence more energy and more horse power in proportion. Arc Lamps. The simplest form of arc lamp is shown in 576 PRACTICAL MARINE ENGINEERING. Fig. 314. It consists of a pair of carbon rods, separated by a slight gap as indicated. These carbons form part of an electric circuit, which is completed by the leads to the generator, as shown. To start the lamp the rods must be brought together, thus completing the circuit and permitting the current to flow. The instant the current is set up, however, the rods are separated a slight distance. The space between the two is then filled with hot air and carbon dioxide, and across this the current is able to pass. The resistance is so great, however, that intense heat is developed, and this brings the gases and the particles of N Marine Engineering Fig. 314. Arc Lamp, Simple Form. carbon which are torn off and hurled across the gap all to a state of incandescence. As the lamp burns, the carbons are slowly consumed and the gap thus widens. There is always some width of gap for which the lamp operates best, and a constant adjustment must therefore be made. It is found further that the two carbons do not wear equally or similarly. Referring to Fig. 314, the current is supposed to flow through the lamp downward, and the upper or positive carbon will then wear in a crater-like form, while the lower or negative carbon will take a more rounded or pointed form, as shown. The ELECTRICITY ON SHIPBOARD. 577 positive end will also wear away about twice as fast as the nega- tive end, and this will require a special form of adjustment in order to keep the gap at the same place in reference to a lense or mirror. It is also found that most of the light comes from the crater-like cavity, so that the carbons must be so mounted as to allow the maximum amount of light to escape from this source. A lamp of this character, mounted and provided with suit- able lenses and adjustments for controlling the carbons and for manipulating and turning the beam of light in any direction as desired, constitutes a search-light, as installed on board ship. We shall not attempt here the description of the modes of automatic adjustment for the carbons or of the optical parts of the lamp, as the present purpose is to give only a general idea of the engineering side of the problem. Such lamps require a pressure of from 50 to 60 volts and a current of from 50 to 150 amperes. This corresponds to from 4 to 10 horse power at the lamp, or say 5 to 12 at the engine. Sec. 97. OPERATION AND CARE OF EI/ECTRICAI, MACHINERY. [i] Routine Care. In looking over a generator for the first time the whole machine should be carefully examined, both as to its electrical and mechanical features. All the leads of the wires should be followed through and the binding posts and contacts examined to insure that they are in proper condition. The commutator and brushes should be carefully looked over to see if the seg- ments of the former are in good condition, and if the surface is smooth and free from scores and uneven spots. Carbon brushes are very commonly employed in modern marine practice, but whatever the form of brush the fit of its end on the commutator should be noted, and if necessary it should be refitted so as to bed suitably on the surface. The final adjustment of the brushes cannot be made until the ma- chine is running, but the adjusting and holding devices will be carefully examined and the brushes may be placed in approxi- mate adjustment, according to judgment. The bearings and journals and provision for oiling should then be examined, and carefully cleansed if the condition requires it. The armature should be turned by hand to make sure that there is the neces- 578 PRACTICAL MARINE ENGINEERING. sary clearance between it and the pole pieces, and that it has the proper freedom of motion. These various points having been attended to and every- thing being in a satisfactory condition, the machine may be started. A shunt machine usually excites or builds up best when the external circuit is cut out, so that it operates simply through its own armature and field coil. As the voltage rises, as indi- cated on the voltmeter or pilot lamp, the external circuit may be switched in and the generator will then settle down to its work. The proper lead or adjustment of the brushes is the next thing to be attended to. This must be ascertained by trial until a position is finally found where the sparking is reduced to the smallest limits. If in modern machines the sparking at the brushes is in any degree pronounced, it may be taken as a safe indication that the brush adjustment is not quite as it should be. The exact adjustment will, however, vary as the load changes, and hence in case the load is changing rapidly there will be more sparking than with a steady load. If excessive sparking occurs and cannot be controlled by the brush adjustment, the machine should be shut down at once, as this is an indication that it is out of electrical balance, and to continue running it would mean the possibility of burning out the armature or seriously injuring the commutator and brushes. In some cases such sparking may be due to a dirty commu- tator, and may be corrected by simply cleaning it. The pressure of the brushes on the commutator should also receive attention, as if too heavy undue wear will occur, while if too light they may jump and rur* irregularly, thus causing sparking. A very small amount of lubricant on the commutator is usually found to aid in smooth running and in saving the sur- face from scoring. In amount it should be very small, a drop or two of hydrocarbon oil or a little vaseline or a rub of one of the standard preparations sold for the purpose is sufficient. [2] Faults. One of the most troublesome features connected with the operation of electric machinery is the possibility of the occur- rence of more or less sudden failure at some point, resulting in the sudden extinction of a certain group of lights or the stop- page of a motor, or even the interruption of the entire plant in case the fault lies at the generator itself. ELECTRICITY ON SHIPBOARD. 579 In all such cases the immediate cause of the trouble is the interruption of the current, either in whole or in part. This may be due to a variety of causes, as follows : (i) The resist- ance in the circuit may be enormously increased, thus cutting down the current strength proportionately. (2) The current may be diverted in some other direction, finding an easier path, and thus avoiding the circuits in which it belongs. (3) The gen- erator itself may fail to develop the necessary E.M.F., and hence while the circuits may be in perfect condition the current will be weakened in corresponding degree. The increase of resistance in a circuit may be due to poor contact at binding posts or junctions, arising from improper mechanical construction or fitting, or from the presence of oxide due to corrosion, or from the reduction in the cross section of a conductor due to corrosion, or to any like cause which de- creases the cross section of the conductor or changes its electric conductivity. In case the conductor is broken or the separation is complete, the resistance across the air gap becomes prac- tically infinite, and the current is completely interrupted. The current may be more or less shunted or diverted from its proper path by the accidental establishment of other paths, and the consequent re-arrangement of the current distribution. The generator may fail entirely to develop the E.M.F., if, for example, the field coil circuit should become broken and the cores thus lose their magnetism. In locating a fault the circuit in which it occurs must first be determined, and then the various points at which it might exist must be examined, one after another. The circuit in which the fault is located can usually be inferred from the extent of the disturbance. If only a single light goes out, it is evidently limited to the circuit belonging that light alone, and may be looked for in the lamp itself or in the fuse block, if it has one. If all the lights on a single circuit go out, but no others, the trouble is of course limited to that circuit, and may probably be found at the junctions with the main feeders. If, on the con- trary, the lights in all of the circuits go out or fall off in candle power, the trouble is in the main circuit and must be sought for at the switchboard or generator itself. At the switchboard the cut outs and fuses must be examined, and if the trouble is here it will be soon located. At the generator the brushes should be examined to make sure that they run with proper con- 58o PRACTICAL MARINE ENGINEERING. tact on the commutator. The contact between the brush and holder and all binding posts and contacts about the machine should also be examined, in order to make sure that the trouble is not in a poor contact at these points. If nothing is found here, it is probable that the fault lies in the armature or field coils, and that possibly they have become burned out or un- soldered or otherwise disconnected at, some point. Leakage faults may occur where the insulation is partially or wholly destroyed, and the result of such leakage will be a loss of effect in the lighting and power circuits. Thus, for ex- ample, the insulation between the brush carriers and the base of the machine may become faulty by wear or by the accumula- tion of copper dust and oil and thus form a more or less ready path from one brush to the other through the base of the ma- chine. In such case the current traversing both the field coils and external circuit will be cut down, and due to the former the strength of the magnetic poles will be diminished, and the E.M.F. developed will fall off correspondingly. In case these leakage contacts are good, the entire machine will shut down, due to failure of current in the magnet coils and consequent failure of the magnetic field. In order that such trouble may exist, both brushes must be thus connected to the base. If one only is connected, the machine is said to be grounded. No imme- diate trouble may occur, but if any accidental connection is set up between the external circuit and the structure of the ship the leakage circuit will be complete and trouble will develop immediately, its character and extent depending on what point of the external circuit is thus grounded with the machine. The repair of a fault in the external circuit is often a simple matter of cleaning and readjustment. In the generator itself, however, the exact location and repair of a fault may require a complete dismantling, and perhaps a partial re-building of the machine. Practical Marine Engineering PART II Practical Marine Engineering PART II. COMPUTATIONS FOR ENGINEERS. Sec. i. COMMON FRACTIONS.* [i] Units of Measurement and Definitions. One of the principal duties of the engineer is to measure things. Thus he may be called on to find the length of a sec- tion of shafting, the diameter of a piston-rod, the weight o! a screw-propeller, the volume of an oil-tank, or the capacity of a coal-bunker. Measuring consists in nothing more or less than comparing the quantity to be measured with another quantity of the same kind, and so finding how many times the latter is contained in the former. Thus in measuring a length of shaft with a foot rule we really compare the length of the shaft with the length of the rule, and so find, for example, that the shaft is 14 feet in length; that is, that it is 14 times as long as the rule, or that its length contains the length of the rule 14 times. All these are simply different ways of saying the same thing. Now the foot rule or the foot in such an operation is called the unit. Again, in measuring the weight, say, of a screw propeller, the operation really amounts to making a comparison between the weight of the propeller and the standard weight called the pound. Here likewise the pound is the unit. It is easily seen that the unit must be the same kind of quantity as the thing to be measured, else no direct comparison can be made between them : thus a unit length to measure length, a unit area to 'measure surface, a unit volume to measure volume, a unit weight to measure weight, etc. *The reader is supposed to he somewhat familiar with the general sub- ject of fractions as presented in the elementary text books of arithmetic. The present section is not intended as a complete discussion of the subject, but rather as a short compendium of the more important operations, based on a point of view somewhat different from that given in the usual text books. 582 PRACTICAL MARINE ENGINEERING. Now if we wish to measure the length of our section of shafting with some degree of accuracy we shall probably find that it is not an exact number of feet. We may perhaps find its length between 14 and 15 feet. We then proceed to measure the inches and find, let us say, 14 feet 5 inches, with an additional length less than one inch. With still greater accuracy we might go on and find perhaps 14 feet 5 T 7 inches as the length correct to a sixteenth. Now let us set down this length as follows : 14 feet, 5 inches, 7 sixteenths inch. It is easily seen that if the foot is a unit of length so is the inch, and so is the sixteenth-inch. Here then in measuring a piece of shaft we have used three kinds of units, the foot for most of the length, the inch for most of the remainder, and the sixteenth-inch for the little that finally remained. We know very well that the sixteenth-inch is ob- tained by simply dividing the inch up into sixteen equal parts and taking one of them, while the inch is gotten similarly by dividing the foot into twelve equal parts and taking one of them. It thus appears that these units are all related together ; the six- teenth comes from the inch, and the inch from the foot. A unit which is thus obtained by taking one of the equal parts into which a larger or principal unit may be divided is often called a fractional unit. Thus the inch is a fractional unit relative to the foot; while the half-inch, quarter-inch, eighth- inch, etc., are all fractional units relative to the inch. In general we can always suppose any given quantity considered as a prin- cipal unit, to be divided up into any number of equal parts, as 3, 8, 16, 100, 144, 2196, etc., and w r e can then take one of these parts as a fractional unit and with it proceed to measure any given amount of the same kind of quantity. Now when we measure quantities with fractional units the result is known as a fraction. Thus the fraction five-twelfths (^) is the measure of a quantity in terms of the unit one-twelfth, just as five inches is the measure of a quantity in terms of the unit one inch, and in each case the measure is simply five such units. Or to put the same thing the other way around, if we measure a quantity in terms of a fractional unit such as one-twelfth ( T V), for example, and find that the measure is five such units, then we write the result /V. and such an expression is known as a fraction. For the engineer it is always most natural to bear in mind this idea of a fraction, and to consider that it is simply the measure of a certain quantity in terms of a fractional unit. COMPUTATIONS FOR ENGINEERS. 583 When we are handling fractions simply for exercise in arithmetic we do not always stop to ask what kind of a unit it is, or what kind of a quantity we are dealing with. For an ex- ercise in arithmetic it makes no difference, but the engineer in actual problems always knows what he is dealing with, and what kind of a unit is meant. In the usual way of writing fractions, as y\, y^, y\, T \ 3 T , etc., the number below the line is called the denominator and shows into how many equal parts the larger or principal unit is divided in order to furnish the smaller or fractional unit. The denomi- nator thus shows the relation of the fractional unit to the prin- cipal unit. The number above the line is called the numerator and shows how many of these fractional units are used to meas- ure the quantity in question. PROPER FRACTION. In a proper fraction such as J the nu- merator is less than the denominator, showing that the quantity measured is less than the principal unit. IMPROPER FRACTION. In an improper fraction as yf, the numerator is greater than v the denominator, showing that the quantity measured is greater than the principal unit. MIXED NUMBER, OR WHOLE NUMBER AND FRACTION. Such an expression means that the quantity is measured in terms of two units. Thus 7f\ means seven principal units and five frac- tional units, the latter unit being one-twelfth the former. This is exactly similar to the measurement of length in feet and inches, or weight in pounds and ounces. Thus if the foot is the principal unit, *j{\ means simply 7 feet and 5 inches, or if the pound is the principal unit, 8-j^- means 8 pounds and 9 ounces. We may also recall the illustration used near the beginning of this section where three units were used to find the length of a piece of shafting. [2] Reduction of a Mixed Number to an Improper Fraction. This means simply the reduction of the measure all to terms of the smaller or fractional unit, just as we may re- duce a measure in feet and inches all to inches. Thus to reduce- 7fV to an improper fraction we see that in each of the seven principal units there are 12 fractional units, and hence 7 X 12 or 84 such units in the whole number. In addition, there are 5 more fractional units, and therefore 84 -)- 5 or 89 in all. The reduced value is therefore yf. In a similar way if the principal 5 8 4 PRACTICAL MARINE ENGINEERING. unit were the foot we should reduce 7 feet and 5 inches to inches by multiplying the 7 by 12 and adding in the 5, giving 89 inches similar to the 89 twelfths (ff) above. We have therefore the following : Rule.-^ Multiply the whole number by the denominator and add in the numerator. The result is the numerator of the im- proper fraction, and the denominator is the same as before. Problems Reduce to improper fractions the following : I2|f, 1 7ff, 26 4 -}-Jf. [3] Reduction of an Improper Fraction to a Mixed Number. To reduce an improper fraction such as fj- to a mixed number we must evidently find first how many principal units there are. Since 12 fractional units make i principal unit, it is evident that the number of principal units will be found by dividing 31 by 12. The quotient will then give the number of principal units and the remainder will give the remaining num- ber of fractional units. Thus 31 -f- 12 = 2 principal units and 7 remainder, or 7 fractional units over; or f^ 2 T V Hence the following : Rule To reduce an improper fraction to a mixed number, divide the denominator into the numerator and the quotient will be the whole number, while the remainder will be the numerator of the fraction, and the denominator will be as before. Problems Reduce to mixed numbers the following : 76 198 289 56 95 143 2_6 4 764 TJ> T?> TOT' 2T> T6~> TTT> 8? T [4] Reduction of Fractions Without Change of Value. If we change the size of a unit of measure we shall change the measure of the quantity in like proportion. Thus, for example, the number measuring the diameter of a bolt in sixteenths as a unit will be twice as great as if measured in eighths as a unit. Thus T 6 g- and f represent the same quantity, one measure being in sixteenths and the other in eighths. It follows that we can multiply or divide both terms of a fraction (the numerator and denominator) by the same number without changing its value. Thus f, f, f, {%, ^ if, fj, ff, etc., all represent the same quantity measured in terms of different units, and it is seen that the f may be changed into any of the other forms by multiplying both numerator and denominator COMPUTATIONS FOR ENGINEERS. 585 by the same number, and similarly any of these latter forms may be reduced back to the f by dividing both numerator and denominator by the same number. - 7 A and 'All* . 3X7 24-^- It may often be convenient to reduce a fraction to another of equal value but having some particular or specified denomi- nator. To this end we divide the denominator desired by the denominator of the fraction, and multiply both terms of the fraction by the quotient. That is, we must multiply both nu- merator and denominator by some number which will produce the desired denominator. Thus to reduce f to a fraction whose denominator is 42 we divide 42 by 3 and find 14. We then mul- tiply both terms of f by 14 and thus find ff as the fraction desired. LOWEST TERMS. A fraction is said to be reduced to its lowest terms where there is no whole number which will divide both numerator and denominator without a remainder. Thus in the foregoing string of fractions f is in its lowest terms while none of the others is. To reduce a fraction to its lowest terms we seek a factor which will divide both numerator and denomi- nator and divide, continuing the operation until no further re- duction can be made. Example Reduce ^-f to its lowest terms. We may first see that 2 will divide both terms without remainder. Dividing we have r \ as a reduced value. We then see that 3 will again divide both terms, and thus find | as the lowest reduction. We may also note at first that 6 will evenly divide both terms, and thus find J by a single operation. Problems Reduce the following to their lowest terms : *f. W. -ff#* tf. iWr, K. H> tf ADDITION, SUBTRACTION, AND MULTIPLICATION OF COMMON FRACTIONS. Considering fractions as representing the measures of va- rious quantities, we may be called upon to perform upon them the fo'T fundamental operations of mathematics addition, sub- traction, multiplication, and division. These we will briefly consider in order. 586 PRACTICAL MARINE ENGINEERING. [5] Addition of Common Fractions. We cannot combine directly f and f into a single quan- tity any more than we can 2 feeet and 3 inches, or 6 miles and 8 feet. The reason is that the units are not the same in the two quantities which we seek to combine, and before the com- bination can be effected we must reduce the measures to the same unit in each. To this end we take advantage of the operations explained in [4] and reduce the frac- tions to a common denominator or common unit of meas- ure. We naturally seek for this denominator as ' small a number as possible, and hence proceed according to the com- mon rule for finding the L. C. M. (least common multiple) of the denominators. We then proceed to express the various frac- tions all with this L. C. M. as the common denominator by the method explained in [4]. We may then add the numerators and reduce the result as may be possible. This is the foundation for the usual rule, which may be expressed as follows : Rule, (i) Find the L. C. M.* of all the denominators for a new denominator. (2) Divide each denominator into this L. C. M. and multiply the corresponding numerator by the quotient for a new numerator. (3) Add the new numerators thus found, and the re- sult is the numerator of the sum desired. (4) Write this numerator over the L. C. M. or com- mon denominator, and reduce to the lowest terms. * For convenience in connection with these operations, we give as fol- lows the rule for finding the least common multiple of a series of numbers *. e. y the smallest number which will contain each without a remainder. Rule. Write the numbers in a line (as (i) below), and select any num- ber (as 4 in this case) which will divide at least two of them without re- mainder. Divide and set down the quotients underneath, except where the division would not be exact, in which case bring down agnin the number itself (as shown in line (2) below). Proceed with this line the same as with the first, and so continue until no two numbers have a common divisor. Then multiply together all the numbers remaining on the last line, together with all the divisors, and the product will give the least common multiple desired. Example. Find the L. C. M. of 8, 36, 20, 6. Operation: 4) 8 36 20 6. . . .Line (i) 3) 2 9 56 Line (2) 2) 2 352 Line (3) i 3 5 i Line (4) L. C. M.=4XX2XX= 6 - Ans - COMPUTATIONS FOR ENGINEERS. 587 Examples. Add -^ and {. The L. C. M. of 18 and 4 is 36. We then have : 5 4- 1 - T + 9 _ ! 9 1 x ' 4 ~ "Tfc ~ f*' Add YV, * and f The L. C. M. of 16, 3 and 6 is 48. We then have : -fg 4- f 4- f = -f-J- = by reduction -J^-. If there are but two fractions to be added and both have i for a numerator, a short rule for their addition is as follows : Write the sum of the denominators over their product and the fraction thus formed is the sum desired. Thus i 4- i = if - T 7 T . [6] Subtraction of Fractions. This operation requires reduction to the same unit of meas- ure in the same way and for the same reason as in the case of addition. We have hence the usual rule, which may be expressed as follows : (1) Find the L. C. M. of the two denominators for a new denominator. (2) Divide each denominator into this L. G. M. and mul- tiply the corresponding numerator by the quotient for a new numerator. (3) Subtract the new numerators, and the result will be the numerator of the difference desired. (4) Write this numerator over the L. C. M. or common denominator, and reduce to lowest terms. Thus to subtract % from T 7 ff we have as follows : _7 _ i = T 4 9 _ 36 If both numerators are i a short rule for the subtraction of the fractions is as follows : Write the difference of the de- nominators over their product and the fraction thus formed is the difference desired. Thus i 4- = T V Problems in Addition and Subtraction of Fractions. Perform the following additions : (1 + i + 1), (t + f + T V). ( + I), (* + it), (W + A)- Perform the following subtractions : /3_. 