Engineering Library STEAM-ENGINE PRINCIPLES AND PRACTICE TERRELL CROFT, EDITOR CONTRIBUTORS The following have contributed manuscript or data or have otherwise assisted in the preparation of this work : EDMUND SIROKY H. C. CROFT A. J. DIXON E. R. POWELL Terrell Croft Engineering Company BOOKS BY TERRELL CROFT PUBLISHED BY McGRAW-HILL BOOK COMPANY, INC. THE AMERICAN ELECTRICIAN'S HANDBOOK, Flexible Leather, 7 X 4*4, 823 Pages, 897 Illustrations. WIRING OF FINISHED BUILDINGS, Cloth, 8 X 5 1 A, 275 Pages, 234 Illustra- tions. WIRING FOR LIGHT AND POWER, Flexible Cover, Pocket Size, 507 Pages, 428 Illustrations. ELECTRICAL MACHINERY, Cloth, 8 X 5^, 318 Pages, 304 Illus- trations. PRACTICAL ELECTRIC ILLUMINATION, Cloth, 8 X 5>, 225 Pages, 170 Illus- trations. PRACTICAL ELECTRICITY, Cloth, 8 X 5%, 646 Pages, 583 Illus- trations. CENTRAL STATIONS, Cloth, 8 X 5% 332 Pages, 310 Illus- trations. STEAM BOILERS, Cloth, 8 X 5M, 412 Pages, 518 Illus- trations. STEAM POWER PLANT AUXILIARIES AND ACCES- SORIES, Cloth, 8 X 5H, 447 Pages, 411 Illustrations. STEAM ENGINE PRINCIPLES AND PRACTICE, Cloth, 8 X 5>^, 495 Pages, 548 Illustra- tions. STEAMI-ENGINE PRINCIPLES AND PRACTICE TERRELL CROFT, EDITOR M CONSULTING ENGINEER. DIRECTING ENGINEER, TERRELL CROFT ENGINEERING CO. MEMBER OP THE AMERICAN SOCIETY OP MECHANICAL ENGINEERS. MEMBER OP AMERICAN INSTITUTE OP ELECTRICAL ENGINEERS. MEMBER OP THE ILLUMINATING ENGINEERING SOCIETY. MEMBER AMERICAN SOCIETY TESTING MATERIALS. FIRST EDITION FIRST IMPRESSION McGRAW-HILL BOOK COMPANY, INC. NEW YORK: 370 SEVENTH AVENUE LONDON: 6 & 8 BOUVERIE ST., E. C. 4 1922 C 7 ngineeri library COPYRIGHT, 1922, BY TERRELL CROFT THE MAPLE PKESS VOKK FA PREFACE STEAM-ENGINE PRINCIPLES AND PRACTICE has been very carefully prepared to satisfy what is thought to have been a long-felt need for a "practical" book which would contain the information that an operating engineer or a plant super- intendent requires concerning steam engines. Although there exists a popular impression that, since the advent of the steam turbine, the steam engine is no longer of any conse- quence in the generation of mechanical energy (power), noth- ing could be more erroneous. Under certain conditions, the steam engine is still and probably always will be a very desirable and economical prime mover. No attempt has been made to include in this book anything which pertains to the design of steam engines. The treatment has been directed toward what may be termed the "use" of the engines. That is, the aim has been to supply such infor- mation as will enable the reader to wisely select, operate, care for, and repair steam engines and to make a study of and where possible to improve their economy. No "higher mathematics" is employed; a working knowledge of arith- metic should enable one to understand all which is presented. Drawings for all of the 548 illustrations were made especially for this work. It has been the endeavor to so design and render these pictures that they will convey the desired infor- mation with a minimum of supplementary discussion. Throughout the text, principles which are presented are explained with descriptive expositions or with worked-out arithmetical examples. Also, at the end of each of the 16 divisions there are questions to be answered and, where justified, problems to be solved by the reader. These ques- tions and problems are based on the text matter in the division just preceding. If the reader can answer the questions and solve the problems, he then must be conversant with the subject matter of the division. Detail solutions to all of the problems are printed in an appendix in the back of the book. As to the general order of treatment : First the function and principle of the steam engine are considered. These are vii viii PREFACE followed by a division on nomenclature and classification. Next follows a treatment of indicators and their many uses. Then the two most important functioning parts of the engine the valves and the governor are fully treated under the divi- sion titles of: slide valves and their adjustment, Corliss and poppet valves and their adjustment, fly-ball steam-engine governors, and shaft steam-engine governors. The economics of the use of condensers with steam engines and of employing multi-expansion engines are next considered and are followed by a division on steam-engine efficiencies and how to increase them. The material in the next division, on steam engines of modern types, concerns the distinctive features, economics and costs of engines of the present day. The testing of steam engines is then treated. Following this are divisions on the management, operation and repair of reciprocating engines and on the use of superheated steam in engines which, it is hoped, will be of great value to the engineer. Next, the selection of steam engines is discussed from a purely but broadly economic standpoint. Finally, a thorough treatment of lubrication is presented which, although it relates specifically to steam engines, should prove of general value also as it applies to other machinery. With this, as with the other books which have been prepared by the editor, it is the sincere desire to render it of maximum usefulness to the reader. It is the intention to improve the book each time it is revised and to enlarge it as conditions may demand. If these things are to be accomplished most effectively, it is essential that the readers cooperate with us. This they may do by advising the editor of alterations which they feel it would be desirable to make. Future revisions and additions will, insofar as is feasible, be based on such suggestions and criticisms from the readers. Although the proofs have been read and checked very carefully, it is possible that some undiscovered errors may remain. Readers will confer a decided favor in advising the editor of any such. TERRELL CROFT. UNIVERSITY CITY, ST. Louis, Mo., July, 1922. ACKNOWLEDGMENTS The editor desires to acknowledge the assistance which has been rendered by various engine manufacturers of the United States. Among them are the: Allis-Chalmers Manufacturing Company; Ames Iron Works; Chuse Engine and Manufacturing Company; C. & G. Cooper Company; Erie Ball Engine Company; Erie City Iron Works; Fulton Iron Works; Harrisburg Foundry and Machine Works; Nordberg Manufacturing Company; Ridgway Dynamo and Engine Company; Vilter Manufacturing Company. Furthermore, certain of the text material appeared originally as articles in certain trade and technical periodicals among which are : National Engineer, Power, Power Plant Engineering and Southern Engineer. Numerical values for tables and graphs have, in certain instances, been taken from engineering textbooks of recog- nized high standing. In such cases acknowledgment is made at the places in the text where the values are used. Special acknowledgment is hereby accorded Edmond Siroky, Head Mechanical Engineer of The Terrell Croft Engineering Company, who has been responsible for the technical accuracy of the book. Other acknowledgments have been made throughout the book. If any has been omitted, it has been through oversight and, if brought to the author's attention, it will be incor- porated in the next edition. TERRELL CROFT. IX CONTENTS STEAM-ENGINE PRINCIPLES AND PRACTICE BY TERRELL CROFT PAGE FRONTISPIECE iv PREFACE vii ACKNOWLEDGMENTS ix LIST OF SYMBOLS xii DIVISION 1. FUNCTION AND PRINCIPLE OF THE STEAM ENGINE. 1 DIVISION 2. STEAM-ENGINE MECHANISMS AND NOMENCLATURE 19 DIVISION 3. STEAM-ENGINE INDICATORS AND INDICATOR PRACTICE 40 DIVISION 4. SLIDE VALVES AND THEIR SETTING . 84 DIVISION 5. CORLISS AND POPPET VALVES AND THEIR SETTING 146 DIVISION 6. FLY-BALL STEAM-ENGINE GOVERNORS, PRINCIPLES AND ADJUSTMENT 192 DIVISION 7. SHAFT STEAM-ENGINE GOVERNORS, PRINCIPLES AND ADJUSTMENT 228 DIVISION 8. COMPOUND AND MULTI-EXPANSION ENGINES . . . 258 DIVISION 9. CONDENSING AND NON-CONDENSING OPERATION. . 283 DIVISION 10. STEAM-ENGINE EFFICIENCIES AND How TO INCREASE THEM 291 DIVISION 11. STEAM ENGINES OF MODERN TYPES 319 DIVISION 12. STEAM-ENGINE TESTING 342 DIVISION 13. RECIPROCATING-ENGINE MANAGEMENT, OPERATION, AND REPAIR 373 DIVISION 14. USE OF SUPERHEATED STEAM IN ENGINES .... 417 DIVISION 15. SELECTING AN ENGINE 427 DIVISION 16. STEAM-ENGINE LUBRICATION 447 SOLUTIONS TO PROBLEMS 488 INDEX . . 497 XI STEAM ENGINE PRINCIPLES AND PRACTICE LIST OP SYMBOLS The following list comprises practically all of the symbols which are used in formulas in this book. Symbols which are not given in this list are defined in the text where they are first used. When any symbol is used with a meaning different from that specified below, the correct meaning is stated in the text where the symbol occurs. SECTION SYMBOL MEANING FIRST USED Ai P Area of piston, exclusive of area of rod, in square inches 17 C m Mean specific heat of superheated steam 317 Dps Density of steam, in pounds per cubic foot 129 di Diameter, in inches 360 E Voltage or electromotive force, in volts 361 Ed Efficiency, expressed decimally 362 Erf TO Mechanical efficiency, expressed decimally 321 E therefore, the greatest theo- ItS Work By Virtue Of En- retical efficiency that any engine can attain ergy Which It Abstracts From when working between the pressures shown ' ; The Steam; see A, Fig. 8. That this is true is shown by every steam-engine test. It was shown in Sec. 1 for the engine illustrated in the frontispiece, that the steam was cooled in passing through the engine from 364 deg. fahr. to 130 deg. fahr. Furthermore, a test would have shown that the quality of the steam was also decreased in passing through the engine. The loss in heat, which the steam undergoes due to the lowering of its temperature and the decreasing of its quality, represents heat abstracted from the steam. As will be ex- plained, all or part of this heat loss may have been the result of the conversion of heat energy into mechanical energy (or work). EXAMPLE. If, in the plant illustrated in the frontispiece, the quality of the steam entering the engine is 99 per cent, and that of the leaving (exhaust) steam is 80 per cent., how much heat energy is abstracted from each pound of steam that the engine uses? SOLUTION. From 8 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 1 steam tables and charts, the total heat of 1 Ib. of steam at 364 deg. fahr. and of 99 per cent, quality is 1186 B.t.u. Likewise, the total heat of 1 Ib. of steam at 130 deg. fahr. and of 80 per cent, quality is 913 B.t.u. Therefore, for this engine the heat abstracted = 1186 - 913 = 273 B.t.u. per pound. 10. The Ratio Of The Work Done By The Steam To The Heat Abstracted From The Steam depends on how much heat is wasted (L, Fig. 8) within the engine cylinder. If an engine could be constructed with non-heat-conducting cylinder and piston it would be possible to convert into work all of the heat which is abstracted from the steam. But, since no non-heat- conducting material has ever been discovered, much less a heat non-conductor which could be used for cylinder and piston construction, the steam within an engine cylinder will always lose heat (waste it) through the walls and the piston. This heat which is lost from the steam within the cylinder is called a thermal loss. 11. The "Total Work Done By The Steam" Constitutes Useful Work And Mechanical Losses ; U and MI, Fig. 8. The work done by the steam can be computed (Sec. 17) from the pressures which it exerts upon the piston and the distance it causes the piston to move. As will be shown in Div. 3, this work can be measured. If, now, all of the engine's moving parts were f rictionless, all of the work done by the steam would then be available for transmission, as mechanical energy, to some other machine. But, since friction cannot be entirely eliminated in any engine mechanism (Div. 16), it follows that a portion of the work done by the steam will be used up or lost within the engine itself in overcoming the friction of its own parts. This portion of the work constitutes a loss and may be termed the mechanical loss or losses. Evidently, only that energy which remains after the friction is overcome can be utilized as mechanical energy. It follows, therefore, that: (2) Work done by steam = Mechanical losses + Useful energy. 12. There Is A Heat Balance For Every Steam Engine; see Fig. 8. The meaning of this is that the total energy leav- SEC. 13] PRINCIPLE OF THE STEAM ENGINE ing the engine in various forms is equal to the total heat energy which the engine receives. The various ways in which energy leaves a steam engine have been discussed in preceding sec- tions and may be summarized as follows and as shown in Fig. 8 : Of the heat, H, which an engine receives only a small part, A, is abstracted whereas the greater part, R, is rejected (Sec. 6). The rejected heat is not useful for work but may be utilized for building-heating or other industrial services. The heat, A, which the engine abstracts may be divided into: (1) That, T, which is converted into work. (2) That, L, which constitutes thermal losses. The heat, T, may again be separated into: (1) Useful work, U. (2) Mechanical losses, M, Sec. 11. Heat Flowing To Engine^ Abstracted Heaf-,. .Total Work Useful \ Done By Steam Work -. 777/5 Heat May Be Employed, But Cannot, Be Returned To The Engine Wasted Heat \IO% FIG. 8. An elementary heat balance for a typical high-grade steam engine. NOTE. AN EFFICIENT STEAM ENGINE is one in which the ratio of useful work to heat received is large. An efficient power plant is one in which such use is made of the rejected heat, R (Fig. 8) that the portion thereof which is wasted is a minimum. EXAMPLE. For the engine, the heat balance of which is shown in Fig. 8, H represents all (100 per cent.) of the heat added to the water in the boiler to convert the water into steam. Upon receiving the steam, the engine abstracts 26 per cent, of this heat and rejects the remaining 74 per cent. Within the cylinder, 8 per cent, of the original 100 are lost thermally, L, while 18 per cent, is converted into work, T. Of this 18 per cent., 2 per cent, is lost in overcoming mechanical friction and the remaining 16 per cent, of the original 100 appears as useful work. That is, for this engine, as explained in Sec. 7, the theoretical efficiency = heat abstracted/ heat received = 26 -5- 100 = 0.26 = 26 per cent. 13. How Steam Does Work By Direct Pressure may be understood by a study of Fig. 9 (see also the author's PRAC- TICAL HEAT). If, with the piston in the position illustrated, valve Vi is opened, steam will be admitted into the space to 10 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 1 the left of the piston. It will exert against every square inch of the piston's face a pressure equal to that at which the steam is generated in the boiler. This pressure will exert a force tending to push the piston to the right. At the same time, however, the air acting on the right-hand face of the piston is exerting against every square inch thereof a pressure equal to that of the atmosphere. It is evident that if the boiler-pres- sure exceeds the atmospheric pressure, there will be an unbal- anced force on the piston tending to move it to the right. If this force is capable of moving the piston, work will be done upon the piston. EXAMPLE. If the boiler pressure (Fig. 9) is 100 Ib. per sq. in. abs. and the atmospheric pressure is 1.5 Ib. per sq. in. abs., and if the piston's area is 100 sq. in., the total force which acts on the left face of the piston will be 100 sq. in. X 100 Ib. per sq. in. = 10,000 Ib. Likewise, the force acting on the piston's right face will be 100 sq. in. X 15 Ib. per sq. in. = 1,500 Ib. The net or unbalanced force will be 10,000 1,500 = 8,500 Ib. If, now, this force is able to move the piston, the work done for each foot that the piston is moved will be 1 ft. X 8,500 Ib. = 8,500 ft. Ib. If the stroke (distance moved by the piston) is 2 ft., then the work done per stroke will be 8,500 X 2 = 1 7,000 ft. Ib. NOTE. THE "NET PRESSURE" ON THE PISTON, at any instant, is the difference between the pressures on its two sides. The work done during a stroke is equal to the product of the average net pressure, the piston's area and the length of the stroke. In the above example the net pressure is 100 15 = 85 Ib. per sq. in. 14. Work Must Sometimes Be Done Upon The Steam In Expelling It From The Cylinder. If, in Fig. 9, after the piston reaches the position, M , shown by dotted lines, Vi is closed and F 2 is opened, the pressure at the left of the piston will be reduced as the steam escapes through V 2 until the pressure in the cylinder is equal to that within the vessel into which the steam exhausts. This pressure is called the back pressure. The value of this back pressure may vary from 1 or 2 Ib. per < -Stroke - I-Seciion Through Cylinder FIG. 9. Work diagram for an engine which takes steam for a full stroke. SEC. 14] PRINCIPLE OF THE STEAM ENGINE 11 sq. in. abs. (when a condenser is used, Div. 9) to 35 Ib. per sq. in. abs. or more. Whenever the back pressure is in excess of atmospheric pressure (in a single-acting engine as shown in Fig. 9,) the net pressure on the piston will act opposite to the direction in which the piston must be moved to exhaust the steam from the cylinder. Under such circumstances this net pressure must be overcome by using some external means for exhausting the steam. The external force then does work upon the steam in overcoming the net pressure. As in the preceding section, the work done is equal to the net pressure times the piston area times the distance moved or stroke. EXAMPLE. If, in Fig. 9, the back pressure on the engine is 20 Ib. per sq. in. abs, what work must be done upon the steam to exhaust it and what is the net work done by the steam per double-stroke? SOLUTION. The work done on the steam during each exhaust stroke is (20 15) X 100 X 2 = 1,000 ft. Ib. Since, by the example of Sec. 13, the work done during the admission stroke is 17,000 ft. Ib., the net work for the two strokes is 17,000 - 1,000 = 16,000 ft. Ib. NOTE. THE "EFFECTIVE PRESSURE" ON AN ENGINE PISTON, for any of its positions, is the difference between the two net pressures which act upon it when it is travelling in opposite directions through that position. Thus, for the engine of Fig. 9, the effective pressure for any position is 85 5 = 80 Ib. per sq. in. The net work of the steam upon the piston could have been found by multiplying together the piston area, stroke, and effective pressure. Thus: net work = 100 X 2 X 80 = 16,000 A Ib. NOTE. THE "WORKING STROKE" OR "POWER STROKE" of any heat engine is understood to mean the movement of the piston from one end of its travel to the other while one charge of the working substance urges the piston onward. Thus, in the engine of Fig. 9, the movement of the piston toward the right constitutes a working stroke. The return of the piston to the left is termed its return stroke. A working stroke together with a return stroke constitutes a double stroke. In formulas in this book, N a = number of working strokes per minute. NOTE. SINGLE AND DOUBLE-ACTING ENGINES are those in which working strokes are performed as the piston moves respectively in one or both directions. The engine of Fig. 9, since steam is admitted only on one side of its piston, is a single-acting engine. Steam engines are usually constructed so as to admit steam to both sides of the piston (Fig. 3) ; they are then double-acting since working strokes are then performed as the piston moves in either direction. From these definitions it follows that in double-acting steam engines each stroke is a working stroke, whereas in single-acting steam engines only alternate strokes are working strokes. 12 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 1 15. How Steam Does Work By Expansion may be under- stood by reference to Fig. 10. The same engine as illustrated in Fig. 9 is now shown taking steam for only one-half stroke. The line AB represents the pressure during the first half- stroke while Vi is open. When Vi is closed (B), the net pressure of the steam is still 85 Ib. per sq. in. Further move- ment of the piston to the right, however, will cause the pressure within the cylinder to decrease. Thus, as the piston completes its stroke, the pressure will drop as indicated by the curve BC. The net pressure on the Steam Admitted; Steam Expanding -. . . ,., . , | VtOpen. Both va/^s closed piston likewise decreases. Thus, at the end of the stroke, the net pressure is as repre- sented by GC. The back pressure is represented by EF or by GD. Just as the net pressure varies from B to C, so does the effective pres- sure now vary for different positions from B to C. Effective pressures are now represented by the vertical .- Steam Outlet -Stroke H 31- Section Through Cylinder FIG. 10. Work diagram for an engine which takes steam for only part stroke, distances trom HiD tO (This engine is taking steam for only one- ^IsO, the net WOrk is half stroke.) , _ _ sented by the shaded area ABODE. The net work is computed by multiplying together the piston area, stroke, and average or mean effective pressure. Methods of finding the mean effective pressure are given in Div. 3. EXAMPLE. For the engine of Fig. 10, the mean effective pressure is 68 Ib. per sq. in. Therefore, the net work = 100 X 2 X 68 = 13,600 ft. Ib. Of this, 100 X 1 X 80 = 8,000 ft. Ib. were done along AB and 13,600 - 8,000 = 5,600 ft. Ib. were done along BC. 16. The Economy Of Using Steam Expansively is illustrated by the example of the preceding section. It should be noted that, in Fig. 10, since steam was admitted to the cylinder for only one-half stroke, the weight of steam admitted was little more than one-half that admitted to the engine of Fig. 9. As used in Fig. 9, the weight of steam admitted in Fig. 10 would SEC. 17] PRINCIPLE OF THE STEAM ENGINE 13 do only about 8,000 ft. Ib. of work. But in Fig. 10 it was found to do 13,600 ft. Ib. Now, the difference of 5,600 ft. Ib. was done at the expense of no greater quantity of steam and, therefore, of heat. The saving effected by the expansive use may be expressed as 5,600 *- 8,000 = 0.70 or 70 per cent. Note, however, that although the Fig. 10 arrangement works the more economically than does that of Fig. 9, it does less total work 13,600 ft. Ib. as against 16,000 ft. Ib. It follows that the Fig. 10 cylinder, to do the same amount of work as in Fig. 9, would have to be increased in size in the ratio of 16,000 to 13,600. Or, it would have to be about 18 per cent, larger. The conclusions to be drawn from the above are: (1) That expansion increases the ratio of work done to heat used. (2) That expansion necessitates a larger cylinder for a given work output. Further considerations which attend expansive use of steam are given in Div. 10. NOTE. THE EXPANSIVE USE OF STEAM Is NOT DESIRABLE IN ENGINES OF CERTAIN CLASSES, such as hoisting engines, steam pumps, and steam hammers. An engine which uses steam expansively, if stopped in a position where the admission valve is closed, cannot be started without moving the engine mechanism, by some outside means, until the valve opens. This, of course, is undesirable in engines which must be frequently stopped, as must those listed above. These engines, therefore, are not usually so made as to use steam expansively. 17. To Compute The Work Done Per Double-Stroke By Any Steam Engine, use the following formula, which is simply the mathematical expression of the rules of Sec. 14: (3) W = A ip Lj 8 P m (ft. Ib. per double stroke) Wherein : W = work done in one end of a cylinder per double stroke (Sec. 14), in foot pounds. A ip = area of piston, exclu- sive of any rod, see note below, which passes through the cylinder end, in square inches. L Js = length of stroke, in feet. P m = mean effective pressure (Sec. 15), in pounds per square inch. NOTE. THE EFFECT OF ROD AREA, since the rod area subtracts from the total area upon which the steam can act, is cared for by subtracting the area of the rod from the total cross-sectional area of the cylinder whenever a rod extends through the cylinder end or head. Single-acting engines (Sec. 14) seldom have a rod extending through the cylinder head. 14 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 1 Double-acting engines may have a rod extending through one cylinder head or they may have rods extending through both heads. Since the area of the piston rod seldom exceeds from % to 1% per cent, of the cylinder area, it may well be neglected in practical problems and in approx- imations. In exact determinations, however, it must be considered. EXAMPLE. A single-acting engine, which takes steam at only one end and has no rod passing through the head, has a piston 10 in. in diameter and a stroke of 30 in. If the mean effective pressure is 66 Ib. per sq. in., what work is done per double-stroke? SOLUTION. Substituting in For. (3): W = A ip L f8 P m = (10 X 10 X 0.785) X (30 + 12) X 66 = 12,925.5 ft. Ib. per double-stroke. 18. To Compute The Power Developed In Any Steam Engine, the elements of time must be introduced into the work equation of Sec. 17. Since power is the rate of doing work (see the author's PRACTICAL HEAT) it may be expressed in foot pounds per second or in foot pounds per minute or in B. t. u. per hour and so on. In this book, power will usually be measured in horse power. The horse power is equivalent to 550 ft. Ib. per sec. or 33,000 ft. Ib. per min. The following formulas, which follow from the preceding, give the power which is developed in only one end of the cylinder. For a double-acting engine compute for each end separately, allow- ing for the piston-rod area if necessary. Then add the two results. (4) P = PmLjsAipN, (ft. Ib. per min.) Wherein: P = power developed in one end of the cylinder, in foot pounds per minute. P ihp = power developed in one end of the cylinder (indicated power), in horse power. P m = mean effective pressure, in pounds per square inch. L fs = length of stroke, in feet. A ip = area of piston, exclusive of the area of any rod which passes through the cylinder end, which is under consideration, in square inches. N s = number of double strokes per minute, see note under Sec. 14; for steam engines with rotative crank shafts: N 8 = N = the angular speed of the crank shaft, in revolutions per minute. (Only engines with rotative crank shafts will be considered in this book.) SEC. 19] PRINCIPLE OF THE STEAM ENGINE 15 EXAMPLE. If the engine of the example of Sec. 17 has a crank shaft which makes 100 r.p.m., what is its indicated power in foot pounds per minute and in horse power? SOLUTION. By For. (4) : P = P m Lf S A ip N s = WN S = 12,925.5 X 100 = 1,292,550 ft. Ib. per min. By For. (5): Pa p = P^L/aAip^/33,000 = P/33,000 = 1,292,550 -^ 33,000 = 39.2 h.p. See also the example under Table 20. 