1\ (M 1 \ /814 13\ /430 10 4\ /17 "1\ (i TT/I VTI T*/> (TTT ~~ TT; vtti ~ Tirf/ UT T-) 588 PRACTICAL MARINE ENGINEERING. Note. In the operation of multiplication and division we should always distinguish between the operator and the subject or thing operated on. Thus in 6 times 5, the number 6 is the operator and 5 is the subject. The latter is usually the measure of some quantity. The former is the sign of an operation to be per- formed, and this distinction, which is most important, must not be forgotten. [7] Multiplication of Fractions. We shall first consider the operator as a whole number and the subject as a fraction. Thus suppose that we wish to multiply -% by 6. The operation is exactly the same as if we wished to mul- tiply 5 inches by 6. The result in the latter case is 30 inches and in the former it is 30 twelfths, or as we may write it: f, or by reduction f, or 2^. This illustrates the familiar principle that to multiply a quantity we must multiply its measure, and since in a fraction the numerator is the measure, we multiply the numerator to multiply the fraction. Furthermore, it is plain if we multiply the denominator of a fraction that we 'decrease the size of the fractional unit, and hence with the same numerator or same number of such units we 'decrease the value of the fraction in like proportion. Simi- larly if we 'divide the denominator we increase the size of the fractional unit, and hence with the same numerator or same number of such units we increase the value of the fraction in like proportion. Hence if we can divide the denominator of the fraction by the given multiplier and leave the numerator the same, it will have the same effect as multiplying the nu- merator and leaving the denominator the same. Thus -^ X 3= \-_ This may also be seen by first multiplying the numerator and then reducing to lowest terms. Thus ^ X 3 = -fr = by reduction \. Hence we have the following rule for multi- plying by a whole number : Rule Multiply the numerator of the fraction or divide the denominator of the fraction by the given number. Problems Perform the following multiplications : f X 2, f X 3, A * 4, T V X 6, -If X 7, fi X 12, ^V x 3^- [8] Divisions of Fractions. As before, we first consider the divisor or operator as a whole number, and the dividend or subject as a fraction. Then we may COMPUTATIONS FOR ENGINEERS. 589 remember that division is simply the inverse of multiplication, and that by inverting the procedure for the latter we shall effect the former. Thus to divide -J-f by 2 we divide 18 by 2 and have -^ as the result. Or again we may multiply the denominator, thus dividing the value of the fractional unit and thus dividing the value of the fraction as explained in [7]. Thus -^f -r- 2 = . This being reduced to its lowest terms gives $ as before. The operations on fractions involved in multiplication and division by whole numbers may be summarized as follows : n, , . 1 . ,, f numerator ") ( multiplies ) Multiplying the { denominator } (divides } lts j j. . -,. ( numerator | ( divides ) value, and dividing the ] denominator [ {multiplies} its value. Problems Perform the following divisions : f - 4, 1 - 3, A -*- *, *- 7, M -+- 4, - 3, Hi -*- ii. [9] Multiplication and Division by Fractions. In these operations the operator is expressed as a fraction, and the latter in this case is therefore not the measure of a quan- tity, but the sign of something to be performed. When the frac- tion is used as a multiplier it is simply a short-hand way of ex- pressing two operations (i) a multiplication by the numerator and (2) a division by the denominator. Thus if is used as a mul- tiplier it is simply a short-hand way of expressing a multiplica- tion by 2 and a division by 3. Thus 8 X I is another way of expressing 8X2-^3 or 8-^-3X2. Similarly and since division is exactly the inverse of mul- tiplication, when a fraction is used as a divisor it is simply a short-hand way of expressing two operations : (i) a division by the numerator, and (2) a multiplication by the denominator. Thus if f is used as a divisor it is simply a short-hand way of expressing a division by 2 and a multiplication by 3. Thus 8 -r- | is another way of expressing 8-^2X3 or 8X3-^- 2. When the thing operated on is also a fraction these prin- ciples work out as follows : 5 X i means that f is to be multi- plied by 2 and divided by 5. But we can multiply by multiplying the numerator, and we can divide by multiplying the denomina- tor. Hence 3. x f = ^ = -$ = j\. Hence for the multiplication of 4 x 5 590 PRACTICAL MARINE ENGINEERING. one fraction by another we have the usual rule as follows : Rule Multiply together the two numerators for a new numerator and the two denominators for a new denominator, and the fraction thus formed is the product desired. Similarly for division, f -r- -f- means that f is to be divided by 2 and multiplied by 5. But this is the same as the pair of operations expressed by using 4 as a multiplier. Hence t - 1 = f X f = ; . Hence for the division of one fraction by another we have the usual rule as follows : Rule Invert the terms of the divisor and proceed as in multiplication. This might naturally be expected by remembering the. rela- tion between multiplication and division, and that one is the exact inverse of the other. For the multiplication of a series of fractions into each other these principles work out as follows : If X X f X i means that -J is first considered as a subject and f as an opera- tor. Then the result of this is the subject and f is the operator 1X3X2X5 and so on. The final result will be therefore 2 X 5 tttt, Tttir. TIF. V- [6] To Add Decimals. Set down the decimals in a column so that the points shall all stand under each other. Then add as in whole numbers and bring down the decimal point in the sum under thosev standing above. Example Add .025, .64, .231, .4685, .003. Operation :* .025 .64 .231 4685 .003 1.3675 [7] To Subtract Decimals. Set down the subtrahend under the minuend, the two deci- mal points one under the other, adding ciphers to the right if necessary to fill out to the same number of places. Then sub- tract as in whole numbers and bring down the decimal point qn- der those above. * If desired, the numbers may be filled out all to the same number of places, by adding ciphers on the right, such operation being, in fact, the reduction of the decimals all to the same denominator or unit of measure. In the summing, however, such ciphers play no part, and therefore the filling out is unnecessary in the actual operation. COMPUTATIONS FOR ENGINEERS. 595 Example Subtract .263 from .83. Operation : .830 .263 .567 18] To Multiply Together Two Numbers Expressed Decimally. Multiply as in whole numbers and point off for the decimal portion as many places as there are in the two factors taken together. Examples 16 X 24 = 3-84 72. X .OOO4 =: .0288 . 162 X .O4I = .006642 21. 14 X 13 = 274.82 21. H X 13 = 2.7482 21. H X I 3 = 27.482 Problems Perform the following multiplications : 2.72 X 14 143.26 X 24.2 12.16 X -018 4214.3 X 22.3 .14 X .21 .06 X .0084 [9] To Find the Quotient of Two Quantities Expressed Decimally. Clear both dividend and divisor of decimals by moving" the point to the right an equal number of places in each, adding ciphers as may be necessary. The number of places moved will be that necessary to clear the term of higher order. Thus modified, consider the two terms as whole numbers and proceed with the division, pointing off according to the rule given above for the reduction of a common fraction to a decimal. Examples .16 -5- 2.5 or "J = jfo = .064 1.6 -5- 2.5 or II- = ft = .64 596 PRACTICAL MARINE ENGINEERING. 1.6 - .25 or = Jfli = 6.4 16. -5- .025 or- - = -uy^. = 640. .016 -* 250 or 1 ^ 2irUin> = .000064 1.6 -*- .243 <*~ m W = 6.5761 4- Problems Perform the following divisions : 7.25 - 16 72.54 6.4 .00864 .14400 8.64 .96 1.25 .0144 .024 .0025 Sec. 3. PERCENTAGE. [i] In percentage, fractional reations are expressed deci- mally, but it is understood that the denominator shall always be 100. The fractional unit is therefore always one one-hun- dredth of the principal unit, and therefore occupies to it the same relation as that of the cent to the dollar. The words per cent are commonly represented by the symbol %, so that 16% is the same as 16 per cent or .16, while 5% equals similarly .05, etc. Care must be had not to fall into confusion with the use of both the decimal point and % mark. Thus .4% is not .4, but .4 of one per cent or .004. A number written in percentage is usually an operator, and not a quantity or measure by itself. Thus 16% is not a quantity by itself, but rather expresses the relation between two quantities, or represents an operation to- be performed on one quantity in order to obtain another. The handling of percentages is the same as that of decimals, re- membering that the term per cent is simply a special name for a fractional unit one one-hundredth of the principal unit, what- ever the latter may be, and that it is with this fractional unit that all quantities are measured in percentage operations. Re- membering the rules for decimals we readily see the following : COMPUTATIONS FOR ENGINEERS. 597 Examples i6foof8o =80 X. 16=12.8 3% of 2.1 = 2.1 X .03 = .063 23% of $145.24 = $i45- 2 4 X .23 = $33.4052, or $3341- From the above it follows that : To reduce any number expressed in per cent to terms of decimals, we divide by 100 and express the result decimally, or shift the decimal point two places to the left; while to reduce any decimal to terms of per cent we multiply by 100 or shift the decimal point two places to the right. Thus: .16 = 16.% i .60 = 160.% .016 = 1.6% .0016= .16% To FIND THE PERCENTAGE RATIO BETWEEN Two NUMBERS. Rule Multiply the dividend or numerator by 100 and then divide and express the result as a decimal according to the rules of Section 2 [9]. Thus: 7 -5- 25 or fa = ^% = 28%. Similarly : 3 - 5o or A = 6 % 7 -* 16 <> r = 43-75 6.4 -5- 160 or ' = 4% TOO 6.4-5- 1 6 or ^- = 40% 19 6.4 -T- 1.6 or ' = 400% i .6 6.4 -T- .16 or ' = 4000% . ID In percentage problems it is usually required to find certain percentages of various quantities, or to find the percentage re- lations between various quantities. The only difficulty likely to arise is not with the operations themselves, but with a correct interpretation of the problem and a clear understanding as to the relations desired. 598 PRACTICAL MARINE ENGINEERING. Examples (1) A broker buys a ship for $160,000 and sells her for $172,000. What per cent does he gain? Solution : The amount of gain is $12,000. To find what per cent this is of $160,000 we proceed as above and find 12,000 -- 160,000= ?.$%. (2) A broker buys a ship for $160,000 and sells her so as to gain 6%. What was the selling price ? Solution : Six per cent of $160,000 = .06 X $160,000 = $9,600. Hence selling price = $160,000 + $9,600 = $169,600, (3) A broker sells a 1 , ship for $171,200 and thereby gains 7% on her cost. What was the cost ? Solution : Since he gains 7% or 7 cents on every dollar of cost, there will be $1.07 in the selling price for every $1.00 in the cost price. Hence the cost price will be as many dollars as 1.07 is contained in 171,200 or 160,000. Problems (4) Thirty-six pounds of gun metal contain the following : Copper 32 pounds Tin i pound Zinc 3 pounds Find the percentage composition. Ans. Copper f| or 88 . 89% Tin -jV or 2.78% Zinc -$ or 8.33% (5) A ship starts on a voyage of 2,200 miles. After going 800 miles what per cent of the voyage remains to be. covered ? Ans. 63.6%. (6) A ship starts on a voyage of 1,800 miles. After three days she has made 42% of the distance. With 12% increase of speed for the rest of the time how long will it take her to finish the voyage ? Ans. 6.3754 days. (7) A marine engine requires 2.1 Ibs. of coal per I. H. P. per hour. After certain changes are made the figure is reduced to 1.89 Ibs. What is the percentage gain? Ans. 10%. In one ton of coal (2,240 Ibs.) there was found to be 250 Ibs. of ashes. What per cent of the coal was combustible? Ans. 88.8%. COMPUTATIONS FOR ENGINEERS. 599 Sec. 4. COMPOUND NUMBERS. WEIGHTS AND MEASURES. [i] IfOng or I/inear Measure. Inches. Feet. Yards. Rods. Furlongs. Miles. Meters. i 0833 .0278 .00505 .000126 .000*016 .0254 12 =i 333 .0606 .00152 .000189 305 36 3 .182 00455 .000568 .914 198 i6# S*/* =i .025 .00313 5.029 7920 660 220 40 125 201.166 63360 5-280 1760 320 8 =i 1609.3 39-371 3.281 1.094 .199 .00497 .000621 = i SPECIAL MEASURES. 6 feet = i fathom. 120 fathoms = i cable's length. 6080.27 feet = i nautical mile (United States). 6080 feet = i nautical mile (British). 3 nautical miles = i marine league. [a] Avoirdupois Weight or Measure. Tons. Drams. Ounces. Pounds. Long or Short or Kilos. British. Legal. i 0621 OO^Q 16 j 062^ .02835 256 16 = I .000446 .0005 .4536 573440 35840 2240 i 1. 12 1016 512000 32000 2uOO .89 = I 907 564-38 35-27 2 . 2046 .000984 .OOI IO2 = i [3] Square Measure, Square Inches. Square Feet. Square Yards. Square Meters. i .00694 .000772 .000645 144 = i .IIH .0929 1296 9 = i .8360 i55o 10.765 1.196 = i 6oo PRACTICAL MARINE ENGINEERING. [4] Cubic or Volume Measure. Cubic Inches. Cubic Feet. Cubic Yards. Cubic Meters. i 0005788 1728 46656 61033 = i 27 35-32 037 = i 1.308 .0283 .7645 = i [5] I/iquid Measure. Cubic Inches. Gills. Pints. Quarts. Gallons. Barrels. U.S. British. 8.665 34-659 69.318 231 277.274 "54 = i 4 8 32 32 1008 , .02885 25 =i 2 8 8 252 .0144 .125 50 = i 4 4 126 00433 .03125 125 25 = i 1.2 31/2 .00361 .3125 .125 25 833 3I# .003175 .003175 = i [6] Dry Measure. Cubic Inches. Pints. Quarts. Pecks. Bushels. i 33-6 67.2 537-6 2150.42 .02976 = i 2 16 64 .01488 5 8 32 .00186 .0625 .125 4 .0004641 .01^625 03125 25 [7] Shipping Measure. i register ton = mo cubic feet, i United States shipping ton = \ ^ u^d^es bushels, i British shipping ton = j 4^ fmp^riafbushels. [8] The Metric System of Weights and Measures. MEASURES OF LENGTH. 10 millimeters (mm) 10 ctntimeters 10 decimeters 10 meters 10 dekameters 10 hektometers. . = i centimeter. cm. = i decimeter dm. = i meter m. = i drkameter Dm. = i hektometer Hm. = i kilometer. . ... Km. COMPUTATIONS FOR ENGINEERS. 601 MEASURES OF SURFACE (Nox LAND). 100 square millimeters (mm 2 ). . i square centimeter . . .cm 2 . 100 square centimeters = i square {decimeter. ...dm 2 . 100 square decimeters = i square meter m 2 . MEASURES OF VOLUME. 1000 cubic millimeters (mm 3 ). . . = i cubic centimeter cm 3 . 1000 cubic centimeters i cubic decimeter dm 3 . 1000 cubic decimeters = i cubic meter m 3 . MEASURES OF CAPACITY. 10 milliliters (ml). 10 centiliters 10 deciliters 10 liters 10 dekaliters 10 hektoliters. . centiliter cl. deciliter dl. liter 1. dekaliter.... .....Dl. hektoliter HI. kiloliter . . . . Kl. NOTE. The liter is equal to the volume occupied by i cubic decimeter of pure distilled water at its temperature of maximum density, or 39.2 F. MEASURES OF WEIGHT. 10 milligrams (mg). 10 centigrams 10 decigrams 10 grams 10 dekagrams 10 hektograms 1000 kilograms centigram eg. decigram dg. gram g. dekagram Dg. hektogram. ...... Hg. kilogram Kg. ton.. ..T. NOTE. The gram is the weight of i cubic centimeter of pure distilled water at a temperature of 39.2 F. ; the kilogram is the weight of i liter of water; the ton is the weight of i cubic meter of water. [9] Conversion Tables. ENGLISH MEASURES INTO METRIC. English. Inches to Millimeters. Feet to Meters. Pounds to Kilos. Gallons to Liters. i 25.4001 .304801 45359 3-78544 2 50.8001 .609601 .90719 7.57o88 3 76.2002 .914402 1.36078 ii.35<>32 4 101 .6002 1.219202 i-8i437 I5-MI76 5 127.0003 1.524003 2 . 26796 18.92720 6 152.4003 1.828804 2.72156 22.71264 7 177.8004 2 133604 3-I75I5 26.49808 8 203 . 2004 2.438405 3.62874 30.28352 9 228.6005 2.743205 4.08233 34.0^896 602 PRACTICAL MARINE ENGINEERING. METRIC MEASURES INTO ENGLISH. Metric. Meters to Inches. Meters to Feet. Kilos to Pounds. Liters to Gallons. i 39.3700 . 3-28083 2 . 20462 .26417 2 78.7400 6.56167 4.40924 52834 3 118. i loo 9.84250 6.61386 .79 2 5i 4 157.4800 13-12333 8.81849 1.05668 5 I96.85x) 16.40417 11.02311 1.32085 6 236.2200 19.68500 13.22773 1.58502 7 275 -59 22.96583 15.43235 1.84919 8 314.9600 26.24667 17.63697 2.11336 9 354.3300 29.52750 19.84159 2-37753 USE OF THE CONVERSION TABLES. Example : Change 243.6 feet into meters. 243.6 = 200 4- 40 -f- 3 + .6. These parts separately may all be directly converted from the table by an appropriate use of the decimal point. Thus, keeping simply three places of decimals : 200 feet = 60.960 meters. 40 feet = 12.192 meters. 3 feet = .914 meters. .6 feet = .183 meters. Hence, adding: 243.6 feet = 74.249 meters. Other examples may be solved in an entirely similar manner. [10] Reduction of Compound Numbers. Example (i) Reduce 7 miles, 12 rods, 10 feet to feet. We may proceed in two ways : (a) We may reduce the rods to feet and add in the 10 thus: 12 X i6J + 10 = 198 + 10 = 208. Then reduce the miles to feet and add in the 208 thus: 7 X 5,280 + 208 = 36,960 + 208 = 37,i68 feet; or (b) we may reduce the miles to rods and add in the 12 thus : 7 X 320 + 12 = 2,240 + 12 = 2,252. Then reduce the rods to feet and add in. the 10 thus: 2,252 X i6J + 10 = 37,158 + 10 = 37,168 feet. The result will, of course, be the same in either cas^. The factors for making the reductions may be either taken from the tables of Sec. 4 or readily found by separate com- putation. Example (2) Reduce 37,168 feet to miles, rods and feet. This is the inverse of the above and may likewise be solved in two ways : (a) We may reduce the feet to miles with feet" COMPUTATIONS FOR ENGINEERS. 603 as a remainder, thus: 37,168 ~ 5,280 = 7 miles and 208 feet remainder. Then reduce the feet to rods with feet again as a remainder, thus : 208 -f- i6J = 12 rods and 10 feet remainder. Hence, 37,168 feet 7 miles, 12 rods, 10 feet; or (b) we may reduce the feet to rods with feet as a remainder, thus: 37,168 -f- i6J =: 2,252 rods and 10 feet remainder. Then reduce the rods to miles with rods as a remainder, thus : 2,252 -r- 320 = 7 miles and 12 rods remainder. We have, therefore, as before, 37,168 feet = 7 miles, 12 rods, 10 feet. These examples will sufficiently illustrate the mode of procedure so that all similar problems may be readily solved. ADDITION, SUBTRACTION, MULTIPLICATION AND DIVISION OF COMPOUND NUMBERS. [n] Addition of Compound Numbers. Example Add the following: 16 miles 43 rods 21 miles 308 rods 7 miles 318 rods 44 miles 669 rods 28^ feet or 46 miles 30 rods 12 feet The columns are added as in whole numbers and the sums are brought down. This gives a correct result, but it is not in its simplest form, since 28J feet are more than I rod, and 669 rods are more than i mile. We therefore reduce the feet to rods, giving i rod and 12 feet, and then carry the I to the column of rods, giving 670. We then reduce the rods to miles, giving 2 miles and 30 rods, and carry the 2 to the column of miles, thus giving the final result as stated in the second line of the answer. [12] Subtraction of Compound Numbers. Example In the following subtract the lower from the upper : 3 miles 18 rods 14 feet 21 miles 43 rods 6 feet In the column of rods, the 43 being greater than the 18, we cannot subtract directly, and therefore borrow i mile or 320 rods from the 36 miles, thus putting the minuend into the form as follows : 35 m'les 338 rods 14 feet 2i miles 43 rods 6 feet 14 miles 295 rods 8 feet 604 PRACTICAL MARINE ENGINEERING. We may then subtract each column as in whole numbers, thus giving the result as shown. In the actual operation the borrowing may be done mentally, thus making it unnecessary to rewrite the minuend as shown. [13] Multiplication of Compound Numbers. Example Multiply 14 miles, 276 rods, 12 feet by 5. Operation : 14 miles 276 rods 12 feet 5 feet 70 miles 1,380 rods 60 feet 74 miles 103 rods io feet We first multiply each term by the multiplier 5 and obtain the result entered in the first line below. This is correct, but not in its simplest form, since 60 feet are more than i rod and 1,380 rods more than i mile. We therefore reduce the feet to rods, giving 3 rods and 10^ feet, and carry the 3 to the column of rods, giving 1,383. We then reduce the rods to miles, giving 4 miles and 103 rods and carry the 4 to the column of miles, giving the final result as stated in the second line of the answer. [14] Division of Compound Numbers. Example Divide 142 miles, 296 rods, 15 feet by 6. Operation : 6)142 miles 296 rods 15 feet 23! miles 494 rods 2^ feet We first divide each term separately by the divisor 6 and obtain the result as written below the line. This is correct, but not in its simplest form, since f mile may be reduced to rods and feet, and ^ rod may be reduced to feet. We therefore simplify as follows : 23 49 2 j 213 ii 23 262 13^ Since there are 320 rods in i mile, we have f miles = f x 320 rods = 213 ^ rods. We set down the 213 in the column of rods, and, adding the -g- to the other -^ belonging with the 49, we have f rod in addition. Since there are i6J feet in I rod, we have f rod = f X i6J = n feet. This we enter in the column of feet and add, giving the final result as shown. These examples will sufficiently illustrate the principles in- volved in the addition, subtraction, multiplication and division COMPUTATIONS FOR ENGINEERS. 605 of compound numbers so that all similar problems may be readily solved. Sec. 5. DUODECIMALS. It is often necessary to determine areas or volumes, the dimensions of which are given in feet and inches. To this end we may either reduce the dimensions to feet and decimals, or treat them directly by the method of duodecimals. In this system of expressing numbers, use is made of a series of numerical units, each one-twelfth of the unit of next higher order. The fundamental unit will be either the linear foot, the square foot, or the cubic foot, according to the geometrical nature of the quantity to be expressed. Lengths are thus expressed in feet, inches and twelfths; or, as they are termed feet, primes and seconds. Similarly areas are ex- pressed in square feet, primes and seconds, and volumes in cubic feet, primes and seconds, the prime in each case being one-twelfth the foot, and the second one-twelfth the prime. Duo-decimals should be written with a series of accents thus: 6 7' 10". The stands for the fundamental unit, the foot ; which may be a length, an area or a volume, accord- ing to the problem; the single accent ' stands for the prime, and the double accent " for the second.* Thus, if the unit were a foot of length, the above expression would mean 6 feet, 7 primes or inches, and 10 seconds or -f-| inch. If the unit were a square foot it would mean 6 square feet, T V of a square foot and || of y 1 ^, or y 1 ^ of a square foot. Hence, in all, 6 square feet and 94 square inches. If the unit were a cubic foot it would mean 6 cubic feet, T 7 ? of a cubic foot and T f of y 1 ^ or y 1 ^ of a cubic foot. Hence, in all, 6 cubic feet and 1,128 cubic inches. The importance of noting the character of the fundamental unit is thus clearly indicated. ADDITION OF DUODECIMALS. The addition of duodecimals is carried on exactly as in compound numbers, quantities of the same order being written under each other and their sums, where necessary, reduced to units of higher order by division by 12. * Care must be taken to avoid confusion between this method of writing duo-decimals and the common method of expressing feet and inches by one and two accents. 606 PRACTICAL MARINE ENGINEERING. Example Add I7 <> _ 8 _ I0 " 14 2' - 9" 7 i' 8" Sum: 39 i' 3" SUBTRACTION OF DUODECIMALS. The subtraction of duo- decimals is carried on exactly as in compound numbers, quan- tities of the same order being written under each other and units of a higher order being borrowed where necessary. , MULTIPLICATION OF DUODECIMALS. This operation, which is the one of greatest importance in the treatment of duo- decimals, is carried on according to the following: Rule Set down the two quantities, with terms of the same order under each other. Multiply each term of the multiplicand by each term of the multiplier. The order of any such product will be determined by adding the indices of the two terms used. If the product is greater than 12, reduce to the next higher order by dividing by 12, and set down the quotient and re- mainder in their proper columns. Proceed in this way, taking care in the product to set down terms of the same order under each other. Then add and reduce where necessary to the higher order by dividing by 12. Example Multiply together : 6 _ 10' 4" 4 - 8' 462 3 i 8 24 4 4 31 n' 2" 8'" We have first 8' X 4" = 32'" = 2" 8'", which is set down. We have next 8' X 10' = 80' = 6' 8", which is set down. We have next 8' X 6 = 48' = 4, which is set down. In the same way we use the other term of the multiplier, 4, and then add and reduce the columns as shown. For purposes with which the marine engineer is concerned, feet and inches are alone involved, and operations with duo- decimals are correspondingly simplified. Examples (i) Find the area of a boiler plate 12 5' long by 6 f wide. Multiplying as before, we find for the product 81 8' n", or taking the result to the nearest prime, 81 -9' or square feet or 81 square feet 108 square inches. COMPUTATIONS FOR ENGINEERS. 607 (2) Find the volume of a bunker 26 4' by 9 7' by 7 10'. Taking first the product of 26 - 4' by 9 7' we have 252 - 4' 4". Then multiplying this by 7 - - 10' we have 1,976 10' 1 i" 4"', or taking the result to the nearest prime, 1,976 -n', or 1,976 H cubic feet or 1,976 cubic feet 1,584 cubic inches. Sec. 6. RATIO AND PROPORTION. [i] Simple Proportion. The ratio between two numbers is simply their numerical relationship expressed as the quotient of the first divided by the second. Thus the ratio of 6 to 3 is 2; of 1.2 to 3 is .4; of 4 to 5 is .8, etc. Ratio is often expressed by the sign : which is simply an abbreviation of the sign of division -H. Thus 6 : 3 = 2; 1.2 : 3 = .4, etc. Ratio is also expressed by the sign of division or in the form of a fraction. Thus 6:3 or 6 H- 3 or f 2 1.2 : 3 or 1.2 -T- 3 or ^-^ = .4, etc. [i] A proportion is a statement of the equality of two ratios. The equality is commonly expressed by the symbol : : Thus: 6 : 3 : : 4 : 2 (i) A proportion may also be written in other ways, as follows : 6:3 = 4- 2 (2) I = * (3) A proportion always contains four terms, two for each ratio, and when written as in (i) and (2) the first and last terms are called extremes and the second and third are called means. To solve a proportion three terms must always be known and then the remaining term can always be found. From the na- ture of a proportion it follows that the product of the. extremes must equal the product of the means, and this gives the usual rule for solution as follows : Rule If the unknown term is an extreme, multiply to- gether the two means and divide by the other extreme. If the unknown term is a mean, multiply together the two extremes and divide by the other mean. In either case the quotient will give the remaining term desired. In a proportion two of the terms always relate to one kind of quantity, while the other two relate to another. Likewise two of the terms always relate to one set of conditions, while 6o8 PRACTICAL MARINE ENGINEERING. the other two relate to another set. In problems to be solved by proportion, therefore, where three terms must be given, two terms will be of one kind and the remaining term will be of another and of the same kind as the answer. Also two terms will relate to the given set of conditions, and the remaining term to the set involving the unknown term or answer. Again, proportions are of two kinds, direct and inverse. In a direct proportion the relation between the two quantities different in kind is such that both increase or decrease to- gether. In an inverse proportion the relation between these two quantities is such that one increases as the other decreases. Thus if the question involves the relation between distance and speed, the time being the same, the proportion is direct, be- cause, for a given time, the more speed the more distance, or the more distance the more speed. On the other hand, if the question involves the relation between speed and time for a given distance, the proportion is inverse, because for a given distance the more speed the less time, or the more time the less speed, and vice versa. Our general knowledge of the relation between the quantities involved will thus enable -us to determine whether the proportion will be direct or inverse. Example of a direct proportion : If a ship steams 1,400 miles in 5 days, how far will she steam in 8 days at the same rate? Here two of the given terms are days and one is miles, be- ing of the same character as the answer desired. Also two relate to one performance or set of conditions (1,400 in 5 days), while the other relates to another set (the desired performance in 8 days). Our right to solve this example by direct propor- tion lies in the fact that the relation between the 5 days and 1,400 miles must be the same as that between the 8 days and the distance desired, and hence there must be an equality in the ratios showing these relations, and similarly for problems of like character. A simple direct ( proportion, like that involved in the ex- ample above, may be stated in various ways, of which two will serve our present purpose. (2) (2) (I) (I) (a) Ans. (miles) : 8 (days) : : 1400 (miles) : 5 (days) (2) (i) (2) (i) (b) Ans. (miles) : 1400 (miles) : : 8 (days) : 5 (days) COMPUTATIONS FOR ENGINEERS. 609 The numbers in ( ) relate to the two sets of conditions, the first being the set given, and the second being the set for which the distance is desired. It is thus seen that the proportion may be stated as in (a), with each set of conditions forming a ratio, the items of proportion alternating : miles, days, miles days ; or it may be stated as in (b), with the set of conditions alternating 2d, ist, 2d, ist, the two items of each ratio being the same. Example of an inverse proportion : If a ship at 10 knots does a certain trip in 5 days, how many days will be required at 12 knots? The relation between time and speed, as we know, is such that, for a given distance, the more speed the less time, or the less speed the more time. The time is, therefore, said to be in such case inversely proportional to the speed. That is, for ex- ample, if the speed is doubled the time will be halve'd, etc. An inverse proportion may be stated as follows : (2) (I) (I) (2) (c) Ans. (days) : 10 (knots) : : 5 (days) : 12 (knots) (2) (I) (I) (2) (d) Ans. (days) : 5 (days) : : 10 (knots) : 12 (knots) The difference between these methods of statement and those above for direct proportion will be readily seen by com- parison. As another general way of stating a proportion whether direct or inverse we may proceed as folows : Put the anszver, or letter representing it, for the first term, and the other quantity of the same kind for the second term. Then, according as the first term or answer should be greater or less than the second term, write the third and fourth terms in the same order. That is if the relation of the quantities is such that the answer should be greater than the second term, write the third and fourth terms in the order greater lesser: or if the answer should be less than the second term, write the third and fourth terms in the order lesser greater. After having become familiar with the methods of stating a proportion, the names of the quantities and the numbers de- noting the sets of conditions may, of course, be omitted, and we should have instead of (a) and (b) Ans. : 8 : : 1400 : 5 Ans. : 1400 : : 8:5 6io PRACTICAL MARINE ENGINEERING. Solving either of these according to the rule given, we have: Distance = 8 X 1400 -=- 5 = 2240 ans. Likewise instead of (c) and (d) we should have : Ans. : 10 : : 5 : 12 Ans. : 5 : : 10 : 12 Solving either of these we have : Days 5 x 10 -5- 12 = 50 -i. 12 = 4^ Ans. [2] Compound Proportion. In many cases the result depends on more than one chang- ing condition. In such case the problem is treated by the method of compound proportion as iljustrated in the following example. When coal is $4.20 per ton the fuel bill for a ship requiring 34 tons per day on a voyage of 2,100 miles is $1,020. At the same speed what would be the bill on a 2,8oo-mile voyage, with coal at $3.60 per ton, and a consumption of 40 tons a day? The resulting cost evidently depends on three conditions, and the proportion is stated as follows : 3.60 : 4.20 Ans. : 1020 : : 40 : 34. 2800 : 2100 This consists really of three simple direct proportions, each stated exactly according to the rules already given, as may be readily seen. For the solution of such a proportion the same rules may be used, but the "product of the means" or the "product of the extremes" must here be understood to mean the product of all the separate numbers forming these terms. Thus for the foreging proportion we multiply together the means and divide by the extremes, giving as follows : Ans. =3.6o x 4 X 2800 x 102 = $ I37I . 43 . 4.20 X 34 X 2100 Cancellation can usually be made to assist in the reduc- tion of such expressions, and we thus readily find the answer as stated. Where the relations are such that the answer is inversely proportional to certain of the varying conditions, the ratio in- volving these conditions must, of course, be so stated as to make this part of the proportion inverse instead of direct. In COMPUTATIONS FOR ENGINEERS. 611 fact, each of the ratios in the second part of the proportion should be carefully examined in order to make sure whether it should be stated direct or inverse. Example involving both direct and inverse proportion: When coal is $4.00 per ton, the fuel bill for steaming a certain distance at a speed of 12 knots, with a ship requiring 48 tons per day, is $1,800. For the same distance, what would be the bill if the ship steams 10 knots on 40 tons per day, with coal at $3.20 per ton? The statement would be as follows: 3.20 : 4.00 (direct) Ans. : 1800 : : 12 : 10 (inverse) 40 : 48 (direct) In this case we have : Ans. = x 3- 2 ^_X I2 X 4Q 4.00 x i X 48 PROBLEMS IN PROPORTION. (1) An engine with 34 Ib. mean effective pressure gives 1,400 I.H.P. All other conditions remaining the same, what would the engine give with 39 Ib. mean effective pressure? Ans. i ,606 I.H.P. (2) An engine making 98 revolutions per mt. gives 1,800 I.H.P. All other conditions remaining the same, what would the engine give if the revolutions were 90? Ans. 1,653 I.H.P. (3) An engine with stroke of 3 ft. gives 900 I.H.P. All other conditions remaining the same, what would be the power with stroke of 42 in.? Ans. 1,050 I.H.P. (4) An engine cylinder whose area is 1,200 sq. in. gives 800 I.H.P. All other conditions remaining the same, what would be the power with an area of 1,000 sq. in.? Ans. 666.67 I.H.P. (5) A given engine has mean effective pressure 33, revolu- tions 120, stroke 42 in., and gives 1,800 I.H.P. Other condi- tions remaining the same, what would be the power with a mean effective pressure of 38, revolutions of 100 and stroke of 4 ft.? Ans. 1,974 I.H.P. 612 PRACTICAL MARINE ENGINEERING. (6) A boiler with tubes 7 ft. long, and 2^4 in. diam., has 2,168 sq. ft. of tube-heating surface. What would be the sur- face, with the same number of tubes, 7 ft. 6 in. long and 2^2 in. diam.? Ans. 2,112 sq. ft. (7) An engine with 34 Ibs. mean effective pressure and 98 revolutions develops a certain power. If the mean effective pressure were 38 Ibs., what revolutions would give the same power? Ans. 87.7 rev. (8) A given engine has a mean effective pressure 33, revo- lutions 120, stroke 42 in., and develops a certain power. With mean effective pressure of 38 and stroke of 3 ft., what would be the revolutions for the same power? Ans. 121.6 rev. (9) A pump making 40 double strokes per mt. can empty a tank in i| hrs. In what time could the same pump, making 30 double strokes per mt., empty a second tank, 20 per cent larger than the first? Ans. 2.4 hours. (10) A propeller at 100 revolutions and 20 per cent slip gives a speed of 18 knots. What will be the speed at 120 revo- lutions and 25 per cent slip? Ans. 20.25 knots. Sec. 7. EVOLUTION AND INVOLUTION.* [i] EVOLUTION is the operation of raising a number to successive powers, or of multiplying it into itself as a factor a certain number of times. The number of times the number is used as a factor is called the index of the power, and is indicated by a small figure written to the right and above as follows : 4 2 = 4 X 4 = 16 5 3 = 5 X 5 X 5 = ^5 3 5 = 3X3X3X3X3 = 2 43 Evolution involves, therefore, simply continued multiplica- tion. The powers most commonly used by the engineer are * Hand books with convenient tables of powers and roots are so com- mon at the present day that the engineer has small use for the actual operations of raising to powers or of extracting roots. In practice the use of such tables is always counseled as tending toward accuracy and speed. The importance of these operations, however, merits a brief outline of the process as given herewith. COMPUTATIONS FOR ENGINEERS. 6i3 the second and third, or square and cube, as they are commonly called. INVOLUTION is the inverse of evolution, and consists in finding a number which, used on itself as a factor a certain number of times, will produce a given number. The former is then called the root of the latter. The number of times the root is used as a factor is called the index, and is represented either by writing this number at the upper left hand angle of the sign of involution, \/ , or by the use of a fractional index, written as in evolution. The roots most commonly used by the engineer are the square and cube roots, corresponding to the second and third or square and cube powers. When square root is indicated by the symbol y , it is customary to omit the 2 from the upper angle. Thus we have : 3 1/27 or (27)4 = 3 because 3 x 3 X 3 = 2 7- 1/49 or (49)2 = 7 because 7 x 7 = 49- Occasionally the engineer has to deal with the index -f. which is simply a short way of indicating two operations, (i) Raising to the square. (2) Extracting the cube root. Thus 64! means the 3d root of the 2d power of 64, or the 2d power of the 3d root of 64. Either order of operation will give the same result. Thus: (64) 6 = 1/64 x 64 = 1/4096 = 16 '2 3 2 or (64) 3 = (1/64) = 4 2 = 16 [2] To Extract the Square Root. This is best illustrated by an example. Find the square root of 746.2. Rule* (i) Point off the given number into periods of two figures each, beginning at the right or at the decimal point, if there is one, and in the latter case point both ways, adding ciphers on the right of the decimal as may be necessary to complete the periods. Thus: * The brackets [ ] contain the numbers in the example which corre- spond to the special indication of the rule, and thus make its application to the given case more easily followed. *i 4 PRACTICAL MARINE ENGINEERING. Number Pointed off. 2643 26-43 867 8-67 424-362 4-24.36-20 . 024 .02-40 .6 60 (2) Write a o on the left, thus heading two columns (i) and (2), as shown. Find by trial the greatest number [2] which when squared is equal to or less than the left hand period. Put this on the right as the first figure of the root. (I) (2) o 7-46.20(27.316 4- 2 4 2 346 2 329 40 1720 7 1629 47 9120 7 546i 540 3639 00 3 543 3 5460 i 54620 (3) Place this figure [2] under the o in col. (i) and add. Multiply the sum [2] by the root figure [2], and place the product [4] Under the left hand period in col. (2). This product will be, of course, the square of the root figure. Subtract and bring down the next period for a partial dividend [346] . (4) Again place the root figure [2] on the left and add [4] . Annex a o and the result [40] will be a trial divisor for the next root figure. (5) Divide and take on trial the resulting whole number for the next root figure [7]. (6) Bring down this figure [7] in col. (i) under the o. Add and multiply the sum [47] by the same root figure [7] and place the product [329] in col. (2) under the partial dividend. Subtract and bring down as before for a new partial dividend [1720]. COMPUTATIONS FOR ENGINEERS. 615 (7) Place the root figure [7] again in col. (i), add and annex a cipher for a new trial divisor [540]. (8) Find another root figure as before and proceed in this manner till as many figures are obtained as are desired. If the product found, as in (6), is greater than the partial dividend, it indicates that the trial figure was too great, and the next lower must be taken. If at any time the trial divisor is greater than the partial dividend, enter a o in the root, bring down the next period in col. (2) for a new partial dividend, an- nex a o on the right in col. (i) for a new trial divisor and pro- ceed as before. [3] To Extract the Cube Root. This is best illustrated by an example. Find the cube root of 12.593. (i) (2) (3) o o 12.593 (23.26 2 4 8 2 " 4 4593 2 8 4167 4 66 1200 426000 2 3 189 320168 60 690 1389 105832000 J _! I9 63 692 158700 3 2 1384 694 160084 2 1388 6960 I6I47200 Rule Point off the given number into periods of three figures each, beginning at the right or at the decimal point, if there is one, and in the latter case point both ways, adding ciphers on the right of the decimal as may be necessary to com- plete the periods. Thus : Number Pointed Off. 1724 I'724 17243 17*243 I7-24 17.240 .64 . 640 . 0032 . 003 ' 2OO (2) Write ciphers on the left thus, heading the columns (i), (2) and (3), as shown. Find by trial the greatest number [2] which when cubed is equal to or less than the left hand period. Put this on the right as the first figure of the root. 616 PRACTICAL MARINE ENGINEERING. (3) Place this figure under the o in col. (i), add, multiply sum [2] by root figure [2], place product [4] in col. (2), add, multiply sum [4] by root figure [2] again, and place product [8] in col. (3) under left hand period. This product will be, of course, the cube of the root figure. Subtract and bring down the next period for a partial dividend [4593]. (4) Again place the root figure [2] in col. (i), add, multiply sum [4] by root figure, put the product [8] in col. (2), and add [12]. (5) Again place the root figure [2] in col. (i), and add as before [6] . (6) Annex one o to the result in col. (i) [60] and two os to that in col (2) [1200] . The latter is then a trial divisor for the next root figure, which is thus seen to be probably 3. (7) The same process of bringing down, adding and multi- plying in cols, (i), (2) and (3) is then repeated as just described, and as shown in the example. Continue in this w r ay until as many figures of the root are found as are desired. If the final product to be entered in col. (3) is greater than the partial dividend, it indicates that the trial figure was too great, and the next lower must be taken. If at any time the trial divisor is greater than the partial dividend, enter a o in the root, bring down the next period in col. (3) for a new partial dividend, annex one o in col. (i) and two os in col. (2) for a new trial divisor, and proceed as before. It will be noted lhat in these methods for square and cube root the former requires for each root figure two operations in col. (i) and one in col. (2), while the latter similarly requires three operations in col. (i), two in col. (2), and one in col. (3). Care should be taken that none of these are omitted, and that the entire process is carried through with regularity and order. Sec. 8. MATHEMATICAL SIGNS, SYMBOLS AND OPERATIONS. Mathematical signs are simply shorthand methods of indicating mathematical language. Those most commonly met with are the following: + The sign of addition called plus. This means that the two numbers or quantities between which it is placed are to be added. Thus 12 + 3 is read 12 plus 3 and means that 12 and 3 are to be added, the result being 15. COMPUTATIONS FOR ENGINEERS. 617 The sign of subtraction called minus. This means that the number or quantity which follows the sign is to be subtracted from that which precedes it. Thus 12 3 is. read 12 minus 3 and means that 3 is to be taken from 12, the result being 9. X The sign of multiplication. This means that the two numbers or quantities between which it is placed are to be mul- tiplied together. Thus 12 X 3 is read 12 times 3 or 12 multi- plied by 3, the result being 36. -r- The sign of division. This means that the number or quantity which precedes the sign is to be divided by that which follows. Thus 12 -r- 3 is read 12 divided by 3, the result being 4. / A sign of division. A fraction is really a mode of ex- pressing division, and a common way of writing a fraction all in one line is to make use of the oblique line. Thus 12/3 means the same as -^ or 12 -f- 3 or 4. Frequently the horizontal line as shown is used, thus: ^, ^, 1-2 all indicate one-half, or I divided by 2. The horizontal line used in this connection must not be confused with the minus sign ; usually the sense is plainly indicated by the connection in which it is used. . Placed before and in line with the bottom of a number is a decimal point, showing that the number is the numerator of a fraction which has some power of 10 for its denominator; as .1 = T V -25 = T \\, which reduced to its lowest terms is 1-4. See section 2. : The sign of ratio. This signifies the ratio or numerical re- lationship of the two quantities between which it is placed, and is equivalent to a sign of division, since the quotient of the first quantity divided by the second is the measure of the ratio be- tween them. Thus 12 : 3 is read the ratio of 12 to 3 or 12 is to 3, and the real measure of this ratio is 12 -f- 3 or 4. The sign of proportion or equality of ratios. This sign is placed between two ratios and signifies that they are equal. Thus 12 : 3 :: 20 : 5 is read 12 is to 3 as 20 is to 5, or the ratio of 12 to 3 equals the ratio of 20 to 5. This is seen to be the case since 4 is the measure of each ratio. = The sign of equality. This signifies that the two quanti- ties separated by the sign are equal in value. Thus 12-^3 = 4 is read 12 divided by 3 equals 4, and thus states the equality be- tween the two sides of the relationship. 618 PRACTICAL MARINE ENGINEERING. Equation. Two quantities or expressions related by the sign of equality, =, form an equation. Thus 4 + 2 = 6 a = 3 a + b c ( ), [], i. Parentheses or brackets. These symbols mean that all numbers or quantities within a parenthesis or pair of brackets are to be considered as one quantity and thus treated in all numerical operations. Thus 2 (3 + 4) means that 3 + 4 is to be taken as the single quantity 7, and then multiplied by 2. Similarly 2 ( 3+4 2)=io 3 [16-2 (3+4-2)] =18 NOTE: The sign multiplication, X, is often omitted between a number and a parenthesis or bracket containing a quantity into which it is to be multiplied, as in the expressions here shown. In some cases a bar or vinculum is drawn over numbers thus to be taken together. Thus 2X3 + 6 means 2 multiplied by the quantity 3 + 6, or 2 X 9> or 18. The difference between 2X3 + 6 and 2X3 + 6 or 12 will be noted. In reducing quantities thus affected by the signs +, , X, -r- and connected by brackets, the difference in significance between the sign +, and X -r- must be carefully noted. Thus 2X3 + 6 means 2 times 3 added to 6 or 12 and not 2 times (3+6) or 18. As a general principle, it may be remembered that the signs + and effect a separation of the expression into separate terms, while the signs .X and -r- bind together the two quantities between which they stand into a single term. Examples These principles are further illustrated by the following : 3X16 2X3 + 4--2 + 4X3-- 1 =55 3[i6 2 x 3 + 4 2 + 4 X 3 -- i] = 69 3[i6 2 (3 + 4) - - 2 + 4 (3 - - i)] =26 3fi6 2 (3 + 4 - - 2)] + 4 (3 - - i) = 24 I/' This sign placed over a quantity denotes the extraction of a root. If no number is placed at the upper left angle, it denotes the square root; otherwise a root corresponding to the index thus indicated. Thus |/ 49 denotes the square root of 49 or 7, ->/ 2 7 COMPUTATIONS FOR ENGINEERS. 