19. To Compute The Approximate Mean Effective Pres- sure of a simple steam engine (Sec. 33) when an indicator diagram (Sec. 78) cannot be obtained, the following formula may be useful. Since engines with throttling governors (Sec. 215) do not take steam at boiler pressure except under very heavy load, the formula can only be used for such engines when it is known that the governor valve is wide open. (6) P m = 0.9[K(P ff + 14.7) - P a ] (pounds per square inch Wherein: P m = the approximate mean effective pressure, in pounds per square inch. K = a constant, as found from Table 20, depending on the apparent cut-off. P g = the pressure of the steam in the engine's supply pipe, or the boiler pressure, in pounds per square inch gage. P a = the back pressure on the engine, in pounds per square inch absolute; for non-con- densing engines P a may be taken at 17 Ib. per sq. in. abs.; for condensing engines, P a is found from the condenser vacuum gage and barometer readings. 20. Table Of Constants For Use In Calculating Approxi- mate Mean Effective Pressure. The values of K tabulated below are those to be used in For. (6) of the preceding section. Cut-off K Cut-off K Cut-off K Frac- tion Per cent. Frac- tion Per cent. Frac- tion Per cent. H 17 0.545 M 37 0.773 H 67 0.943 X 20 0.590 % '40 0.794 Ko 70 0.954 K 25 0.650 H 50 0.864 M 75 0.970 Mo 30 0.705 H 60 0.916 H 80 0.981 H 33 0.737 K 63 0.927 y 8 88 0.993 16 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 1 NOTE. In this table the fraction or percentage cut-off is obtained by dividing the distance that the piston has travelled from the beginning of its stroke when the steam is cut-off, by the whole length of stroke; that is, it is the apparent cut-off, Sec. 135. EXAMPLE. Find the mean effective pressure of a non-condensing engine, which cut-offs at one-half stroke, if the boiler pressure is 80 Ib. per sq. in. gage. If the engine is double-acting, runs at 320 r.p.m., has a piston 7 in. in diameter, and has a 10-in. stroke, what is its horse power? SOLUTION. By Table 20, K = 0.864 for % stroke. Substituting in For. (6): P m = 0.9 [K(P a + 14.7) - P.] = 0.9 X [0.864(80 + 14.7) - 17] = 58.3 Ib. per sq. in. Then, by For. (5) : P ihp = P m Lf S A ip N s /33,QOO = [58.3 X (10 -^ 12) X (7 X 7 X 0.785) X 320] -^ 33,000 = 18.1 h.p., for one end. Now, since the engine is double-acting, the total horse power will (disregarding piston-rod area) be twice that of one end or: total horse power - 2 X 18.1 = 36.2 h. p. 21. The Form Of The Expansion Line For Steam, as it expands within the engine cylinder, is different for different JT 160 | .40 120 g 100 % 80 a 60 !*> < lateral Hyperbola '/abatic Expansior Curve 10 20 30 40 50 60 10 60 90 100 110 120 130 140 Volume Per Pound Of Steam, Gu. Ft. Fia. 11. Graphs comparing adiabatic expansion curve and equilateral hyperbola for Steam expanding from 165 Ib. per sq. in. abs. to 2 Ib. per sq. in. abs. engines. As assumed in the Rankine cycle (Sec. 8), if the cylinder and piston were of non-heat-conducting material the expansion would be adiabatic. That is, the steam would suffer no gain or loss of heat by heat transfer. During expan- sion the heat content of the steam would decrease at the same rate as that at which the steam does work upon the piston. The exact form of the expansion curve would depend some- what upon the initial and final steam pressures. Since, how- ever, no cylinder or piston is non-heat-conducting, the form of the actual expansion line will differ from the adiabatic curve. Experiments show that the expansion generally SEC. 21] PRINCIPLE OF THE STEAM ENGINE 17 follows very nearly an equilateral hyperbola. The construc- tion of the equilateral hyperbola is given in Sec. 108. EXAMPLE. The adiabatic expansion curve for steam expanding from 165 Ib. per sq. in. to 2 Ib. per sq. in. is plotted in Fig. 11. An equilateral hyperbola is also plotted alongside it (dashed). QUESTIONS ON DIVISION 1 1. What is the primary function of the steam engine? 2. How is heat energy derived? 3. How is mechanical energy transmitted? How heat energy? 4. Draw a sketch of a steam engine and enumerate the principal parts. 5. Explain the term clearance. Define displacement volume. How is clearance usually expressed? What is piston clearance? How is it measured? 6. Explain, with a sketch, the operation of an elementary steam engine with hand- operated valves. How can the valves be made to operate automatically? Show with a sketch. 7. Show, by a sketch, the form of a single valve which controls the steam flow to both ends of a cylinder. 8. In what forms is energy available for man's use? In what forms is it most fre- quently employed? How is energy transformed to the useful forms? 9. State the mechanical and electrical-energy equivalents of the British thermal unit. 10. Why cannot an engine convert into work all of the heat which it receives? What becomes of that which is not abstracted? 11. Define theoretical efficiency. Upon what does the theoretical efficiency of an engine depend? Give the formula for theoretical efficiency. 12. Explain the construction and operation of the theoretically most perfect steam engine. Why is it not practical? What is its cycle called? 13. Whence does a steam engine derive its' ability to do work? 14. Into what two classes does the heat which an engine abstracts from the steam first divide? Which of these constitutes a direct loss? The abstracted heat which does not constitute a direct loss is how used? 15. Draw a heat balance diagram to show the disposition of all of the heat which an engine receives. 16. Explain what distinguishes an efficient steam engine. An efficient power plant. Can an efficient power plant be made up of inefficient steam engines? Why? 17. Explain how steam does work by direct pressure. Define net pressure. 18. Explain how work is sometimes required to drive exhaust steam from an engine cylinder. Define effective pressure. Define a working stroke. 19. Explain how steam does work by expansion. Define mean effective pressure. Explain, with a diagram, the economy of using steam expansively. What classes of engines do not use steam expansively? Why? 20. Give the formula for finding the net work done per double-stroke by the steam upon the piston. Explain its derivation. 21. Define power. What are its units? State the horse power formula for engines. 22. Give the formula for finding the approximate mean effective pressure of a steam engine. To what classes of engines may it be applied? Upon what three variables does the mean effective pressure depend? 23. What form does the expansion line take for steam which expands in an actual engine cylinder? What form has it in the Rankine cycle? PROBLEMS ON DIVISION 1 1. A 10-in. by 12-in. engine has a clearance volume of 185 cu. in. at the head end and 180 cu. in. at the crank end. If the piston rod is 1.5 in. in diameter, what are the clear- ances in per cent, of the displacement volumes? 2 18 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 1 2. A steam engine is supplied with dry saturated steam at a pressure of 160 Ib. per sq. in. abs. and exhausts steam of 89 per cent, quality at 17 Ib. per sq. in. abs. What is its theoretical efficiency? 3. A double-acting hoisting engine with a 9-in. -diameter piston and 12-in. stroke takes steam (for full stroke. Sec. 13) at 125 Ib. per sq. in. gage and exhausts at 4 Ib. per sq. in. gage. How much work does the steam do per working stroke? If the engine is running at 200 r.p.m., what is its horsepower? Neglect piston-rod area. 4. If the engine of Prob. 3 were arranged to cut off at H stroke what would be its horse power? DIVISION 2 STEAM-ENGINE MECHANISMS AND NOMENCLATURE 22. The Classification Of Steam -Engine Types which follows is rearranged from an outline in STEAM POWER by Hirshfeld and Ulbricht. As there is an overlapping of the various types, it would be impractical to discuss engines according to this table. Hence no effort will be made to do so. Defini- tions of the various terms employed in this table are given in following sections. These are then followed by brief descriptions of some other frequently used steam-engine terms, and of the types of governors. 23. Table of Classifications of Steam-Engine Types. Basis of classification Primary subdivision Secondary subdivision (1) Cylinder arrangement (A) Single cylinder (B) Tandem (C) Cross (Z>) Duplex (E) Opposed (F) Angle (2) Longitudinal axis (A) Vertical (B) Inclined (C) Horizontal (3) Rotative speed (A) High speed (B) Medium speed (C) Low speed (4) Ratio of stroke to diame- ter (A) Short stroke (B) Long stroke (5) Vai^e gear (A) Slide valve (a) D-slide valve (6) Balanced valve (c) Multiported valve (d) Gridiron valve (e) Piston valve (B) Corliss valve (a) Detaching (b) Positively-operated (C) Poppet valve (a) Detaching (b) Positively-operated 20 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 Basis of classification Primary subdivision Secondary subdivision (6) Engine mechanism (A) Standard (B) Back-acting (C) Trunk-piston (D) Oscillating-cylinder (7) Steam expansion (A) Single expansion (B) Multi-expansion (a) Compound (b) Triple (c) Quadruple (8) Steam flow (A) Counter flow (B) Uniflow (9) Steam conditions (A) Initial pressure (a) High pressure (b) Medium pressure (c) Low pressure (B) Initial temperature (a) High superheat (b) Low, or no superheat (C) Back pressure (a) Condensing (b) Non-condensing Cylinder-- Piston - -Piston Valve 24. A Vertical Steam Engine (Fig. 12) is one which has the center line of its cylinder, M, in a vertical position. 25. A Horizontal Steam Engine (Fig. 13) is one which has the center line, CL, of its cylinder in a horizontal position. 26. An Inclined Steam Engine (Fig. 14) is one which has the center lines, CL, of its cylinders inclined from the horizontal or vertical position. 27. A Side-Crank Engine (Figs. 17 to 21) is one which has its crank attached at the end of the shaft overhanging the main bearing. In engines of this type the crank, C (Fig. 15), is generally forged as a separate part and fastened securely to the shaft, S. 28. A Center-Crank Engine (Fig. 12) is one which has its crank located between the crank- FIG. 12. A vertical steam engine. SEC. 29] STEAM ENGINE MECHANISMS 21 shaft bearings. In this type of engine, the crank, C (Fig. 16), is generally forged as part of the shaft, S. Flywheel ~^ Connecting Crosshead' 'NN. *--_! j_ .>**,;>" FIG. 13. A horizontal steam engine. Remote- Con trolled Throttle Valve Main Bearing Drum Shaft Cor/iss- Valve Engine Steam Supply' FIG. 14. An inclined Corliss engine as used for large-capacity mine hoists. 29. A Right -Hand Engine (Fig. 17) is a side-crank engine the flywheel of which is mounted on the right side of the ,--Crank Pin FIG. 15. Forged crank for a side- crank engine. Counterweight - FIG. 16. Solid forged crank and shaft for a center-crank engine. cylinder axis, CL, as viewed from the head end of the cylinder, 0. FIG. 17. A right-hand engine. FIG. 18. A left-hand engine. 30. A Left-Hand Engine (Fig. 18) is a side-crank engine the flywheel of which is mounted on the left side of the cylinder axis, CL, as viewed from the head end of the cylinder, 0. 22 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 31. An Engine Is Said To "Run Over" (Fig. 19) when the top of the flywheel, T, is turning away from the cylinder, C. This term is applied only .to horizontal and inclined engines. NOTE. THE DIRECTION OP ROTATION OF A VERTICAL ENGINE Is ORDINARILY SPECIFIED As CLOCKWISE OR COUNTER-CLOCKWISE as viewed from the valve side of the engine. Clockwise (sometimes called right-hand) rotation is in the direction of motion of the hands of a clock. Counter-clockwise (left-hand) rotation is in the reverse direction of clock- wise rotation. Thus, in Fig. 19, the flywheel is turning clockwise. In Fig. 20, the flywheel is turning counter-clockwise. NOTE. STATIONARY ENGINES USUALLY ARE DESIGNED To "RUN OVER," so the pressure between the crosshead and the crosshead guide, Direction Of Rotation Flywheel--^/, Cylinder FIG. 19. Engine "running over. Direction Of Rotcrtion- nywheeh Cylinder FIG. 20. Engine "running under. due to the angularity of the connecting-rod, comes on the lower side of the crosshead only, and also so the belt, which usually leads away from the engine, will have the driving pull on the lower side. Hence the direction for running over is sometimes referred to as " running forward. Sometimes the term "running clockwise" is intended to mean "running over, " or forward, and in the same direction as the hands of a clock to an observer viewing an engine with the shaft to his right hand and the cylinder to his left. It follows that the terms clockwise and counter- clockwise applied to an engine are often confusing, as the direction will appear to be clockwise to a person standing on one side and counter- clockwise to one standing on the other side. Therefore it is best to confine the designations of directions of rotation to the terms " running over" and "running under. " 32. An Engine Is Said To "Run Under" (Fig. 20) when the top of the flywheel, T, is turning toward the cylinder, C. This term is applied only to horizontal and inclined engines. 33. A Simple Engine (Figs. 12 and 21) is one in which the conversion of the heat energy of the steam into mechanical SEC. 34] STEAM ENGINE MECHANISMS 23 work occurs in one stage or step only. This conversion is brought about in one cylinder, C (Fig. 21), only and by using but one piston, P. Flywheel Cylinder^ Drain Cock -' Exhaust FIG. 21. Simple D-slide valve engine with fly-ball governor. NOTE. A TWIN-CYLINDER ENGINE, SOMETIMES CALLED A DOUBLE ENGINE, (Fig. 22) is one which consists of two simple-engine cylinders which are placed side by side and parallel, and whose pistons are con- nected by separate connecting rods to the same crank shaft. Twin cylinder engines are widely used for hoist- ing and for driving heavy machinery. 34. A Compound Engine (Fig. 23) is one in which the conversion of the heat energy of the steam into work takes place in two stages or steps. Steam enters the high- FIG. 22. Plan view of a twin- cy i- pressure cylinder, H, where it inder engine - undergoes the first stage of its expansion. The steam is then exhausted into the receiver. From the receiver it passes into the low-pressure cylinder, L, where the second-stage expansion occurs. 35. A Tandem-Compound Engine (Fig. 23) is a compound engine with its two cylinders, H and L, along a common axis, Flywheel-' 24 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 or "in line." A tandem-compound engine has only one crosshead and one connecting rod and has both of its pistons on a common piston rod, R. 36. A Cross-Compound Engine (Fig. 24) is a compound engine which has two parallel cylinders, H and L, on the Steam High- Pressure Piston FIG. 23. A tandem-compound engine (Ball Engine Company). same side of the crank shaft, each piston being connected by a separate connecting rod to the one crank shaft. 37. A Duplex-Compound Engine (Fig. 25) is a compound engine, the cylinders of which are parallel and adjacent to each other as shown. H is the high-pressure cylinder con- ,'High -Pressure Cylinder -Path of Steam Exhaust /Low-Pressure Cylinder Pipe^ / Low-Pressure Crank Disk, Flywheel' V ' r -- Low -Pressure Cylinder Fia. 24. Diagrammatic plan view of a cross-compound engine. 'H/'ffh-Pressure\ ^-High-Pressure Piston Rod Cylinder ^^ eam s upp/u Pipe FIG. 25. A duplex-compound engine. nected to, L, the low-pressure cylinder. The piston rods, RI and R 2 , are connected to the same crosshead, C. This type of engine occupies the same floor space as does a simple engine, but has the advantages of a compound engine with respect to economy of steam consumption (Div. 8). SEC. 38] STEAM ENGINE MECHANISMS 25 38. An Angle -Compound Engine (Fig. 26) is a compound engine which has its two cylinders, A and B, placed at right angles to each other. The connecting rods are connected to the same crank shaft and usually to the same crank pin. , Low-Pressure i. Cy/ina'er f -Flywheel High-Pressure ^Intermediate Cylinder Cylinder* ; -^Low- Pressure Cylinder |^>|H|>:;:.->llKllllx-^ Flywheel. '' High- Pressure \ Cylinder- 1 ' FIG. 26. Elevation of an angle- compound engine. '///// 7///// Bearing- *" ; FIG. 27. Elevation of a triple-expansion engine. 39. A Triple -Expansion Engine, Sometimes Called A Triple -Compound Engine (Figs. 27 and 28) is one in which the heat energy of the steam is converted into work in three successive stages and in at least three separate cylinders, as High -Pressure , Direct ion of Cylinder^ / Steam Flow ' * .Frame Bearing^ Cylinders High .First Intermediate Pressure, j .Second \ Intermediate ' Pressure FIG. 28. A plan view of a triple- expansion engine with two low-pressure cylinders. Outboard ,- ( Bear -ing -''; FIG. 29. Elevation of a quadruple- expansion vertical engine. A, B, and C, Fig. 27. A triple-expansion engine with four cylinders is shown in Fig. 28 in which A is the high-pres- sure, B is the intermediate, and C and D are the low-pressure cylinders. 26 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 40. A Quadruple -Expansion Engine, Sometimes Called A Quadruple -Compound Engine (Fig. 29) is one in which the heat energy of the steam is converted into work in four succes- sive stages, and usually in four separate cylinders, A, B, C, and D. A is the high-pressure cylinder, B the first inter- mediate cylinder, C is the second intermediate cylinder, and D the low-pressure cylinder. 41. A Slide Valve (7, Fig. 30) is a positively operated valve which has a reciprocating motion and which slides upon a face, S, called its seat. As the valve slides back and forth on its seat, j UnCOVCrS ports (holes in the '-Cylinder Port Cylinder Port ' FIG. 30. Cross-section of a valve and its seat. D-siide sea leading to either end of the cylinder) placing these ports into communication with either the supply or exhaust pipe. There are two principal types of slide valves: (1) Flat type, Figs. 21 and 30. (2) Piston type, Figs. 12 and 33. NOTE. STEAM-ENGINE VALVES ARE DISCUSSED IN DETAIL IN DIVISIONS 4 and 5. The illustrations and definitions following are merely to acquaint the reader with the several valve-types in their more simple forms. 42. A D -Slide Valve (Figs. 21 and 30) is a flat valve, V Fig. 30, having a cross-sectional form similar to the letter "D." The pressure of the steam in the steam chest forces the valve against its seat, S, preventing leakage of the steam between V and S. In cases where the D- valve is very large, the force due to the steam pressure on the Balancing H le Steam Space Wand v Valve ; Space I Seat 'Cylinder Ports' FIG. 31. Balanced, flat, D-slide valve. valve is apt to be very great and cause excessive friction at the rubbing surfaces. To prevent excessive resistance due to this friction, balanced valves are used. 43. A Balanced Slide Valve (Fig. 31) is one in which the bearing pressure of the valve, V, upon its seat due to the SEC. 44] STEAM ENGINE MECHANISMS 27 pressure of the steam is minimized by some special design, which usually permits the same steam pressure to act on both sides of the valve; for explanation see Sec. 139. The piston valve, Fig. 12, is also a balanced slide valve. ; 44. A Multiported Valve (Fig. 32) is one in which there are two or more passages through which steam can flow into or out of the cylinder ports. Multiported valves permit shorter valve travel and quicker opening and closing of the ports than is possible with common (single-ported) slide valves. In Fig. 32, the ports, H, are the cylinder ports; and the port, L, is the exhaust-steam port. Multiported slide valves are also frequently made in the " balanced" form (see Div. 4). Tai -f (Exhaust Bearing* ' 'From _ . Boiler,'?' 5 ? ,' Valve Valve Sfem * Cylinder Ports'' FIG. 32. Multiported slide valve. ^Cylinder FIG. 33. Section of cylinder with a piston valve. (Chandler and Taylor Company.) 45. A Piston Slide Valve (Fig. 33) is a cylindrical-shaped valve, V, which is given reciprocating motion in a cylindrical seat, S. Its action is very similar to that of the simple D- valve. There are these differences, however: (1) The piston valve is "balanced." (2) The piston valve usually is of the "center admission" construction, whereas D-valves usually are of the "center exhaust" construction.; see Sec. 136. NOTT. PISTON SLIDE VALVES ABE PARTICULARLY DESIRABLE IN VERTICAL ENGINES, since, by making the upper portion of the valve of greater diameter than the lower portion, it is thereby possible to balance the weight of the valve and its valve rod and thus minimize the wear on the eccentric. 46. A Riding-Cut-off Valve (Fig. 34) is one having at least two moving parts, each controlled by a separate eccentric 28 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 Steam Chest , Hand wheel For '. Riding- ^ Adjusting Cut-Off ' Cut-Off \blve "Cul/nder Lynn Port ^Main ^-Exhaust Valve Port (see Div. 4). In Fig. 34, M is the main valve controlling the points of admission, compression, and release; and R is the cut-off valve riding upon the main valve, and controlling only the point of cut-off (Sec. 135). NOTE. THE POINT IN THE STROKE AT WHICH THE CUT-OFF VALVE CUTS OFF may be: (1) Fixed, in which case the cut-off valve is neither hand ad- justable nor governor-operated. (2) Variable, in which case the cut-off valve may be either hand-adjustable or governor-operated. With a hand- adjustable cut-off valve, the point of cut-off may be adjusted to any required point, while the engine is running; thereby the speed of the engine can be changed for a given load or for a changed load the point of cut-off may be altered to that which is most economical or which will give the desired speed. With a governor-operated cut-off, the advance-angle of an eccentric associated with the flywheel governor changes automatically the cut-off to maintain the engine speed constant with varying load. 47. A Gridiron Valve (Fig. 35) is a reciprocating valve which has the form of a gridiron or grating. In Fig. 35, the riding- cut-off valve and the main valve, M , are both of the gridiron type. The valve seat, S, has long rectangular openings between the little bars just as have the valves themselves. Main Steam ,'Riding- Va/ve, Space* [Cut-Off Valve ,'VWVW : Stem FIG. 34. Section of a Meyer riding- cut-off valve. FIG. 35. Section of a cylinder with a grid- iron valve (Mclntosh and Seymour valve). FIG. 36. Single-ported Corliss valves. Evidently, then, gridiron valves are multiported valves with a large number of ports. 48. A Corliss Valve (Figs. 36 and 37) is a valve the ends of which are cylindrical and which oscillates about its axis in a cylindrical cavity or seat at right angles to the engine SEC. 48] STEAM ENGINE MECHANISMS 29 Admission Valve-. 'Steam Supply ^Ac/mission Valve Exhaust Valve ^ ''Steam Exhaust FIG. 37. Section of cylinder with double-ported Corliss valves. - 'Steam-Supply Pipe -Throttle Valve "'Exhaust Pipe FIG. 38. Chuse positively-operated Corliss-valve mechanism 30 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 cylinder axis. The cylinder ports are opened or closed by this oscillatory motion. Corliss valves are employed two to a cylinder end one for admitting steam to the cylinder, the other for exhausting the spent steam from the cylinder. An engine with Corliss valves is therefore a four-valve engine. Corliss valves may be either single-ported (Fig. 36) or, as more commonly constructed, multiported (Fig. 37). 49. A Positively-Operated, Or Non-Releasing, Corliss- Valve Mechanism (Fig. 38) is one in which the admission FIG. 39. Detaching Corliss-valve mechanism. valves, A, and the exhaust valves, E, are at all times positively connected to, and under the influence of, the valve-operating (eccentric) mechanism to which they are linked by the reach rods B and C. 50. A Detaching, Or Releasing, Corliss -Valve Mechanism (Fig. 39) is one in which the admission valves, A, are not positively connected to, nor under the influence of, the eccen- tric mechanism except when these valves are open. A dash- SEC. 51] STEAM ENGINE MECHANISMS 31 pot mechanism, D, provides a suction for quickly closing the steam valves as soon as they are detached from the eccen- tric mechanism. Detachment is effected by releasing a snap- catch, C, which is controlled by the governor. The exhaust valves, E, are positively connected to the eccentric mechanism at all times. 51. A Poppet Valve (Figs. 40, 41, and 42) is a circular valve, V, Fig. 40, having an opening and closing movement perpen- dicular to its seat, S, and which allows steam to flow under or through it. This type of valve effects a large port-opening with a small valve-lift and is free of the friction occurring with valves which slide upon their seats. Pop- pet valves, on account of their sym- metrical construction and small size, are well adapted for use with high- temperature superheated steam. ..-Valve Bonnet ^Piston FIG. 40. Section of cylinder with single-seated poppet admission valve. //C y I i n d e r *5f earn Space to Cylinder FIG. 41. Half-section of end of Nordberg- engine cylinder showing positively-operated poppet admission valve. 52. A Positively-Operated Poppet Valve (Fig. 41) is one that is positively opened and closed by, and at all times under the influence of, the valve-operating (eccentric) mechan- ism. In Fig. 41, V is the poppet valve and M the eccentric rod from an eccentric on a lay-shaft which is located on the side of the engine and parallel to the cylinder axis. 53. A Detaching, Or Releasing, Poppet Valve (Fig. 42) is one that is opened by the eccentric mechanism, but is closed by a spring, dash-pot, or other mechanism; the valve is, there- 32 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 fore, under the direct influence of the eccentric mechanism only during the opening period. In Fig. 42, V is the poppet valve, S the valve-closing spring, and M the eccentric rod from a lay-shaft eccentric. 54. A Single-Valve Engine (Figs. 12 and 21) is one in which one valve controls both steam admission and exhaust for both ends of the cylinder. Thus, engines with D-slide valves, whether single or multiported, balanced or unbalanced, and engines with simple piston valves are all single-valve engines. Valve-Opening Roller FIG. 42. Half-section of a Hamilton-engine cylinder with detaching-poppet admission valve. 55. A Multi-Valve Engine (Fig. 37) is one in which more than one valve is employed for admitting and exhausting steam at the two ends of the cylinder. Thus, all Corliss, poppet, and gridiron-valve engines are of this type. 56. A Short-Stroke Engine is one the stroke of which is less than the diameter of its cylinder. For example, an engine which has a cylinder 12 in. in diameter and a 10-in. stroke is a short-stroke engine. 57. A Long-Stroke Engine is one the stroke of which is greater than the diameter of its cylinder. Thus an engine which has a cylinder 7 in. in diameter and a 10-in. stroke is a long-stroke engine. 58. A Counterflow, Or Double-Flow, Engine (Figs. 43 and 44) is one in which the direction of steam flow in its cylinder on the exhaust stroke is opposite to the direction of steam flow during the admission stroke. Thus in Fig. 43, steam is shown entering the cylinder and flowing toward the SEC. 59] STEAM ENGINE MECHANISMS 33 right. In Fig. 44, the steam is being exhausted and, as is seen, must flow in the opposite direction or toward the left. Exhaust Cylinder Port --Steam-Supply Pipe ; Steam Chest ,D-Va/ve ,Valve -Steam -Supply Pipe Steam Chest D- Valve -Valve Stem ^Piston Direction of Admission-Steam Flow FIG. 43. Showing direction of steam flow into an engine cylinder employing the counterflow principle. 'Direction of Exhaust-Steam flow FIG. 44. Showing direction of steam flow during exhaust from a cylinder employing the counterflow principle. NOTE. CERTAIN ENGINES WITH SEPARATE ADMISSION AND EXHAUST VALVES ARE ALSO COUNTERFLOW ENGINES, if the exhaust valves take the steam out of the cylinder at its end. Thus, the Corliss engine (Fig. 37) is a counterflow engine. Cylinder Jacket ^ Direction of \ ,' Admission-Steam Flow ' FIG. 45. Showing direction of steam flow into a uniflow-engine cylinder. 59. A Uniflow Engine (Figs. 45 and 46) is one in which the steam flows in only one general direction in the cylinder. 34 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 The direction of steam flow during the exhaust period is the same as during the admission period. Fig. 45 shows steam ...-Valve ' Bonnet Cylinder Valve Jacket Direction of Exhausf- : Steam Flow "Steam Supply 'Steam Exhaust Crank Shaft, Steam Air Discharge FIG. 46. Showing direction of steam flow during exhaust from a uniflow-engine cylinder. being admitted into a uniflow engine cylinder and flowing toward the right. Fig. 46 shows the same steam being ex- hausted from the cylinder and also flowing toward the right. 60. A Standard Crank-Mechanism (Fig. 21) is one consist- ing of a cylinder, C, a piston, P, a piston rod, R, a crosshead, a connecting rod, L, a crank, B, and a crank shaft, M and in which the crosshead is located between the cylinder and the crank and crank shaft. 61. A Back-Acting Crank- "connecting Rod Mechanism (Fig. 47) consists of **"** the same principal parts as the FIG. 47. A double-connecting-rod, back-acting crank-mechanism as applied standard crank-mechanism; in to air compressors. the back-acting crank-mechan- ism, however, both the crank shaft, S, and the cylinder, C, are always on the same side of the crosshead, H. This SEC. 62] STEAM ENGINE MECHANISMS 35 Wrist Pin Flywheel, mechanism, will usually necessitate either two piston rods or two connecting rods, or a combination of two piston rods and two connecting rods. 62. A Trunk -Piston Mechanism (Fig. 48) is one employing an un- usually long, or trunk piston, P, in which one end of the connect- ing rod is pivoted on a pin, thus rendering unnecessary the cross- head used in other types of steam-engine mechanisms. En- gines with trunk pistons are single-acting. That is, the steam for them is admitted to, and does work on, only one side of the piston. Internal combustion FIG. (automobile, etc.) engines are usually of the trunk-piston type. 63. An Oscillating-Cylinder Engine (Fig. 49) is one, the mechanism of which consists of a cylinder, C, pivoted in .-Flywheel 48. Trunk-piston mechanism of the Model Acme engine. (Auto matic Furnace Co., Dayton, O.) ,Z? -Slide Valve r Pi voted ,'' Cylinder ~~ Bearing FIG. 49. An old engine of the oscillating-cylinder type.' bearings, B\ a piston and piston rod, R] a crank, L; and a crank shaft, S. In this type of engine, the oscillating cylinder 36 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 takes the place of the connecting rod and crosshead employed in the standard crank-mechanism. 64. A Condensing Engine is one which normally operates on an absolute back (exhaust) pressure which is less than that of the atmosphere. The back pressure is reduced by condensing the exhaust steam by the use of some condensing device (Div. 9). 65. A Non-Condensing Engine is one which operates on a back (exhaust) pressure equal to, or greater than, atmospheric pressure. 66. A High-Speed Engine is one which operates at a speed of about 200 r.p.m. or more. 67. A Medium-Speed Engine is one which operates at some speed between about 110 and 200 r.p.m. Note: Exhaust Valves are on Opposite Side of Cylinder and Not Shown Steam f Valve Governor^ ^^^^^ Shaft Extending to Other Side of Engine, Operates Exhaust Valves FIG. 50. An engine equipped with a variable-cut-off valve-mechanism. Allen engine.) (Porter- 68. A Low-Speed (Or Slow-Speed) Engine is one which operates at a speed of 100 r.p.m. or less. 69. A High-Pressure Engine is one which takes steam at its throttle at a pressure greater than 225 Ib. per sq. in. gage. 70. A Medium-Pressure Engine is one which takes steam at its throttle at some pressure between 80 Ib. and 225 Ib. per sq. in gage. 71. A Low-Pressure Engine is one which takes steam at the throttle at a pressure less than 80 Ib. per sq. in. gage. 72. A Fixed-Cut-Off Engine (Fig. 21) is one in which the point of cut-off remains constant throughout all ranges of load and speed. The eccentric, E, is fixed to the shaft, M. Therefore, the eccentric rod, F, valve stem, S, and valve SEC. 73] STEAM ENGINE MECHANISMS 37 always have the same motion relative to the engine cylinder and valve seat. That is their relative motion is independent of the engine load or speed. 73. A Variable-Cut-Off Engine (Fig. 50) is one in which the point of cut-off varies with each change of load or speed. In Fig. 50, as the engine speed increases, the governor rod, R, lowers the link block, B, thus diminishing the travel of the steam rod, S, and the steam valves, Vi and F 2 . By means of this mechanism the point of cut-off varies with different speeds and hence with different loads; see following sections on governors. 74. A Steam -Engine Governor (Figs. 51 and 52) is a device which changes the steam input to an engine to meet Flywheel FIG. 51. Typical shaft governor. the varying demands of different engine loads, and at the same time maintains the engine speed as nearly constant as possible. (See Divisions 6 and 7.) Steam-engine governors are of two general types (1) Shaft type, Fig. 51. (2) Fly-ball type, Fig. 52. 75. A Shaft Governor (Fig. 51; see also Div. 7) is one which rotates with the flywheel in a plane perpendicular to the crank-shaft axis. In this type of mechanism, weights, W and Wi, are rotated with the flywheel, F. Rotation of these weights introduces centrifugal or inertia forces which act against the pull of springs, S, attached to F. The position of the weights depends upon these forces which are proportional to the engine speed. The position on the shaft of the eccentric, E, is varied by the movement of the weights which fly outward 38 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 2 as the flywheel speed increases. Since the relative position of the eccentric on the shaft controls the valve action, a governor of this type will perform the necessary functions as given in the preceding section. See Div. 7 for further discussion of shaft governors. 76. A Fly-Ball Governor (Figs. 50 and 52; see also Div. 6) is one in which two or more " fly-balls" rotate, usually in a horizontal plane. Rotation introduces centrifugal forces which hold the balls away from the axis of rotation. Suitable mechanism affords a relation be- tween the position of the balls and the amount of steam fed to the engine. In Fig. 52, the position of the fly-balls, G and Gij fixes the amount of opening of the throttle valve, V, thus regulating the steam supply to the engine. Since the governor pulley, P, is belted to the engine shaft (see Fig. 21), the fly-ball positions depend upon the engine speed. As the load increases, the engine speed begins to decrease. The gov- ernor opens the throttle valve and thereby again increases the engine speed. Likewise when the FIG. 52. Section of a typical fly-bail load decreases, the engine speed increases and the goveror closes the throttle valve thereby maintaining the speed practically constant. QUESTIONS ON DIVISION 2 1. How are engines classified as to: (a) Cylinder arrangement? (b) Longitudinal axis? (c) Rotative speed? (d) Ratio of stroke to diameter? (e) Valve gear? (/) Engine mechanism? (g) Steam expansion? (h) Steam flow? (i) Steam conditions? SEC. 76] STEAM ENGINE MECHANISMS 39 2. What is a vertical engine? A horizontal engine? An inclined engine? 3. Explain the chief difference between a side-crank and a center-crank engine. 4. What is a right-hand engine? A left-hand engine? 5. When is an engine said to run "over"? To run "under"? 6. Explain fully the meaning of the following terms: (a) A simple engine. (6) A compound engine. (c) A tandem-compound engine. (d) A cross-compound engine. (e) A duplex-compound engine. (/) An angle-compound engine. (g) A triple-expansion engine. (h) A quadruple-expansion engine. 7. What is a slide valve? 8. What is a D-slide valve? 9. Describe and give the features of a balanced slide valve. 10. What is a multiported valve? 11. Describe the piston slide valve. 12. Describe the riding-cut-off valve. 13. What is a gridiron valve? * 14. Describe fully the features of the Corliss valve. 15. What is the chief difference between a positively-operated and a detaching Corliss- valve mechanism? 16. Describe the principle of operation of a poppet valve. 17. Explain the difference between a positively-operated and a detaching poppet valve. 18. What is a single-valve engine? 19. What is a multi- valve engine? 20. When is an engine said to have a "short stroke"? A "long stroke"? 21. What is the difference in principle between a counterflow engine and a uniflow engine 22. Describe the following engine mechanisms: (a) Standard crank-mechanism. (6) Back-acting crank-mechanism. (c) Trunk-piston mechanism. (d) Oscillating-cylinder mechanism. 23. What is a condensing engine? 24. What is a non-condensing engine? 25. Give the speed ranges for: (a) A high-speed engine, (b) A medium-speed engine, (c) A low-speed engine. 26. Give the steam-pressure ranges for: (a) A high-pressure engine. (6) A medium- pressure engine, (c) A low-pressure engine. 27. What is a fixed-cut-off engine? 28. What is a variable-cut-off engine? 29. Explain the purposes of a steam-engine governor. 30. What is a shaft governor? 31. Describe the fly-ball governor DIVISION 3 STEAM-ENGINE INDICATORS AND INDICATOR PRACTICE 77. The Steam-Engine Indicator (Fig. 53) is simply an in- strument which records graphically on an "indicator diagram" (D, Fig. 54) the variations of pressure within an engine cylinder, as the engine piston occupies different positions Cap- Handle-^ FIG. 53. External view of a Thompson indicator without reducing motion. (American Steam Gage and Valve Co.) throughout its stroke. It might well be called a recording pressure gage, the chart of which is moved always at a speed proportional to the speed of the piston. See the author's PRACTICAL HEAT for a discussion of the principle of the elementary indicator. 78. The Indicator Diagram Is Extremely Useful (D D, Fig. 54) because it enables one to analyze what is taking 40 SEC. 79] STEAM ENGINE INDICATORS 41 ,51-op place inside the engine cylinder while the engine is running. There are, briefly, three ultimate ends to which such analyses lead: (1) They reveal whether the engine steam and exhaust valves are opening and closing properly in relation to the position of the engine piston. (2) They enable one to calculate the power developed by the expansion of the steam within the engine cylinder. (3) With further cal- culations, they enable one to determine, approximately, the amount of steam which the engine is using. Besides these three important functions, the indi- cator diagram may reveal ex- traordinary troubles or defects which would otherwise be diffi- cult to allocate. These uses of the indicator diagram will be considered separately in subse- quent sections. 79. Watt's Indicator Is Per- haps The Simplest Form (Figs. 54 and 55). Steam enters the indicator cylinder, C, from the engine cylinder, E. The pres- sure of the steam forces the pis- ton P, upward, compressing the spring, S, and raising the pencil, A. The sheet of paper, R, being moved at the same time by cord, F, which is attached to the crosshead of the engine, will have described upon it a "diagram," DD, which indicates, at every instant during a revolution of the engine, the pressure within the engine cylinder. At any instant, the height to which the pencil has been raised will be a measure of the pressure at that instant within the engine cylinder, whereas the horizontal distance through which the paper has been moved from either end (for example, M, Fig. 54) will denote the position of the piston in the engine cylinder at that instant. From this it follows that the length, L, of the diagram repre- sents the length of the engine piston's stroke. FIG. 54. External diagrammatic view of Watt's steam-engine indicator. 42 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 NOTE. MODERN INDICATORS (Figs. 53, 56, and 57) DIFFER FROM WATT'S TYPE only in constructional details. In a modern indicator the paper, upon which the diagram is traced, is held by clamps, K (Fig. 53) to a cylindrical drum, D, which is given a rotative motion by the cord, F, from the engine crosshead. Also, the pencil, A, in a modern indicator is made to move a distance greater than the motion of the indicator piston. This is accomplished by means of a pencil mechanism. Then too, some modern indicators have the spring, S, outside the hot cylinder (Fig. 57), better adapting them for use with superheated steam. FIG. 55. Sectional diagrammatic view FIG. 56. Sectional view of a Thompson of Watt's steam-engine indicator. indicator. 80. The Pencil Mechanism (Figs. 58 and 59) permits the use of strong indicator springs (Sec. 92) which need not be compressed (or extended) through a great distance and still affords a diagram of reasonable height. By thus minimizing the extent of motion of the heavier parts, meanwhile reducing the weight of those which have greater movement, modern indicators have been made reasonably free from inertia effects at the usual engine speeds. A good pencil mechanism will trace a straight vertical line upon a card held on the drum (not in motion). It will also cause the pencil to move through a distance exactly proportional to (usually four to five times) the movement of the indicator piston. SEC. 81] STEAM-ENGINE INDICATORS 43 81. The Two Principal Types Of Pencil Mechanism Are The "Parallel-Link" And " Curved -Slot" mechanisms (Figs. 58 and 59). The parallel-link mechanism, in some makes of indicators, differs slightly in details from the arrangement of Fig. 58 (see PRACTICAL HEAT). In the curved-slot mechanism the roller on the pencil arm is kept within the slot, S, which is so formed that the point is given the desired vertical motion. -Pis ton Rod Fastened to Spring Union FIG. 57. Crosby outside-spring indicator with reducing wheel attached. 82. An Indicator Reducing Mechanism Usually Called A "Reducing Motion" (Fig. 60) is necessary (whenever the stroke of the engine is greater than the longest diagram that can be drawn on the indicator drum) to insure that the full motion of the engine piston may be represented on the indicator card. As the length of diagram attainable with 44 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 most indicators is from 4 to 6 in., it is evident that nearly all engines will require reducing mechanisms of some kind. NOTE. Experience shows that for speeds over 300 r.p.m. the length of diagram should not exceed 3 in.; speeds over 200 3J^ in.; speeds 100 to 200 4 in.; speeds under 100 optional. Pencil I - Upper Position Revolving Bracket .--. 83. There Are Four Principal Types of Indicator Reducing Mechanisms. These are the: (1) Pendulum lever, Fig. 60. (2) Panto- graph, Fig. 62 (3) Reducing wheel, Fig. 66 (4) Inclined Plane, Fig. 69. The first three are the ones most commonly used. Any of these '$' reducing mechanisms can be made practically perfect but, if not care- I fully set up, may give results which ^ are very much in error. Each type will be discussed. - Lower Position FIG. 58. Lever pencil-mechanism for producing a straight vertical line. (This is used on Thompson indicators.) FIG. 59. Curved-slot parallel motion of Tabor indicator. 84. The Pendulum -Lever Reducing Mechanism (Fig. 60) is very widely used and gives an accurate reduction if certain requirements are observed in its construction. The pendulum lever, P, should be at least as long as the engine stroke and must, in its mid-position, ab (Fig. 60), be at right angles to the direction of motion of the crosshead. The connecting link, C, between the pendulum lever and the crosshead should SEC. 84] STEAM-ENGINE INDICATORS 45 be about half the length of the engine stroke, L. The pendu- lum lever and the connecting link must be so arranged that the point, m, where they are fastened will be the same distance above the line cd when the crosshead is at either end of its H Ci/K/e Pulley^ / Engine y. Cylinder-^ b K- -Stroke^- FIG. 60. Pendulum-lever reducing motion. travel, as it is below cd when in mid-stroke. The line cd is a line, parallel to the axis of the engine cylinder, which passes through the center V of the point of attachment of the connect- ing link to the crosshead. Also the drum cord must be led FIG. 61. Inverted pendulum-lever with brumbo pulley. off at an angle of 90 deg. to the mid-position, ef, of its lever arm. To do this, it is sometimes necessary to enlarge that portion of the lever as shown. Frequently, a segment of a 46 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 grooved pulley (Fig. 61) is substituted for the pin, H, on the pendulum lever. This segment is called a brumbo pulley. NOTE. THE PIVOT POINT, n, Is FREQUENTLY PLACED BELOW THE CROSSHEAD (Fig. 61) when it is inconvenient to provide a bearing for it overhead. In such cases, the entire mechanism is simply inverted and very often the bearing is fixed to the floor. NOTE. To FIND THE POINT OP ATTACHMENT, H, (Fig. 60) or the distance, Hn, from the pivot point to the pin (or radius of brumbo pulley), to produce a certain length of diagram: RULE. Multiply the total length of the lever, mn, by the desired length of indicator diagram and divide by the stroke ,L, of the engine, all in inches. To FIND THE LENGTH OF DIAGRAM produced with the cord at a certain point of attachment: RULE. Multiply the distance from pilot, n, to point of attachment, H, by the stroke, L, and divide by the total length of the lever, mn, all in inches. EXAMPLE. An engine with a 30-in. stroke is provided with a pendulum lever 35 in. long. To obtain an indicator diagram 3 in. long, how far from pivot must the pin be placed? SOLUTION. 35 X 3/30 = 3^ in. EXAMPLE. An engine with a 24-in. stroke has a 5-ft. pendulum lever with a brumbo pulley having a radius of 10 in. How long an indicator diagram will it give? SOLUTION. 10 X 24/60 = 4 in. 85. The Pantograph Is An Instrument Which May Be Used As A Reducing Mechanism (Figs. 62 and 63) because it con- tains two points whose motions are always parallel and propor- tional to each other. It may be briefly described as a number of links pivoted together so that they form two sets of parallel links. One point, A, (Fig. 62 or 63) is fixed stationary. Another point, J5, is given a certain motion, while a third point, C, will receive a motion proportional and parallel to that of B. Points A, B, and C must originally be selected, however, on the same straight line, as shown. Figs. 64 and 65 show methods of using pantographs on engines. Note that the cord is always taken from the pantograph in a direction parallel to the axis of the cylinder. NOTE. THE POSITION OF POINT C CAN BE FOUND if the travel of B and the desired travel of C (Figs. 62 to 65) are known, by substituting in this formula, . travel of C X distance AB (7) Dufamo, AC = - EXAMPLE. If Fig. 65 represents an engine whose stroke is 24 in., and an indicator diagram 4 in. long is desired, and if, in the position shown it SEC. 85] STEAM-ENGINE INDICATORS 47 - I nd i c a t o r s - - ~ Engine Cy 'Under- \ FIG. 62. Simple pantograph for indicator-reducing purposes. FIG. 63. Adjustable pantograph for indicator-reducing use. Cylinder* Pantograph fastened Here C to Crosshead Connecting Rod Cord- ~ ' ~5ta tionary Support FIG. 64. Plan view of an engine fitted with pantograph and indicators. 48 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 is 36 in. from A to B, what must be the distance AC? SOLUTION. Distance AC = 4 X 36/24 = 6 in. 86. The Reducing ^..-Engine Cylinder ..Indicator Crosshead., Wheel, Figs. 66 and 57, is a device in which a cord is run directly from the crosshead onto a pulley which it rotates, while another cord is run from a second pulley to the indicator drum the second pulley being either smaller or geared to a slower rotative speed than the first and driven directly from the first. 87. Features That Must Be Observed When Using Reduc- ing Wheels are: (1) The wheels should be so designed that under FIG. 65.- -Elevation of an engine with a pantograph. Indicator "' ''Crosshead Cord-. Pin-' FIG. 66. Principle of the reducing wheel. operating conditions the momentum of the moving parts will not become sufficient to produce slackness in the cord at any time. r {-Enq/ine Fro/me .'Core/ \ I - T o p View Reducing Mot!on-\[ I-Top View Reducing Motion incorrect wrecr Gu! J e p, ///e yj E-S i d e View Cock--' FIG. 67. Correct method of connect- ing indicator cord to crosshead. FIG. 68. Ifcfrrect and corrected methods of Connecting indicator cord to crosshead. (2) A cord should be used which will not stretch to an\ appreciable extent. Nearly all indicator manufacturers can furnish reduc- SEC. 88] STEAM-ENGINE INDICATORS 49 ing wheels and cords which will satisfy the above requirements and which are applicable to different types and sizes of engines. CAUTION. WHEN USING REDUCING WHEELS always see that the cord (Figs. 67 and 68) from the crosshead to the wheel is practically parallel to the axis of the engine cylinder (K, Fig. 67) and that the drum cord leaves its pulley at right angles to the axis of the pulley (R, Fig. 67). This will prevent angular distortion of the diagram. Conditions A and B (Fig. 68) besides causing distortion will tend to make the cord run off the pulleys. Condition D will give a very poor reduction but may be remedied either as shown dotted at C, or as K, Fig. 67. 88. The Inclined -Plane Reducing Mechanism (Fig, 69) gives a very good reduction when the angle through which the bell-crank, L, turns is kept Dram Corof-. ,-Gu/c/e Crossheacf-^ fairly small. The length of \ ,,r] Y \ . / f diagram is fixed by the incli- nation of the plane, P, and the lengths of the two arms of the lever, L. The upright arm can be of such length as to bring the COrd in line with the indi- FlG - 69. Inclined-plane reducing mech- &nism cators. A catch, C, (Fig. 69) can be arranged to hold the roller free of the plane and thereby stop the indicator without unhooking the cord. This, at the same time, prevents flapping of the cord. 89. Every Indicator Reducing Motion Should Be Given Two Tests Before Using: (1) Test for accuracy of reduction. First divide the stroke of the crosshead into eight equal parts (Fig. 70). Attach an indicator, without a spring, to the cylinder. Now, with the indicator attached to the reducing motion and the crosshead at zero, make a vertical mark on the indicator card by raising the pencil lever. Then move the crosshead successively to positions 1, 2, 3, etc., making a vertical mark on the indicator card for each position. If the spaces between the lines on the card are equal, the reduction is satisfactory. (2) Test for lost motion and inertia or momentum effects. Now run the engine slowly and take an " atmospheric line" (Sec. 100), holding the pencil on during a complete revolution. Let the engine get up to speed and take another line about J-f g in. above the first. A considerable difference 50 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 in the lengths of the two lines, indicates momentum effects in the reducing mechanism or the drum itself, or stretching of the cord. The remedies are taking up all lost motion, using a short cord or a wire, and so adjusting the drum spring that the discrepancy will be a minimum. Scribe Mark Scribe Marks on Crosshead^ on Ou ; de _ It-Mechanism On Engine FIG. 70. Method of testing reducing mechanism for accuracy of reduction. 