619 4 denotes the cube root of 27 or 3, 1/76 denotes the fourth root of 1 6 or 2, etc. 3 2 or 4 3 or a 4 . A small number written to the right and above another number or quantity is called an index or exponent, and signifies that the lower number or quantity is to be used as a factor on itself a number of times equal to the index. Thus : 3 2 = 3 X 3 = 9 43 = 4X4X4 = 64 a 4 = aXaXaXa ' " These signs set to the right and above any figure or figures (superior) signify feet and inches. These signs are much used in dimensioned drawings. J__ Signifies perpendicular to. (_ Signifies .angle. L Signifies right angle. . *. Signifies hence or therefore. '.' Signifies because. TT Denotes the ratio between the circumference and diameter of a circle. Its value is usually taken as 3.1416. G Square sometimes used in denoting pressures ; as 220 Ibs. per D" or per square inch. % Signifies per centum or per hundred. FORMULAE. A formula is simply a brief way of denoting a series of mathematical operations. Once understood, the directions given by a formula are much more readily followed than when given in the form of a rule. In fact a formula may be considered as simply a brief or short hand way of expressing the same direc- tions as are given by the rule in ordinary words. In formulae, quantities are usually represented by letters, as in the well- known horse power formula : LH P - 2 P LA N 33,000 In this formula p denotes the mean effective pressure per square inch of piston area, L the length of stroke in feet, A the piston area in square inches, and N the revolutions per minute. In thus writing letters to represent quantities the sign of multiplication, X, is usually omitted. Thus in the foregoing the numerator 2 p L A N means the same as 620 PRACTICAL MARINE ENGINEERING. or that the continued product is to be taken of these five factors. It must be noted, however, that where both factors are numbers the sign for multiplication cannot be omitted. Thus, 23 does not mean 2 X 3, but 20 + 3 or 23. Division may be expressed by the usual sign, but it is more commonly indicated by writing the dividend as the numerator and the divisor as the denominator of a fraction. Or in general we multiply by putting a factor in the numerator, and divide by putting a factor in the denominator. Thus in the horse power formula the product 2 p L A N is to be divided by 33,000. As a further illustration, take the formula P- 7 ^ ~ 6A! In this formula p is the pressure per square inch in a boiler, T is the tensile strength of the material of the shell, t is the thick- ness of the plate, and R is the half diameter or radius of the shell. The whole gives the pressure per square inch allowed by U. S. rules on marine boilers. The formula directs us, in order to find the desired pressure, to multiply together T and t and to divide the product by 6 times R', or, in the words of the U. S. rule : "Multiply one-sixth of the lowest tensile strength . . . by the thickness . . . and divide by the radius or half diameter." In this formula all dimensions are in inches and the result is the pressure per square inch allowed on the boiler. Thus let T = 60,000, t 1/4 in. and R = 6 feet or 72 in. Then : 60,000 x 1.2=5 -, . 7 p - -=174 pounds per square inch. Take again the formula In this formula p is the pressure per square inch allowed on a flat surface of a boiler supported by staybolts, t is the thickness of the plate expressed in sixteenths, and L is the pitch of the bolts, or distance from center to center. The formula thus directs us to multiply 112 by the square of the thickness of the plate in sixteenths, and then to divide the product by the square of the pitch of the bolts. Thus let the thickness be 9-16 in. and pitch be 7 in. Then we have : / II2 X 9 X 9 _ l85 pounds per square inch. COMPUTATIONS FOR ENGINEERS. 621 Sec. 9. GEOMETRY AND MENSURATION.* [i] Square. A square is a figure, such as A B C D, having four sides all equal, and four angles all equal, each being a right angle. DIAGONAL, A C. To find the length of a diagonal, A C, hav- ing given a side of the square, as A B : B C Rule Square the side, multiply by 2, and take the square root; or A C = 512 = or Rztle Multiply the side by 1.4142. Example: A B = 16. Then A C = V 2 x 256 = 22.627, or A C 16 x 1.4142 = 22.627. AREA, A B C D. To find the area of a square, having given the length of a side, as A B : * The following definitions are here given as introductory to this sec- tion. Other definitions will be given as the terms are introduced. An angle is formed when two lines, O A and O B, having different directions meet in a point, as O. The angle refers, then, to the difference in direction of the two lines, and its measure is a measure of such difference in direction. An angle is usually denoted by three letters, the one at the apex being placed between the other two. Thus, in Fig. a the angle would be called A O B or B O A. D When a line, CD, meets another line, A B, in such a way that the four angles at E are all equal, the two lines are said to be perpendicular to each other, or, in more common terms, one line is square with the other. An angle such as those formed at E is called a right angle. An angle less than a right angle, as A O B, Fig. a, is called an acute angle. An angle greater than a right angle, as F E B, Fig. b, is called obtuse angle. an 622 PRACTICAL MARINE ENGINEERING. Rule Square the side, or multiply it by itself; or Area - AH? = A B x A B. Example: A B 6. Then area = 6 x 6 = 36. [2] Rectangle. A rectangle is a figure, such as A B C D, having four sides, the opposite sides being equal and parallel (A B = D C and B C = A D), and four angles all equal, each being a right angle. DIAGONAL, B D. To find the length of a diagonal, B D having given the two sides, as B C and C D : Rule Square the two adjacent sides, add, and take the square root; or B D Example : B C = 6, C D = 8. Then B D = V 36 + 64 \/ 100 10. AREA, A B C D. To find the area of a rectangle, having given the two sides, as A B and A D : Rule Find the product of the two adjacent sides ; or Area = A B X A D. Example: A B = 6, A D == 8. Then area = 6 X 8 = 48. [3] Parallelogram. A parallelogram is any figure, such as A B C D, having four sides and four angles, the opposite sides being equal and parallel, and the oposite angles being equal. AREA, A B C D. To find the area of a parallelogram, hav- ing given a side and the perpendicular distance between this and the side opposite : COMPUTATIONS FOR ENQINEERS. 623 Rule Multiply one side by the perpendicular distance be- tween it and the side opposite : or Area = A D X E F ; = also A B X G H. Example: A D = 16, E F = 9. Then area = 9 X 16 : 144. [4] Trapesoid. A trafezoid is any figure, such as A B C D, having four sides and four angles, two of the sides, as B C and A D, being parallel. AREA, A B C D. To find the area of a trapezoid, having given the parallel sides and the perpendicular distance between them : B E c Rule Multiply the half sum of the parallel sides by the perpendicular distance between them, or Area 'B C + A D ) X E F. Example: B C= 10, A D = 16, E F = 8. Then aiea = -L l6\ ) X 8 = 104. [5] Triangle. A triangle is any figure, such as A B C, having three sides and three angles. In a triangle placed as in the figure, A C is called the base, and B D the perpendicular distance from B to A C is called the altitude. ANY SIDE, A B. To find the length of any side, having given the triangle complete : 624 PRACTICAL MARINE ENGINEERING. Rule Square the other two sides and add, and according as the angle between them is greater or less than 90 degrees, add or subtract twice the product of one of these sides by the projection* of the other upon it. Then take the square root of the result thus found; or A B = V A C B C - 2 A C x DC. Similarly B C = V A B 2 + A C 2 - 2 A C X A D, C = ^~A~B* + B~C + 2 B C x B E. Example: A C = 12, B C = 9, D C = 8. Then A-B = ^/ 144 + 81 _ 2 X 12 X 8 = \/~33~= 5-745- AREA. To find the area of a triangle, having given the triangle complete, or any side and its perpendicular distance from the opposite vertex : Rule Multiply any side by the perpendicular distance from the opposite vertex to such side (produced, if necessary, to meet the perpendicular), and take half the product thus found; or take half the product of the base by the altitude; or Area = y* (A C X B D), = y* (B C X A E), = y 2 (A B X C F). Example: A C = 120, B D = 32. Then area = % (120 X 32) = 1,920. [6] A Right-Angled Triangle. In a right-angled triangle one of the angles, as C, is a right angle. The side opposite is called the hypothenuse. HYPOTHENUSE, A B. To find the length of the hypoth- enuse, having given the other two sides : Rule Square the other two sides and add, and take the square root of the sum; or A B = V ATC* +~B~C a . Example : A C = 9, B C = 1 2. Then A B = 81 + 144 = ^225 = 15. SIDE A C or B C. To find the length of one of the sides about the right angle, having given the hypothenuse and the other side: * Let B D be drawn perpendicular to A C. Then D Cis called the projection of B Cupon A C. Similarly A D is the projection of A B upon A C, A .Fthe projection of A C upon A B produced, and E C the projec- tion of A Cupon B C produced. COMPUTATIONS FOR ENGINEERS. 625 Rule Square the hypothenuse and the given side. Subtract the squares, and take the square root of the difference ; or A C ^ A If - B C. Example: A B = 15, B C = 12. Then A C = 225 H4 = v Bi = 9 AREA, ABC. To find the area of a right-angled triangle, having given the two sides about the right angle : B Rule Multiply together the two sides about the right angle, and take half their product ; or Area = y 2 (A C X B C). Example: A C = 9, B C = 12. Then area = ^ (9 X 12) = 54. These rules are special cases of those for the general tri- angle, as in [5]. [7] Trapezium. A trapezium is a figure, such as A B C D, having four angles and four sides, no two of the latter being parallel. AREA, A B C D. To find the area of a trapezium, having given the figure complete : Rule Divide the trapezium into two triangles, and proceed with each separately, and then add. A ** - K3 A * --- [8] Regular Polygons. A regular polygon is a figure, such as A B C D E, having any number of equal sides and a like number of equal angles. They are named as follows : 626 PRACTICAL MARINE ENGINEERING. Number of Sides. Names. 3 Triangle 4 Square 5 Pentagon 6 Hexagon 7 Heptagon 8 Octagon 9 Nonagon 10 Decagon AREA. To find the area of any regular polygon, as A B C D E, having given the figure complete : R u l e Divide the polygon into as many triangles as there are sides, the apexes all being at the center. Find the area of one of these, and multiply by the number of sides. [9] Irregular Figures. AREA. To find the area of a figure, such as A B C D E F G having given the figure complete : Divide into triangles in any convenient way; pro- ceed with each separately, and add the results. [10] Circle. A circle is a figure bounded by a curved line, every point of which is equally distant from a point within, called the center. The distance across from one side to the other through the center is called the diameter (see A B or F G). The diameter is usually represented by D. The distance from the center to the curved boundary line is called the radius, and is plainly one- half the diameter (see A C, F C, etc.). The radius is usually represented by r. The curved boundary line A F H B G K A, is called the circumference. Any part of the circumference, as A F, F H, etc., is called an arc. COMPUTATIONS FOR ENGINEERS. 627 CIRCUMFERENCE. To find the circumference, having given the diameter: Rule Multiply the diameter by 3.1416, or more exactly by 3.1415927, or less exactly by *-f-. This ratio is frequently denoted by the symbol >r. or Circumference = 3.1416 X Diameter ^ D. Example: Diameter = n. Then circumference = n X 3.1416 = 34o576. DIAMETER. To find the diameter, having given the cir- cumference : Rule Divide the circumference by 3.1416, or more exactly by 3.1415927, or less exactly by - 2 T 2 -. or Diameter = Circumference -I- 3.1416, or Diameter Circumference x -31831. Example: Circumference = 48.7. Then diameter = 48.7 -f- 3.1416 = 15.50 + AREA, A H B K. To find the area of a circle, having given the diameter or the radius : Rule Multiply the square of the diameter by .7854, or 3.1416-7-4. or multiply the square of the radius by 3.1416, or find half the product of the radius by the circumference, or Area == .7854 x (Diameter) 2 - 4 = 3.1416 x (Radius) 2 = TT r\ J (Radius x Circumference). Example: Diameter = 10. Then area = .7854 X 100 = 78-54- , LENGTH OF ARC. To find the length of an arc, as A F, having given the corresponding number of degrees and the cir- cumference or diameter : Rule Divide the circumference by 360, and multiply by the number of degrees in the arc ; 628 PRACTICAL MARINE ENGINEERING. or multiply the number of degrees by .008727 and the product by the diameter, _ Circumference r or Length A F = - ,- X (Number of Degrees) or Length A F = (Number of Degrees) X .008727 X Diameter. Example: Find the length of an arc of 60 degrees in a circle whose diameter is 20. Length = 60 X .008727 X 20 = 10.4724. [n] Circular Ring or Annulus. The surface lying between two circles, as shown by the shaded part of the figure, is called a circular ring or annulus. AREA. To find the area of a circular ring, having given the radii of the two circles : Rule- Find the difference between the areas of the two circles, or Area = 3. 1416 1J7T-- 3.141670 == 3.1416 (U~B - OA 2 .) [13] Sector of Circle. The surface lying between two radii and the corresponding part of the circumference, as shown by the shaded part of the figure, is called the sector of a circle, or a circular sector. A AREA, ABO. To find the area of the sector of a circle, having given the corresponding number of degrees and the diameter: Rule Find the area of the entire circle, divide by 360, and multiply by the number of degrees in the sector; COMPUTATIONS FOR ENGINEERS. 629 Area of Circle ,. or Area = - - (Number of Degrees in Sector) ; or, by proportion, 360 : Number of Degrees in Sector : : Area of Circle : Area of Sector; or, otherwise, find half the product of the arc by the radius, or Area = y 2 (O A X A B). Example: Find the area of a sector of 60 degrees in a circle whose radius is 10. Area of entire circle = 78.54, hence Area = l$ x 60 = Ljl* _i 3.09. 360 6 [13] Segment of Circle. A line, such as A B, cutting across a circle is called a chord. A part of the surface of a circle between a chord and the cir- cumference, as shown by the shaded part of the figure, is called a segment of a circle. C %>. B AREA, A C B. To find the area of the segment of a circle, having given the angle, A O B, and the diameter or radius of the circle : Rule Find the area of the sector, O A C B, as in [12], and of the triangle O A B, as in [5], and subtract the latter from the former, or Area = % (A C B X O A O E X A B). Example: O A = 10, O E = 5, A B = 17.32, A C B = 20.944, then Area */ 2 (20.944 X 10 5 X 17.32) = 61.42. [14] Ellipse. If the surface of a circle, as shown by the dotted line, be uniformly stretched in one direction (horizontal in the figure) until the diameter, A, B,, becomes equal to A B, the circum- ference will be changed into a curved line, A C B D, and the figure thus formed is called an ellipse. The two lines, A B and C D, are called the diameters of the ellipse. <6 3 o PRACTICAL MARINE ENGINEERING. AREA, A C B D. To find the area of an ellipse, having .given the two diameters : Rule Multiply the product of the two half diameters by or Area = 3.1416 X O C X O B. Example: O C = 5, O B = 8. Then area = 3.1416 X 5 X 8 = 125.664. [15] Figures With an Irregular Contour. To find AREA, A B C D, representing, for example, an indi- cator card. This cannot be done with absolute exactness, but there are a number of rules for finding the approximate area as closely as we may desire. Divide the base O X into any appropriate number of in- tervals, usually 10 for an indicator card, and draw lines across the card as shown. Rule (i) (Trapezoidal). Measure the successive ordinates or breadths on the full line and from their sum subtract one- half the sum of the end ordinates. Multiply the remainder by the length of the interval or by O X -^ 10, and the product is the area desired; or calling the breadths y , y^ J 2 , etc., we have by formula in this case. COMPUTATIONS FOR ENGINEERS. 631 Area = ( J y + y t + j/ a + j/ 3 + j/ 4 + jr. + y< + J 7 + / 8 + y 9 + As a slightly different and preferable mode of procedure with this rule we may measure the breadths midway between the lines of division as indicated by the dotted lines. Their sum, without modification, is then multiplied by the length of the in- terval as before. Any number of spaces as desired may be employed with this rule. Rule (2) (Simpson s or Parabolic). Measure the ordinates as before. Take : Once the first and last. Four times every other one beginning with the second. Twice the remaining. (These multipliers are shown in the figure below the line O X.) Add the products and multiply by one-third the interval, or in this case by O X -4- 30 ; or by formula in this case : n x Area = -~ (y Q + 4j>, + zj 2 + 4 / 3 + zj/ 4 + 4 j s + 2j 6 + 47, + With this rule the number of spaces must be even. Rule (3) (Durand's). Measure the ordinates as before. To their sum add one-twelfth the sum of those next the end and subtract seven-twelfths of those at the end. Multiply the result by the interval and the product is the area desired ; or by formula in this case : With this rule any number of spaces as desired may be em- ployed. The measurement and addition of ordinates as in rules (i) and (3) may be quickly effected by means of a strip of paper on which their lengths are marked off directly from the card and without the use of a scale, joining the end of one to the be- ginning of the next and thus effecting mechanically the addi- tion desired. 632 PRACTICAL MARINE ENGINEERING. To a reduced scale the strip when marked would resemble the figure, the ordinates being as indicated on the margin. The sum total is then directly found by means of a scale. Example: Suppose that the ordinates of an irregular area at one-half inch intervals are found by measurement to be as follows in column (i) : fl) (2) (3) Ordinates. > Multipliers. Products. Jo -44 i 44 y, .42 4 5.68 y. .61 2 3.22 7 3 .56 4 6 24 ^4 5 1 2 3.02 ?* .46 4 5-84 ^6 . 20 2 2.40 y 7 -95 4 3.80 Js .71 2 1.42 y 9 -49 4 1.96 y .18 i .18 Sums 11.53 34-20 We then have, according* to rule (i) : Sum of ordinates = 11.53 Difference.... =. 11.22 Interval = .5 Area = Product = 5.61 square inches. According to rule (2), we have the multipliers and products as given in columns (2) and (3). We then have : Area = YZ X -5 X 34-2O = 5.70 square inches. According to rule (3), we have from column (i) : Sum of ordinates = H-53 T V sum of next to ends = .16 Sum = 11.67 sum of ends .36 Difference = 11.31 A'rea = .5 X 11.31 = 5-66 square inches. COMPUTATIONS FOR ENGINEERS. 633 Areas of irregular figures, such as indicator cards, etc., may also be found by an instrument called the planimeter. In this instrument a pointer is traced around the contour of the figure, while the area is read off from a wheel, which is given appro- priate motion by the movement of the pointer. Such instru- ments, with instructions for use, may usually be obtained from the makers of steam-engine indicators or from dealers in mathe- matical instruments. [16] Prism. A prism is a solid body, bounded by two equal and parallel ends and by three or more sides or faces, forming at their junc- tion a like number of parallel edges. iWhen the sides are perpendicular to the ends, and are therefore all rectangles, the solid is known as a right prism. When the sides and ends are all square, the solid is known as a cube. K F r* M H SURFACE. To find the surface of any prism, having given the figure complete : Rule Find the area of the base (or top) by such of the preceding rules as may be appropriate. For the side or lateral surface, multiply the perimeter or boundary of the base by the perpendicular or shortest distance between any two correspond- ing lines of the base and top (as K L in Fig. a). VOLUME. To find the volume of any prism, having given the base and altitude : Rule Multiply the area of the base or end by the altitude or perpendicular distance between the two ends. RIGHT PRISM. In a right prism the preceding general rules hold, but the lateral faces are all rectangles, and the perpen- dicular distance between their ends, as K L ; the length of an edge, as M N, and the altitude or perpendicular distance be- tween the ends, all three become equal. 6 34 PRACTICAL MARINE ENGINEERING. RIGHT PRISM, WITH RECTANGULAR BASE. In a solid of this character (see Fig. b) the preceding 1 rules still hold, but the sides and ends are all rectangles, and the rules may be simplified as follows : For the LATERAL SURFACE : Rule Multiply the perimeter of the base by the altitude, or Lateral Surface = Length ABCDAXAE. For the VOLUME : Rule Multiply together the length and breadth of base and the product by the altitude, or Volume = ABXADXAE. Example: AB = 8, AD = 6, AE = 10. Then lateral surface = (8 + 6 + 8 + 6) X 10 = 28 X 10 = 280, and volume = 8 X 6 X ip = 480. [17] Cylinder. A solid with a circular cross section of constant size is called a cylinder. If the center of the top is vertically over the center of the base, the solid is called a right cylinder. LATERAL SURFACE OF RIGHT CYLINDER. To find the lateral surface of a right cylinder, having given the diameter of base and the altitude : Rule Multiply the circumference of the base by the altitude, or Lateral Surface = Circumference A B C D X A E = 3.1416 X A C X A E. Example: A C = 10, A E = 20. Then lateral surface = 3.1416 X 10 X 20 = 628.32. VOLUME OF RIGHT CYLINDER. To find the volume of a right cylinder, having given the base and altitude : Rule Multiply the area of the base by the altitude, or Volume = Area ABCDXAE= .7854 ATC X A E. COMPUTATIONS FOR ENGINEERS. 635 Example: A C = 10, A E = 20. 100 X 20 = 1,570.8. Then volume = 7854 X [18] Any Solid With a Constant Section Parallel to the Base, Either Right or Oblique. Such a solid is the general case of which the prism and cylinder are but special examples. The rules will therefore be similar to those of [16] and [17]. SURFACE. To find the surface of such a solid, having given the figure complete : Rule Find the area of the base (or top) by such of the pre- ceding methods as may be appropriate. For the side or lateral surface, multiply the perimeter or boundary of the base by the perpendicular or shortest distance between any two correspond- ing lines of the base and top (as K L in figure a) : or Lateral Surface = Length ABCDEAXKL. A \ VOLUME. To find the volume of such a solid, having given the figure complete : Rule Multiply the area of the base by the perpendicular distance between the base and the top. or Volume = Area of Base X Vertical Altitude. Example: Area of base =- 120, altitude = 40. Then volume = 40 X 120 =- 4,800. [19] Wedge. A right prism with a triangular base, as in b above, having two sides equal, as A C and B C, is called a wedge. To find the SURFACE or VOLUME, use the same rules as in [16]. [20] Right Pyramid. A solid, bounded by a base and by triangular sides meeting in a point or apc.v, as P, is called a pyramid. If the base is a 6 3 6 PRACTICAL MARINE ENGINEERING. regular polygon [8] and the apex is vertically over the center of the base, the solid is called a right pyramid (see figure a below). LATERAL SURFACE. To find the lateral surface of a right pyramid, having given the figure complete : Rule Take one-half the product of the perimeter or bound- ary of the base by the perpendicular or shortest distance from the apex to one of the sides of the base, as P F, Length ABODE A x PF or Lateral Surface = - 2 VOLUME. To find the volume of a right pyramid, having given the base and altitude : Rule Take one-third of the product of the area of the base by the altitude, as P O, (Area of Base) x (Altitude) or Volume = J Engineering Example: Area of i 80 X 16 base = 180, altitude = 16. Then volume 3 = QOO. General Pyramid. For definition see [20], also Fig. b above. LATERAL SURFACE. To find the lateral surface of any pyramid, having given the figure complete : Rule The surface will consist of a series of triangles, simi- lar or not, according to the nature of the pyramid. These must be computed according to the rules for triangles and the re- sults added. VOLUME. To find the volume of any pyramid, having given the base and altitude : Rule Take one-third the product of the area of the base by the vertical altitude, as G H, COMPUTATIONS FOR ENGINEERS. 637 (Area of Base) x G H or Volume = 3 Example: Area of base = 48, G H 18. Then vol- ume = = 288. 3 [22] Right Circular Cone. Any solid having a base with curved or irregular boundary, an apex, and straight sides, is called a cone in general. If the base is a circle and the apex is vertically over the center, the solid is called a right circular cone (see figure). LATERAL SURFACE. To find the lateral surface of a right circular cone, having given the base and the slant height : Rule Take one-half the product of the circumference of the base by the slant height, Circumference ABC D A x A or lateral surface = - - Example: Diameter = 10, A E = 20. Then surface = 3.1416 X 10 X 20 , - =314.16. VOLUME. To find the volume of a cone, having given the. base and altitude : Rule Take one-third the product of the area of the base by the altitude, Area of Base A B C D X E F or volume = __ _ _ _ 3 Example: Diameter = 8, E F = 15. Then volume = 3 [23] General Cone. For definition see [22] . VOLUME. To find the volume of any cone, having given the base and vertical altitude : 638 PRACTICAL MARINE ENGINEERING. Rule Take one-third the product of the area of the base by the vertical altitude, as -F G, Area of base X F G or volume = _ Example: Area of base = 240, F G 40. Then volume = 240 X 40 _= 200. [34] Frustum of Right Pyramid. The solid contained between the base of a pyramid and a parallel plane, as E F G H, is called the frustum of a pyramid. LATERAL SURFACE. To find the lateral surface of a frustum of a right pyramid, having given the figure complete : Rule Add the perimeters or boundaries of the base and top, and multiply the sum by one-half the perpendicular or shortest distance between two corresponding lines of the base and top, which we may denote by h. or lat. surface - (length A B C D + length E F G H} X h 2 Example: A B = 10, A D = 12, E F = 6, E H = 7.2, k = . Then surface = (44 + *M) X 5 = 5 2 VOLUME. To find the volume of a frustum of a right pyra- mid, having given the base and top and vertical distance be- tween them : COMPUTATIONS FOR ENGINEERS, 639 Rule Add together the areas of the base and top and the square root of their product, and multiply the sum by one-third the vertical altitude, which we may denote by k, orvol __(ABCD + EFGH + [/AB C DyEFG H) X k 3 Example: Area A B C D = 100, area E, F G H = 42, k = rr, (100 + 42 + I/ 4,200) X 12 12. Then volume = v _ Z _ _ _ _ = 827.2. 