90. In Piping For Indicators, great care must be taken that the pipe is of sufficient size to allow the steam to flow through it without throttling (reducing the pressure) and that the pipe has not sufficient volume to affect the working of the engine by increasing its clearance volume. NOTE. THE BEST METHOD OF PIPING AN INDICATOR is to drill and tap directly into the counterbore of the engine for ^-in. pipe, as at A, Fig. 71. If the counterbore is too short it is well to chip a channel into the cylinder. Of course, all chips must then be removed from the cylinder to prevent injury to it and the indicator. Where no steam pipes or other obstructions appear at the top of the cylinder, it is best to locate the indicators there, otherwise they are mounted on the side of the cylinder. A straight-way indicator cock (C, Fig. 71) is then screwed into each tapped hole, preferably without any intermediate piping. The ell SEC. 91] STEAM-ENGINE INDICATORS 51 shown below the indicator in Fig. 65 can well be omitted so that the indicator drum will extend out horizontally from the cylinder. NOTE. ALL INDICATOR COCKS SHOULD HAVE A RELIEF PASSAGE (X, Fig. 55) which will relieve the pressure beneath the indicator piston when cock is in the closed position. Cord FIG. 71. Ideal method of connecting an indicator to a cylinder. 91. Using A Single Indicator For Indicating A Cylinder Is To Be Avoided, if possible, but whenever necessary, a three-way FIG. 72. Arrangement for using one indicator for both ends of a cylinder. cock should be used and piped as shown in Fig. 72. The indi- cator is thrown into communication with one end of the 52 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 cylinder and then the other, giving the two diagrams on one card. Diagrams taken with an indicator so arranged cannot be relied on for accuracy because of the time required to fill the pipes with steam up to the pressure within the engine cylinder. The arrangement of Fig. 73 is to be especially avoided, because FIG. 73. Incorrect piping of an indicator. of the excessive steam volume in the piping and because of errors due to the two valves; if found on an engine, this arrangement should be replaced. The arrangement of Fig. 74 may be safely used where it is essential that provision be made for testing with either one or two indicators. NOTE. THE ARRANGEMENT OF FIG. 72 USUALLY GIVES POWER RESULTS WHICH ARE 3 To 7 PER CENT. Too HIGH, although in certain cases it gives results so poor that it is useless. It is well, when using this connection, to compare a diagram so taken with one taken with a direct FIG. 74. Piping arrangement ,. ... . , ,, which is adaptable for either one or connection and the engine under the two indicators. same load. 92. Indicator Springs Are Classified As To Their Stiffness, the number (or scale) of an indicator spring being the pressure (in pounds per square inch) which must be exerted upon the indicator piston to raise the pencil one inch. Thus, a 100-lb. spring, when in an indicator, would permit the pencil to be raised 1 in. by a pressure of 100 Ib. per sq. in. within the Stop Cock SEC. 93] STEAM-ENGINE INDICATORS 53 engine cylinder, 2 in. by a pressure of 200 Ib. per sq. in. and so on. Table 93 shows the different springs made by American manufacturers and the maximum safe pressure to which they can be subjected, when used with a J^-sq. in.-area piston. When used with a J^-sq. in.-area piston the scale and safe pressure are twice the values shown in the table. EXAMPLE. A 50-lb. spring when used with a /^-sq. in.-area piston becomes a 100-lb. spring with safe pressures of 200 to 240 Ib. per sq. in. NOTE. SINCE THE SPRING Is THE ACTUAL MEASURING ELEMENT OF AN INDICATOR, great care must be taken that it actually measures as it should. Springs gradually change their stiffness with continued use and should, therefore, be periodically tested, especially before and after being used on important work. 93. Table Showing Safe Pressures For Indicator Springs, the higher values of safe pressure being for engine speeds below 200 r.p.m.; the lower values for speeds up to 300 r.p.m. Scale of spring, pounds per inch Safe pressure, pounds per square inch Scale of spring, pounds per inch Safe pressure, pounds per . square inch 8 5 to 10 60 120 to 140 10 9 to 15 64 130 to 145 12 11 to 20 70 135 to 150 16 20 to 30 72 140 to 160 20 30 to 40 80 160 to 170 24 40 to 50 90 180 to 190 30 55 to 65 100 200 to 215 32 60 to 70 120 225 to 240 40 80 to 95 125 230 to 250 48 95 to 115 150 265 to 300 50 100 to 120 200 325 to 380 94. In Testing An Indicator Spring (Fig. 75), the indicator should be mounted on a vessel, V, together with a test gage, G, and subjected to steam pressure in 5- or 10-lb. per sq. in. steps, beginning with atmospheric pressure as zero. The cord should be drawn by hand at each pressure to obtain a hori- zontal line (Fig. 76) about half way along the card. After the pressure has reached the maximum it should be lowered again in the same steps. The line corresponding to a certain pres- 54 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 sure may be higher now than before, due to friction within the indicator cylinder. The card, when the test is completed, Indicafor- - Outlet-----) FIG. 75. Apparatus for testing indicator springs (also gages and thermometers). should look like Fig. 76. The mean between the two lines drawn at a certain pressure is taken as the average for that No. Hour &??4 K. __//? .192 /_ WKchBnd. i Different Pressures at Which Spring Area Length HOrd Vac.Gage~_^ 50 Revs ifO HE.P I.H.R %rt^Jf__. 30 20 * 20 \Down t & I L tO J . :- v* Indicator No. 1620 -'-Atmospheric Lines Observer . FIG. 76. Sample card illustrating test of an indicator spring. pressure. The spring scale can then be calculated from each height by substituting in the formula, /ON . 7 (8) Spring Scale pressure, in Ib. per sq. in. , . , . , . . r^- height on card, in inches ; ^\."- Atmospheric SEC. 95] STEAM-ENGINE INDICATORS 55 EXAMPLE. If h, Fig. 76, is measured to be 1.19 in., and is the height to the 50-lb. line, as shown, then: spring scale = 50/1.19 = 42 Ib. per in. This value supersedes the manufacturer's scale, which was 40. NOTE. MANUFACTURERS WILL TEST INDICATOR SPRINGS, when sent to the factory, for those who lack apparatus for making their own tests. The author, however, recommends the construction and installation in every engine room of an apparatus similar to Fig. 75. Besides testing indicator springs, it is very useful for testing gages and thermometers. The indicator cock can readily be replaced by a gage siphon or a ther- mometer well. The gage glass is unnecessary except for thermometer testing, in which tests water in the glass insures saturated steam. 95. In Selecting Springs For Indicating An Engine, bear in mind that the larger the diagram taken, the less will be the percentage error in making cal- culations from it. There are, however, certain limitations to this policy. On high-speed engines, large diagrams are likely to be accompanied by inertia effects in the indicator and its mechanism, Which WOUld intrO- F - 77.-Inertia effects in indicator diagram caused by too weak spring. duce errors offsetting the ad- vantages of the large diagrams. If too light a spring has been selected, these effects will appear on the indicator diagram as in Fig. 77, A and B, and call for a stiffer spring. NOTE. IN GENERAL, THE PROPER SPRING MAY BE SELECTED IN ADVANCE by one of the following rules, which are based on a diagram not over 1% in. in total height: For non-condensing engines (or cylinders), pressure at steam valves (9) spring scale = %/ (lb.;per in.) For condensing engines (or cylinders), , vacuum in condenser pressure at steam valves H ~ (10) spring scale = - r-g/ (Ib. per in.) Wherein: Pressure at steam valves is in pounds per square inch, gage. Vacuum in condenser is in inches of mercury column. Since the vacuum in the condenser is usually between 25 and 30 in. of mercury, For (10) may be simplified to : ,,* pressure at steam valves + 15 (11) spring scale = ^y (Ib. per in.) EXAMPLE. A compound engine is operating under the following 56 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 .Cap C. Not Held in Finger pressures: Pressure at throttle, 200 Ib. per sq. in. gage. Pressure in receiver, 4 Ib. per sq. in. gage. Vacuum in condenser, 27 in. of mercury column. Find spring scales. SOLUTION. Applying For. (9) for the high-pressure cylinder: spring scale = pressure at steam valves /!% = 200 -5- 1% = 114?<7 Ib. per in. Hence a " 120-lb." spring should be used. Now applying For. (10) for the low-pressure cylinder: spring scale = (pressure at steam valves + M X vacuum in condenser) /!% = (4 + % X 27)/l% = 17.5 -5- 1.75 = 10 Ib. per in. Or by applying For. (II) -.spring scale = (pressure at steam valves + 15)/1% = (4 + 15) -J- 1% = 19 * 1.75 = lO^f Ib. per in. A 10- or 12-lb. spring might be used here. CAUTION. ALWAYS USE A STIFFER SPRING THAN COMPUTED rather than a weaker spring, thus avoiding the possibility of the pencil rising above the top of the drum and catching there. 96. In Placing The Selected Spring In The Indicator one end is fastened firmly to its stationary support (Cap, C, Fig. 56, in inside-spring indicators), the other end to the piston (in some indicators to the piston rod). Before placing the piston, spring, cap, and pencil mechanism into the indi- cator body, see that there is no excessive lost motion in the parts (hold cap in one hand and try moving pencil arm with the other) and adjust the pencil to approximately the proper height (Fig. 78). Hold bracket, X, in one hand and turn piston with the other". Then lubricate the indicator piston, P, with a drop or two of cylinder oil, and the f pencil mechanism with a very light machine oil (manufacturers supply porpoise oil) and screw cap, C, into place. If the pencil is too high or low repeat the adjustment until it is correct. The pencil should be about ^ in. above the bottom of the card if the indicator is used on a non- condensing cylinder. On condensing cylinders it must be high enough so that the vacuum on the exhaust stroke will not draw it quite to the bottom of the card. EXAMPLE. On the low-pressure cylinder of the engine of the example under Sec. 95, the pencil should be about l^j in. from the bottom of the card. FIG. 78. Method of adjusting pencil height. SEC. 97] STEAM-ENGINE INDICATORS 57 97. Before Applying An Indicator To An Engine Always Allow Steam To Blow Through The Cock to remove all dust and grit that may have settled there and thereby prevent injury to the finely-finished indicator cylinder. It is well to have caps (Fig. 74) to fit over the indicator cocks when they are not in use to keep out foreign matter. Then connect the drum Center Line Of Inc/tcatorCy/inc/ers " Wpffi^" "~ FIG. 79. Proper arrangement where two indicators, A and B, are operated from one reducing mechanism. cords to the reducing mechanism as shown in Fig. 79, and adjust their lengths to get the diagrams in about the centers of the cards. Try the cord by hand before attaching to the run- ning engine. Adjust the handle (H, Fig. 53) so that, when pressure is applied to it, a very light line will be made upon the card. Then take pencil from drum and open the cock to see 'Drum Paper Being ' Inserted Spring Clips FIG. 80. Method of starting paper on an indicator drum. FIG. 81. Method of placing paper on an indicator drum. that the pencil will not overtravel the drum either at the top or at the bottom. 98. Indicator Paper should be smooth, tough, and well- calendered, so that it can be handled without damage and that it offers little friction to the passage of the pencil over its 58 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 surface. It should be cut to the height of the indicator drum and about 1 in. longer than the circumference of the drum. The paper is put on the drum (Fig. 80) by inserting one corner under the longer clip, bending the card (paper) around the drum and bringing the other corner under the other clip, then pulling it tight around the upper end of the drum. Then, by taking hold of the two corners between the clips, the card is slid down the drum (Fig. 81), pulled tight again around the drum and the ends folded back. A little practice enables one to do this quickly and neatly. 99. The Indicator Pencil should be of hard lead and should be short and kept well pointed. Too long a lead will cause inertia effects in the pencil mechanism. As the point wears down, it must be resharpened by rubbing it on a piece of fine sand paper because a fine line is very essential in indicator work. A metallic point can be used on a paper coated with sulphate of zinc and has the advantage of keeping its point although it offers more friction than a lead point. 100. An "Atmospheric Line" Should Be Drawn On Each Card before taking a diagram. It is best drawn by holding the pencil to the card (cock closed) and rotating the drum through a complete revolution by pulling the cord by hand as far as it will go, before attaching the cord to the reducing mechanism. The importance of always taking an atmospheric line cannot be overestimated. Its uses will be brought out in subsequent sections. 101. The Indicator Diagram Is Taken As Follows : (1) Open indicator cock and allow indicator to "warm up." (2) While indicator is warming up, attach drum cord to reducing mech- anism. (3) Hold pencil to paper for at least three or four revolutions of engine. (4) Close cock and unhook drum cord. (5) Examine card for evidences of indicator errors. As connec- tions in the indicator and at the cord are apt to work loose, it is advisable to frequently try the indicator pencil for lost motion and to watch that the diagram remains in the center of the card (to make sure the drum is not striking its stops). NOTE. CONVENIENT METHODS OP "HooKiNG-Up" AN INDICATOR CORD are illustrated in Figs. 82, 83 and 84. Fig. 85 shows how an adjust- able loop may be arranged in an indicator-cord end. Fig. 86 illustrates a SEC. 101] STEAM-ENGINE INDICATORS 59 [Distance to Point \ of Attachment Indicator ......... > ,-To Reducing Mot/on i .-Wire Hook FIG. 82. Method of arranging drum cord, C, to prevent flapping. (Connection is effected by catching hook, H, in eye, E.) Wooden Pendulum Lever FIG. 83. Connection at pendu- lum lever to prevent flapping of cord. (Eye, L, is placed over pin, //.) ,-lndiccrtor Indicator Cock. .-Engine j Cylinder FIG. 84. Convenient method of arranging an indicator cord. (One end, A, of the cord is attached to the indicator leaving the cord sufficiently long that it will not pull taut when the crosshead, C, is in its extreme position. A loop, L, is provided near the indicator for "hooking in.") For fndfcafor Hook Cord Ino/i'co/tor Cord- ,-To Indicator FIG. 85. Adjustable loop for indieator- cord end. ,,-\\-Cord Bin \^\When In ^ Position Shown uy Dotted Lines FIG. 86. Knot for indicator-cord hook whereby effective cord-length can be adjusted readiJy. 60 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 Iron W/re Vise --. knot, for attaching the cord to the hook,whereby the cord length may be adjusted readily. Indicator cords should preferably be high-grade, smooth fish line known in the trade as "trout line." It should be from %4 to %4 in. in diameter. Any smooth cord which has sufficient strength and which will not stretch will do. Iron wire between ^4 and ^ 2 in. in diameter, is some- times used instead of cord for opera- ting indicators. No. 22 gage an- nealed iron wire or picture wire may prove satisfactory. Kinks may be FIG. 87. Taking kinks out of No. 22 gage taken out of iron indicator wire as annealed iron indicator wire. suggested in Fig. 87. 102. An Ideal Indicator Diagram is shown in Fig. 88. This diagram is for an engine having a stroke of 32 in., cutting off when the piston has traveled 8 in. from the beginning, and the exhaust valve opening 2 in. before the end of the stroke. It is assumed that the exhaust valve closes 5 in. before the end of 5 10 15 20 25 30 32 Position of Piston in Cylinder Cinches from End) FIG. 88. Ideal indicator diagram for a steam engine. the return stroke and that the steam valve opens when the piston is exactly at the end. The engine is supplied with steam at 60 Ib. per sq. in. gage, and exhausts into a condenser where the vacuum is 12 Ib. per sq. in. (about 24 in. mercury SEC. 103] STEAM-ENGINE INDICATORS 61 column). A vertical scale of pressures, XM, (Fig. 88) and a horizontal scale, XN, representing positions of the piston are- laid off on the squared paper. While the piston travels its first 8 in., the pressure, LC, inside the cylinder will, of course, be 60 Ib. per sq. in. because the steam valve is open. The steam then expands along a line, CR, until the exhaust valve opens at R, where the pressure drops rapidly, RE, to that in the condenser. On the return stroke of the piston the pressure, EK, remains that of the condenser until the exhaust valve closes (K). Then the steam which remains in the cylinder is compressed (KB) and finally, when the piston reaches the end of its travel, steam is again admitted (B) from the boiler and the pressure in the cylinder immediately rises, BL, to the pressure of the steam supply. NOTE. THE EXACT FORM OF THE COMPRESSION AND EXPANSION LINES depends upon the clearance volume and will be treated separately (Sees. 108 and 111). 103. The Actual Indicator Diagram Differs Widely From The Theoretical (except in occasional instances) for various reasons: (1) The valves may not be set to give the best diagram. (2) The engine design may not allow of a perfect diagram even with the valves in their best setting. (3) The installation of the engine may be at fault.' However, the indicator diagram enables one to intelligently set the engine valves and to know why a more perfect diagram is, not obtained. In studying the diagram, separately. each "line" of Fig. 88 will be considered FIG. 89. Variations of the admission line. 104. The "Admission Line" Will Be Of Varied Appearance for different engines. BL (Fig. 88) and A, Fig. 89, show the ideal form in which it often appears on cards from slow-speed four-valve engines. On high-speed engines the admission line 62 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 (Fig. 90) is frequently lacking altogether, a condition which is often satisfactory. If the steam valve opens late in the cycle but still opens rapidly, admission line B (Fig. 89) will result. With slow opening this changes to the form of C. Notice, here, that the piston travels outward before the valve is well opened, increasing in speed as it progresses, and that the steam does not get a chance to build up the pressure until the piston is well on in its stroke. Condition, D, occurs when the com- pressed steam in the clearance volume begins to expand before .... f . the steam valve opens. Condition InatcaTor Card---^ E happens seldom; here the ex- haust valve closes just at the end of the return stroke and the piston, moving outward, then expands the steam in the clearance volume, re- ducing its pressure until the steam \~Posifi6h of .Ideal Admission Line: FIG. 9o.-indicator diagram from valve opens allowing the pressure a high-speed engine. (Showing ab- to build Up. Condition F sents what happens to the ad- mission line when the steam valve opens at the proper time but the exhaust valve remains open too long. With condition G, representing too-high compression, the opening of the steam valve allows the steam to flow out of the cylinder and into the steam chest until this is again expanded by the piston moving outward. Just as late admission, C, causes the admission line to slope away from the end, so an early admission causes it to slope backward, as H . In condition 7, the sharp point at the top is another indication of early admission. Decreasing the lead (see Divs. 4 and 5) will usually make the engine run more smoothly and give a rounded top as in A. 105. The "Steam Line" Indicates The Pressure Losses (LC, Fig. 88 and Fig. 91) from the boiler to the engine cylinder and depends on the steam-flow through all the intermediate passages. EXPLANATION. Just as water will flow only from a higher to a lower level, so will steam flow only when there exists a difference of pressure to cause the flow. The greater the velocity of the steam through the passages and the greater the internal surface area, in the passages, over which the steam must pass or rub, the greater, of course, will be the SEC. 106] STEA M -ENGINE IN DIG A TORS 63 amount of frictional resistance produced by the steam passing through the passages. The greater the frictional resistance, the greater again must be the difference of steam pressure to maintain the flow. Now, in a steam engine, the steam is first admitted when the piston is about at the end of its stroke and moving very slowly. The volume to be filled with steam is only the clearance volume, which can be filled quickly and usually with a small steam velocity through the ports. But the velocity of the piston increases as it moves toward mid-stroke and then decreases again. As the piston moves from the end, steam must rush in to fill a rapidly increasing volume and, the faster the volume increases (piston travels), the more swiftly the steam must flow through the ports. Thus, as the piston moves away from the cylinder end, there will be a rapidly increasing frictional resistance in the passages calling, in turn, for a greater pressure difference between the boiler and cylinder. 106. The Ideal Steam Line (BL, Fig. 88 and A, Fig. 91) can only be produced when the velocity of the steam through the passages never becomes great enough to appreciably FIG. 91. Variations of the steam line. affect the frictional resistance. This may occur in a very slow- speed engine with large direct passages. The ideal steam line is very nearly approached in most Corliss engines. In high-speed engines, the steam line looks more like B, Fig. 91, where the difference between x and y represents the additional pressure required to force the steam into the cylinder at the higher velocity after the piston leaves the end. On engines with large steam chests the steam line will appear more as shown at C, where the steam stored in the chest is able to keep up the pressure in the cylinder until the piston has moved farther out in its stroke and attained a higher velocity. Diagram D represents the total absence of a steam line at light load, .cut-off having taken place as soon as the clearance volume was filled with steam. Diagram E shows the varia- tion in pressure-drop in a non-expansive engine as the speed of the piston increases and again decreases toward the end of the 64 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 stroke. The same sort of line is usual where an engine has a very late cut-off point. 107. The Steam-Chest Diagram (Fig. 92), when combined with the cylinder diagrams, is very valuable for segregating the pressure losses between the boiler and the cylinder. The steam-chest diagram is taken on an indicator which is piped to the steam chest and which is driven from the same reducing mechanism as that which is used for the cylinder diagrams. The cylinder diagrams are taken on another card (or combined, by tracing the diagram from one end onto iz'Steam-Chesf Card ^\ : V : ;:'!'.:: /: -.'ijv ':''. ' ^ Boil fr. Pressure Line ':'.', ' ' FIG. 92. Cylinder diagrams superimposed on steam-chest diagram. that from the other end). The cylinder diagrams and steam- chest diagram must be taken with the engine operating under like conditions. The card with the cylinder diagrams is then cut down in size and pasted on the steam-chest diagram with the atmospheric lines along one line and with the ends of the diagrams above one another as shown in Fig. 92. The boiler- pressure line is then drawn on the card by hand at a height measured from the atmospheric line by the same scale as that of the spring with which the diagrams were taken. EXPLANATION. When the crank-end steam valve opens /Fig. 92) the pressure hi the steam chest is reduced. As the piston moves away from the end, the pressure in the chest decreases as does also the pressure in the cylinder. Up to cut-off, e, the drop between the boiler and steam chest, be, and the drop from the chest to the cylinder, cd, both increase SEC. 108] STEAM-ENGINE INDICATORS 65 because of the increasing velocity of the steam. After cut-off, however, steam is supplied from the boiler only to fill the steam chest, and it builds up the pressure there rapidly at first (eg) and then more slowly (gf) until the head-end valve opens, again causing the pressure to drop. Sometimes the momentum of the steam in the supply pipe causes the point g to appear much higher than shown. Line gf is then practically parallel to the boiler-pressure line. NOTE. DISTANCE be CAN OFTEN BE DECREASED and the entire steam- chest diagram flattened out by equipping an engine with a larger supply pipe. Likewise, distance cd can sometimes be decreased by increasing, if possible, the amount by which the valve uncovers the steam port. r-Inii-'ial Po/nt 108. The "Expansion Line" In A Steam Engine Usually Follows A Hyperbolic Curve (CR, Fig. 88 and Fig. 93). That is, the absolute pressure falls inversely as the volume increases. If the vol- ume is doubled, the pressure falls to one half the initial; when the volume is five times the initial, the g> pressure is one fifth and so on. vo urn e-'cu'bSc' Feet Thus, Fig. 93 represents the eX- FIG. 93. Hyperbolic expansion line pansion of one cubic foot of steam for steam - from an initial pressure of 60 Ib. per sq. in. abs. (about 45 Ib. per sq. in. gage). EXAMPLE. Fig. 94 is an indicator diagram taken with a 60-lb. spring from an engine which has a clearance volume equal to 5 per cent, of the piston displacement. From the point of cut-off draw the theoretical (hyperbolic) expansion line. SOLUTION. Since the length of the diagram is 3 in., the clearance volume OA, can be represented as 5 per cent of 3 in. = 0.05 X 3 = 0.15 in., or Ko in., and laid off to the left of the diagram as shown. The zero pressure line, OZ, can also be laid off to scale below the atmospheric line (15 Ib. is near enough for atmospheric pressure except when spring scale is very small). To construct the theoretical curve through C, the point of cutoff, draw line CU, parallel to the atmospheric line and line CB perpendicular to it and divide up BZ into parts (which may be of any length; BE, El, IM, MP, etc., as shown. Erect a perpendicular at each point of division. Draw lines from the points where these pendiculars cut the line CU to point and note where they cut CB. From the points where these diagonal lines cut CB draw horizontals again to cut the perpendiculars, as FG, JK, etc. The points G, K, Y, etc. will determine 66 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 the theoretical expansion curve which can then be drawn through them. As is shown, it is well to draw the perpendiculars DE, HI, etc. closer together for the first part of the expansion curve than for the end, because the curve drops more rapidly at the start. Zero Pressure (Absolute) Li'ne- FIG. 94. Construction of the theoretical expansion line. (Hyperbolic curve.) 109. The Expansion Line May Reveal Leaky Valves (Figs. 95 and 96). With valves properly seated (Fig. 92), the actual expansion curve usually falls below the theoret- ical at the beginning and rises above it toward the end. A leaky exhaust (or drip) valve may cause the expansion ...Cut-Off Point Actual Expansion Afmospnenc LJ - ~~"-- 'Zero 'Pressure Line-** -Cut-Off Point wretical x Cxpansi 'Actual , \Cxpansfon Line _ ---Zero Pressure Line FIG. 95. Indicator diagram showing effect of leaky steam-admission valve. Indicator Card- FIG. 96. Indicator diagram showing effect of leaky exhaust valve. curve to lie exactly on the theoretical or below it, as in Fig. 96. A leaky steam valve, on the other hand, will cause the expan- sion curve to lie well above the theoretical throughout its length (Fig. 95). NOTE. Too MUCH SHOULD NOT BE INFERRED FROM THE APPEAR- ANCE OF THE EXPANSION LINE, however, as there are too many things SEC. 110] STEAM-ENGINE INDICATORS 67 which might affect its shape. The expansion line may follow the theoret- ical very closely in an engine that has leaky steam and exhaust valves. Its study is useful chiefly in revealing general indications of trouble. 110. The "Release" and "Exhaust" Lines Indicate How Effectively The Steam Is Taken From The Cylinder (RE and EK, Fig. 88 w and Fig. 97) . Since they merge into one another they are difficult to study separately. The release line, one might say, begins at the point of release, R, and ends where the pressure is decreased to its minimum value, as at //, Fig. 97. The exhaust line (also called the back-pressure or counter- pressure line) begins at H and ends at K, the point of com- pression, where the exhaust valve closes. Since the pressure in the cylinder during exhaust must, to produce a flow, be more than that into which the cylinder is exhausting, the exhaust line may be expected lie above the atmospheric (when exhausting to the atmosphere). If the exhaust pas- D Late Release With High Terminal P r essur FIG. 97. Variations of release and exhaust lines. sages are short, direct, and large, the pressure difference will not, A and B, be noticeable on the indicator diagram. As it is advisable to have the pressure, urging the piston forward, decrease toward the end of the stroke, a release line as at A is recommended. Of course the maximum of work would be obtained from the steam if it were released along the line GH of A but this would result in condition B in which the loss of work (shaded) is the same as in A . The mean between these two conditions is represented in C. With a high ter- minal-pressure condition B takes the shape of D, due to the inability of the exhausted steam to escape from the cylinder because it is expanding while the volume in the cylinder is decreasing. The dotted line in D shows the advantage of the early release. Condition E represents what may happen to the exhaust line if the exhaust valve restricts the port when it is in its 68 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 extreme position (too much lap); this condition might also appear in a twin-cylinder engine where the cranks are set at 90 deg., the hump being formed while the other cylinder is releasing. If cut-off occurs too early in the stroke, the steam may expand to a pressure below exhaust pressure, F, in which case the opening of the exhaust valve allows previously exhausted steam to flow back into the cylinder. As will be shown (Sec. 114), this over-expansion represents a loss of work. Over-expansion can be overcome by throttling the steam sup- ply, thus causing a later cut-off. 111. The "Compression Line" Varies Widely In Different Engines (KB, Fig. 88 and Figs. 98 to 100) depending on the valve setting, condition of the engine, exhaust pressure, and the clearance volume. In general, it should be the converse of the expansion line, that is, it should also be a hyperbolic curve, the pressure rising as the volume within the cylinder is decreased. The purpose of this increased pressure at the end of the stroke is primarily to aid in stopping the piston before its reversal in direction of travel, but by thus trapping some steam in cylinder, the amount which must (when the steam valve opens) be introduced to fill the clearance volume is materially decreased. To com- pletely fill the clearance space, the compression line would have 'tKv* ^ ra ^ se ^ e P ressure to that of ^ \p the steam line as in Fig. 90; 'Conditions \s\ti,, s i nce this would be more FIG. 98. Variations of the compres- compression than is necessary for stopping the piston, it is recommended that there should be just enough compression to produce smooth running of the engine. Usually this condition is brought about when the compres- sion curve merges with the admission line at about % the height of the diagram (A, Fig. 98). In automatic engines the compression depends upon the load and at light loads fre- quently becomes excessive as at B. Condition C may be caused by the condensation of the cushion steam on the cool walls of the clearance space, but it is more likely to be the result of a leaky exhaust or drip valve. Thus as the movement .Compression I Leaky Too Early | Valve ^Cylinder .onclerr- ,satlon) SEC. 112] STEAM-ENGINE INDICATORS 69 of the piston becomes slower and the pressure higher, the steam escapes as fast as the moving piston tends to compress it. Condition D shows how, with a leaky piston, the compres- sion curve is above the hyperbolic (due to steam leaking in from the other end) up to point a, where release occurs at the other end, falling then from a to b, while leakage takes place to the other side of the piston. NOTE. FIG. 99 SHOWS THE EFFECT ON COMPRESSION OF DIFFERENT EXHAUST PRESSURES in the same engine. It is evident that the pressure at the end of compression increases in direct proportion to the exhaust /' Per Cent\ Piston/ Displacement '6% Clearance^ '*Later Part of Vo/ume X % Exhaust Period o% Compress/on' Period FIG. 99. Illustrating effect of exhaust pressure on compression. (Compression pressure, for any given engine, varies directly with the exhaust pressure.) Per Cent Piston Displacement FIG. 100. Illustrating effect of different clearance volumes on the compression curve. pressure. That is, if the exhaust pressure (absolute) is doubled the compression pressure is also doubled, and so on. Fig. 100 shows how the compressure pressure varies, with the same setting, on engines with different clearances. It is evident from Fig. 100 that if the clearance volume is equal to the portion of the return stroke which is uncompleted when the exhaust valves closes, the compression pressure will be twice the absolute exhaust pressure. If the clearance were but half as great, everything else remaining equal, the compression pressure would be 3 times the exhaust pressure. From this it is evident that in engines with very small clearance volumes the exhaust valve must close late in the stroke or a high compression pressure will result. 112. Examples Of Indicator Diagrams Revealing Faults are included here to better familiarize the reader with their 70 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 analysis. Methods of correcting faulty valve-settings will be discussed in Divs. 4 and 5. Methods of correcting mechan- ical faults will be treated in Div. 13. EXAMPLE. Fig. 101 is a card taken from a simple, high-speed engine. The sloping admission lines at a and c show late admission. Cut-off in the head end at 6 shows a lower pressure than in the crank end at d. This, together with the earlier cut-off at 6, indicates that the port is not well uncovered at the head end to allow the steam to enter. Although '.--Atmospheric Line Atmospheric Line-^. FIG. 101. Example of faulty indicator diagrams from a simple engine. FIG. 102. Example of faulty indicator diagrams from a simple Corliss engine. release, r, is not too late, it could well be advanced a little. At / the uncompleted portion of the return stroke is about twice that at g. Although g occurs too early, / is even worse in this respect. This may account for the curving-off of the compression line at e due to cylinder condensation at the high pressure. EXAMPLE. Fig. 102 is a card taken from a simple Corliss engine. Late admission is again shown at a and b. The sloping steam line toward c shows only partial valve opening. Late release is shown at e and /. Compression takes place a little late at g, whereas it is satisfactory at h. EXAMPLE. Fig. 103 shows diagrams which are satisfactory except for the compression curve at a. An effort has been made here to obtain compression by closing the exhaust valve early in the return stroke but the steam leaks out as the pressure is raised. Since the pressure at a is less than at c, the leak is not at the piston and must be at the exhaust valve or drain cock. 113. In Determining The Horse Power Or Steam Consump- tion Of An Engine The "Mean Effective Pressure" Must Be Known, for reasons which will be explained. But first the methods of finding mean effective pressure will be discussed. 114. In Finding The Mean Effective Pressure By The Method Of Ordinates (Figs. 104 to 106) the length of the dia- gram is divided into ten equal parts and perpendiculars are ^^Atmospheric Line FIG. 103.- -Indicator card from a simple Corliss engine. SEC. 114] STEAM-ENGINE INDICATORS 71 erected at the middle point of each division. The length of each perpendicular is measured or the pressure which it repre- sents is found by a scale corresponding to the spring number. The average height or average pressure is then found as explained below. The use of lengths is better than that of Diameter 24- Stroke 46* Revolutions 10 Spring Scale 50 Indicator Card -^ FIG. 104. Finding P m by the method of ordinates. pressures because it permits of correction for the true spring scale (Sec. 94). EXAMPLE. Fig. 104 illustrates the method of measuring the pressure along each perpendicular. (Scales to correspond to those of indicator springs can be had from indicator manufacturers.) The' length of each perpendicular is measured and written at its foot; for example, with a 50 scale, the length of ab is 87. The ten pressures are then added and the sum divided by ten. The result is the "mean effective pressure" which in Fig. 104 is 42.45 Ib. per sq. in. NOTE. A CONVENIENT WAY To ERECT THE TEN PERPENDICULARS (Fig. 105) is to first draw vertical lines AC and BD at the ends of the diagram, then lay a ruler with the zero and 5-in. marks on these lines and place a dot at each ^- and %-inch mark as shown, and later erect perpendiculars through each dot as indicated. EXAMPLE. Fig. 106 shows a convenient method of adding the lengths of the perpendiculars on the edge of a strip of paper. The paper is placed in position 7, with its edge along the first perpendicular and with its Fig. 105. Locating mid-points for find- ing P m by the method of ordinates. 72 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 corner at the lower end of the perpendicular, and a mark, 1, is made on the paper at the upper end of the perpendicular. This mark is then placed (Position II) at the lower end of the second perpendicular and mark 2 is made at the upper end. This is continued until the ten 1 j^-'Paper Strip .'[Penciled- in'.-' . Ordinates^ ' ( '"Pencil Mark ^ S| \ ^j.'- -'-.''. ;.'' . indicator Diagram- -Atmof- phenc Line V 2 <-- -Paper Strip *"*? 1 1 \ N i u -Second Position I- First. Position FIG. 106. Adding lengths of perpendiculars on a paper strip. perpendiculars have been laid off. The length of the strip of paper from its end to mark 10 is then the sum of the lengths of the perpendiculars, which can be divided by 10 to get the average length. The average --Indicator Diagram III! ~\ T Heights Of Perpendiculars-"'' Ind/cator Card-....^( FIG. 107. Finding P m , when over-expansion takes place, by the method of ordinates. length multiplied by the "true scale" of the indicator spring gives the mean effective pressure. NOTE. IN CASES OF OVER-EXPANSION (Fig. 107) after point a is passed, the forward pressure on the piston is less than the back pressure SEC. 115] STEAM-ENGINE INDICATORS 73 on the return stroke. This means that, instead of being forced forward by the steam, the piston is actually doing work on the steam in expanding it. The loop, therefore, represents work lost during that portion of the stroke. Hence the pressures of the loop must be subtracted from those of the main portion. Adding ordinate pressures for Fig. 107, the sum of the pressures in the main portion = 97 + 93+41+20 + 6 = 257 Ib. per sq. in. The sum of the pressures in the loop = 3 + 9 + 13 + 15 + 12 = 52 Ib. per sq. in. The difference = 257 - 52 = 205 Ib. per sq. in. Then the average or mean effective pressure = 205 -5- 10 = 20.5 Ib. per sq. in. 115. The Planimeter Affords A More Accurate Means For Finding The Mean Effective Pressure than does the method of FIG. 108. Amsler polar planimeter and its correct use in finding areas of indicator diagrams. ordinates. Generally speaking, a planimeter is an instrument for finding the area of any closed figure. In some of its forms it enables one to find directly the average height of an indi- cator diagram or even the mean effective pressure. 116. The Amsler Polar Planimeter (Fig. 108) is one of the most simple and enables one to find the area enclosed by the indicator diagram by guiding the tracer point, T, around the diagram in a clockwise direction. The planimeter measures the area in square inches. OPERATION. The indicator card should be fastened with thumb tacks to a smooth board and on a piece of drawing paper or Bristol board which 74 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 is large enough to include the card and the planimeter in every position it will take. The fixed point, P, should be so placed that the planimeter arms will not be closed when T is nearest to P and that the arms will not open too nearly into a straight line when in their maximum position (Fig. 108 shows a good position). The point, T, is then placed at some point on the diagram and a slight pressure applied to it so as to make a depression in the card at that point. The reading of the wheel, W, and the vernier is then recorded. The point, T, is then guided carefully around the diagram in the clockwise direction, as shown, until the depression is again reached. Another reading of the wheel and vernier is taken. The difference between the two readings will be the area of the diagram. The length of the diagram is then measured between perpen- diculars erected at the ends (AC and BD, Fig. 105). The area of the diagram divided by its length gives its mean height. The product of the mean height and the true scale of the indicator spring is the mean effective pressure. FIG. 109. Diagrammatic illustration of polar planimeter with adjustable arm for finding mean height of indicator diagrams. NOTE. WHENEVER THE DIAGRAM Is So Low ON THE CARD THAT THE WHEEL MIGHT CROSS THE EDGE OF THE CARD, the card should be inverted into the position shown dotted in Fig. 108. EXAMPLE. An indicator diagram, taken with a 60-lb. spring, is found by planimetering to have area of 1.05 sq. in. and is 3> in. long. What is the mean effective pressure? SOLUTION. Mean effective pressure = (1.05 -T- 3>^) X 60 = 20 Ib. per sq. in. 117. Polar Planimeters With Adjustable Tracer Arms (Fig. 109) are averaging planimeters; that is they have the advantage that they will measure the average or mean height of a diagram directly on the wheel arid vernier (usually in fortieths of an inch). To accomplish this the tracer arm, A, SEC. 118] STEAM-ENGINE INDICATORS 75 Indicator Card- which slides in or out through H, must be so set that the dis- tance between M and N is equal to the length of the indicator diagram. 118. The Coffin Planimeter Is Also An Averaging Instru- ment (Fig. 110). The indicator diagram is placed with its atmos- pheric line along the horizontal clip, K, and ends almost touching the fixed and movable vertical clips, F and S. It is then plani- metered as with the Amsler planimeter. If the start and finish point is selected at the ex- treme right of the diagram (G, Fig. 110), the final reading of the wheel and vernier need not be taken. The tracer point can be moved up vertically along the movable clip, S } with the operator keeping his eye on the vernier until the reading of the wheel is the same as before tracing the diagram. Assume that this condition obtains when the tracer point reaches H. Then the height, GH, is the mean height of the diagram. If the scale, Drawing -Groove "^Smooth Brlsfol Board M Surface For Wheel To a!Ho nn Ride On (Ash ~ FIG. 111. Willis planimeter with adjustable tracer arm. (Jas. L. Robertson and Sons.) S, which forms the moving clip, is the same as the number of the spring, and if its zero be set at G, the mean effective pres- sure, in pounds per square inch can be read off directly at H. 76 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 119. The Willis Planimeter (Fig. Ill) has a wheel, W , which moves longitudinally along its axis, XY, a distance propor- tional to the area circumscribed by its tracer point, T. The movement of the wheel will give the mean effective pressure directly, if the length of the tracer arm, A, is equal to the length of the diagram, and if scale, S, is of the same number as that of the indicator spring. 120. In Computing Horse Power From Indicator Diagrams, there are briefly four steps: (1) Find the horse power constants, k, for 1 Ib. mean effective pressure and 1 r.p.m., for each end of each cylinder. (2) Find the mean effective pressures from indi- cator cards, for each end again. (3) Find horse power for each end. (4) Find total horse power of engine. The theory of the computation of indicated horse power from indicator diagrams is treated in Sec. 18. As developed there : (12) Pi h p = m/aP (horse power) Wherein : P ihp = indicated horse power developed in one end of the cylinder. P m = mean effective pressure, in pounds per square inch. L JS = length of stroke, in feet. Ai p = area of piston, exclusive of rod, if rod extends through the head, in square inches. N = speed of engine shaft, in revolutions per minute. 121. The Horse-Power Constant, k, is made up of the terms that cannot change in For. (12). These are evidently L/ s , A ip , and the denominator (33,000). P m and N will depend upon operating conditions load, steam pressure, etc. If the latter are each taken equal to one, For. (12) becomes (13) P ihp = < = k (horse power constant) Wherein : k is the horse power constant for a certain end of an engine cylinder = h.p. for 1 Ib. mean effective pressure and 1 r.p.m. EXAMPLE. An engine has a stroke of 30 in., a piston 18 in. in diameter, and a 2% in. diam. piston rod. What are its horse power constants? SOLUTION. For head end of cylinder: A ip = 18 X 18 X 0.7854 = 254.5 sq. in.; L /s = 2.5 ft.; k = 2.5 X 254.5/33,000 = 0.0193 = 1/51.8. SEC. 122] STEAM-ENGINE INDICATORS 77 For crank end of cylinder: Ai P = 254.5 (area of piston rod) = 254.5 3.547 = 251 sq. in.; k 2 = 2.5 X 251/33,000 = 0.019 = 1/52.6. NOTE. To avoid the use of decimal fractions, it is convenient to use the horse power constant expressed as a fraction whose numerator is one. 122. Methods Of Finding The Mean Effective Pressure, P m , Have Already Been Given, Sees. 114 to 119. It may be well here to lay down two rules for use when P m is not found directly. (14) P.- area of diagram in sq. in. X scale of spring in Ib. per in. length of diagram in inches (Ib. per sq. in.) Or: (15) P m = mean height of diagram in in. X scale of spring in Ib. per in. (Ib. per sq. in.) 123. To Find The Horse Power For Each End Of One Cylinder one needs only to multiply the horse power constant by the mean effective pressure for that end and by the speed. Or: (16) P ihp = P m Nk (horse power) EXAMPLE. In the engine of the example of Sec. 121, if P m for the head end were 49 Ib. per sq. in., for the crank end 53 Ib. per sq. in., and if N = 105 r.p.m., what horse power is developed in each end? SOLU- TION. For head end, substituting in For. (16), P ihp = P m Nki = 49 X 105 X 0.0193 or 49 X 105 -f- 51.8 = 99.3 h.p. For crank end, P ihp = P'm N X & 2 = 53 X 105 X 0.019 or 53 X 105 -J- 52.6 = 105.8 h.p. 124. The Horse Power As Computed From The Indicator Diagrams Is Called The Indicated Horse Power and repre- sents the power actually developed by the steam within the engine cylinder (Sec. 11). Since some portion of this power is lost by friction within the engine, as at the several bearings and sliding members, all of it cannot be realized from the engines for further work. 125. "Friction Horse Power" Is That Part Of The Indi- cated Horse Power Which Is Lost Within The Engine Itself 78 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 (Sec. 11). With a given engine, the magnitude of the friction horse power depends upon the load and the steam pressure but changes only slightly under the varying conditions. If the engine is unbelted or uncoupled from all its load, then all the power developed by the steam (indicated horse power) becomes friction horse power. 126. The Brake Horse Power Is The Power That The Engine Delivers, at its shaft, or pulley to some other machine (Sec. 11). It is, of course, less than the indicated horse power by the -amount of the friction horse power. Where an engine is driving an electric generator the efficiency of which is known (and in certain other cases, see Div. 12) the brake horse power can be determined separately. 127. The Brake Horse Power Is Computed From Indicator Diagrams, indirectly, whenever it cannot otherwise be found; see Div. 12. Thus, the indicated horse power may be com- puted from the indicator diagrams directly. Then if the friction horse power is subtracted from the indicated horse power, the brake horse power will result. That is (17) Brake h.p. = Indicated h.p. Friction h.p. (horse power) NOTE. MANUFACTURERS OF ENGINES WHICH ARE TESTED BEFORE LEAVING THE FACTORY CAN GIVE THE FRICTION HORSE POWER OF THEIR ENGINES AT DIFFERENT LOADS. This information is often very valuable when tests are to be made or performance guarantees verified. 128. The Weight Of Steam Used By An Engine Can Be Computed from the volume of the cylinder, the number of times it is filled in a certain time and the weight of a unit volume of steam at the pressure at which the cylinder is filled. If steam were a perfect gas (see PRACTICAL HEAT) or a liquid, and if there were no leakage either at the piston or the valves, such a computation would be reasonably accurate. But, since steam is a vapor continually changing in the engine cylinder (some of it) either from the liquid to the vapor or from the vapor to the liquid state, and, since leakage is quite common, the calculated weight of steam used is never equal to the actual, being usually less because the steam is partially condensed inside the cylinder. The calculation is of use, SEC. 129] STEAM-ENGINE INDICATORS 79 however, for comparison purposes and as a measure of the ideal minimum amount of steam which could be used by an engine under the conditions. 129. The Weight Of Steam Used By An Engine With No Clearance (Fig. 112) can be found by the following formula, the derivation appearing below: /ION TIT- 13,750 D' ps x s (18) W ih = 5 (Ib. per i.h.p.hr.) * m Wherein: W,-* = weight of steam used by one end of an engine, in pounds per indicated horse power hour. D' ps = density of steam at a selected point on the expansion line , in pounds per cubic foot. x s = fraction of stroke completed (Fig. 112) at that point. P m = mean effective pressure, in pounds per square inch. DERIVATION. The volume of the cylinder is A.pL/,/144 cu. ft. (A,- p = area of piston in square inches. L/ s = length of stroke in feet.) It is | ^. Cu f-off Point filled N (r.p.m.) times per minute or 60 N times per hour. The total vol- ume to be filled per hour is then 60 NAifLft/144; cu. ft. If release occurs at d, the end of the stroke, where the pressure is P a and the density is D ps Ib. per cu. ft., the weight of steam used per hour is then 60 NA ip Lf S D ps /l4:4: Ib. As the engineer usually wants to FlG - 112- Theoretical diagram from i ,r r , / an engine with no clearance. know the weight of steam used per indicated horse power per hour (W,-*) and as the indicated horse power of the engine is by For. (12) P m L f& A ip N/33,OOQ, it follows that: W weight used per hour _ 60 NA ip Lf s D ps /l4:4 horse power ~ P m L fs A ip N/ 33^000 60 NAipLfsDp, 33,000 13,750 D pi /1U ~~ (lb - per 1 - h - p - hr - } Since at any other point, 6 (Fig. 112), after cut-off, the weight of steam within the engine cylinder must be the same as at d, it would be possible to go through the same reasoning for any point and get the same result. The volume filled each stroke would be only a fraction, x s (Fig. 112) of the total; but the pressure being P' , the density would be D' ps . We would get: (20) W ih = i?,750 D^x. Qb ^ .