3 [25] Frustum of General Pyramid, as [21]. To find the LATERAL SURFACE : Rule The surface will consist of a number of trapezoids, similar or not, according to the nature of the frustum. These must be computed according to [4] and the results added. To find the VOLUME : Rule Same as for [24]. [26] Frustum of Right Cone. The solid contained between the base of a cone and a parallel plane, as E F G H, is called the frustum of a cone. LATERAL SURFACE. To find the lateral surface of a frustum of a right cone, having given the base and top and slant height : Rule Add the circumference of the base and top, arid mul- tiply the sum by one-half the slant height, as A E, or lat. surface = * A B C D + C.E F G H)-*A>E 2 Example: Diameter A C t = 12, diameter E G = 10, A E = 8. Then surface = (3-i4i6 X 12 + 3.1416 X 10) X 8_ 2 VOLUME. To find the volume of a frustum of a right cone, having given the base and top and vertical altitude : Rule Same as for [24] . Or in slightly different form, we have the following : 640 PRACTICAL MARINE ENGINEERING. Rule Add together the square of the upper diameter, the square of the lower diameter, and their product, and multiply the sum by the vertical altitude and by the number .2618, or volume = .2618 / 7 (ETG'-j-^TC'-f E G X A C). Example: E G = 6, A C = 8, I J = 4. Then volume = .2618 X 4 (36 + 64 + 48) = 155. [27] Frustum of General Cone, as [23]. To find the VOLUME : Rule Same as for [24]. [28] Sphere. A solid inclosed by a curved surface, every point of which is equally distant from a point within called the center, is called a sphere. The distance, A B, from one side to the other through the center is called the diameter. The distance, A 0, from the surface to the center is called the radius, and is plainly one-half the diameter. SURFACE. To find the surface of a sphere, having given the diameter : Rule Square the diameter and multiply by 3.1416, or Surface = 3.1416 (Diameter) 2 . Example: Diameter = 20. Then surface = 3.1416 X 400 = 1,256.64. VOLUME. To find the volume of a sphere, having given the diameter or radius : Rule Multiply the cube of the radius by 4.1888, or multiply the cube of the diameter by .5236, or volume = 4.1888 A O 3 . or volume = .5236 A B 3 . [29] Volumes of Irregular Shape. Volumes of irregular shape in which the areas of a series of equally-spaced sections may be found. COMPUTATIONS FOR ENGINEERS. 641 Rule Find the areas of a series of equally-spaced cross sec- tions and treat them by the rules given in [15], using areas for ordinates. The result will give the volume desired. Examples: (1) Find the volume of an irregular box, 12 feet long; area, of one end, 6 square feet; of the other, 15 square feet, and of a section midway between, 10 square feet. The interval is 6 feef. Then with Simpson's rule, Volume = 2 X (& + 4 X 10 + 15) = 122 cubic feet. (2) Find the volume of a coal bunker, 20 feet long, having, cross sections every 4 feet, as follows : Taking rule (3), in [15], we find the result as below: 297 8-3 305.3 554 249.9 4 999.6; or, say, 1,000 cubic feet. A_ = Sum = [30] Volume Generated by Any Area Revolving About an Axis. To find the surface or volume of such a body, the so-called "Rules of Pappus" are most readily applicable. These may be 642 PRACTICAL MARINE ENGINEERING. illustrated by the example of the Torus or Ring as in the figure. SURFACE. To find the surface of a ring, having given the necessary dimensions : Rule Multiply the length of the generating line by the length of the path followed by its center of gravity. Example, as in the figure. The length of the generating line is 2 TT r. The length of the path of the center, C, is 2 K a. The surface is.-. 2 TT r x 2 TT a = 4 x 2 a r VOLUME. To find the volume of a ring, having given the necessary dimensions : Rule Multiply the generating area by the length of the path traveled by its center of gravity. . Example, as in the figure. The generating area is n r 2 . The length of the path of the center, C, is 2 n a. The volume is .-. 2 x 2 a r*. The same general rules apply, no matter what the form of the generating area, and they will often be found of use in solving problems not readily treated in any other manner. Sec. 10. PROBLEMS IN GEOMETRY. [i] At Any Point in a Straight I^^v V V U Z ' ~- _______ ____^_ " < W will be points on the development of B C. Other points may be found in a similar manner and the development of B C com- pleted as shown by the curve G F L The curve H E J as the development of A D may be found in an entirely similar man- ner, and if B C and A D are equally inclined to the elements of the cylinder, L M will naturally be located midway between them, and H E J will be symmetrical with G F I about TV P, and both may thus be found at the same time by laying off above and below N P the distances determined as above shown. Sec. H. PHYSICS. [i] Acceleration Due to Gravity. In engineering computations there frequently enters a quantity known as the acceleration of gravity or the acceleration due to gravity, and denoted by the symbol g. This is the change per second which the gravity or attraction of the earth is able to bring about in a freely falling body. For engineering purposes its value is usually taken at 32.16 or 32.2. [2] Specific Gravity. The specific gravity of a given substance is the relation be- tween the weights of equal volumes of the given substance, and of some standard substance, usually water. Thus a specific grav- COMPUTATIONS FOR ENGINEERS. 65' ity of 8 means that, volume for volume, the given substance is 8 times as heavy as water. [3] Heat Unit. Heat is measured in terms of a unit defined as the amount of heat required 1 to raise i Ib. of water I deg. in temperature at 62 deg. Fahrenheit, or from 62 deg. to 63 deg. [4] Specific Heat. The specific heat of a substance is the relation between the amount of heat required to raise it I deg. at the given tempera- ture and under given conditions as to pressure or volume, and the unit of heat as just defined. Thus a specific heat of .32 means that under the given conditions it will require to raise the tem- perature i deg., .32 of the heat necessary to raise i Ib. of water from 62 deg. to 63 deg. [5] Expansion of Metals. Nearly all substances expand with the addition of heat, and usually with nearly equal amounts per degree rise of temperature, especially where the substance is not near its melting or boiling point. The following table gives the coefficient of linear or length expansion for various substances. This is the expansion in unit length for i deg. Fahr. rise of temperature. Substance. Coef. Substance. Coef. Aluminum 000012^ Iron cast Brass cast . 0000006 Iron wrought Brass, drawn .0000105 Lead OOOOI ^7 Brick OOOOO^I Mercury Bronze OOOOO99 Steel cast .UOUU^j Bismuth OOOOOQ8 Steel wrought Concrete . OOOOoSo Tin . .' 00001 ] 6 Conner . . OOOOO8Q Zinc 0000141 v_-yHF cl (jiass 000004 s; To find the expansion in the length of any bar for any given rise in temperature we have the following: Rule Multiply the coefficient taken from the table by the number of degrees, and this by the length of the bar, and the product is the expansion desired. Example: What is the expansion of a steel bar 20 ft. long between 60 deg. and 350 deg. Fahr.? Ans.: .0000069 X 290 X 20 = .04 ft. = .48 in. 6$2 PRACTICAL MARINE ENGINEERING. The coefficient for area or surface expansion is taken twice that for linear expansion, and that for cubic or volume expansion is taken three times that for linear expansion. Example: What is the increase in area between 60 deg. and 300 deg. Fahr. in a copper sheet having an area of 54 sq. ft.? Ans.: .0000178 X 240 X 54 = -231 sq. ft. = 33.3 sq. in. What is the increase in volume between 100 deg. and 200 deg. Fahr. in a piece of brass having a volume of 2 1-2 cu. ft.? Ans.: .0000288 X 100 X 2.5 = .0072 cu. ft. = 12.44 cu. in. Sec. 12. MECHANICS. [l] It is a general law of nature that all bodies tend to remain unchanged as regards their condition of rest or relative motion. A body at rest does not move unless caused to do so by some outside agency. A body in motion continues to move until it is brought to rest by outside agencies such as friction, resistance of the air, or of water, etc. [] Force. Any agency which changes or tends to change the condition of a body as regards its rest or relative motion is called a force. For engineering purposes force is measured by the pound or ton as unit. In marine engineering the ton, unless otherwise stated, is usually of 2,240 Ib. [3] Specification of a Force. A force has three characteristics or particulars : (1) Its line of direction, as north and south. (2) The way it acts in that line, as north. , (3) Its magnitude. A force may therefore be completely represented by a line A B of length to represent the magnitude, and drawn in the direction of the line of action of the force. B Thus the force A B would mean a force represented in amount according to some scale by the length A B, and acting along the line A B from A to B. The direction of action is also frequently denoted by an arrow point, thus : B COMPUTATIONS FOR ENGINEERS. 653 [4] Moment of a Force. This is the product of the magnitude or measure of the force multiplied by the perpendicular distance from its line of action to a given reference point. Thus in the figure let the full line represent a force, P denote its measure, and the reference point. Then P X A is the moment of the force P about the point 0. In the term moment of a force a point of reference is therefore always implied. [5] Resultant. The resultant of a 1 system of forces two or more in number with their lines of action all meeting at a common point, is the single force which represents the combined action or result of the system. [6] Work. Work is done when a force (or resistance, as it may be called in such case) is overcome ; as for example when a weight is lifted or a ship is forced through the water. Work is measured by the product of the resistance by the distance through which it is overcome. The two essential factors of work are therefore force or resistance on the one hand, and motion or distance on the other. The unit of work is the foot pound or the work done in raising one pound weight one foot in height. Thus if 16 Ib. be lifted 20 ft. the work done is 20 X 16 = 320 ft. Ib. [7] Power. Work in itself is independent of the time required to do it, and depends simply on resistance and distance. Power means a certain amount of work performed in a given time. The com- mon unit is the horse power, which is 33,000 ft. Ib. of work per- formed in one minute. The added element involved in power should not be! forgotten. Thus 33,000 ft. Ib. of work performed in i hour would not mean one horse power, but only -fa of such amount, while 33,000 ft. Ib. of work performed in I second would mean 60 horse power. Likewise 550 ft. Ib. per second represents one horse power as also 1,980,000 ft. Ib. per hour. To find the horse power in any given case we have therefore the following : 654 PRACTICAL MARINE ENGINEERING. Rule Find the foot pounds of work performed per minute and divide by 33,000. Example: An engine in one-half hour performs 118,800,000 ft. Ib. work. What is the horse power? 118,800,000 Horse power = - - 120 3 X 33>ooo, From the above general expressions for work and power there come two forms of especial interest to the engineer. These relate to the work done by or on a fluid in a cylinder with a moving piston, as in a steam engine or a pump. Let A = the area of the cylinder in square inches. p = the average working pressure per square inch. L = the length of stroke in feet. N = the number of revolutions or double strokes per minute. Then pA = the average total pressure or load on the piston. This is the force factor. 2LN = the distance per minute assuming the engine or pump to be double acting. This is the distance factor. Then: Work per mt. = (pA) X &LN) ft. Ibs ................ (a) or as it is frequently written by changing the order of the factors, Work per mt. = 2pLAN ft. Ibs ....................... (ai) To reduct this to horse power we simply divide by 33,000 and have : 2pLAN Horse power = 33,000 Now for the second form let us arrange the factors thus : Work per mt. = (p) X (2LNA). Then multiply p by 144 and divide A by the same number. This will not change the value and we shall have : Work per mt. = (144 /) x(- - J \ 144 / The first factor (i44/>) is the pressure per square foot. Also A -H 1 44 is the area of the piston in square feet while 2LN is the distance it moves through per mt. measured in feet. Hence 2LN A -L- 1 44 is the volume swept through per mt. Hence we have for work the following form : Work per mt. = (pressure per unit area) X (volume swept through per mt.) . . . .................. ................... (b) COMPUTATIONS FOR ENGINEERS. 655 In this form it must be noted that the unit area and the volume must both refer to the same unit, and since work is measured in foot Ibs. this unit must be the foot. Hence we may write more definitely : Work per mt. = (pressure per square foot) X (volume swept through in cubic feet) ............................. (bi) In a still more general sense when a liquid is moved under pressure we may put volume moved or change of volume for the second factor and thus write : Work per mt. = (pressure per square foot) X (volume moved in cubic feet) [8] Energy. This is the capacity for performing work, and depends on special conditions of motion or location. For convenience energy is considered of two kinds. Kinetic Energy is the energy possessed by a body in virtue of a condition of motion. As we know, such a body resists an attempt to stop it, and it will overcome a certain resistance through a certain distance before being brought finally to rest. W v* This kind of energy is measured by the formula E = -- where W is the weight in pounds, v is the velocity in feet per second, and g is the acceleration due to gravity or 32.2. Since energy is directly convertible into work it must be really similar in char- acter to work, and we may therefore speak of so many foot pounds of energy just as well as of so many foot pounds of work. Potential Energy is the energy possessed by a body in virtue of its location or condition relative to the forces acting on it. Thus a weight lifted to the top of a building has potential energy relative to the street because it could do \\ ork if allowed to move downward. Similarly a compressed spring or a compressed gas has potential energy because either, if properly allowed to return to the condition toward which it tends, will perform work. Po- tential energy is measured by the work which could be thus per- formed, or by its equal the work which must be done upon the body in order to produce the given condition ; as for example the work done in lifting the weight to the top of the building, or in compressing the spring or gas. Potential energy is therefore measured directly in foot pounds. 56 PRACTICAL MARINE ENGINEERING. [9] Conservation of Energy. It is a fact of universal experience that energy can neither be destroyed nor created. The seeming appearance or disappear- ance of energy or work is always the result of a change of form. Energy may exist in a variety of forms, as (i) Mechanical, (2) Thermal, (3) Electrical, (4) Chemical, and when there is an increase in any one form there must be a decrease in the other forms of exactly the same total amount, and likewise when there is a decrease in any one form there must be an increase in the other forms also of exactly the same total amount. There may be a like exchange between kinetic and potential energy, the one increasing as the other decreases, and vice versa. Thus with mechanical energy if there is no change to other forms we shall find that the sum of the kinetic and potential energies is always the same, and that one increases as the other decreases and vice versa. In this view work simply appears as an attendant upon the exchange of energy, or more definitely, as a measure of the exchange. Again if we fix our attention upon one body, its changes of total energy measure the work which it receives or gives out. If its energy increases it has had work done upon it. If its energy decreases it has given out work to some other body. [10] Statics. If the forces which act on a body are properly related or balanced, the body remains at rest. The conditions necessary to the realization of this state of rest under the action of forces form the subject of statics. [11] Dynamics. If the forces are not so related, the body does not remain at rest and motion results. The amount and nature of such motion and its relation to the system of forces form the subject of dynamics. [12] Propositions in Statics. Following are a few simple propositions in statics given without proof: (1) A force may be transferred along its line of action with- out changing its effect. (2) Two forces equal and directly opposite will balance or produce equilibrium. (3) PARALLELOGRAM OF FORCES. If two forces whose lines of action meet in a point are represented in amount and direc- COMPUTATIONS FOR ENGINEERS. 657 tion by the lines A and B, then will the resultant of these two forces be represented also in amount and direction by the diagonal C of the parallelogram A C B erected on A and B as adjacent sides. (4) A force G represented by the diagonal C reversed will balance C or the resultant, and therefore will balance P and Q. c, (5) POLYGON OF FORCES. Let there be a system of forces represented as in (a). In (b) starting at any point Oi and Oi Ai equal and parallel to A. Then from A^ as starting point draw Ai Bi equal and parallel to B, and so on, drawing finally Ei Fi equal and parallel to F. Then will the closing line Oi Fi in direction and amount represent the resultant of the system of forces, while (X Fi reversed, or Fi Oi will represent similarly the balancing force of the system that is, the single force which will balance the system and with it produce equilibrium. In the construction in (b) the order in which the forces are taken is in- different, but we have here supposed them taken in regular order to the right, beginning with A and ending with F. It is readily seen that this proposition is a generalization of (3) extended to cover the case of any system of forces. It follows from this proposition that if any system of forces may be repre- sented as in (b) by the sides of a completely closed polygon, then such system will produce equilibrium, for the resultant in such case would be zero. Again in such case any force may be considered as the balancing force for the system composed of all the others, 6 5 8 PRACTICAL MARINE ENGINEERING. and any force reversed may be considered as the resultant of the system composed of all the others. (6) COMPONENTS. In the figure the two forces P and Q are at right angles. In such case they are known as the com- ponents, or, more correctly, the rectangular components, of their resultant R along the lines D and E. In general the com- ponent B of any force C along any line E is found by draw- ing from C a line C B perpendicular to E, thus determining the length B. D B E (7) CONDITIONS FOR EQUILIBRIUM. The conditions for the equilibrium of any body are as follows : (a) The sum of all the components of all the forces acting on the body taken along any line, or more particularly along any pair of lines at right angles, must balance. (b) Taking any point as origin, the sum of the moments of all the forces tending to turn the body in one direction about this origin must equal or balance the corresponding sum in the other direction. If all the forces act through a single point, only the first of these conditions is necessary. If instead they act through dif- ferent points of a body, both conditions are necessary. (8) PARALLEL FORCES. The resultant of a system of parallel forces is the algebraic sum of the forces. The center of a system of parallel forces is a point such that if a force equal and opposite to the resultant be here applied, the whole system will be maintained in equilibrium. Or otherwise, it is che point at which the resultant of the whole system may be considered as acting. The center of gravity of a body is the center of the system of sensibly parallel forces due to the attraction of gravitation. Or otherwise, it is the point at which the entire weight of the body may be considered as centered, or through which it may be considered as acting. COMPUTATIONS FOR ENGINEERS. 659 Or otherwise, it is the point of the body which, if supported, the whole body will be supported in equilibrium, and perfectly free to turn into any position. [13] Mechanical Powers. LEVER. A lever consists essentially of a bar which supports a weight or applies a force at one point by means of a force ap- plied at another point, the bar in the meantime being supported and turning about a third point called the fulcrum. According to the relation of these three points, levers are divided into three classes as below : LEVER OF THE FIRST CLASS. In this the fulcrum R is be- M- I ~ U- a -M*- b -n R* P tween the points of application of the forces P and W '. The fol- lowing proportions and equations apply to this case : P \W ::b :aorPa=Wb p : P+W ::b : I or P l=(P+W)b W : P + W : : a : I or W I = (P + W) a /> + v\ p - b I v - W ~ P + n LEVER OF THE SECOND CLASS. In this the weight lifted or resultant force W is between the applied force P and the fulcrum a *t*- b -M W R. The following proportions and equations apply in this case : P : W : : b : / or P 1 = W b P) b 66o PRACTICAL MARINE ENGINEERING. LEVER OF THE THIRD CLASS. In this the applied force P is between the weight lifted or resultant force W and the fulcrum R. The following proportions and equations apply to this case : P \W : : / : a or P aW I (pW):W::b:a or (P W} a = W b (PW):P::b:l or (P W) I = P b II W W P = L w = ~(P- m a b v An ordinary crowbar, a pair of scissors, an air pump lever, are all examples of a lever of the first class. A pair of nut crackers, an oar (the water being the fulcrum), and often many of the levers about the starting and drain gear of an engine, are ex- amples of a lever of the second class. The forearm (the elbow being the fulcrum), or a ladder when raised against a house, are examples of the third class. WINDLASS AND CRANK. In this device a barrel B is carried on an axle supported in bearings at A and C, and operated by a crank D. The weight W may then, by means of a rope wound on the barrel, be raised or lowered by the action of a force P applied at the crank. The following proportions and equations give the relations between the various quantities concerned : P: W :: r : R or P R = Wr P = ~ W W=^P P W W R R -^p r r = radius of barrel. R = radius of crank. COMPUTATIONS FOR ENGINEERS. WHEEL AND AXLE. This device is the same as the pre- ceding, except that the wheel A takes the place of the crank. The same proportions and equations apply as for the windlass and crank above. Illustrations of the principles involved in this- and the preceding figures are found in all forms of windlasses, deck winches, etc. r = radius of barrel. R =. radius of wheel. **, I w GEARED HOIST. This device is similar to the two preced- ing, with the addition of gearing between the force P and the weight W. The following equations apply to this case : P W P , , r, w Most deck winches are illustrations of a simple geared hoist. 7?i = radius of A n := radius of B R 2 = radius of C rz radius of D SINGLE FIXED PULLEY. A is a pulley or sheave supported from R and turning about its center. B C is a single rope led over the pulley, to one end of which the force P is applied, and to the other end of which the weight W is attached. The follow- ing equations apply to this case : 662 PRACTICAL MARINE ENGINEERING. P = W R = P + W = 2P Velocity of W = velocity of P A single whip used for raising light weights is an illustration of this purchase. SINGLE MOVABLE PULLEY. A is a pulley or sheave to the frame of which is attached the weight W. B C is the rope rove around the sheave, having one end made fast to the support D, while to the other is applied the force P. The following equa- tions apply to this case : W = 2 P W R = P = 2 Velocity of W 1-2 velocity of P Tacks and sheets on light sails are illustrations of this form of purchase. tfl B W LUFF TACKLE. In this purchase there are two sheaves at A and one at B. The rope is led as shown from the frame of B up COMPUTATIONS FOR ENGINEERS. 