^ ^ } * m which is the same as For. (18). NOTE. Wih is computed separately for each end of the cylinder. 80 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 3 130. The Weight Of Steam Used By Any Simple Engine Can Be Computed From The Indicator Diagrams by the following formula, the derivation of which follows : (21) x c )D' pa - (lb. per i.h.p. hr.) Wherein : x c = clearance volume expressed as a fraction of the piston displacement. x' a = fraction of return stroke uncom- pleted at a chosen point on the compression curve. D" ps = density of steam at that point in pounds per cubic foot. The other symbols the same as in For. (18). Scale of Spring = 40 Pm = 47.5 Lb. Per Sq. In. **$ i C j. T4^^^lf.- Compression Point k- (y-K - r:7 4* j- -? Pa=/PLfe AT5?.//* ^ eroPressureLfne j Sq. In Indicator Fia. 113. Indicator diagram from a simple engine. (Calculation of steam consumption.) DERIVATION. Referring to Fig. 113, the diagram being from an engine having a clearance volume of 5 per cent, of the piston displacement, the volume in the cylinder at 6 is (x, + x c }A ip Lf S /l44. Proceeding as in the preceding section the result would be, if this volume were filled every revolution w , u . IMSOJJ^ (grosS; lb . per i. h . p . hr0 (22) But, since some steam is trapped in the cylinder at k, when the exhaust valve closes, all the steam necessary to fill the volume at 6 and at a pressure P' a will not have been admitted every revolution. It is possible likewise to find the weight not rejected by taking some point, /, on the compression line and applying to it the same reasoning. The result would be: (23) W" (unrejected, lh per i.h.p. hr.) Wherein: x' 8 = uncompleted fraction of stroke at/. D" ps = density of SEC. 131] STEAM-ENGINE INDICATORS 81 steam at /, in pounds per cubic foot. The net weight of steam required will, of course, be the difference between W'i/, and W"a, which is n\ w -W w- 13.750 P' P .Qc.+s) 13,750 P",.(s'.+s e ) \^j Wi/i w ih vv ih -p ^ * m * m = ^^ \(x s + x c )D' ps - (x' s + x c )D" ps ] (Ib. per i.h.p. hr.) "m L J which is the same as For. (21). NOTE. THE POINTS, 6 AND /, ARE BEST CHOSEN NEAR THE LOWER ENDS of their respective lines, because there the quality of the steam is apt to be highest (during expansion, the quality increases; during compression, it decreases) and errors due to moisture in the steam will be minimized. EXAMPLE. Fig. 113 represents a diagram, showing, with a 40-lb. spring, a mean effective pressure of 47.5 Ib. per sq. in. How much steam is accounted for by the diagram? SOLUTION. The whole length of the diagram is 4 in. x s = 3.5 in./4 in. = 0.875. x c = 5 per cent. = 0.05. x's = 0.4 in. /4 in. = 0.10. P' = 32 Ib. per sq. in. abs: andP" = 19 Ib. per sq. in. abs. From steam tables, D' ps = 0.077,3 and D" pi = 0.047,46 Ib. per cu. ft. Substitution in For. (21) gives, ~ (X ' S + Xc}D ' ] = 0.05)0.077,3 - (0.10 + 0.05)0.047,46] = 289.5[(0.925 X 0.077,3) - (0.15 X 0.047,46)] = 289.5(0.071,5 - 0.007,1) = 289.5 X 0.064,4 = 18.65 Ib. per i.h.p. hr. 131. To Find The Total Steam Used By An Engine Per Hour multiply the weight used per indicated horse power per hour for head and crank end each by the indicated horse power developed by the steam in that end and add together these two products. EXAMPLE. An engine shows, at the head end, 40.5 i.h.p. and 20.2 Ib. per i.h.p. hr. ; at the crank end, 38.8 i.h.p. and 20.6 Ib. per i.h.p. hr. What is its total steam rate? SOLUTION. The head end uses 40.5 X 20.2 = 818 Ib. per hr. The crank end uses 38.8 X 20.6 = 799 Ib. per hr. The engine, therefore, uses 818 + 799 = 1617 Ib. per hr. 132. More Specific Uses Of Indicators And Indicator Diagrams As Applied To Compound Engines will be treated in Div. 8. QUESTIONS ON DIVISION 3 1. What is a steam-engine indicator? 2. What uses can be made of the indicator diagram? 3. What determines whether a pencil mechanism is satisfactory or not? 4. When should an outside spring indicator be used? G 82 STEAM ENGINE PRINCIPLES AND PRACTICE [Div 3 5. Why must a reducing motion be used in connection with an indicator? 6. What is a brumbo pulley and where is it used? 7. What is a pantograph? 8. What must be the direction of the drum cord leading from a pantograph? 9. What is the principle of the reducing wheel? 10. What precautions must be taken to avoid distortions of the diagram when using reducing wheels? 11. What are the limitations of the inclined-plane reducing mechanism? 12. What two tests will show up a faulty indicator reducing mechanism? 13. How should a cylinder be piped for indicators? 14. Why must indicator cocks have a relief passage? 15. Why is it better to use two indicators on a cylinder than only one? 16. What is meant by the "number" of an indicator spring? 17. Why must indicator springs be tested? 18. How can indicator springs be tested? 19. What results from using too light an indicator spring? 20. What results from using too heavy an indicator spring? 21. What are the steps in assembling an indicator? 22. What kind of paper should be used on indicators? 23. What sort of pencil should be used in an indicator? 24. What does an atmospheric line show? 25. What are the steps in taking an indicator diagram? 26. What "lines" comprise an indicator diagram 27. What influences the appearance of the admission line? 28. What causes variations in the steam line? 29. What is a steam-chest diagram and what does it show? 30. What may the expansion line reveal? 31. What form should the expansion line have if an engine is in good order? 32. What do the release and exhaust lines indicate? 33. What defects in an engine may the compression line reveal? 34. On what does the compression pressure depend? 35. How can the mean effective pressure be found without a planimetcr? 36. How is the mean effective pressure found with a planimeter? 37. What are averaging planimeters? 38. What are the horse power constants of an engine? 39. What are indicated, brake, and friction horse power? 40. What is the basis of determining steam consumption from indicator cards? 41. Why cannot the weight of steam used by an engine be accurately determined from indicator cards? PROBLEMS ON DIVISION 3 1. With the pendulum lever mechanism shown in Fig. 114, what length diagram will result? What must be the radius of a brumbo pulley on this lever to give a diagram 3-in. long? 2. What length of indicator diagram will be produced by the reducing-wheel mechanism shown in Fig. 115? 3. By the method of ordinates find the mean height of the diagrams shown in Fig. 1 16. 4. If the diagrams of Fig. 116 were taken with a 60-lb. spring what are the mean effective pressures shown? Fio. 114 (1) What ' ^ ne diagrams of Fig. 116 are from an engine having a length will the diagram s t r ke of 15 in.; a cylinder 12 in in diam.; and a piston be? (2) What radius for roc * 2 ^ in> in diam - If & runs at 22 r.p.m., what is its brumbo pulley? horse Power? 6. If the clearance at each end of the engine of Prob. 5 is 15 per cent, of the piston displacement, construct the theoretical expansion curves beginning at points C and D. From points X and Y, construct the theoretical com- pression curves. SEC. 132] STEAM-ENGINE INDICATORS 83 7. From the results of Prob. 6 can you make any statement as to the conditions of the engine, valves, etc. 8. Find the steam rates for the crank and head ends of above engine using points R, S, X, and Y. : I k -36" 'stroke - >| Vff//////////////////^ FIG. 115. What will be the length of the indicator diagram? Atmospheric Line--'' FIG. 116. Find the mean height of each diagram. 9. Find the total steam used per hour by above engine. 10. Trace off the diagrams of Fig. 116 and measure the areas with a planimeter, and find the mean effective pressures. Compare the results with those of Probs. 3 and 4. DIVISION 4 SLIDE VALVES AND THEIR SETTING 133. Slide Valves Are Employed In Steam Engines Where Simplicity And Low Price Are More Important than the actual economy of the engine in its use of steam. Slide-valve engines employ but one valve per cylinder and a compara- tively simple valve-operating mechanism, whereas engines of greater refinement generally employ a riumber of valves per cylinder (see Div. 5) and require a more complex mechanism for operating the valves. The scope of this division is to discuss : (1) How slide valves function. (2) Terms appertaining to slide valves and their operating mechanisms. (3) The advan- tages and disadvantages of slide valves of various types. (4) Methods of adjusting slide-valve operating mechanisms. These adjustments are commonly known as il valve setting" 134. "Valve Diagrams," (Bilgram, Zeuner, Reuleaux) And "The Valve Ellipse" are names given to graphical methods for proportioning engine valves and valve mechanisms. These diagrams are useful chiefly in engine designing, which is beyond the scope of this book. A treatment of these graphical methods is not given herein because they are of little value to the practical operating man. For a discussion of valve dia- grams see VALVE GEARS by C. H. Fessenden, or THE DESIGN AND CONSTRUCTION OF HEAT ENGINES by W. E. Ninde. 135. The Function Of The Slide Valve Is, as explained in Sec. 4, to open and close, at the proper instants, passages through which steam may flow into or out of the engine cylinder. This slide valve, therefore, permits the steam to perform its cycle, Sec. 102, within the engine cylinder. Since a slide valve performs its functions in the same manner for both ends of the engine cylinder, the following explanation, of the method whereby a slide valve controls steam flow into and out 84 SEC. 135] SLIDE VALVES AND THEIR SETTING 85 of the head end of a cylinder, is descriptive of its performance for both ends. EXPLANATION. In Fig. 117, the valve, V, is shown moving to the right and is ready to admit high-pressure steam from the steam chest, S } to , Exhaust Port Valve \ Steam Slide Direction of -. Chesty Valve* [Valve Mot ion Piston-' ^Direction of Piston Motion FIG. 117. Point of head-end admission steam about to enter the head end of the cylinder. the head-end cylinder port, H, and thence to the head-end of the cylinder. The steam will then force the piston, P, toward the right. In the position shown in Fig. 118, V has been moved to the right, stopped, and is now moving to the left. It has returned to its former position. Up to this point, high-pressure steam has been admitted to the head-end of the High- Pressure Ste ^Exhaust Port .-Slide .-Direction. Of tValre Motion "High -Pressure Steam About To Expand FIG. 118. Point of head-end cut-off steam supply from the steam chest has just been cut off from the head end of the cylinder. cylinder. As V moves farther to the left, no more steam will be admitted to H because V completely shuts it off from S. Hence, since the head- end of the cylinder is isolated from the high-pressure steam, the piston continues to move toward the right due only to pressure of the expanding steam in the head-end of the cylinder. 86 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 When, as shown in Fig. 119, the piston has almost reached the end of its stroke, traveling toward the right, any further movement of the valve toward the left will allow the expanded steam in the head-end of the cylinder to flow through H to the exhaust port, E. High-pressure steam is about to be admitted to the crank-end of the cylinder where it will force ^-Exhaust Port .-Slid? .-Direction Of : Valve Motion * Direction Of Piston Motion " ^Expanded Steam Fia. 119. Point of head-end release expanded steam in the head end of the cylinder about to be released or exhausted into the exhaust port. the piston toward the left. Fig. 120 shows the position of the piston and valve after the expanding steam in the crank-end of the cylinder has forced the piston to the left. The valve has been moved to the left, stopped, and is now moving to the right again. Further movement of the valve toward the right will shut off the head-end of the cylinder from High- Pressure Si-earn Steam* Chest-, , -Exhaust Port 5lide Direction Of Valve- 'Valve Motion 98B ^'Expanded Steam ^Expanding About To Be Compressed Steam FIG. 120. Point of head-end compression the expanded steam remaining in the head end of the cylinder is about to be compressed by the piston. E, thus confining the remaining steam in the head-end of the cylinder to serve as a ' compression" cushion for the piston as it approaches the end of its travel. NOTE. THE POINTS OF " ADMISSION," "CUT-OFF," "RELEASE," AND "COMPRESSION" are understood to be the positions of the engine mechan- SEC. 136] SLIDE VALVES AND THEIR SETTING 87 ism and the corresponding positions of the indicator pencil on the indicator diagram (Fig. 88) when the valve is in the act of opening or closing the cylinder port. The positions of the slide valve at each of these points are shown in Figs. 117 to 120. Obviously there will be one of each of these points for each end of the cylinder. These are specified as head- end admission, crank-end admission, head-end cut-off, etc. 136. The Terms "Outside -Admission" Or "Direct" And "Inside -Admission" Or "Indirect" As Applied To Slide Valves relate to the manner in which steam is admitted to the cylinder. Thus an " outside-admission " or " direct" valve (Fig. 121) is one which has live, or boiler-pressure steam, S, beyond the two ends of the valve and exhaust steam between Outside Edge Of Valve Exhaust Live Steam / lnside Edge Steam* -Space -^ ,' Of Valve Exhaust' \ ^ Inside \ Port ; Edge Of Valve *Cy finder Ports ' Fia. 121. An outside-admission slide valve. Valve FIG. 122. An inside-admission slide valve. the two ends of the valve. Steam enters the cylinder past the outside edges, 0, of the valve and exhausts from the cylinder past the inside edges, I. An " inside-admission " or "indirect" valve (Fig. 122) is one which has exhaust steam, E, at the two ends of the valve and live steam between the two ends of the valve. Steam enters the cylinder past the inner edges, 7, of the valve and exhausts from the cylinder past the outside edges, 0. NOTE. "EXTERNAL," AND "INTERNAL" ARE OTHER TERMS APPLIED To SLIDE VALVES to denote whether they are of the inside or outside admission type. Outside-admission valves are sometimes called external. Also inside-admission valves are sometimes called internal Piston slide valves are practically always designed for inside admission (indirect) whereas other slide valves are nearly always of the outside-admission (direct) type. 137. The Advantages And Disadvantages Of Plain D -Slide Valves may be briefly stated thus: (1) Advantages, (a) Con- 88 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 struction is very simple. (6) Operating mechanism is simple, (c) Maintenance is low, because of the simplicity. (2) Dis- advantages, (a) Because of unequal pressures on the two sides, D-slide valves are forced strongly against their seats; this is likely to produce excessive friction and wear at the seat. (6) Cylinder ports are opened and closed slowly; this is the cause of wire-drawing or throttling of the steam, especially at cut-off, (c) Admission, cut-off, release and compression are not independently adjustable. That is, adjustment say of head-end cut-off is likely to affect the adjustment of all events of both ends of the cylinder, (d) Engines with D-slide valves must have comparatively large clearance volumes. (e) Because of unequal temperatures on the two sides of the valves, D-slide valves are apt to warp. This makes them unsuited to engines which operate on superheated steam. NOTE. THE DISADVANTAGES OF D-SLIDE VALVES MAY BE PARTIALLY OVERCOME by using slide valves of certain special types which are dis- cussed in the following sections. But no one of these special types eliminates entirely all of the disadvantages. The valve designs dis- cussed in Div. 5 afford the most logical means for overcoming the disadvantages listed above. 138. Advantages And Disadvantages Of Piston Slide Valves : (1) Advantages, (a) Construction is almost as simple as that of the D-slide valve. (6) Operating mechanism is simple, (c) Steam pressure does not produce any unbalanced force on the valve, (d) Temperatures on different parts will not distort the valve; it is therefore suited for superheated steam. (e) Maintenance is low, because of the simplicity. (2) Dis- advantages, (d) Cylinder ports are opened and closed slowly. (6) Valve events are not independently adjustable, (c) Clearance volume of engine must be very large, (d) Wear of the valve or its seat is apt to cause leakage past the valve and is difficult to take up; frequently wear necessitates replacement of the valve or its seat. NOTE. PISTON VALVES ARE USUALLY OF THE INSIDE-ADMISSION TYPE. With inside admission (Fig. 33) the stuffing box on the valve stem seals the opening only against exhaust steam, whereas with outside admission (Fig. 21) the stuffing box holds high-pressure steam. Leaks at the stuffing boxes of inside-admission valves do not, therefore, waste steam because the leaking steam has already been used by the engine. D-slide SEC. 139] SLIDE VALVES AND THEIR SETTING 89 valves cannot be of the inside-admission type because high-pressure steam, if within the D, would raise the valve off its seat and would thus escape, without doing work, into the exhaust passage. 139. Advantages And Disadvantages Of Balanced Slide Valves (Fig. 123) : (1) Advantages, (a) Construction is almost as simple as that of the plain D-slide valve. (6) Operating mechanism is simple, (c) Pressure of the steam on the two sides of the valve is nearly balanced ; therefore, friction and wear are less than with D-slide valves, (d) Valve is not so badly distorted by temperature differences on its surfaces * Cylinder Ports---'' FIG. 123. A balanced slide valve. as is a plain D-slide valve, (e) Maintenance is low and com- pensation for wear is automatic. (2) Disadvantages, (a) Cylinder ports are opened and closed slowly. (6) Valve events are not independently adjustable, (c) Clearance volume must be large, though not larger than with the plain D-slide valve, (d) Steam leakage at the valve is likely to be greater than with plain D-slide valves. EXPLANATION. Since the exhaust steam enters S (Fig. 123) through balance hole, 0, the downward pressure on V, due to the exhaust steam within the area enclosed by ring, R, is practically the same as the upward pressure on V due to the exhaust steam in the exhaust cavity, C. Hence the pressure, due to the exhaust steam, which V exerts against X u practically zero. Now, P is held rigidly in position by bolts, B. Therefore, the live steam in steam space L can exert no downward pressure within the area 90 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 enclosed by R. The only downward pressure which the live steam can exert is that exerted downward on that projected area of V which is outside of R. This area outside of R is, in actual engines, relatively small; in fact it can be made practically zero if the ring, R, is arranged around the extreme edge of V. But in actual engines it is desirable that there be some downward thrust of V against X to hold V snugly against its seat to prevent leakage. In actual engines, the projected area of V which is outside of R is so made by the engine designer that the resultant downward pressure of V and X is sufficient to effectively prevent this leakage but still not induce exces- sive friction between V and X. If some live steam leaks from L past R into S, it passes through to the exhaust. Thus prevents the pressure in S becoming greater than the exhaust pressure. Pressure Plate- Spring^ .-Live-Steam Space Ba/arnced Doub/e -Ported Valve- FIG. 124. Longitudinal section of Sweet valve (Erie Ball Engine Co), same valve as is shown in Fig. 125. 140. Advantages And Disadvantages Of Multiported Slide Valves (Fig. 32, see Sec. 44 for definition) are: (1) Advantages, (a) Construction is almost as simple as that of plain D-slide valve. (6) Operating mechanism is simple, (c) Cylinder ports are opened and closed more quickly than with the valves already discussed, (d) Valve travel need not be so great as with single-ported valves; this means that less power will be required to slide the valve on its seat. (2) Disadvan- SEC. 141] SLIDE VALVES AND THEIR SETTING 91 tages. (a) Unless the valve is balanced, see note following, the steam pressure is likely to cause excessive friction and wear at the seat and also to cause distortion of the valve, (b) Valve' events are not independently adjustable, (c) Clear- ance volume must be large. Engine Cylinder Va/ve 5weet Seat, 'Valve .-Pressure Plate "\ (Balance P/ate) I-Sectional Elevation FIG. 125. Transverse section and side view of Sweet valve. NOTE. BALANCED MULTI- PORTED VALVES COMBINE THE FEATURES OF THE BALANCED AND THE MULTIPORTED slide valves. Figs. 124 and 125 show a modern form of balanced mul- tiported valve. It is to be noted that in this valve the auxiliary ports affect only the admission of high-pressure steam to the cylinder. The exhaust steam passes through only a single valve-port. Some balanced multiported valves also exhaust through an auxiliary port. 141. Advantages And Disadvantages Of Riding-Cut-Off Slide Valves (Fig. 34) : (1) Advantages, (a) Cut-off is effected rapidly; that is, cut-off takes place when the riding blocks are near their mid-travel position and travelling relatively fast. (b) Cut-off can be effected at the same fraction of both the forward and the return stroke ; thus, the work done in the two ends of the cylinder can be equalized, (c) The construction of the cylinder, valves, and their operating mechanism is simpler than with other engines which have advantages (a) and (6) . (2) Disadvantages, (a) Except when made in piston form as in the Buckeye engine the valve is unbalanced and presents two surfaces along which excessive friction may act; hence much power is required to move the valves and wear may be excessive, (b) Engine clearance is large, (c) The valve-operating mechanism consists of twice as many parts as does that for a simple slide valve; hence, the riding-cut-off valve is apt to give more trouble and require more attention. 142. Features Of The Gridiron -Valve Engine (Figs. 126 to 128) arc that: (1) The valves require small movement (from J^ in. to \}^ in.). (2) Having four valves and two eccentrics , all events of both ends of the cylinder are independently adjustable. 92 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 SEC. 142] SLIDE VALVES AND THEIR SETTING 93 (3) Clearance is very small (usually less than with Corliss valves). (4) The valve-operating mechanism permits of high engine speeds. (5) Cut-off occurs quickly, while the valves are moving fast, and it is the only event that need be changed during governing. Its chief disadvantages are that the valve- operating mechanism is relatively complex, the construction of the engine makes it costly, and adjustment of the valve- mechanism is relatively difficult. EXPLANATION. In the Mclntosh Seymour Engine (Figs. 126 to 128) each cylinder has four main valves two steam and two exhaust and 'Link 'Shaft ''Shaft FIG. 127. Section through head of Mclntosh & Seymour engine showing main- valve operating-mechanism. two auxiliary or riding-cut-off valves, all of which are of gridiron construc- tion. The four main valves are driven from a main rock shaft, M , (Fig. 127) which is rocked by the mechanism of Fig. 126 from a fixed eccentric, F, on the crank shaft. The main valves control the points of admission, release, and compression which can be adjusted independently for each end of the cylinder. The auxiliary or riding cut-off valves are driven from another rock shaft, A, (Fig. 128) which is operated from a governor- controlled eccentric, G, as shown in Fig. 126. The motions derived from the eccentrics are so distorted by the several links that the valves move quickly in opening, pause when full open, and remain almost stationary when closed. 94 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 NOTE. THE SETTING OF GRIDIRON VALVES is rather complex and will not be discussed in this book for lack of space. The reader is, there- fore, referred to the manufacturer for instructions for setting gridiron valves. Shaft'' FIG. 128. Section through head of Mclntosh & Seymour engine showing cut-off-valve operating-mechanism. Valve in Mlda 'le of its Travel^ Head-End.. 1 '''Exhaust 'Crank-End Cylinder Port Space Cylinder Port FIG. 129. Outside-admission (D-slide) valve showing lap. Head- End Steam f Lap. Head- A -' End ^ir /I Exhaust, \ | jH5 ^-j" | I 1 Crank- End Steam Lap^ . \\Exhaust I I La f> "Exhaust \ "'Valve ''-Live "Crank- Space '- in Middle Steam End Head- End \"f '* 5 P ace C ^ er CylinderPorf Trave ' Hort . Exhaust Space ' FIG. 130. Inside-admission (piston) valve showing lap. 143. Valve "Lap" is (Figs. 129 and 130) the amount (length) by which a valve overlaps or extends beyond the cylinder port when the valve is mid-way between its extreme SEC. 144] SLIDE VALVES AND THEIR SETTING 95 positions. As a slide valve has four edges with which it cuts off steam flow, there will be valve lap measured to each of these edges. Various terms which are used to designate the lap at the different points are defined graphically in the follow- ing illustrations: exhaust lap and steam lap, Figs. 129 and 130; inside lap and outside lap, Figs. 131 and 132. 0- >j \f - - Outside Lap - >| \<- Q Exhaust I \ --^-Inside Lap A\\<-\ \ -Exhaust \Space\\ l| I I I \\ s f*ice 0->| Y- -Out side Lap ---- Valve in Hiddeof\ | Trt Head -End \ Exhaust Crank -End Cylinder Port' Space Cylinder Port FIG. 131. Illustrating inside and out- side lap of an outside-admission CD- slide) valve. Valve in ^Head-End V/W 'Crank- End Middle of Cylinder steam c y lincler its Travel & rt |JJ Port FIG. 132. Illustrating inside and out side lap of an inside-admission (piston) slide valve. in Middle fs7ve ' NOTE. INSIDE CLEARANCE OF A SLIDE VALVE (Fig. 133) is the amount (length) of opening, N, of the cylinder ports to the exhaust pas- sage, E, when the valve, V, is mid-way between its extreme positions. It is the exact opposite of inside lap and is sometimes called negative lap. Inside clearance permits of very early release and late compression. 144. The Purposes Of Steam And Exhaust Lap Are: (1) Steam lap enables a valve to cut off the high-pressure steam supply to the cylinder before the piston reaches the end of the stroke. In other words it per- mits the use of steam expan- Head-End sively, Sec. 15. (2) Exhaust lap delays release and brings about earlier compression in engines where the valves have sufficient steam lap to effect a desirable cut-off. Increased steam lap necessitates greater valve movement which in turn provides a longer exhaust period. In engines with valves which have plenty of steam lap but no exhaust lap, the working steam in the cylinder would be released too early, thus preventing the proper steam expansion. FIG. 133. A slide valve with negative ex- haust lap or "inside clearance." 96 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 145. To Change The Lap Of A Slide Valve it is necessary to either cut away part of the valve or add to the valve. As it is usually very expensive to add to the valve, a new valve would usually be procured whenever this is necessary. Engine valves should always be furnished by their manufacturers with the proper lap to suit the operating conditions. There- fore, it is seldom necessary to change the lap of a valve except when the engine is to be used under steam pressures different from those for which it was designed. If, however, it does become necessary to change the valve dimensions, the best procedure is to have the engine builder furnish a new valve to suit the new conditions. If the manufacturer cannot be reached and if it is firmly established that the valve lap must be changed, then the changes may be made in accordance with Table 146. 146. Table Showing Effects Of Changing Valve Lap. The lap should always be changed by equal amounts on both the head-end and the crank-end cutting edges. Lap change Effect on point of Admission Cut-off Release Com- pression Steam lap Increased Decreased Later Earlier Earlier Later Unchanged Unchanged Unchanged Unchanged Exhaust lap Increased Decreased Unchanged Unchanged Unchanged Unchanged Later Earlier Earlier Later 147. "Lead" Is Understood To Mean the amount (length, Fig. 134) by which a valve, V, opens a cylinder port for the admission of supply steam when the piston is exactly at the end of its stroke within the engine cylinder. Unlike lap, lead is not determined by the dimensions of the valve. Lead is determined wholly by the adjustment of the valve mechanism. The purpose of so adjusting the valve that it provides lead is to insure that steam will enter the cylinder shortly before the piston reaches the end of a stroke. The objects of thus admit- ting the steam are: (1) To have it aid, by its compression, in bringing the piston to rest before its reversal in direction of SEC. 148] SLIDE VALVES AND THEIR SETTING 97 motion. (2) To insure full steam-supply pressure behind the piston as it begins its next stroke. EXPLANATION. It requires a short time interval for sufficient steam to enter the cylinder to completely fill the clearance volume to supply pressure. If steam were first admitted to the port, just as the piston reached the end of its stroke, the momentum of the flywheel would cause Valve .-Lead Piston At End Of Stroke' FIG. 134. Engine on head-end dead center showing head-end lead. the piston to recede from the cylinder end before enough steam were admitted to fill the clearance volume. If, however, the cylinder port is opened shortly before the piston reaches the end of the stroke, the pressure within the clearance volume will rise to supply pressure before the piston leaves the end. Thus lead, or earlier opening, adds to the pressure behind the piston during the first part of the stroke, and there- fore adds to the work done by the steam on the piston (Div. 1). 148. The Slide Valve Usually Receives Its Motion From An Eccentric (E, Fig. 135) which is attached to the engine shaft, Va/i/e Slide :Seat : ' Valve \:-,.Yalve5tem MyValve Block ' j/" ^Eccentric Rodr* ,-G Crankshaft-/ '-Valve- Block ''$ Guide Eccentric-'' FIG. 135. Eccentric mechanism. S. The valve, V, and valve block, B, are fastened to opposite ends of the valve stem, I. B serves the same purpose as does the crosshead in the standard engine crank-mechanism. The eccentric rod, R, is fastened at one end to B and at the other end to the eccentric, E. Thus the motion of the eccentric is transmitted through R, B, and I to the valve V. 98 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 NOTE. THE ECCENTRICITY OR THROW OF AN ECCENTRIC (Fig. 136) is the distance, R, between the center of the crank shaft and the center of the eccentric itself. It can be considered as the distance the eccentric is "off-center" from the crank shaft. The circle of radius R (Fig. 136) is called the eccentric circle. 149. The Motion Derived From An Eccentric is equivalent to that from a crank whose radius is equal to the throw of the eccentric. That this is true is demonstrated below. Direction Of Rotation^ .Eccentric Circle Eccentric Rod* Crank _a^C-x^ -~CeZterOf^ ^' 'W/jk'^///////// Crank Shaft HC . Position n Center Of \'+'\ Eccentric-.. Center Of '^%-f^ Connecting Rod-, '////fo^ValveSeat Position I crfVery Nt '(2R)* 1 Position M FIG. 136. Illustrating valve travel with eccentric motion. h*1 Crank Circle-^''^^ >( Y-- -.*>-){ Radius**' (2R) Position m FIG. 137. Showing valve operated by a crank on the shaft. EXPLANATION. In Fig. 136, an eccentric attached to a slide valve is shown in three successive positions. The eccentricity is represented by the distance, R. As the eccentric moves from Position / to Position //, the valve moves the distance a. Likewise, as the eccentric moves from position 7 to Position ///, the valve moves the distance 6. In Fig. 137 the same valve is shown attached by a connecting rod to a crank. This crank has a crank-arm length, BC, or distance from the center of the crank pin to the center of the crank shaft which is represented by R. The distance, R, in Fig. 137 is the same as the throw, R, of the eccentric in Fig. 136. As the crank in Fig. 137 moves from Position 7 to Position 77, the valve moves the distance a. As the crank moves from Position 7 to Position 777, the valve moves the distance b. Measurement will show that the distances a and 6 in Fig. 136 are the same as the distances a and 6 in Fig. 137. Hence, an eccentric motion is equivalent to a crank motion and an eccentric can be considered as a developed form of the crank with the crank pin sufficiently enlarged to encircle the crank shaft. 150. Valve "Travel" Can Be Denned (Fig. 136) as the dis- tance between its extreme positions or the distance the valve SEC. 151] SLIDE VALVES AND THEIR SETTING 99 moves in one-half revolution of the eccentric. Thus in Fig. 136, 7, the slide valve is shown in a position with the eccentric, E, in its head-end extreme position. In III, E is in its crank- end extreme position. The distance 2R through which the slide valve has moved during the shifting of the eccentric from I to III is its travel. NOTE. THE TRAVEL OF A VALVE Is EQUAL To TWICE THE "ECCEN- TRICITY" OR "THROW" OF ITS ECCENTRIC. R, Fig. 136, is the eccen- tricity or throw of the eccentric and is the radius of the circle described by the eccentric center. In some engines, intermediate levers or rocker arms are introduced between the eccentric and the slide valve; see Fig. 291. In such construction, the valve travel is not necessarily equal to twice the eccentricity. 151. The Angle Of Advance (Figs. 140 and 141) is the angle through which the eccentric must, when the piston is at one end of its stroke, be rotated on its crank shaft to draw the valve from the Eccentric Direction of Rotation-'* ~ 7 ' FIG. 138. Valve in mid-travel position with crank on head-end dead center. (Advance angle = 0.) middle of its travel to its operating position. In other words, the angle of advance is, when the engine is at one end of its stroke (on dead center) the angle between an imaginary line which is drawn through the eccentric and the crank-shaft centers and another imaginary line which is drawn through the crank-shaft center and at right angles to the cylinder axis. EXPLANATION. In Fig. 138 an engine is shown with its eccentric so set that its advance angle is zero. The piston is at its extreme head-end position. The slide valve, V, is in the middle of its travel and the eccentric center line, AB, is perpendicular to the cylinder axis line OL. It is evident that, with the valve in the position shown, the engine will not operate properly since no steam is being admitted to the cylinder 100 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 when the piston is at the end of its stroke. To insure proper operation, the eccentric must, as will be shown, be shifted forward through a sufficient angle to allow steam to enter the cylinder. In Fig. 139 the crank, C, is shown in its original position but the eccentric has been shifted forward through a sufficient angle to move V forward a distance equal to its steam lap. The center line of the eccentric in the new position is DF. The angle, AMD, through which it was Valve Moved Forward a Distance Equal to its Lap Eccen trie Center L ine - . Lap Angle ''' j^\ p/< ' Eccentr FIG. 139. Valve moved forward a distance equal to its lap with crank on head-end center. The lap angle is shown here. (Lead angle = 0). necessary to shift the eccentric to move the valve, V, a distance equal to its lap is called the lap angle. But this setting of the valve provides no lead, (Sec. 147). Now since, to insure satisfactory operation, all engines must have a definite amount of lead (Sec. 147) the eccentric must again, to provide this lead, be shifted ahead from the position shown in Fig. 139 to that shown in Fig. 140. The additional angle, DMH, through which the eccentric has been shifted from position, DF (Fig. 139) to obtain the lead V\-Va/ve Moved Forward a Eccentric Center Line, Distance Equal to Lap + Lead . . D <'' Angle of Advance--- - ^'.'/V H Center-/'/ ef B' FIG. 140. Valve moved forward a distance equal to the sum of its lap and lead with crank on head-end center. Lap angle, lead angle, and angle of advance are shown. is called the Lead Angle. The Angle Of Advance, AMH, as defined above is therefore the angle between the eccentric positions AB and GH and is equal to the sum of the lap angle and the lead angle as shown in Fig. 140. NOTE. WITH INSIDE-ADMISSION VALVES THE ANGLE OF ADVANCE (Fig. 141) is determined by the same rule (above). It is to be observed, however, that with inside-admission valves the eccentric lags behind the SEC. 152] SLIDE VALVES AND THEIR SETTim : 101 crank by the angle OMH = QQdeg. angle of advance whereas, with outside-admission valves the eccentric leads the crank by the angle OMH (Fig. 140) = 90 deg. + angle of advance. NOTE. THE "DISPLACEMENT" OF A SLIDE VALVE is the distance that the valve has, at any instant, been moved from its central position. Thus, when an engine is on dead center: displacement of the valve = the steam lap + the lead. Valve Moved From Mid-Travel /'Position By A Distance* Lap + Lead Direction Of Rotation- D \ A Angle Of Advance FIG. 141. Showing angle of advance for an inside-admission (piston) slide valve. 152. The "Angularity" Or "Obliquity" Of A Connecting Rod is its ever-changing angular position with respect to the engine- cylinder axis line. At the instant pictured in Fig. 142, it is the angle FBD. When the crosshead is at the end of its stroke (Fig. 143, 1) the angularity is zero. The effects of connecting- rod angularity are: (1) It makes the average velocity of the crosshead during the first half of its stroke, on the forward stroke (toward the shaft) , greater than that during the second half of its stroke. (2) On the return stroke, angularity makes the average velocity of the crosshead during the first half stroke less than that during the second half. Since the motion of a slide valve is not appreciably affected by the angularity of its connecting (eccentric) rod, 1 the unlike speeds of the crosshead during the forward and return strokes will tend to make unequal the valve events for the two ends of the cylinder. Thus, if any one event, such as cut-off, were made to occur at the same fraction of both the forward and return strokes, all other events would occur at unequal fractions of the two strokes. 102 ST3AM ENGINE PRINCIPLES AND PRACTICE [Div. 4 . . 1 NOTE. THE ANGLE, AT ANY INSTANT, BETWEEN THE ECCENTRIC ROD AND THE VALVE-STEM Axis LINE WOULD BE CALLED THE ANGU- LARITY OF THE ECCENTRIC ROD. Now, since the eccentric rod is ordinarily of great length as compared to the throw of the eccentric, the angularity of the eccentric rod never becomes very large. For small angularities the effects explained above are so small that they may practically be neglected. EXPLANATION. Fig. 142 is a dia- gram of a crank-and-connecting-rod mechanism of a constant-speed engine. The crosshead, B, is shown in the middle of the stroke, AO, under which condition the crank pin is at F. It is evident that, as the crosshead completes the first half of its forward stroke, the crank pin moves from Q to F. Also, as the crosshead completes the last half of its stroke, the crank pin moves from F to E. Thus, since the rotating speed of the crank pin of a con- stant-speed engine does not vary, the average piston speed must be greater from A to B than from B to 0. The reason is that half of the stroke, AO, has been completed before the crank pin has turned a quarter of a revolution; that is, before the crank pin has reached G. Likewise, on the return stroke (mechanism is shown dotted on return stroke) the crank pin turns from E to H, or more than a quarter revolution, while Mechanism On Return Stroke-'' Crank,' C/rc/e FIG. 142. Showing position of crank when crosshead is at half stroke. Diagram Of 3 Yoke Velocity In Scotch -Yoke o Mechanism 'Mict-5troke\ . Position \ Crosshead "Piston Rod 'Connecting Rod "rank-Pin Circ/e II. Scotch-Yoke Mechanism. I. Standard Crank Mechanism. FIG. 143. Velocity diagrams for standard crank and scotch-yoke mechanisms. the crosshead completes the first half of its return stroke, or O to B. Furthermore, the crank pin turns from H to Q while the crosshead completes the last half of its return stroke, or B to A. Hence, on the return stroke, the average speed of the piston from O to B is less than its average speed from B to A. Hence, it is evident that even though the circumferential speed of an engine crank pin is constant, the average speed of its crosshead will, because of angularity, be greater during the first half of its stroke than during the last half or vice versa. SEC. 153] SLIDE VALVES AND THEIR SETTING 103 NOTE. THE VARIATIONS OF THE CROSSHEAD VELOCITY DURING A STROKE may be shown by plotting the velocity on a graph (Fig. 143, /). It is evident from this graph that the crosshead velocity during the head- end part of the stroke is greater than that at corresponding points in the crank-end part of the stroke. The Scotch-yoke mechanism (Fig. 143, //) gives a velocity diagram which does not show such characteristics. This is because there is no angularity with this mechanism. 153. "Dead Center" denotes the position of an engine mechanism (Figs. 144 and 145) when the piston is exactly ..-Direction Of Rotation X/ ^- 77-^ -Crank Shaft //^rs.-''w* Space \ 'Cylinder Port Cylinder Por f - ' ^'Exhaust Space FIG. 154. Illustrating method of setting an inside-admission valve where the cylinder ports are not accessible. SEC. 157] SLIDE VALVES AND THEIR SETTING 109 The method is explained below. See also the example under Sec. 167 wherein the setting of a piston slide valve by an indi- rect method is described. EXPLANATION. After the valve-chest cover is removed some line, such as A, Fig. 154, is selected as a reference point, from which measurements are to be taken. The line, A , must be so chosen that it will not be covered by the valve at any time during its motion. The distances, AB and AE, are then measured ac- curately with a steel scale while the valve is removed from the chest. Also the lengths of the valve from C to F and from C to D are measured. The valve may What Lead?^ p- 8 "- >j "Valve Seat "Piston Valve FIG. 155.- Finding lead by indirect measure- ment. then be replaced into the seat. The edges F and B of the valve and seat may then be placed to coincide by moving the valve until the distance from A to C or AC = AB CF. Likewise the edges D and E will coincide when AC = AE CD. The exact opening of the cylinder port at any time can also be determined by similar measurement to the face, C, of the valve. EXAMPLE. If (Fig. 155) AB = 8 in., CF = 2i in., and when the engine is on dead center AC measures 5^ in., what is the lead? SOLU- TION. Obviously, the lead = 8 - (5^ + 2>) = '8 - 7% = H in. 'Piston Valve Reference Edge ,-' on Va/ve Seat Cut A Reference Mark on Board I- Accessible Valve by Measuring from Reference 'Cut Along Dotted Lines H- Inaccessible Valve Seat FIG. 156. Showing methods of making templets of valves and seats. (Whenever the templet material can be placed against the valve or seat, use the method at the left. Templets of inaccessible seats are made as shown at the right.) 157. The Templet Method Of Ascertaining Valve Opera- tion is a modification of the indirect-measurement method. Templets (Fig. 156), or full-size working models, of the valve and its seat are cut from thin material such as sheet metal, cardboard, or thin wood. Templets of inaccessible valve seats must be made from measurements. Templets of valves and 110 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 accessible seats may be made by placing the templet material with its edge against the valve or seat (Fig. 156, 1), and marking the working edges directly from the valve or seat. After the templets are made, the valve may be replaced in its chest and set into its midtravel position (Fig. 157) either by direct Templet Of Piston tffD ; v ; ders -Board Kept Near Engine For Use In Setting Valves ' -Templet Of Valve Seat Tacked To Board Center Punch. . ' Marks p -'" I- Position Of Templets H-Position Of Valve In Seat FIG. 157. Method of establishing marks for setting a slide valve with templets. observation or by indirect measurement. In this position the laps at the two ends of the valve should be equal. The valve-seat templet is then tacked to a board and the valve templet placed against it (Fig. 157, 7) in the same relative position as the valve in the seat. Punch marks, P, are then - Dividers I" Position Of Templets Position Of Valve In Seat Fia. 158. Method of determining lead when setting a slide valve by means of templets. made on the valve chest and the valve rod a convenient distance apart (4 in. in Fig. 157, II). Similar marks, M, are made, as shown, on the valve templet and on the board. Once these templets have been made and marked, future SEC. 158] SLIDE VALVES AND THEIR SETTING 111 valve adjustments can be effected without removing the valve chest cover. Likewise (Fig. 158), the position of the valve upon its seat can be determined at any instant as, for instance, during adjustment simply by making equal the distances, X, between the two pairs of marks. See also the example under Sec. 167 which describes how wooden battens may be used instead of templets. 158. Adjustment Of A Slide -Valve Mechanism Can Be Effected In Only Two Ways : (1) By changing the position of the eccentric on the crank shaft, thus changing the angular advance of the eccentric. (2) By changing the position of the valve upon its seat for any eccentric position. This is done by altering the total length from the eccentric center to the valve, Vafve-Stem Adjusting Nuts, Lock /: Lock- Guide.. Stem. -Locknut Piston ' '7/1 Valve Adjusting '"Eccentric Oil Va/ve-Stem \ Rod Reservoir Slider Or Block--' FIG. 159. Valve-stem adjustment at the valve-stem slider. (Chuse engine & Mfg. Co.) FIG. 160. -Method of adjusting stem length at valve. as measured along the valve mechanism, that is, by changing the effective length of the valve stem. Evidently, this length can be changed by altering either the distance from the eccen- tric center to the valve block, or the distance from the block to the valve. Each of these distances may, with certain engines be altered at either of the two ends of the rods which maintain the distances. On other engines, adjustment is provided only at one end of the valve stem or eccentric rod or at one end of each. Figs. 159 and 160 show means provided for this adjustment. NOTE. IN MOST SHAFT-GOVERNED ENGINES THE ANGLE OF ADVANCE CANNOT BE ADJUSTED, that is the eccentric position is fixed by the governor. In these engines the valve is obviously only adjustable by altering the effective length of the eccentric rod and valve stem. 112 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 159. Table Showing Effects On the Steam-Engine Cycle Of Slide-valve Adjustments For The Outside -admission Slide Valve. Adjustment End of cylin- der Effect on valve events Admis- sion Cut-off Release Com- pression Valve-stem effective length Lengthened Head Later Earlier Earlier Later Crank Earlier Later Later Earlier Shortened Head Earlier Later Later Earlier Crank Later Earlier Earlier Later Angular advance of eccentric Increased Head Earlier Earlier Earlier Earlier Crank Earlier Earlier Earlier Earlier Decreased Head Later Later Later Later Crank Later Later Later Later NOTE. To USE THE ABOVE TABLE FOR INSIDE-ADMISSION VALVES bear in mind that: (1) Effects of changing effective valve-stem length are opposite to those given in the table. (2) Effects of changing the angular position (advance) of the eccentric are the same as for outside admission slide valves. It must not be forgotten, however, that for inside-admission valves (Sec. 151) the angle of advance is measured in the direction of rotation from a line 90 deg. behind the crank position to the line of the eccentric position. 160. In Setting The Valves Of A New Engine, before putting the engine into operation, do not at first change or disturb any adjustments of the valve mechanism. Remove the steam- chest cover and, turning the engine by hand, watch the motion of the valve upon its seat. With piston- valve engines the indirect-measurement method (Sec. 156) must be employed. Valve and seat dimensions may be obtained, without removing the valve from its seat, by consulting the engine-maker's blueprints. If, upon examination of the valve action with the cover removed, it is thought probable that the engine will run with the existing adjustment, replace the cover and start the engine. If desirable, the engine may be started without first examining the valve operation, as no harm can result even if the valves are not properly set. Then equip the engine with SEC. 161] SLIDE VALVES AND THEIR SETTING 113 indicators and take cards first under no load and then with gradually increasing loads. Engine builders usually carefully adjust the valves for their correct operation before shipping an engine. If, however (Sec. 112) the indicator diagrams reveal faulty valve motion and not until then it may be con- cluded that adjustment is necessary. The adjustment should be made in accordance with builder's instructions. If these instructions were not sent with the engine, they should be procured by writing to the factory. If valves must be set without specific instructions from the engine makers, the methods of succeeding sections may be employed. 161. In Setting The Valves Of An Old Engine, it is advisable to procure the manufacturer's instructions, if possible, and then to make the adjustments as recommended by the manu- facturer. If it is impossible to obtain factory instructions, the valve may be set as hereinafter explained. 162. All Slide Valves May Be Set For One Of Three Con- ditions, any of which may give satisfactory operation. The ideal setting of engine valves is not attainable with a single valve because of the angularity of the connecting rod (Sec. 152). The setting of a slide valve must, therefore, be a com- promise. The valve may be set for: (1) Equal leads at both ends of the stroke. This setting will make all events, especially cut-off, unequal for the two ends of the cylinder. (2) Equal cut-offs, in per cent of stroke, during the forward and return strokes. This setting will make all of the other events unde- sirably unequal for the two ends of the cylinder. (3) Inter- mediate between equal leads and equal cut-offs. By setting an engine for more lead at the crank end of the stroke than at the head end, the cut-offs are made more nearly equal for the forward and return strokes. Setting slide valves for each of these conditions will be discussed separately in following sections. v 163. The Firs'f Step In Setting Any Slide Valve Is, therefore, to decide whether it is to be set for: (1) Equal leads. (2) Equal cut-offs. (3) Intermediate between equal leads and equal cut-offs. It really makes little difference which condition is selected. An engine will probably operate most quietly when set for equal leads. When set for equal cut-offs, it will probably operate most economically. A setting intermediate 114 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 between (1) and (2) provides reasonably quiet 'operation and good economy. But, in any case, the difference in the operating results obtained from any of the three methods of setting is usually very small. Therefore, since setting for equal leads is the easiest of the three, this condition is usually sought by operating engineers and is frequently recommended by engine builders, especially for small engines. For large engines condition (3) above is usually recommended. For vertical engines, the lead on the top or head end, is usually considerably less than on the bottom end because the cut-offs are so more nearly equalized and because the weight of the reciprocating parts acts against the steam pressure on the up stroke. Checking valve settings with an indicator is always the safest method of determining the proper leads for any given engine. 