663 around one of the sheaves A, then down around the sheave B and up over the other sheave A to the point P, where the power is applied. The following equations apply to this case : W = 3 P R = 4 P If upper block is fixed, Velocity of W = 1-3 velocity of P. If lower block is fixed, Velocity of R = 1-4 velocity of P. In order to obtain the greatest advantage with this purchase, therefore, B should be the fixed block. A PAIR OF BLOCKS, AS IN THE LUFF TACKLE FIGURE, WITH ANY NUMBER OF SHEAVES IN EITHER BLOCK. W total number of ropes at the lower block, passing through P ~ and attached. R total number of ropes at the upper block, passing through P ~ and attached. Thus in the figure the number of ropes at the lower block is 3 and the number at the upper block is 4, which, according to the rule, would give the same relations between P, R and W as in the equations above. R W DIFFERENTIAL PULLEY. In this purchase there are two sheaves at A fastened together, or made in one piece, and one sheave at B. A rope or chain is rove as shown in the figure, and 664 PRACTICAL MARINE ENGINEERING. the force is applied at P while the weight W is supported from the lower block. The following equations apply to this case : R = radius of larger upper pulley r = radius of smaller upper pulley W 2 R Then -p-=^-_- - Velocity of W = (velocity oLP) The differential pulley is commonly found in all engineer's out- fits on board ship. P INCLINED PLANE. W & P ~ h W : : P and P = -. W o WEDGE. R R = 'IP a and P = T COMPUTATIONS FOR ENGINEERS. 665 SCREW. p = pitch of screw P = force applied at radius r W = pressure exerted P : W ::p : 2 TT r or P : W : : p : 6.2832 r ^ 6.2832 r or W = - - P P P P - W '- 6.2832 r V Examples of the applications of the last three figures will be too familiar to need special mention. [14] Examples in Mechanics. We give below the solutions of a few simple examples as il- lustrations of the preceding principles of mechanics. In all cases the effects of friction are omitted. (1) In a lever of the first class as shown, a = 48 and 6 = 8. With a pull P of 1 60 lb., ; what weight W can be raised? W := a .P= ^ X 160 960 Ib. O o (2) In a lever of the second class as shown, / = 72 " and b = 12 " '. What force P will be required to raise a weight W of 600 Ib.? P = ~ W =~ X 600 =: ioo Ib. / 72 666 PRACTICAL MARINE ENGINEERING. (3) In a lever of the third class as shown, / = 40 " and W 30 Ib. Where must a force P of 80 Ib. be located so as to maintain equilibrium? (4) The dimensions of a windlass and crank as illustrated are as follows: Radius of crank = 14". Radius of barrel = 41-2 ". What weight can be raised with a force of 60 Ib. applied at the crank? W = P = -, X 60 = 186 2-3 Ib. r 44 (5) With a wheel and axle as illustrated, the diameter of the wheel is 6' and of the axle 10 ". What force P will be required to hoist a weight W of 600 Ib.? p = Z W = 4r X 6o = 8 3 i-3 lb - K 36 (6) The dimensions of a geared hoist as illustrated are as follows : Diam. of A = 24 " ; number of teeth in B 16 ; num- ber of teeth, in C = 96; diam. of D = 10". What weight W can be hoisted if P = 100 lb.? Since the diameters and radii of wheels are in the same ratio as their numbers of teeth, we have : *' 8 X * 8 X I0 =: I44 o lb. r*r a 8x5 (7) With a single movable pulley as illustrated, what weight can be raised with a pull P of 90 lb.? W = 2 P = 2 X 90 = 180 (8) With a luff tackle purchase as illustrated, what force P will be required to raise a weight W of 372 lb., and what will be the load at R? W = 3 P or P = W -f- 3 = 372 + 3 = 124 R = 4 P = 4 X 124 = 496 (9) The dimensions of a differential pulley as illustrated are as follows : Larger diameter, 13 " ; smaller diameter, n ". With a pull P of 80 lb., what weight W can be raised? T/r7 2 R 2 x 6J x 80 W = - - P = - - - 1040 ID. R-r 6J - 5 J COMPUTATIONS FOR ENGINEERS. 667 (10) An inclined plane as illustrated has dimensions as fol- lows : Slant length, b = 72 " ; height, h == 18 ". With a pull P of 40 lb., what weight W can be moved up the plane? W = % P = 7 ~ s X 40 == 1 60 lb. (n) A wedge as illustrated has the following dimensions: Back, a = 4 " ; length, h = 26 " . What resistance R can be over- come by a force P of 216 lb.? Ji 7 , 26 R - P = - - x 216 = 1404 lb. a 4 (12) A screw as illustrated has the following dimensions : Pitch p = 1-4 " ; radius r = 12 " ; force P = 60 lb. What pres- sure W can be exerted? 6.2832 x 12 X 60 (13) Given a boiler brace A with crowfoot or forked at- tachment to the plate B C. With a known load on A, required the load on B and C. Evidently the three forces on A, B and C keep the joint in equilibrium. If represented according to the polygon of forces [12] (5), they must form a closed triangle. This is rep- resented by A D, where A represents the force on the brace, A D that on B and D that on C. Hence if A is laid down to some convenient scale to represent the load on the brace, then A D and D respectively will, according to the same scale, represent the loads on O B and C. (14) Given a boiler brace A oblique to the shell C D. With a known load in the direction B 0, required the load on A. 668 PRACTICAL MARINE ENGINEERING. The point of attachment is again maintained in equilib- rium by the action of the three forces, one along A, one in the direction B 0, and a third C existing as a tension in the plate. The triangle of forces in this case is represented by B A. Hence if B is laid off to any scale to represent the known load, then will A represent to the same scale the resulting load on the brace. (15) Let C A B represent the moving parts of an engine. With a known piston load acting along C A, required the re- sultant loads on the connecting rod and on the guide. The point A is kept in equilibrium by the action of the three forces, one acting down along C A, one acting up the rod along B A and one acting from the guide along DA. It is the two latter which are required. The triangle of forces in this case is represented by A E F. Hence if A E is laid off to represent to any convenient scale the known piston load, then to the same scale will A F and F represent the loads on the connecting rod and crosshead respectively. It thus appears that the load on the connecting rod is in general greater than that on the piston rod, and that it is greater in the same ratio that any length A F is greater than the corresponding distance A E. (16) Let the diagram represent a davit C D supporting a weight W and braced by a stay A B. With a given weight W, required the tension on the stay and the forces at the foot of the davit. The tension T may be represented by its two components P and Q, and the reaction at C by two components N and R. In COMPUTATIONS FOR ENGINEERS. 669 this case we require the use of both conditions of equilibrium, and without giving all details we will simply write the equations and the resulting values of the forces. Equating vertical forces W + Q = N Equating horizontal forces P = R Taking moments about C We also have W a = Ph r >- From these equations we find : Q = W = *4 w R = N I a -f (a -f- ^\ = \~~F~) w W 670 PRACTICAL MARINE ENGINEERING. Answers to Examples in Part II. Sec. i. COMMON FRACTIONS. i>] -v 7 -, v-, w, vy, w w. -fit-- [3] 5ii 'i 2 T v T , 2|, 4, if, 3*. 4o T V [4] *, fV> A. i W, TT, iA. 3, t- [6] i^ 4. 4, 2fV isff. 2 7 ^ H 4Ht, AY, A* [7] 4, 2, 2 T 2 T , 3-i-, 9|, 7, 2j. [8] T 3 ^ A, TV, A. T3> i A- [9] f A. W. A. if' 'I. 9t, it. . i*. iff' TV [10] T 5 , I Of, f- Sec. 2. DECIMAI, FRACTIONS. [5] .4, 2.4, 24.4, .072, .1307+, 4.5, 2.6, 1.1951+, .001875, .007368+, 3.2857 + . [8] 3.808, 3466.892, .21888, 93978.89. .0294, .000504. [9] .4531+, 11.334+, 0000006., 600, 4000, 500. MISCELLANEOUS EXERCISES. 671 MISCELLANEOUS EXERCISES. (1) One ton of coal is found to contain 300 pounds of ashes. What percent is combustible and what percent ashes? (See Part II, Sec. 3). Ans. 86.6% and 13.4%. (2) In a certain boiler it requires 1,120 heat units to evap- orate one pound of water. With the addition of a feed heater this is reduced to 1,030. Find the percent of saving. (See Part II, Sec. 3). Ans. 8.04%. (3) A ship steams 2,800 miles in 11 days. How long will it require to steam 740 miles at the same rate? (See Part II, Sec. 6), Ans. 2.9 days. (4) A given engine with a reduced mean effective of 36 pounds, stroke 33 inches and revolutions of 120 develops 1,200 I. H. P. With revolutions 140 and stroke 30 inches what would be the reduced mean effective for 1,300 I. H. P. (See Part II, Sec. 6 [2]). Ans. 36.77. (5) A propeller at 90 revolutions and 24 per cent slip gives a speed of 12 miles per hour. With TOO revolutions and 26 per cent slip what speed will be attained? (See Part I, Sec. 80; Part II, Sec. 6). Ans. 12.98. (6) How many gallons of oil will be contained in a tank of rectangular form, 4 feet long, 27 inches wide and 2 feet high? (See Part II, Sec. 4 [5l, Sec. 9 [16]). Ans. 134.6. 672 PRACTICAL MARINE ENGINEERING. (7) An oil tank 55 inches long has trapezoidal cross sec- tions. The two parallel sides are 28 inches and 40 inches, and the distance between them is 40 inches. Find the capacity in gallons. (See Part II, Sec. 4 [5], Sec. 9 [4] [16]). Ans. 323.8. (8) What is the capacity of a pump in gallons per mt. if the cylinder is 9 inches in diameter, 10 inches stroke and 60 strokes per mt.? (See Part II, Sec. 4 [5], Sec. 9 [17]). Ans. 165.2. (9) A coal bunker of rectangular form is 18 feet fore and aft, 40 feet wide by 13 feet deep. Find the capacity in tons, al- lowing 42 cu. ft. per ton. (See Part I, Sec. n [7] ; Part II, Sec. 9 [16]). Ans. 223. (10) A coal bunker of irregular form has three cross sec- tions, as follows : The first is a rectangle 12 ft. by 18 ft. The sec- ond is a trapezoid with parallel sides 12 and 10 ft. by 16 ft. be- tween them, and the third is a trapezoid with parallel sides 12 and 8 ft. by 14 ft. between them. . These sections are 24 feet apart. Find the capacity in tons of 44 cu. ft. each. Solution. The areas of the three sections are as follows : 216, 176, 140. Then by Simpson's rule, Part II, Sec. 9 [15] [29] the volume is bound as follows : V = (216 + 4 X 176 + 140) -T- 3 X 24, or Volume = 8,480 cu ft. Then tons = 8,480 -f- 44 = 192.7. (n) An oil can in the form of a frustum of a cone is n inches high, and the diameters of the base and top are respect- ively 5 and 4 inches. Find the capacity. (See Part II, Sec. 9 [26]). Ans. .76 gallon. (12) Will a boiler 60 in. diam., y 2 in. thickness of plate stand as much pressure as a boiler 48 in. diam., T 7 in. thickness of plate? (See Part I, Sees. 19, 63). Ans. No. (13) Find the required weight for a safety valve whose diam. is 4", fulcrum 3", length of lever 34", weight of lever \? Ibs., weight of valve and stem 6 Ibs., steam pressure 65 Ibs. (See Part I, Sec. 61). Ans. 65.5 pounds. (14) What would be the safe working pressure of a boiler MISCELLANEOUS EXERCISES. 673 i. 08 in. thickness of plate, tensile strength 60,000 Ibs. per sq. in. diameter of boiler 12 ft.? (See Part I, Sec. 19). Ans. 150 pounds per square inch for single riveting or 180 pounds per square inch for double riveting. (15) The diameter of a boiler shell is 15 feet. The work- ing pressure desired is 180 pounds per square inch. The strength of the material is 60,000 pounds per square inch. Find the thickness with double riveting. (See Part I, Sec. 19). Ans. 1.35 inches or say i%. (16) The diameter of a steel screw stay bolt at bottom of thread is i l /4 inches. The area supported by each is 49 square inches. Find the pressure allowed. (See Part 1, Sec. 19). Ans. 200 pounds per square inch. (17) What would be the thickness of plate required for the same boiler as in (16) the spacing being 7 by 7 inches, and the bolts being simply riveted over on ends? (See Part I, Sec. 19). Ans. 17-32 in. (18) For other problems in boiler bracing see Part I, Sec. 62. (19) Temperature of feed 160. Steam pressure 180 pounds gauge. Quality of steam 97 per cent. Thermal value of coal 13,800 thermal units per pound. Efficiency of boiler .68. Find the pounds of water evaporated per pound of coal into steam of the given quality. (See Part I, Sec. 58). Ans. 8.76 pounds. (20) With a coal consumption of 1.80 per I. H. P. per hour how much coal will be required in the bunkers of a ship making a lo-day trip, the I. H. P< being 1,800 and a margin of 12% being allowed for emergencies? (See Part I, Sec. 59). Ans. 388.8 tons. (21) A corrugated furnace has a diameter of 44 inches and thickness of 1-2 inch. Find the pressure allowed. (See Part I, Sec. 19). Ans. 170 or 159, according to the style of corrugation. (22) Find the necessary thickness of a copper steam, pipe for 200 pounds working pressure, the diameter of the pipe being 9 inches. (See Part I, Sec. 19). Ans. .2875 inch. (23) With cut off at 62 per cent of stroke and clearance of 12 per cent, what is the expansion ratio? (See Part I, Sec. 68). Ans. 1.51. 674 PRACTICAL MARINE ENGINEERING. (24) The I. H. P. is 2,100, pitch of propeller 18 feet, revo- lutions 100. Find the indicated thrust in pounds. (See Part I, Sec. 71). Ans. 38,500 pounds. (25) What is the weight of a rectangular piece of boiler plate 14 feet long, 5 feet 6 inches wide and I 1-8 inch thick? (See table page 30). Ans. 12,474 cu. in. - - 3,530 pounds. (26) Given speed of ship 12 knots, revolutions no, slip of propeller 20 per cent, find the pitch. (See Part I, Sec. 80 [i]). Ans. 13.8 ft. (27) Allowing an Admiralty constant of 280, what would be the I. H. P. required for a displacement of 8,600 tons with a speed of 10 knots? (See Part I, Sec. 82). Ans. 1,500. (28) Given speed of ship 18 knots, revolutions no, pitch 20 feet. Find the slip ratio. (See Part I., Sec. 80 [i]). Ans. 17.1 per cent. (29) Given the pitch of a propeller 54 inches, revolutions 360, slip 21 per cent. Find the speed in miles per hour. (See Part I., Sec. 80 [i]). Ans. 14.54. (30) Given the diameter of the rolling circle of a paddle wheel 30 feet, slip 28 per cent., revolutions 24. Find the speed in miles per hour. Ans. 18.5. (31) Given displacement 120 tons, I.H.P. 420. Allowing an Admiralty-Constant of 160, what speed may be expected? (See Part L, Sec. 82). Ans. 14.03 knots. (32) Given I.H.P. = 33,ooo, D = 20,000, speed = 23 knots. Find the Admiralty-Constant. (See Part L, Sec. 82). Ans. 272. (33) Allowing an Admiralty-Constant of no, what would be the I.H.P. required for a displacement of 4 tons at a speed of 7 knots* 11 (See Part L, Sec. 82). Ans. 7.86. (34) On a trial trip over a course of two nautical miles, suppose the observations as follows : Run North 2 m. 36 sec. Revolutions 648. Run South 2 m. 24 sec. Revolutions 604. MISCELLANEOUS EXERCISES. 675 Pitch of propeller 24 feet. Find average speed and slip of propeller. (See Part L, Sec. 84). Ans. 24 knots, 19 per cent. (35) Given the ship in example (27). With the same Ad- miralty-Constant, what percentage increase in power would be required for 30 per cent, increase in displacement? (See Part L, Sec. 82). Ans. 19 per cent. (36) Given the ship in example (27). With an Admiralty- Constant of 250, what percentage increase in power would be required for a 30 per cent, increase in speed? (See Part I., Sec. 82). Ans. 146 per cent. 676 PROPERTIES OF SATURATED STEAM* Vacuum Gauge, Inches of Mer- cury, Absolute Press- ure. Ibs. per square inch. yS *% 11 f Total Heat above 32 - F. Latent Heat L. = II- h. Heat- units. Relative Volume. Vol. of Water at 39 F. = i. Volume Cn. ft. in 1 Ib. of bteam. Weight of 1 cu ft. {-team Ib. In the Water h Heat- units. In the Steam H Heat- units. 29.74 .089 32 1091.7 1091.7 208 80 3333.3 .00030 29.67 .122 40 8 1094.1 1086.1 154330 2472.2 .00040 29.56 .176 50 18 1097.2 1079.2 107630 1724.1 .00053 29.40 .254 60 28.01 1100.2 1072.2 76370 1223.4 .00082 29.19 .359 70 38.02 1103.3 1065 3 54660 875.61 .00115 28.90 .502 80 48.04 1106.3 1058.3 39690 635.80 .00158 28.51 .692 90 58.06 1109.4 1051.3 29290 469.2) .00213 28.00 .943 100 68.08 1112.4 1044.4 21830 349,70 ,00286 27.88 1 102.1 7009 1113.1 1043.0 20623 334.23 .00299 25.85 2 126.3 94.44 1120.5 1026 10730 173,23 ,00577 23.83 3 141.6 109.9 1125.1 1015.3 7325 117.93 .00848 21.78 4 153.1 121.4 1128.6 1007.2 5588 89.8J .01112 19.74 5 1623 130.7 1131.4 1000.7 4530 72.50 .01373 17.70 6 170.1 138.6 11338 91*5.2 3816 61.10. .01631 15.67 7 176.9 145.4 1135 9 990.5 3302 53.00 .01887 13.63 8 1829 151 5 1137.7 986.2 2912 46.60 ,02140 11.60 9 188.3 156.9 1139.4 982.4 2607 41.82 ,02391 9.56 10 193.2 161.9 1140.9 979.0 2361 37.80 .02641 7.52 11 197.8 166.5 11423 975.8 2159 34.61 .02889 549 12 202.0 170.7 1143.5 972.8 1990 31.90 .03136 3.45 13 2)5.9 174.7 1144.7 970.0 1846 29.58 .03381 1.41 14 209.6 178.4 1145.9 967.4 1721 27.50 .03G25 Gauge Pressure Ibs. per. 14.7 212 180.9 1146.6 965.7 1646 26.36 .03794 SQ. in. 0.304 15 213.0 181.9 1146.9 965.0 1614 25,87 ,03868 13 16 216.3 1853 1147.9 96? 7 1519 21.33 .04110 2.3 17 219.4 188.4 1148 9 9605 14^4 22.98 .04352 33 18 222.4 191.4 1149.8 958 3 1359 21.78 .04592 4.3 19 225.2 194.3 1150 6 956.3 1292 20.70 .04831 53 20 227.9 197.0 1151.5 954.4 1231 19.72 .05070 6.3 21 230.5 199.7 1152 2 952.6 1176 18.84 .05308 7.3 22 2330 202.2 11530 95J.8 1126 18.03 .05545 8.3 23 235.4 204.7 .7 949. 1 1080 17.30 ,05782 9.3 24 237.8 207.0 1154.5 947.4 1038 16.62 .06018 10.3 25 240.0 2093 1155.1 945.8 998.4 15.99 .06253 11.3 26 242.2 211.5 .8 944.3 962 3 15.42 ,00487 12.3 27 244.3 213.7 1156.4 942.8 928.8 14.88 ,06721 13.3 28 246 3 215.7 1157.1 941.3 897.6 14.38 .06955 143 29 2483 217.8 ,7 9399 868.5 13.91 .07188 15.3 30 250.2 219.7 lir8.3 938.9 841.3 13.48 .07420 * Reprinted, by permission, from POWER CATECHISM. ! PROPERTIES OF SATURATED STEAM. 677 Gauge Pressure. Ibs. per sq. in. Absolute Press- ure. Ibs. per square inch. Temperature Fahrenheit. Total Heat above 32 F. tLl It! G^S I" 1 Relative Volume Vol. of Water at39F. = 1. VolumeCu.ft. in 1 Ib. of Bteam. is 51 15 &$ In the Water Ji Heat- units. In the S tea m Heat units. 16.3 31 252.1 2216 .8 937.2 815.8 13.07 .07652 17.3 32 254.0 223.5 1159.4 935.9 791.8 12.68 .07884 18.3 33 255.7 2253 .9 934.6 769.2 12 32 .08115 19.3 34 257.5 227.1 1160.5 933.4 748.0 11.98 .08346 20.3 35 2592 228.8 1161.0 932.2 727.9 11.66 .08576 21.3 36 260.8 230.5 .5 931.0 708.8 11.36 .08806 22.3 37 262.5 232.1 1162.0 929.8 690.8 11.07 .09035 23.3 38 264.0 2338 .5 928.7 673.7 10.79 .09264 24.3 39 265.6 235.4 .9 927.6 657.5 10.53 .09493 25.3 40 267 1 236.9 1163.4 926.5 642.0 10.28 .09721 263 41 268. (i 238.5 .9 925.4 627.3 10.05 .09949 27.3 42 270.1 240.0 1164.3 924.4 613.3 9.83 .1018 28.3 43 271.5 2414 .7 923.3 599.9 9.61 .1040 29.3 44 272.9 242.9 1165.2 922.3 587.0 9.41 .1063 30.3 45 274.3 244.3 .6 921.3 574.7 9.21 .1086 31.3 46 275.7 245.7 1166.0 920.4 563.0 9.02 .1108 32 3 47 277.0 247.0 .4 919.4 551.7 8.84 .1131 33.3 48 278,3 2484 .8 918.5 540.9 8.67 .1153 34.3 49 279.6 249.7 1167.2 917.5 530.5 8.50 .1176 35.3 50 280.9 251.0 .6 916.6 520.5 8.34 .1198 36.3 51 282 1 252.2 1168.0 915.7 510.9 8.19 1221 37.3 52 283 3 253.5 .4 914.9 501.7 8.04 1243 38.3 53 2845 254.7 .7 914.0 492.8 7.90 .1266 39.3 54 285.7 256.0 1169.1 913.1 484.2 7.76 1288 40.3 55 286.9 257.2 .4 '912.3 475.9 7.63 1311 41.3 56 288 1 258.3 .8 911 5 467.9 7.50 .1333 42.3 57 289.1 259.5 1170.1 910.6 460.2 7.38 .1355 43.3 58 290.3 260.7 .5 909.8 452.7 7.26 .1377 44.3 59 291.4 261.8 .8 9U9.0 445.5 7.14 .1400 45.3 60 292.5 262.9 1171.2 908.2 438.5 7.03 .1422 463 61 293.6 264.0 .5 907.5 431.7 6.92 .1444 47.3 62 294.7 265 1 .8 906.7 425.2 6.82 .1466 48.3 63 295.7 2662 1172.1 905.9 418.3 6.72 .1488 49.3 64 296.8 267.2 .4 905.2 412. 3 6.62 .1511 50.3 65 297.8 268.3 .8 904.5 406.6 6.53 .1533 51.3 66 298.8 269.3 1173.1 903.7 400.8 6.43 .1555 52.3 67 299.8 270.4 .4 903.0 395.2 6.34 .1577 53.3 68 300.8 271.4 .7 9 2.3 389.8 6.25 .1599 54.3 69 301.8 272.4 1174.0 901.6 384.5 6.17 .1621 55.3 70 3027 273.4 .3 900.9 379.3 6.09 .1643 56.3 71 303.7 274.4 .6 900 2 374.3 6.01 .1665 57.3 72 304.6 275.3 .8 8995 369.4 5.93 .1687 68.3 73 305.6 2763 1175.1 8989 364.6 6.85 .1709 59.3 74 306.5 277.2 .4 898.2 360.0 5.78 .1731 6 7 8 PROPERTIES OF SATURATED STEAM. 2 - m Total Heat K3 o> a t_i . 4JS 3 g.3 1M *d above 32 = F. *> . 02 $?<. |ln ~J 5 ^* .S -5 H In the In the fitl &* ^2 ^ *o| 4> ^.c Water SSteam "S^-S ?*c n P^ CJ32 c S ^s || 2. -4 " In the In the *~'k* i -. c *3 P< 2 Water Steam 7? ^*CJ S "i3nn ^ "o 2, Srf h H ^3_; co ~~* .sJ . zj 03 l-i C* ,Q p Cfi *PM Heat- Heat- -2 K J^>~c3 C H > < a ! units. units. ^ & '- 146.3 161 363.8 336.4 .9 856.5 172.9 2.79 .3588 147.3 162 364.3 336.9 1193.0 856.1 171.9 2.77 .3609 148.3 163 364.8 337.4 .2 855.8 171.0 2.76 .3630 149.3 164 365.3 337.9 .3 855.4 170.0 2.74 .3650 150.3 165 365.7 338.4 .5 855.1 169.0 2.72 .3671 151.3 166 366.2 338.9 .6 854.7 168.1 2.71 . 3692 152.3 167 366.7 339.4 .8 854.4 167.1 2.69 .3713 153.3 168 367.2 339.9 .9 854.0 166.2 2.68 .3734 154.3 169 367.7 340.4 1194.1 853.6 165.3 2.C6 .3754 155.3 170 368.2 340.9 .2 853.3 164.3 2.65 .3775 156.3 171 368.6 341.4 .4 852.9 163.4 2.C3 .3796 157-3 172 369.1 341.9 .5 852.6 162.5 2.62 .3817 158.3 173 369.6 342.4 .7 852.3 161.6 2.61 .3838 159.3 174 370.0 342.9 .8 851.9 160.7 2.59 .3858 160.3 175 370.5 343.4 .9 851.6 159.8 2.58 .3879 161.3 176 371.0 343.9 1195.1 851.2 158.9 2.56 .3900 162.3 177 371.4 344.3 .2 850.9 158.1 2.55 .3921 163.3 178 371.9 344.8 .4 850.5 157.2 2.54 .3942 1C4.3 179 372.4 345.3 .5 850.2 156.4 2.52 .3962 165.3 180 372.8 345.8 .7 849.9 155.6 2.51 .3983 166.3 181 373.3 346.3 .8 849.5 154.8 2.50 .4004 167.3 182 373.7 346.7 .9 849.2 154.0 2.48 .4025 168.3 183 874.2 347.2 .1 848.9 153.2 2.47 .4046 169.3 184 374.6 347.7 1196.2 848.5 152.4 2.46 .4066 170.3 185 375.1 348 1 .3 848.2 151.6 2.45 .4087 171.3 186 375.5 348.6 .5 847.9 150.8 2.43 .4108 172.3 187 375.9 349.1 .6 847.6 150. 2.42 .4129 173.3 188 376.4 349.5 .7 847.2 149.2 2.41 .4150 174.3 189 376.9 oSO.O .9 846.9 148.5 2.40 .4170 175.3 190 377.3 350.4 1197.0 846.6 147.8 2.39 .4191 176 3 191 377.7 350.9 .1 846.3 147.0 2.37 .4212 177.3 192 378.2 351.3 .3 845.9 14G.3 2.36 .4233 178.3 193 378.6 : : 51.8 .4 845.6 145.6 2.C5 .4254 179.3 194 379.0 352.2 .5 845.3 144.9 2.34 .4275 180.3 195 379.5 352.7 .7 845.0 144.2 2.33 .4296 181.3 196 380.0 353.1 .8 844.7 143.5 2.12 .4317 182.3 197 380.3 353.6 C] 844.4 142.8 2.:i .4337 183.3 198 380.7 354.0 1198 !l 844.1 142.1 2.29 .4358 184.3 199 381.2 354.4 .2 843.7 141.4 2.28 .4379 185.3 200 381.6 354.9 c 843.4 140.8 2.27 .4400 186.3 201 382.0 355.3 m 4 843.1 140.1 2.26 .4-120 187.3 202 382.4 355.8 .6 842.8 139.5 2.25 .4441 188.3 203 382.8 356.2 .7 842.5 133.8 2.2i .4462 PROPERTIES OF SATURATED STEAM. 681 Si en o5-r2 -kJ 12. 2 CH .jS -3 5 ii Absolute I ure. Ibs. ] square in Tomperat Fahreuh In the \\ater h Heat- units. In the B ,e r Heat- units. ..'{ 950 540.3 521.3 1246.7 725.4 31.4 .505 .080 985.3 1000 546.8 528.3 1248.7 720.3 30.0 .480 2.082 *The discrepancies at 205.3 Ibs. gauge are due to the change from Dery's to Duel's figures. 682 APPENDIX. Appendix QUESTIONS ON THE SUBJECT MATTER OF PART I, WITH PAGE REFERENCES. CHAPTER I. Principal Materials of Engineering Construction. PAGE. What are the chief properties and uses of aluminum? i What are the chief properties and uses of antimony? i What are the chief properties and uses of bismuth? 2 What are the chief properties and uses of copper? 2 How does heat affect the tensile strength of copper? 2 Describe the operation of brazing 2 What is meant by burning copper? 2 What is cast iron? 4 What are gray, white and mottled irons? 4 W T hat is meant by combined and by graphitic carbon? 4 What is the influence, of silicon on cast iron? 5 What is a chilled cast iron? 6 What is the influence of sulphur on cast iron? 6 What is the. influence of manganese on cast iron? 7 What is the influence of chromium on cast iron? 7 What is the shrinkage of cast iron? 7 On what is the hardness of cast iron chiefly dependent? 7 On what is the strength of cast iron chiefly dependent? 7 What are the chief uses of cast iron in marine engineering? 8 What chief points are to ; be kept in mind in the inspection of cast- ings ? 8 What is malleable iron and how is it made? 9 What are its properties and uses in marine engineering? 10 What is wrought iron and how is it made? 10 What is the effect of sulphur on wrought iron? .' n What is the effect of phosphorus on wrought iron? u What special properties has wrought iron? n Describe the operation of welding n What are its chief uses in marine engineering? n What is steel ? . 12 Describe briefly the Bessemer and Open-hearth processes 13, 14 Compare the two products 14 What is the influence of sulphur on steel? 15 What is the influence of phosphorus on steel? 15 What is the influence of silicon on steel? 15 What is the influence of manganese on steel? 15 What is semi steel ? 16 What are the leading mechanical properties of steel? 16 What special properties has steel? 21 Describe the operation of tempering 22 What is nickel steel ? 22 What is chrome steel?. 23 What is tungsten steel? 23 What are the chief uses of steel in marine engineering? 23 APPENDIX. 683 PAGE. What are the chief properties and uses of lead? 23 What are the chief properties and uses of tin? 24 What are the chief properties and uses of zinc? 24 What is an alloy? 24 What are the proportions of some common alloys? 25 To what tests are metals subjected? 26 What is meant by the terms ultimate strength, elastic limit, elongation, reduction of area ? 26 Wlnt forms of test pieces are employed, and how are the various tests carried out? 28, 29 CHAPTER II. Fuels. What are the chief constituents of coal? 31 What are the chief varieties of coal? 31 What are about the proportions of volatile matter and carbon in the different varieties ? 32 What per cent of ash is usually found in good coal? 32 Describe briefly the process of combustion with anthracite coal and with bituminous or semi-bituminous coal 32 How much heat is liberated by the complete combustion of I Ib. of carbon ? 32 How much for T Ib. of hydrogen? 32 How much air is required to barely furnish the oxygen necessary for the combustion of an average Ib. of coal? 33 How much is actually required and why is the excess necessary?. ... 33 What is soot and how is it formed? 33 What is clinker and how is it formed? 35 What is meant by the weathering of coal? 36 What influence does iron pyrites have on weathering? 37 What is spontaneous combustion and what are the conditions on which it depends? 37 How many cubic feet bunker space are usually allowed per ton of coal ? 40 What are briquettes?. 41 What are the constituents of liquid fuel? 42 What are the conditions for the combustion of liquid fuel? 43 What are the conditions affecting the likelihood of the explosion of gases arising from liquid fuel? 44 How does the evaporative power of liquid fuel compare with that of coal ? 44 What are the chief advantages of liquid fuel? 45 What is the present chief difficulty attending the extended use of liquid fuel ? 46 CHAPTER III. Boilers. What are the two fundamental types of boilers? 48 ]nto what classes may fire-tube boilers be divided? 49 Give a general description of these various classes 50 Give a general description of a few leading types of water-tube boilers 53 Compare the two types water-tube and fire-tube as regards their advantages and disadvantages for marine use 56 In what way may a riveted joint fail? 68 What is meant by sinorle and double shear? 77 Describe the various forms of riveted joints, and show how they may be proportioned so as to give approximately equal strenght in plate 'and rivet section 71-86 684 APPENDIX. PAGE. What material is used for modern boilers? 86 Are rivet holes usually punched or drilled? 86 Compare the relative advantages of the two methods 86 What is meant by caulking a joint and how is it done? 87 In Scotch boilers what form of joints is used for the longitudinal seam? what for the circumferential seams? 87 Why should the longitudinal seams have a higher efficiency than the circumferential ? 88 What is the relative strength of the boiler to resist rupture in these two directions? 88 How are the head plates usually flanged? 88 Describe the styles of corrugated furnace in common use 88 Describe various modes of connection between the furnace and the combustion chamber 88 What are the two usual forms of combustion chamber top? 90 How are the tubes secured in the tube sheet? 90 What are stay tubes and how are they secured? 92 What is the Serve tube and what advantages are claimed for it?. ... 93 W T hat are retarders and what is their use? 93 What is the Admiralty ferrule and what is its use? 93 What fundamental principles govern the bracing of a boiler? 94 How were furnaces stiffened before the invention of the corrugated form ? 95 Describe the various forms of braces used in modern boilers, and the method of fitting them up 95 Of what advantage is the hollow or drilled screw stay bolt? 98 Describe the form of girder or crown bar with which the top of the combustion chamber is usually supported 100 What is a man-hole and cover, and what is its use? 101 Give approved methods of fitting them up 101 Describe the fitting up of the ordinary furnace door 103 Describe the usual form of grate bar and the methods of supporting it in the furnace 104 What is the bridge wall and how is it fitted up? 104 Where do the gases pass after leaving the tubes? 106 Describe the usual style of front connections and uptakes 106 Describe the funnel and the usual method of fitting it up 106 What is the ratio of heating surface to grate, surface? 112 How is the horse power of a boiler related to the heating surface or to the weight? 112, 113 Mention the various boiler mountings 115, 129 Of what use is a safety valve? 115 Name the principal valves on a boiler 115, 127 Describe the U. S. Standard safety valve 115 Describe the usual type of spring safety valve 116 What is a muffler and what is its use? 118 What is the use of the boiler main stop valve? 118 What is an automatic closing valve, and what is its use? 118 What is the dry-pipe and how is it fitted up? 120 Describe the usual form of boiler check valve 121 What are the bottom and surface blows and how are they fitted?. . . . 122 Describe the usual form of Bourdon steam gauge 124 Describe the usual manner of fitting up water cocks and water gauges 125 What is a hydrokineter and what is its use? 127 What is a hydrometer and what is its use? 127 How are the boilers supported in the ship? 128 Describe the usual forms of boiler saddles 128 To what is draft due? 129 How is draft measured? 131 What are the chief methods in use for increasing the draft? 132 APPENDIX. 685 PAGE. Describe briefly the closed stoke-hold system the closed ash-pit system the use of exhaust fans in the uptakes and of jets in the base of the funnel 133-137 What advantages are there in heating the air introduced into the furnace's? 135 Describe briefly the Howden system of forced draft 133 Describe briefly the Ellis & Eaves system of induced draft 135 (iive ;he U. s. rule for t!vj pressure allowed on cylindrical shell boilers 138 What is the relation between the test pressure and the working pressure allowed? 138 What is the relation between the thickness of butt straps and the thickness of shell plates ~ J 138 How would you compute the size of stays for a given steam pres- sure? .139. 480 How would you compute for a given steam pressure the thickness of a flat plate supported by stays? 139 Give rules for corrugated furnace flues 141, 142 Give rules for ribbed furnace flues 142 What are the proportions for flue lining subjected to external pressure? 144 How do yon compute for a given pressure the necessary dimensions of crown bars? ' 145 How do you compute the thickness of a bumped head? 146 How do you determine the pressure allowed on unstayed flat heads. . 146 How do you determine the pressure allowed for concave heads?. .. . 147 What are the rules for fitting manholes? 147 What are the rules for fitting safety plugs? 148 \t what temperature does a safety plug melt? 24 Wha f are the rules for fitting gauge cocks? 148 What are the rules for fitting safety valves? 148 What considerations govern the area of a safety valve? 115. 148 How would you compute for a given steam pressure the thickness of copper steam pipe? 150 What rules govern the use of iron and steel pipe? 150 In the construction of coil and tubulous boilers what provision is made for the use of cast steel manifolds, tees, return bends and elbows? 152 What special rules relate to the construction of drums for tubulous boilers ? 152 CHAPTER IV. Marine Engines. Explain the chief characteristics of the typical marine engine 154 Explain the more important arrangements which may be made of tin- cylinders and cranks of multiple expansion engines 160 Explain the chief features of an engine cylinder 165 What is a liner and how is it fitted? 165 Explain the different forms of cimine columns and how they are titled " 168 flow are cylindrical columns braced and why? 171 Explain the more common ways of fitting up the guide surface.... 171 Describe the usual form of bed-nlate 772 Describe the usual form of engine seating 174 Describe the usual form of marine piston with its packing rings and springs \-~ What other forms of piston are employed? 178 What is the purpose of the piston rod and how is it fitted up? 179 Dc-cribe the various styles of crosshead to be met with in marine practice 180 636 APPENDIX. PAGE. Describe the various styles of connecting rod to be found in marine practice 184 Describe the built-up and the solid forged styles of crank-shaft.... 185 What are the advantages of making shafting hollow? 187 To what extent may the same practice be applied to other cylindrical members ? 187 Describe the usual form of thrust shaft 188 How is the propeller or tail shaft fitted up at the after end, and how is it secured to the length of shafting next forward in the case of twin screws ? 189 Describe the usual forms of crosshead and guide bearings 190 Describe the usual form of bearing for the crosshead pins 191 Describe the usual form of bearing for the crank-pin 192 Describe the usual form of bearing for the crank-shaft 192 Describe the usual form of bearing for the line shaft 193 Describe the two leading types of thrust bearing 193 Describe the usual form of stern and bracket bearings 196-10:9 Describe the usual type of western river boat engine. 200 What are the essential features of the valve gear employed on such engines ? 201 What is a western river boat "doctor"? 204 Describe the Parsons steam turbine 207 What are its advantages and disadvantages for marine practice?. .. . 209 What is the office of the throttle valve, and what forms of valve may be employed for this purpose? 209 What is the office of the main stop valve, and what is its usual form? 212 Describe the usual forms of globe, angle and straightway valves. .213, 214 What is the office of the cylinder drain and relief valves, and how are they usually made? 215 What are starting valves? 216 What is the purpose of the reversing gear? 217 Describe the "floating lever" type of reversing gear 217 What other forms of reversing gear are employed? 219 What is the purpose of the turning gear, and what are its main fea- tures ? 220 Describe the various forms of packing used for making the various fixed joints about a steam engine 221 Describe the more common forms of packing used in the piston- rod and valve stem stuffing boxes 221, 224 W r hat is a reheater, and what is its purpose? 225 What is the office of the governor? 225 Describe the usual principles on which marine governors are de- signed 225 What is the office of the counter gear, and of what does it consist? 227 What is the purpose of lagging on cylinders, valve chests, etc., and how is it usually fitted ? . . . 228 What kinds of oil are nsea ior luhncation, and what are their special characteristics? 22 g What other forms of lubricant are employed? 228 At what point in a bearing should the lubricant be applied? 229 About how much lubricant may be allowed per 1,000 I. H. P. per day in usual practice ? 229 In the adjustment of the bearing how much clearance may be left be- tween the journal and bearing surface ? 236 Describe the various devices in use for distributing oil or lubricant to a bearing 230-235 Describe the leading features of a modern system of oil distribution 235 What are the principal systems of piping found on shipboard? 237 What materials are in use for steam and water piping? 237 What are the relative advantages of copper, wrought iron and steel? 238 APPENDIX. 687 PAGE. What is the purpose of an expansion joint? -' . . . 239 Describe the usual form of expansion joint 239 CHAPTER V. Auxiliaries. What is the office of the circulating pump? 241 Describe the usual type of centrifugal pump and explain its mode of operation 241 Describe a usual type of outboard discharge valve 242 Describe the usual type of condenser 243 1 1 ( >\v are condenser tubes packed ? 245 What is the office of the air pumo? 245 Describe the usual type of construction and explain its mode of operation 246 What are the relative advantages and disadvantages of the attached and independent forms of air pump? 249 Why is the feed pump necessarily of different type from the circulat- ing pump? 251 Describe the usual form of attached plunger pump and explain its mode of operation 251 Why is the area of the steam-piston larger than that of the water plunger ? 253 What is the common ratio between these two areas? 236, 266 Describe a common form of injector and explain the principle of its operation 253 What is the difference between what are commonly known as auto- matic injectors and inspirators? 255 What is the office of the feed heater? 255 What are the two fundamental types of heater? 255 What is the source of the gain in the case of heaters using the fun- nel gases as a source of heat? 255 What are the styles of feed heater using steam as the heating agent? 256 What is tlie source of the gain in the case of heaters using steam as the source of the heat ? 256, 259 What is the purpose of the feed water filter? 260 What materials are used* as the filtering medium? 260 What is the purpose of the evaporator, and of what does it consist? 261 What are the chief points to be observed in the operation of the evaporator? 262 Describe a standard form of independent feed pump and explain its mode of operation 26^ What advantage has the "Admiralty" type of feed pump over other forms? 2Q -. Wlni are the uses of fans or blowers? 267 Di-M-ribc the usual form of centrifugal fan or blower, and explain its operation 2 6y What is the office of the separator? .'.'.'.'.' ' 267 Describe a usual type of construction ...... 268 Describe the ash ejector and explain its mode of operation ! ! . ' ^fo What principles govern the general arrangement of machinery on " shipboard? '. f. ... 272 CHAPTER VI. Operation, Management and Repair. A general examination of the boiler and fire-room equipment is to be made previous to getting up steam. Mention the more im- portant points to be attended to in such an examination 273 638 APPENDIX. PAGE. How are fires laid and started? 274 After lighting fires what points may receive special attention? 274, 275, 276 What precautions should be taken in opening a valve connecting a boiler with a pipe in which there is no steam pressure? 275 What fundamental points should be kept in view throughout the en- tire course of these operations? 276 What steps may be taken when s.team is formed and a moderate pressure is developed ? 276 What auxiliary machinery in particular should receive attention at this time ? 276 What attention should be paid the funnel guys during this period? 277 Describe briefly the routine of firing 277 What difference of method may be employed according as the coal is hard or soft ? 277 What is the usual thickness of the fire? 278 How is the thickness of the fire related to the draft pressure? 278 What is the result if thin spots are formed? 278 What means are available for working, cleaning and caring for the fire in the intervals of coaling? 278 Describe the duties of the water tender 279 Describe the "double shut off" method of making sure that the gauge glass is clear 279 For what purposes is blowing off now employed? 281 What is the special use of the bottom blow? Of the surface blow? 281 How may a plug cock be tested to ascertain whether it is open or closed ? 281 What means are available for ascertaining the density or saturation of the water? 127, 282 Describe the various means available for the disposal of ashes.. .269, 282 Describe the method of cleaning a fire 282 What means are available for removing the soot and ashes which accumulate in the tubes? 283 What preparations are made for sweeping tubes, and how is the operation carried out? 283 What dispositions may be taken when making a momentary or very short stop ? 284 If the stop is to be of longer duration what dispositions may be necessary or suitable? 284 What principles lie at the foundation of these various steps? 285 What mode of firing is usually most effective with water-tube boilers? 285 Why with such boilers is it especially necessary to pay strict attention "to the feed? 285 What trouble is met with on the fire side of the tubes of water- tube boilers ? 285 What dispositions may be made just previous to coming into port, or to a long stop, during which the fires are to be hauled, and the boilers opened ? 286 What are foaming and priming, and what steps may be taken to con- trol these conditions? 287 What causes may affect the working of the feed pump, and what steps may be taken to locate and remove the trouble? 288 What may be done in case the check valve is jammed? 291 What may be done in case the water gauge glass bursts? 291 What steps may be taken in the case of low water in the boilers?. . . . 292 What steps may be taken in the case of collapse or rupture of fur- nace crowns or combustion chambers? 294, 295 What steps may be taken in the case of serious leakage in the boiler tubes ? 295 What steps may be taken in the case of a ruptured steam pipe?. .. . 297 What are the first steps to be taken in connection with getting under way in a ship with whose machinery you are not familiar? 298 APPENDIX. 689 PAGE. Mention the various auxiliaries which must be examined and tested 298, 299 Describe the process of warming up the engine 299 Mention the various steps to be taken in connection with turning the engine over under steam 300 Trace in detail the passage of the steam from its formation in the boilers through its entire round, and to its return to the boilers as feed-water 301 What dispositions are made when stopping the engines momentarily? What if the stop is to be of some little duration, but with the engines ready for immediate start? What if of longer duration and steam is to be shut off the engine? 303 What derangements are likely to occur in the oiling gear? 304 What causes may lead to a hot bearing, and what measures may be taken to control the situation? 304 What are the causes of pounding, and what measures of relief may be taken ? 306 What are the evidences of priming or lifting water, and what should be done under such conditions? 307 What causes may lead to a poor vacuum with a hot condenser?. .. . 307 What causes may lead to a poor vacuum with a cool condenser? 307 What are the necessary conditions in order that rusting may pro- ceed continuously at ordinary temperatures? 308 What means does this suggest for preventing the formation of iron rust? 308 Describe the process of corrosion by an acid 309 Why are brass, bronze and copper used for many fittings which might otherwise be made of iron? ! 309 What is black or magnetic iron oxide and how is it formed? 310 What is one of the purposes of the ferrules sometimes fitted in the back ends of boiler tubes? 310 How may air and carbon dioxide gain access to the inside of a boiler? 310 Explain the nature of animal and vegetable oils and how they may give rise to the formation of a fatty acid 311 Explain the troubles which were formerly met with due to the presence of fatty acids in boilers 311 How are these difficulties now avoided? 311 What other acids may be present in the boiler? 311 What is meant by pitting? 312 Explain briefly what is meant by electro-chemical action, and its relation to boiler corrosion 312 What are the various means which may be employed to reduce or prevent the internal corrosion of boilers? 315-318 What are the special conditions necessary to reduce or prevent electro-chemical action ? .* 316 How does the use of soda aid in preventing corrosion? 316 How does the use of zincs aid in this purpose? 317 How should the zincs be fitted in order to be most effective? 317 Should 7.'mcs be fitted in boilers used for distilling purposes? 317 What treatment should be applied to spots in the boiler showing marked corrosion? 318 Explain the beneficial action of scale in preventing corrosion 318 What means may be taken for the protection of boilers which are to be laid up? 318 What is the proportion of solid matter in ordinary sea water? 319 What is the average composition of this solid matter? 319 What is the chief component of the solid matter in ordinary fresh water? 320 What are the chief constituents of boiler scale from river water, from brackish water, and from sea water? 320 690 APPENDIX. PAGE. Explain the manner in which calcium carbonate is deposited from so- lution , 321 Explain the manner in which calcium sulphate is deposited from solution 321 What ill effects may arise from the accumulation of scale in the boiler? 321 State some of the various ways in which the formation of fresh water scale may be reduced or prevented 322 Explain why the present condition with regard to the formation of salt water scale is quite different from that existing in former years with the very light steam pressures then common 324 Why was blowing off and making up with salt feed then admissible, while now inadmissible ? 324 What is the present condition with regard to make up feed, and how is it preferably obtained or carried? 325 State some of the various ways in which the formation of salt water scale may be reduced or prevented 326 In what manner may sea water be prepared for use in the boiler by the removal of the scale-forming constituents? 326 Can scale formation be entirely prevented, and if not what steps must be taken to insure the safety and efficiency of the boiler? 326 Describe the combinations of oil and scale which may be formed with- in a steam boiler 326 What is the surest means of preventing the formation of such com- binations? 328 In the inspection of boilers after use what points should be specially looked for in the furnace fronts, in the grates and bearers, in the bridge wall, in the tubes, in the joints and seams, in the front connections and uptakes, in the bracing, in the fittings? 328, 329 What special points should be held in view in examining the char- acter and amount of scale ? 330 What special points should be held in view in looking for corrosion? 330 What is the hydraulic test and how is it carried out? 331 What steps may be taken in the case of leakage about the joints on boiler mountings ? 333 What steps may be taken in the case of leakage about shell joints? 333 What steps may be taken in the case of leakage about the various in- ternal joints of a Scotch boiler? 335 What is a soft patch and how is it applied? 336 What is a hard patch and how is it applied? 336 Describe various means for taking care of small cracks or holes. .. . 336 What are blisters and laminations and what may be done with them? 337 How may leaky tubes be treated? 338 What steps may be taken in the case of leakage about braces and stays ? 339 What steps may be taken in the case of bulging or collapse of fur- nace and combustion chamber plates? 339 What may be done with a small split in the feed pipe? 341 In the case of overhauling and repairing the main engines, what special points must be looked for in the cylinders? 342 What points in the various pin joints and bearings? 343 What methods may be used in adjusting the bearings? 344 What points in the crosshead and guides? 345 Explain the general operation of lining up and adjusting a ma- rine engine 347 What points in the valve gear? 352 What points in the thrust bearings? 353 What troubles are liable to be met with in the condenser, in the air- pump or in other pumps? 353-^-- Men.tion the spare parts usually carried 356 APPENDIX. 691 PAGE. Describe the general methods in use in laying up marine machinery, and the points requiring special care " 356 CHAPTER VII. Valves and Valve Gears. E\ plain the meaning of the terms steam lap, exhaust lap, steam lead, e.\l:;,ust lead, cut-off, compression or cushion 359 Explain the general operation of a plain slide valve 359, 300 What is a double ported slide valve, and what is the purpose of this style of valve ? 360 What is a piston valve, and what is its chief advantage over the flat slide valve? 361 What is the purpose of an equilibrium piston and how is it fitted up? 365 What is the purpose of Joy's assistant cylinder and how is it fitted up? 366 What is the purpose of an equilibrium ring on the back of a flat slide valve, and how is it fitted up? 367 Explain the difference between an outside and an inside valve 368 What is an excentric and what is meant by its throw and angular advance? 369, 370 Explain the difference in the angular location of the excentric relative to the crank in the case of an outside, and of an inside valve. . . . 371 Explain the oval valve diagram for representing the movement of the valve relative to the piston, and for showing the various events and items of the operation 372 Explain the influence on the various events and items due to change in the three items, angular advance, steam lap and exhaust lap, , 376 Explain the Bilgram valve diagram for showing the same features as mentioned above in connection with the oval diagram 377 Explain the Zeuner valve diagram for showing the same features as mentioned above in connection with the oval diagram 379 Describe tVie main features of a Stephenson link valve gear 380 When partly linked up, how may the motion of the valve be deter- mined ? 382 What is the difference between the two arrangements known as crossed rods and open rods? 384 Whnt are the various effects due to linking up, and what is the difference as regards the lead in the case of open and crossed rods? 385 Describe the main features of the Braemme-Marshall valve gear.... 386 Describe the main features of the Joy valve gear 391 Describe the main features of the Walschaert valve gear 391 What ".iv the chief advantages of the radial types of valve gear?. ... 393 Describe the main features of the crank valve gear, and explain its mode of operation 394 Describe the usual form of excentric 397 I Fo\v is it fitted ur> and secured to the shaft? 397 Describe the usual form of excentric rod and strap 398, 399 Describe the usual form of double bar link, and the method of its control by bridle rods 400 Describe the usual form of link-block and valve-stem 402 How may an engine be put on the center or dead noint? 405 How would you set the main valve of an engine? 406 In setting a valve what will be the result of an incorrect length of valve rod ? 406 What will be the i-ftV.M of an incorrect angular location of the ex- centric relative to the crank? 407 Can a perfect balance of steam and exhaust events and items be obtained? 407, 408 Describe the general operation of setting a valve by observation of the valve itself 407 692 APPENDIX.. PAGE. Describe the use which may be made of indicator cards to the same purpose 48 CHAPTER VIII. Indicators and Indicator Cards. Describe briefly what is shown by an indicator card and name the various lines 4 10 In what manner does an actual card differ from an ideal card, or a card referring to ideal conditions? 4H To what are these differences due? 4H What are the two chief uses of indicator cards? 412, 4*3 As shown by the indicator card, what is the result on the steam dis- tribution of setting the excentric too far ahead of a line at right angles to the crank, that is, of too large an angular advance? .... 413 What is the result similarly with too small an angular advance? 413 What is the result with the steam lap too large? 414 What is the result with steam lap too small? 414 What is the result with exhaust lap too large? 414 What is the result with exhaust lap too small? 414 W r hat is the result with excessive compression? 415 What is the result with excessive expansion? 415 What is the result with valve stem too long or too short? 415 What is the result of a leaky piston or piston rod stuffing box? 416 What is the result with ports and passages too small? 416 Describe in detail the method of working up indicator cards for power, both by ordinates and by the planimeter 417 Describe and explain the method of combining a set of indicator cards from a triple or multiple expansion engine 426 Describe a steam engine indicator, name its various parts and state their uses 4 2 9 What is the object of the reducing motion? * 431 Describe various kinds of reducing motions 431-434 In examining and adjusting an indicator for service on the engine, what are the chief points to which attention should be given? 434, 435 Describe the operation of taking a card 436 How is the atmospheric line drawn? 436 What information should be placed on each card as it is taken? 436 CHAPTER IX. Special Topics and Problems. In what three physical states may bodies exist? 43& Name the characteristics of each 438 Describe the results of continually applying heat to a lump of ice. ... 439 What is the difference between a gas and a vapor? 440 What are the two chief kinds of change which the addition or sub- traction of heat may produce? 440 What is meant by the terms sensible heat and latent heat, and how are each related to the energy of the molecule? 441 What is meant by the term temperature? 442 How is it measured? 442 What thermometer scales are in use and how are they related? 442 How is heat measured as to its quantity? 442 What is the heat unit employed? 443 What is meant by Joule's equivalent or the mechanical equivalent of heat, and how much is it? 443 In how many ways may heat be transferred from one body or place to another? 444 Describe radiation, conduction and convection 444 Describe emission and absorption 444 APPENDIX. 695 PAGE. Describe how these verious operations enter into the heating of the water in a boiler 444 Describe the formation of steam from water 445 How does the temperature of the boiling point vary with the pressure ? 44& What is saturated steam?. 44& What is moist or wet steam ? 44$ What is dry and saturated steam? 449 What is superheated steam? 449 What is meant by the total heat of steam? 45O How do you find the total heat of a mixture of steam and water? . . 451 Mention various ways in which the economy of a steam boiler may be considered 453 Describe in particular the conditions affecting fuel economy 454 What is meant by the evaporation per pound of coal, and how is it found ? 456 What is meant by the evaporation per pound of combustible, and how is it found? 459 Describe the cycle or routine corresponding to the so-called ideal engine 461 Upon what does the efficiency of such an engine depend? 462 Describe the various heat wastes which prevent the actual engine from realizing the efficiency of the ideal 464 In what fundamental ways may the efficiency of the actual engine be improved ? 465 In particular what methods may be taken for reducing the heat wastes of actual engines? 465-468 Explain the gains which may result from the use of superheaters, re- heaters, jackets, feed heaters 467 Explain the relation of expansion to gain in efficiency 469 State for various representative types of engines the economy which may be expected in terms of coal per I.H.P. per hour and Ibs. of steam per I.H.P. per hour 471 Derive the formulae required for a general discussion of the lever safety valve 447-480 Explain the suppositions made in connection with the subject of boiler bracing, and show how the principles of mechanics are applied to these problems 480-484 Derive the formulae for the strength of cylindrical boilers, for both longitudinal and for circumferential rupture, and show that, aside from the influence of the riveted joints, the boiler is twice as strong in the latter as in the former direction 485-488 Derive the formulae for the strength of a bumped boiler head 488 Derive the formulae required for the discussion of the loss by blow- ing off, and show how to apply it to special cases 489 Explain the operation of the different types of feed water heaters, and how they may effect a saving in the heat required . .. .255. 491 How may the various diameters for the cylinders of triple and quadruple expansion engines be proportioned? 492 What is a clearance volume ? 494 Describe methods for its determination 495 How does the clearance affect the apparent expansion ratio as given by the point of cut-off? 496 Whit is the "engine constant" for power, and how is it found? 497 What is meant by the term "indicated thrust," and how is it found?. . 498 What is meant by the expression "reduced mean effective pressure" or "mean pressure reduced to the L.P. piston"? 499 How is .this reduced pressure found, and what is its relation to the indicated thrust ? 500-501 How may we compute the load on the main guides? 502 How may we compute the force required to move a slide valve?. .. . 503 694 APPENDIX. PAGE. How may we compute the number of pounds of condensing water per pound of steam for any given set of conditions? 504 How may we compute the work done by pumps, knowing the de- livery head and the amount of water handled? 505-50? How may we compute the discharge of steam from an orifice? 507 Explain some of the short cuts and convenient methods which may be employed in the computation of the weights of parts of marine machinery 508-512 CHAPTER X. Propulsion and Powering. What is the unit of speed used in navigation, and what is its value in feet per hour ? 5*4 How may knots be reduced to feet per minute? 514 How may miles per hour be reduced to feet per minute? 514 Explain briefly the fundamental problem in propulsion 515 Describe a screw propeller, and name its various parts and pro- portions 5 X 7 What is slip or slip ratio, and how is it computed? 519 What is the condition of the water in which the propeller works? 520 What is the difference between the true slip and the apparent slip?. . . 521 Describe various forms of screw propellers 523 When the blades are east separately, how are they secured to the hub? 524 Describe the attachment of the propeller to the shaft 525 What materials are used for screw propellers? 526 Describe methods of measuring the pitch of a screw propeller. . . .526-529 Describe the radial paddle wheel 530 Describe the feathering paddle wheel 530 Describe the two methods employed for operating the floats in the feathering wheel 530 What is the "rolling circle" ? 533 How is the slip of the paddle wheel estimated? 533 Give the Admiralty coefficient formula for powering ships 534 In general, how does the coefficint vary with the speed and geo- metrical characteristics of the ship? 53=; Name average values for typical cases 536 Explain the reduction of power developed by a ship when towing, or when undergoing a dock trial 537 W'hat are the general purposes of trial trips? 539 For the determination of speed alone, what observations are neces- sary? 540 Describe various ways in which tidal influence may be eliminated 540-542 Describe the manner in which such information may be plotted or represented graphically 541-543 Describe the various conditions which should be attended to in trials intended to develop the maximum speed and power 544 CHAPTER XI. Refrigeration. Explain the general principles of refrigeration 545 How are these principles carried out by the use of freezing mixtures? 546 How are they carried out by the use of ammonia or similar sub- stances ? 547 Give the principal features of ammonia refrigerating apparatus and explain its operation 549 How are the principles of refrigeration carried out by the use of a compressed gas? 553 Give the principal features of compressed air refrigerating machinery and explain its operation 554 APPENDIX. 695 PAGE. "What special points must be attended to in the operation and care of refrigerating machinery? 556 CHAPTER XII. Electricity on,. Shipboard. Explain the fundamental properties of a common magnet 559 What principle serves to connect magnetism with electric currents? 561 Whur are the fundamental principles upon which the operation of the electric generator depends? 562 Define the following terms: Electro-motive force, volt resistance, Ohm, Ampere, Watt 563-564 What are the two leading subdivisions of electric machinery? 565 Which form is commonly used on shipboard? 566 What are the leading features of a modern marine generating set? 567 How does a motor differ from a generator? 570 For what are motors chiefly used? 570 Explain the method of distribution of electric current for incan- descent lamps 572 What is the purpose of the switchboard? 573 Mertion the chief instruments and appliances found on the switch- board and give their uses 573~574 Describe the usual type of incandescent lamp 575 Describe a simple type of arc lamp 576 What points are of chief importance in the operation and care of electrical machinery ? 577 What are faults and how may they be located? 578, 580 INDEX. 697 Index. Adamson ring 94 Adjustment of bearings 230, 344 Adjustment of engines 34 1 Air casing 107 Air lock 133 Air pump 245 Air pump valve 248 Alloys , 24 Almy boiler 54 Aluminum I Ammonia refrigerating apparatus 549 Angle valve 213 Antimony I Arrangement plans, general 271 Arrangements of cylinders 164 Ash ejector 269 Ash gun 270 Ash pit door 104 Ashes, disposal of 282 Auxiliaries 241 Babcpck and Wilcox boilers 65 Beading tool 92 Beam engine 162 Bearing bars 104 Bearing, hot 34 Bearings 19 Bearings, adjustment of 230, 344 Bedplates 172 Belleville boiler 66 Bending tests 29 Bessemer process 13 Bilgram valve diagram 378 Bismuth I Blisters and laminations 1 1 Blowers 267 Blowing off 281 Blowing off, loss by 489 Blow-off cock " 122 Boilers 47 Boiler brace problem 480 Boiler bracing 94, 100 Boiler construction ' 86 Boiler corrosion 308 Boiler design in accordance with U. S. Rules 138 698 INDEX. PAGE. Boiler economy 453 Boiler heads 146 Boiler lagging 129 Boiler mountings 115 Boiler overhauling and repairs 328 Boiler-room routine 273 Boiler saddles 128 Boiler scale 319 Boiler test 331 Boiler tubes, leakage in 295 Boilers, laying up 318 Boilers, relative advantages of different types 56 Boilers, strength of 485 Boilers, weights of 1 12 Bottom blow 122 Bourdon steam gauge 124 Bowling ring 94 Brace, boiler, problem 480 Braces, boiler 94 Braemme Marshall valve gear 386 Brazing copper joint 2 Bridge wall 104 Bridle rods 401 Briquettes 41 Bucket valve? 246 Built-up crank shaft 186 Bulging or collapse of furnace and combustion chamber plates 339 Bumped heads 146 Butt straps 138 Butterfly valve 210 Calking tools 87 Carbon, influence of on cast iron 4 Cast iron 4 Casualties and emergencies in fire-room 287 Center, putting an engine on 405 Center of gravity 658 Centrifugal pumps 241 Check valve 121 Check valve jammed 291 Chrome steel 23 Chromium, influence of on cast iron 7 Circulating pumps 241 Cleaning fires 282 Clearance and its determination 494 Clearance, effect of in modifying the apparent expansion ratio 496 Clinker, formation of 35 Coal 31 Coal consumption, problems 472 Coil and tubulous boilers 152 Collc.pse of furnace crowns or combustion chamber plates 294 ( ollapse or bulging of furnace and combustion chamber plates 339 Columns 168 Combined indicator cards 425 Combustion 32 Combustion chamber 89 Coming into port 286 Common fractions 581 Compound engine 155, 157 Compressed air 'refrigerating machinery 554 Compressed grease cup 233 Computations for engineers 581 INDEX. 699 PAGE. Computing weights of machinery 508 Concaved heads 147 Condenser tube packing 246 Condensers 243 Condensing water, amount required 504 Connecting rod 184 Copper 2 Corrosion 308 Corrugated furnace flues 141 Corrugated furnaces 88 Corrugation, styles of 88 Counter gear 227 Cracks and holes 336 Crank valve gear 393 Crankshaft 185 Crosshead marks , 346 Crossheads 180 Crown bar 99, 145 Crucible steel , 13 Cylinders 165 Dead plate 104 Decimal fractions 592 Direct act ing pumps 263 Direct tubular boiler 50 Disc valve with balance piston 211 Distribution of power in a multiple expansion engine 428 Dock trial, reduced power at 537 Doctor on western river boats 204 Double beat poppet valve 210 Double end boiler 50 Double ported slide valve 360 Downflow pipes 53 Draft 129 Draft gauge 130 Drain gear 215 Dry pipe 120 Duodecimals 615 Dynamo, electric 565 Fconomy, steam boiler 453 Economy, steam engine 460, 471 Elastic limit . 26 Electric generator 565 Electric lamps 575 Electric machinery, faults in 578 Flfctrical machinery, operation and care of 577 Electric motors 570 Electricity on shipboard 559 Ellis and Eaves draft 135 Elongation 26 Emergencies and casualties in fire-room 287 Fmergencies in engine room 304 Engine constant 407 Engine economy 460 Engine fittings 209 Engine overhauling, adjustment and repairs 241 Engine room routine and management 298 Equilibrium piston 365 Evaporation per pound of coal 455 F.vanoration per pound of combustible 459 Evaporators 261 Excentric 397 700 INDEX. PAGE. Excentric rod 397 Excentric strap 397 Expansion joint 239 Expansion of steam, relation to economy 469 Fans 267 Feed check 121 Feed heaters 255 Feed pipe, split in 34 1 Feed pump , 251 Feed pump disabled 288 Feed water heating, gain by 49 1 Ferrule, condenser tube 245 Ferrules, boiler tube 93 Filters 260 Fire-room routine 277 Fire-tube boiler 48 Fires, cleaning the 282 Firing 277 Flange coupling 188 Flexible coupling 188 Flue and return tube boiler 51 Flue boilers 52, 113 Foaming 287 Foot valves 246 Forced draft 132 Forged crank shaft 187 Front connections 106 Fuels 31 Funnel 106 Furnace doors 102 Furnace fronts 102 Fusible plug 148 Gain by feed water heating 491 Gate valve 214 Gauge cocks 148 Gauge glass, bursting of 291 General arrangement of machinery 271 Geometrical problems , 642 Geometry and mensuration 621 Getting under way 273, 298 Girder brace 99 Globe valve 213 Governors 225 Grate 104 Grate bars 105 Grease cup, compression 233 Gridiron valve 210 Guides, main 190 Gusset brace 100 Hammer tests 29 Hard patch 336 Head valves 246 Heat and the formation of steam 438 Heat, its relation to matter 439 Heat, total of steam 450 Heat unit 442 Horizontal back acting engine 159 Horizontal direct acting engine 159 Hot bearing 304 Howden draft 133 Hydrokineter '. 127 INDEX. 7oi PAGE. Hydrometer I2 7 Ideal indicator card 4 12 Inclined engine I 6 Indicated thrust 49$ Indicator card, operation of taking 434 Indicator cards with deranged valve gear 4 : 3 Indicator cards, working up for power 4 1 ? Indicators and indicator cards 4 IQ Indicators, steam engine 429 Induced draft 135 Injector 254 Inside valve 368 Iron 3 Joint, expansion 239 Joints and packing 220 Joints boiler 86 Joints, riveted 67 Joy radial valve gear 39 Joy's assistant cylinder 366 Lagging, boiler 129 Lagging, engine 228 Lagrafel and D'Allest boiler 64 Lap 359 Latent heat 44i> 452 Laying up boilers 318 Laying up marine machinery 356 Lead 23 Lead of a valve 359 Leakage about stays and braces 339 Leakage at internal joints 335 Leakage in boiler tubes 295 Leg boiler 51 Lever safety valve 115 Lever safety valve problem 476 Line shaft bearing 193 Liners 166, 167 Lining up engines 347 Linings < 144 Link block 402 Link, Stephenson 400 Liquid fuel 42 Liquid fuel, use of, combined with coal 46 Locomotive patch 336 Locomotive type boiler 51 Loss by blowing off 489 Low water -. 292 Lubricants 228 Lubrication and oiling gear 228 Lubricator 233 Main guides, pressure on 502 Malleable iron Q Manganese, influence of on cast iron 7 Manganese, influence of on steel 15 Manhole covers I0 i Manhole fitting ] IOI Manholes Marine engines Marshall valve gear Materials of construction strength of 30 Mean effective pressure by planimeter 421 Mean effective pressure from indicator card I g 702 INDEX. PAGE. Measures and weights 599 Mechanical powers 659 Mechanics 652 Mensuration 621 Metallic packing 223 Monkey tail valve 216 Mosher boiler 57 Muffler 118 Multiple expansion engines, proportions of cylinders for 492 Mushet steel 23 Nickel steel 22 Niclausse boiler 63 Normand boiler 61 Oil and scale 326 Oil cup, sight feed 233 Oil cup with adjustable feed 232 Oil distribution, modern systems of 235 Oil fuel 42 Oil pump 235 Oiling gear 228 Oiling gear, derangement of 304 Open hearth process 14 Oscillating engine 159, 161 Outboard discharge valve 242 Outboard shaft 189 Overhauling of engines 341 Packing 220 Packing, condenser tube 245 Paddle wheel, feathering 530 Paddle wheels 530 Passover valve 216 Patch for boiler tube sheet '. 337 Patch for leaky j oint 334 Patch, hard, soft, locomotive 336 Percentage 596 Phosphorus, influence of on steel 15 Physics 650 Pillow block, main 191, 192 Piping 237 Piston 175 Piston, equilibrium 365 Piston rings 176 Piston rods '. 179 Piston valve 361 Pitch, measurement of 526 Pitting 312 Planimeter, use of for working up indicator cards 421 Plunger p'ump 251 Poppet valve 210 Port, coming into 286 Pounding 306 Powering ships 534 Pressure allowed on cylindrical shell boilers 138 Priming 287, 307 Propellers, materials of 526 Propeller, screw 517 Propellers, varieties of 523 Proportion 607 Proportions of cylinders for multiple expansion engines 492 Propulsion 514 Propulsion and powering 514 INDEX. 703 PAGE. Packing, metallic 223 Pump, Admiralty 264 Pump, air 245 Pump, duplex 264 Pump, oil 235 Pump, plunger 251 Pumps, centrifugal 241 Pumps, circulating 241 1 '111111)8, direct acting 263 Pumps, feed 251 Pumps, work done by 54 Quenching tests 29 Ramsbottom rings 177, 178 Ratio and proportion 607 Reduced mean effective pressure 499 Reducing motions 430 R eduction of area 27 Refrigeration 545 Refrigeration by expansion of a compressed gas 553 Refrigeration by freezing mixtures 546 Refrigeration by vaporization and expansion 547 Refrigerating machinery, operation and care of 556 Reheaters 225 Reinforce plate 100 Relief valves 215 Repair of engines 341 R epairs. boiler 328, 333 Retarders 93 Reverse shaft 400 Reversing gear 217 Ribbed furnace flues 142 Rivet holes to be drilled 138 Riveted joints 67 Roberts boiler 55 Rock shaft 400 Routine, boiler room 273 Routine in engine room 298, 301 Rupture of furnace crowns or combustion chamber plates 295 Rm>tnre of steam pipe 297 Saddles 128 Safety plugs 148 Safety valve problem 476 Safety valves 115, i./ifl Saturation, taking the 282 Scale, boiler 319 Scale prevention, fresh water 322 Scale prevention, salt water 324 Scotch boilers 50 Scotch boilers, common proportions of 112 Scotch boilers, common si/es and dimensions no Screw stay bolt 08 Srnlmry boiler 62 Seatings 174 Semi-steel 16 Sensible heat 441 Separators 267 Serve tube 93 Setting a valve 406, 408 Ships, powering 534 Shrinkage of cast iron 7 Side rods 401 7o 4 INDEX. PAGE. Sight feed oil cup 233 Silicon, influence of on cast iron 5 Silicon, influence of on steel IS Single-end boiler 50 Slide valve, force required to move 53 Slide valves 35$ Slipper crosshead 180, 181 Smoke, formation of 33 Socket bolt 98 Socket coupling 190 Soft patch ' 336 Soot, formation of 33 Spare parts '. 356 Specifications for structural steel 17 Speed, measure of 514 Spontaneous combustion 37 Spring bearing 193 Spring safety valve 1 16 Starting fires 273 Starting valves 216 Stay tubes 92 Stays and flat surfaces 139 Stays, boiler 94, 100 Steam 444 Steam chimney 51 Steam, discharge of through an orifice 507 Steam, formation of 438, 445 Steam gauge 124 Steam pipe, copper 150 Steam pipe rupture of : 297 Steam pipe, steel and iron 150 Steam, saturated 448 Steam, superheated 448 Steam, total heat of 450 Steel 12 Steel, mechanical properties of 16 Stephenson link valve gear 380 Stephenson link valve gear, details of 397 Stern bearing 196 Stern brackets 198, 199 Stern tube 197 Stop valve 1 18 Stop valve, main 212 Stopping suddenly 284 Straightway valve 214 Strength of boilers 48^ Strength of the useful metals 30 Stuffing box 222 Sulphur, influence of on cast iron 6 vSulphur, influence of on steel T 5 Surface blow I2 2 Sweeping tubes 283 Temperature 442 Tempering steel 22 Test of boilers ^j Test pieces for iron Test pieces for steel and other materials 28 Test pressure T -^g Testing of metals . 26 Thornycroft boiler \' 58 Throttle, operated by power 212 INDEX. 75 PAGE. Throttle valve 209 Thrust bearing IQ3> 195 Thrust shaft IQ4 Tin 24 To.wing, reduction of power when 537 Trial trips 539 Trial trips, special conditions for 544 Triple expansion engine 156, 15 Trunk engine 163 Tube expander 9 Tubes, boiler 91 Tubes, repairs on 338 Tubes, stay 92 Tungsten steel 23 Turbine, steam 207 Turning gear 220 Ultimate strength 26 Umbrella 107 Unstayed flat heads 146 Uptakes 106 Vacuum falls 307 Valves and valve gears 358 Valve, angle 213 Valves, bucket 246 Valve, butterfly 210 Valve diagram, Bilgram 378 Valve diagram, oval 372 Valve diagram. Zeuner 379 Valve, disc with balance piston 211 Valves, foot 246 Valve, gate 214 Valve gear, Braemme-Marshall 386 Valve gear, crank 393 Valve gear, Joy 3QO Valve gear, Steohenson link 380 Valve gear, Walschaert 391 Valve, globe 213 Valve, gridiron 210 Valves, head 246 Valve, main stop 212 Valve, monkey tail 216 Valve motion by simple excentric 369 Valve, outboard discharge 242 Valve, passover 216 Valve, piston 361 Valve, poppet 210 Valves, relief 215 Valve setting 405 Valves, slide 358 Valves, starting 216 Valve stem 402 Valve stem guide 403. 404 Valve, straightway 214 Valve, throttle 209 \Vatn w top boiler 51 Walschaert valve gear 391 Water gauge glass, bursting of 291 Water gauges and cocks 124 Water tending 279 Water tube boiler 53 Water tube boilers, casualties with 297 7 o6 INDEX. PAGE. Water tube boilers, construction of 108 Water tube boilers, hints regarding management 285 Weathering of coal 36 Weigh shaft 400 Weights and measures 599 Weights of boilers 60, 112 Weights of machinery, computing 508 Western river boat "doctor" 204 Western river boat valve gear 202 Western river boat engines 199 Western river boat boilers 113 Wick cup 230 Wiper 231 Wiring and distribution of light and power 571 Wrought iron 10 Yarrow boiler 59 Zeuner valve diagram 379 Zinc . . . 24 IVERSITY OF CALIFORNIA LIBRARY BERKELEY Return to desk from which borrowed. This book is DUE on the last date stamped below. ENGINEERING LIBRARY SEP 10 ,'48XB399sl6)476 YC 34151' 836454 ; &. THE UNIVERSITY OF CALIFORNIA LIBRARY