164. In Setting A Slide Valve For Equal Leads One Must First Decide Whether It Is To Be Set For "Design-Deter- mined Equal Leads" Or For "Selected Equal Leads." By design-determined equal leads is meant equal leads, be their amount what it may, the dimension of which was pre-deter- mined by the designer of the engine and for which the angular advance of the eccentric or its equivalent has been per- manently fixed. Hence, setting a slide valve for design- determined equal leads involves only changing the valve- stem or eccentric-rod effective length until the leads at both head and crank end are equal. To alter the amount of the equal leads which was thus predetermined and fixed by the designer of the engine, would necessitate changing the angular advance of the eccentric on the engine shaft. This would necessitate the cutting of a new shaft keyway or otherwise making mechanical changes in the engine which would involve more work than mere adjustments. By selected equal leads is meant equal leads the dimension of which is selected, by following a rule (as, for example, that of Sec. 165) by the person who is setting the valve. Setting for selected equal leads probably involves not only changing the valve-stem or eccentric-rod effective length but also changing the angular advance of the eccentric. NOTE. IN SETTING THE VALVE OF A SHAFT-GOVERNED ENGINE IT Is USUALLY DESIRABLE To SET FOR DESIGN-DETERMINED EQUAL LEADS rather than for selected equal leads. As explained in Sec. 158, the eccen- SEC. 165] SLIDE VALVES AND THEIR SETTING 115 trie of a shaft-governed engine is not adjustable on the engine shaft. Hence, it is impossible, with an engine of this type to set, the valve for equal leads other than the "design-determined" lead for which the valve gear and governor was originally designed, without changing the position of the flywheel on the shaft. This will ordinarily necessitate the cutting of a new keyway in the shaft. NOTE. IT Is SELDOM ADVISABLE To SHIFT THE ECCENTRIC (FLY- WHEEL), OF A SHAFT-GOVERNED ENGINE, ON THE ENGINE SHAFT. This may appear to be necessary when it really is not, due to the governor being out of adjustment. See Div. 7 concerning shaft-governor adjust- ment. The eccentrics, and flywheels of shaft-governed engines are carefully located, in relation to the shaft, by their manufacturers before the engine leaves the factory. It is therefore seldom indeed that the shifting of the flywheel which will necessitate the cutting of a new keyway in the shaft is justified. If, after the governor has been correctly adjusted, and the leads are still of incorrect amount, then it may be necessary to shift the eccentric fix the flywheel to the shaft in a new position. 165. The Proper Lead For Any Slide Valve should, finally, be determined with an indicator (Sec. 175). In general, the lead may be set at about J^2 m - for each foot of stroke but it is seldom in any case that the lead should be much less than 3^2 m - That is, an engine which has a 12-in. stroke should have a ^2~ m - lead. One which has a 24-in. stroke should have a JJLG m - l ea d and so on. If the selected lead is not the correct one for the engine, the indicator will reveal the remedy. 166. The Procedure To Be Followed In Setting Plain Slide Valves For Equal Leads is specified in Table 167. This table applies only to plain "D" or to plain piston slide valves; it does not apply, directly to riding-cut-off valves, for which see Sec. 172. See preceding sections for definitions of the terms " design-determined equal leads" and " selected equal leads." Always, when setting valves, turn the flywheel or the eccentric in the same direction, preferably in the direction in which they will move when the engine in running; see Sec. 153. Note that by changing the valve-stem or eccentric rod effective length, the leads at both head and crank ends may be made equal. When the valve opens an equal amount at each end, the eccentric rod and valve rod are then of correct length for equal leads. By shifting the eccen- tric on its shaft changing its angular advance the amounts of the equal leads may be altered. 116 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 167. Table Showing Procedure To Be Followed In Setting Plain Slide Valves For Equal Leads. Read carefully the preceding section. Operation Steps to be taken Engine has a throttling governor Engine has a shaft governor Identifying letter What to do Eccentric is keyed to shaft Eccen- tric is not keyed to shaft Flywheel is keyed to shaft For design- deter- mined equal leads For selected equal leads For selected equal leads For design- deter- mined equal leads For selected equal leads I 1 II | 1 III 1 IV ? 1 V 1 VI 0) > 1 VII 1 '(3 > Indirect valve j IX E 1 8 5 Indirect valve X 1 s Indired 1 5 | ! 1 Q Indired A Select equal lead dimension for which valve will be set, Sec. 165. ' 1 i 1 1 1 i 1 B Establish dead centers and mark on flywheel, Sec. 153 1 2 2 2 2 i 1 2 2 C Remove valve-chest cover or covers 2 2 3 3 3 3 2 2 3 4 3 4 D Block shaft governor to nor- mal operating position, Sec. E Remove valve, measure it and, if desirable, make templet, Sec. 157. 3 4 4 3 5 F Measure the valve seat and, if desirable, make templet, Sec. 157. 4 5 5 4 6 G Replace valve on seat and connect it in proper running order to its valve stem. 5 6 6 5 7 H Turn engine crank to its head- end dead-center position, Sec. 153. 3 6 4 7 3 6 5 8 I Loosen eccentric and rotate it on its shaft to extreme head- end position, Sec. 154. 4 7 J Measure accurately the lead or port opening at this end. Call it Li. 4 7 5 8 5 8 4 7 6 9 K Rotate the eccentric to the extreme crank-end position, Sec. 154. 6 9 SEC. 167] SLIDE VALVES AND THEIR SETTING 117 Steps to be taken Engine has a throttling governor Engine has a shaft governor Identifying letter What to do Eccentric is keyed to shaft Eccen- tric is not keyed to shaft Flywheel is keyed to shaft For design- deter- mined equal leads For selected equal leads For selected equal leads For design- deter- mined equal leads For selected equal leads Direct valve >-> Indirect valve K III I 1 5 Indirect valve ^ Direct valve < Indirect valve ^ Direct valve ^ Indirect valve S H IX E ! 1 Indirect valve ^ L Turn engine crank to its crank-end dead-center posi- tion, Sec. 153. 5 S 6 9 5 8 7 10 M Measure the lead or port opening at this crank end. Call it Li. 6 9 7 10 7 10 6 9 8 11 N Calculate the difference be- tween Li and Lz. 7 10 8 11 8 11 7 10 9 12 13 O So change the valve-stem, effective length that the lead Z/3 will be equal at both head and crank ends, that is, so that Z/3 = (Li + L 2 )/2: The valve-stem effective length must be changed by J^ the difference between L\ and L 2 , which was found in N. See Sec. 166, the note below and the following examples. This should complete the valve adjustment for design- determined equal leads. 8 11 9 12 9 12 8 11 10 P Turn engine crank to its crank-end dead-center posi- tion. 10 13 10 13 Q Rotate the eccentric on the shaft to change the lead to the selected dimension, as selected in A. 11 14 11 14 14 R Fasten the eccentric securely to the engine shaft in this new position, Sec. 164. - 12 15 12 15 8 Rotate flywheel on shaft to change the lead to the re- quired dimension. - 11 118 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 Operation Steps to be taken Engine has a throttling governor Engine has a shaft governor Identifying letter What to do Eccentric is keyed to shaft Eccen- tric is not keyed to shaft Flywheel is keyed to shaft For design- deter- mined equal leads For selected equal leads For selected equal leads For design- deter- mined equal leads For selected equal leads I E 1 Q Indirect valve^S III \ B 5 Indirect valve ^ V 1 Q Indirect valve ^ Direct valve ^ Indirect valve IX ) -5- 2 = 3,Vg -* 2 = (12) To make the openings l^fe in. at each end, the valve-stem effective length must be changed by an amount equal to half the difference between Li and Li = (1%-W) +2 =H +2 = KG in. If the head-end port is opened the widest, the valve-stem should be shortened if there is no rocker arm in the valve mechanism. If the crank-end port is opened furtherest, then the valve- stem length should be lengthened. After the valve-stem effective length has thus been changed by K 6 in., then its length insures that the crank-end and head- end steam ports will always have equal leads; this regardless of the amount of the selected lead, the setting for which is made, in the second step following, by crank- ing the angle of advance of the eccentric. FlG 166 Setting piston valve for selected (13) Turn the engine to its crank- lead. P = M - (V + L.). end dead-center position. (14) Change the angle of advance so that the equal lead at both crank and head ends will be the selected lead, L s = ^2 in. Proceed thus: Set the combination square, as shown in Fig. 166, so that the extending por- tion of the blade, P = 1% in. That is, from Fig. 166, P = M - (V + L s ) = 4> - (2% + YZZ) = 4K - 2^2 = 1 3 ^2 in. Rotate the eccentric on its shaft to the crank-end extreme position, as shown in Fig. 163. Place the extending blade of the combination square, which has been set at I 3 3^2 in. as just described, into the valve cylinder as shown in Fig. 167. Rotate the eccentric on its shaft in the direction the engine is to ' Selected Lead /Cylinder Casting ' --Piston Valve Position Of Crank^ Lock Nut " 'Comb/nation Square Eccentric Strap ' ' FIG. 167. Head-end port opened to the extent of the lead. run until the left end of the valve is just about to leave the square- blade end. The eccentric should now be in the correct position for perma- nent setting for the selected lead of ^2 in. (15) Fasten the eccentric securely to the shaft in this new position; the valve should now be set properly. (16) To check the setting for accuracy, turn the engine to the head-end dead-center position and also measure, as described in 14, the lead at this 122 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 end. If the valve chest is not the same at both ends, it will be necessary to reset the combination square accordingly, in order to make the measurement. (17) If the lead at both ends is now the selected lead of ^2 in., you are through. If it is not ^2 in. at both ends, you have made some error and if so repeat the necessary preceding steps until the lead at both ends is K2 in. or is the selected lead whatever it may be. Va/ve Steam '. Ports-'' - -L = Lead, Or Lead Equivalent, With Valve In Extreme Head-End Position FIG. 168. Determining L\ eccentric of a plain slide-valve engine in extreme head-end position. (Exhaust port not shown.) (18) Replace the valve chest covers. (19) Check your setting with an indicator, if possible. (20) If desirable, spot reference marks, as else- where explained, to facilitate future rapid setting of the valve. EXAMPLE. SETTING THE VALVE OF A THROTTLING-GOVERNED, PLAIN- D-SLIDE-VALVE (DIRECT-VALVE) ENGINE FOR SELECTED EQUAL LEADS. ECCENTRIC Is NOT KEYED To SHAFT. Follow column V of Table 167. Side Graduations -^ A 24-inch stroke engine is to be set for equal selected leads. Proceed as follows: (1) Select the amount for the equal lead: From Sec. 165, the proper lead for an engine is about ^2 in. per foot of stroke; hence, for this engine the proper lead, which will be designated by "L s ," is Me in. (2) Establish and mark the dead-center points on the flywheel; see Sec. 153. (3) Remove valve-chest cover. (4) Loosen the eccentric and rotate it on the engine shaft to its extreme head-end position, as shown in Fig. 168. grl i I i I Mil hhl '-End Graduations FIG. 169. Steel scale having end grad- uations. (Brown & Sharpe Co.) - End-Graduated Steel Scale -D-SI/de Valve ' Valve &uide Block Eccentric Strap -Lead Or Lead Equivalent With Valve In Extreme Crank-End Position Eccentric/ Rod'' Eccentric FIG. 170. Determining Lt eccentric of a plain slide-valve engine in extreme crank- end position. (Exhaust port not shown.) (5) Measure the port opening, as shown in Fig. 168 at this head end; call it LI', say it is % in. A steel scale which has end divisions, as in Fig. 169, is convenient for making such measurements. (6) Rotate the eccentric on the engine shaft to its extreme crank-end position as shown in Fig. 170. (7) Measure the port opening, L 2 , at this crank end. If this SEC. 167] SLIDE VALVES AND THEIR SETTING 123 L 2 happens to be the same amount as Li, the port openings at both ends are equal which shows that the valve-stem effective length is correct. But if they are not equal, the valve-stem effective length will have to be changed. Assume that, in this example, the crank-end port opening; L 2 , is found to measure *Me in. (8) The difference between Li and L 2 = KG - H = % - % = Me in. (9) Then, to be equal at each end, the openings must be changed to L, = (Li + L,) /2 = (iMe + ^e) -2 = ^Me - 2 = % in. To make the openings 2 >^2 in. at each end, the valve-stem effective length must be changed by an amount equal to half the difference between LI and L 2 = Me -*- 2 = H2 in. Hence, the valve-stem effective length must be changed by ^2 in. After the valve-stem effective length has thus been changed by }$2 in., then its length to insures that the crank-end and head-end steam ports will always have equal leads; this regardless of the amount of the selected lead, the setting for which is made, in step 11, by changing the angle of advance of the eccentric. FIG. 171. Setting a plain slide valve for a selected lead, L,. dead-center position.) (Engine is in crank-end (10) Turn the engine to its crank-end dead-center position. (11) Change the angle of advance so that the equal leads at both crank and head ends will be the selected lead, L. = Me m - Proceed thus: Place the eccentric on the shaft about as shown in Fig. 170 and rotate it on the shaft, in the direction that the engine is to run until the crank-end port is, see Fig. 171, open just the KG in., as shown by measurement with an end- divided steel scale. (12) Fasten the eccentric securely to the shaft in this new position; the valve should now be set properly. (13) To check your setting for accuracy, turn the engine to its head-end dead-center position and also measure similarly the lead now shown there. (14) If the lead at both ends is now the selected lead of Me in., you are through. If it is not Me in. at both ends, you have made some error and must repeat the necessary preceding steps until the lead at both ends is lie in. or is the selected lead whatever it may be. (15) Replace the valve-chest cover. (16) Check the valve-setting with an indicator, if possible. (17) If desirable, spot reference marks, as elsewhere explained, to facilitate future rapid setting of the valve. EXAMPLE. SETTING THE VALVE OF A SHAFT-GOVERNED, PLAIN, INDIRECT- VALVE (PISTON-VALVE) ENGINE FOR DESIGN-DETERMINED 124 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 EQUAL LEADS. (This has been modified from an article in Southern Engineer for November, 1919, to follow the procedure which is specified in Column VIII of Table 167). When proper reference marks have, as hereinafter described, been made on the valve stem and seat, the valve may be set very readily and quickly. But when these marks do not appear and no templets (Sec. 157) are available, the following method may be pursued. The exhaust port is not shown in any of the illustra- tions. The numbers in parentheses refer to the step numbers in Table 167: (1) Scribe the dead-center marks on the flywheel as explained in Sec. 153. (2) Remove the valve-chest covers. (3) Take out the valve and measure the length (F, Fig. 161) of its piston portion; say it is 2^ in. (4) Adjust a combination square to the length shown in Fig. 162 with the inner end of its blade against the inner edge of the steam port; measure this distance, M; say it is 4^ in. If the chest is not alike at both ends, measure, similarly, the corresponding distance for the other end of the chest. (5) Re- place the valve in its chest and connect it in running order to the valve stem. (6) Turn the engine in its running direction to exact head-end dead-center position. (7) Measure, with the combination square, as shown in Fig. 161, the distance, N, to the valve end; say it is l 3 ^ 2 in. Now obviously the lead existing on this end is, see Fig. 172, LI = M - (N + F) = 4>^ (1 3 H2 + 2M) = 4K - 4Ke = H2 in. (8) Turn the engine to the crank-end dead-center position. (9) Similarly, measure the lead, L 2 , at this crank end. If L 2 happens to be the same as LI, the engine is set for equal design-determined leads. But assume that, in this example, the lead, L 2 , at the crank end is found to be ^2 in. (10) The difference between LI and L 2 is %2 ;Hj2 = KG in. (11) Then the proper design- determined equal lead, L 3 = (Li +L 2 )/2 = (} 2 + ^2) -* 2 = % -* 2 = KG in. To provide this KG in. equal lead, the valve-stem effective length must be increased by an amount equal to half the difference between LI and L 2 = (%2 ^2) * 2 = %2 -5- 2 = M2 in. Hence, after a change of ^ 2 in. in the valve-stem effective length, the engine valve should be properly set for design-determined equal leads. Measure, as explained above, the new lead L 3 to be sure that it is KG in. at this crank end. (12) Now, for a check, turn the engine again to the head-end dead- center position and by measurement, as before, check the new lead L 3 for the head end. (13) If the leads at both ends are equal, you are through. FIG. 172. Measuring lead. M = N + V + Li or, Li = M - (N + V). SEC. 167] SLIDE VALVES AND THEIR SETTING 125 If they are not equal, you have made some error and must repeat the necessary preceding operations until the leads are equal. (14) Replace the valve-chest covers. (15) Check your setting with an indicator if possible. (16) If desirable, spot reference marks, as explained below, to facilitate future rapid setting of the valve. EXAMPLE. THE SPOTTING OF TRAM REFERENCE MARKS, To ENABLE ONE To QUICKLY MAKE FUTURE VALVE SETTINGS WITHOUT REMOVING THE CHEST COVERS, is effected as follows:. It is assumed that the valve pisfon Valve-Chest ,TmmmeI Gage Valve Cover- . . Eccentric - Direction ^Combination Of Rotation --- Square Rotation Of Crank Pin OnCnank-End. Dead Center FIG. 173. "Trying" the lead at the crank end of the piston-valve cylinder (engine on crank-end dead center). has been correctly set as described above. Make a trammel gage (T 7 , Fig. 173) by pointing the two ends of a piece of steel wire and bending it into trammel form. The size of the trammel the distance between the trammel points may be any that is feasible and convenient. With a center punch, spot a mark at A on the guide block. Place one point of the trammel in this mark, A, and then spot another very light mark, B, where the other point of the trammel gage touches the valve stem. These reference marks used in conjunction with the trammel gage enable one to disconnect the valve stem from the stem guide block and to then Steam Stuffing Position Of Crank Supply- / Box Casting Pin On Head-End ' Dead Center- Eccentric Valve Rod-' Stem Direction Of Rotation-...-? FIG. 174. Locating prick-punch marks, for future valve settings, on valve stem and stuffing box. (Engine on head-end dead center.) replace the valve (in case it was necessary to entirely remove the valve) and to reconnect the valve stem in exactly its original position. Having made the trammel gage and used it as in Fig. 173, now again use it (Fig. 174) for spotting the slide-valve-lead reference marks. Place the engine crank on exact head-end dead center. Then spot a center punch mark, D, (Fig. 174) on the stuffing box not on the gland. Place one end of the trammel gage in this mark and spot another mark, E, on the valve stem where the other point of the trammel touches the stem. 126 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 When testing to verify the setting of the valve: First, place the crank on the head-end dead center. Then, with one point of the trammel gage in the mark, D, the other gage point should lie exactly in the punch mark, E. If the other point does not lie in E, the valve setting is out of adjust- ment. With the gage points in D and E, assuming that the original correct adjustment has not been altered, the valve will have opened the Sheet-Stee/ Head-*. Smooth, Clear Pine Rocf k Long Enough To Reach Bottom Of Steam Chest +6" To Spare FIG. 175. Measuring rod for measuring steam-port opening. head-end port to the amount of the desired lead because the valve was in this position when the gage and the marks D and E were first made. The trammel gage should be carefully preserved so that in future emergencies, such as the slipping of an eccentric, the valve can be promptly readjusted to its correct relation. EXAMPLE. How To MAKE THE VALVE-SETTING TEMPLETS FOR A PLAIN INDIRECT- VALVE (PISTON- VALVE) ENGINE will be explained: While these directions relate specifically to a vertical engine they may, with obvious modifications, be applied to a horizontal engine. Compare this method with the similar method suggested in Sec. 157 and that described in the following example for a riding-cut-off piston valve; all of these three methods vary only in detail procedure, the final result accomplished in each being essen- tially the same. Each method has its applications. Make A Measuring Rod, as shown in Fig. 175, for locating the steam ports in the valve chest. These steam-port locations will, as is here- No. 1 6 Gage Sheet 5 fee/-. Index I N fi**--y" 'Wooden (Preferably Stick FIG. 176. Head of measuring rod. inafter described, be transferred to the steam-port templet. The sheet- steel head, S, (Fig. 176) may be of approximately the proportions there specified. But, in any case, the in. less than the width of the engine dimension L should be at least steam ports. Prepare The Sticks From Which The Templets Will Be Made. Two pieces of smoothed clear pine, each about ^ in. thick and about 1 in. wide will be required. Both should, at the start, be about the same length as the measuring rod. All faces and ends should be square and true. SEC. 167] SLIDE VALVES AND THEIR SETTING 127 Prepare To Measure The Valve Chest. Remove the valve-chest cover and the valve-stem stuffing-box gland. Disconnect and remove the valve from the valve chest. Make The Steam-Port Templet. Insert the measuring rod into the valve chest so that one of its index edges (Q, Fig. 176) is against the furthest edge of the farthest steam port (Fig. 177, 7). With a knife blade, cut a t-Lower Edge, Lower Port I- Upper Edge, Lower Port Upper ECW,,J, Upper Port FIG. 177. Marking steam-port locations and widths of a vertical-engine valve chest on a measuring rod. corresponding line, A, on the face of the rod exactly at the level of the valve-chest face. Similarly, locate on the measuring rod (as shown in Fig. 177, 77, 777, and IV) lines B, C and D, which respectively correspond to the other edges of the steam ports. Now, as shown in Fig. 178, lay one of the sticks, which was prepared as above, on the measuring rod. With a try square and knife blade transfer the lines from the measuring rod to the Y 2 in. face of the stick. In the illustrations, the width of the Steam-Port .-Port Locations^ Templet, .' /Center Line .', W / ' C 1 .'V R' n b- VV^ * V-^ "_ ;P/ston Valve t-- Valve Face DC 'Measuring Rod ''Pencil Hatch Lines Drawn On Templet :::: r :, ^--Va/ve \ F I 'Valve Temp/ef'- Center Line ~ /- - FIG. 178. Laying off the steam- port FIG. 179. Laying off the valve templet, templet. sticks is shown exaggerated for clearness. Draw pencil "hatch" lines on those portions of the stick's face which do not represent the ports. Draw, midway between C' and B' a knife-cut center line, E, across the stick's face. This completes the steam-port templet. Make The Valve Templet. Lay the piston valve (Fig. 179) on the 1-in. face of the other stick which was previously made. The left end of the 128 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 valve should lie about H in. from the left end of the stick. Transfer to the K-in. face of the stick lines representing the locations of the edges of the valve faces, as shown in Fig. 179. Draw a center line, F, midway between the two sets of lines which represent the valve edges. Hatch, with pencil lines, the portions of the stick's face which represent metal. The Valve Templet. Must Be Of A Certain Length so that, when in use (Fig. 180) for valve setting, it will reproduce accurately the events which are occurring in the steam chest. When in use, the lower end of the valve templet rests on the upper end of the valve, while the valve is shifted Va/ve Temp/el -,_ Lines -. Representing, Va/ve Edges --'- Center Lines / On Temp/ets-',- Steam- Port Templet ^-Strap-Iron I Support (j ''Crank-End Steam Port Valve mPort Temple^ ^ Templet FIG. 180. Templets arranged on valve chest for valve setting. , Line C Representing TV Top Face Of Valve Chest fHl JK-U -777/5 End To 1.-T Be Cut Off FIG. 181. Measuring valve tem- plet to cut it off to proper length. vertically to different positions. The valve templet slides alongside the steam-port templet. To determine the proper length of the valve tem- plet proceed thus : Lay the steam-port templet against the valve templet (Fig. 181), with their two center lines F and E exactly in line. Now, as is evident from Figs. 177 IV and 178, the distance EH on the steam-valve templet equals the actual distance from the horizontal center line between the steam ports to the top face of the steam chest. Also, the distance FI on the valve templet equals (See Figs. 179 and 181) the actual distance between the horizontal center line of the valve and either end face of the valve. Hence, from Fig. 181, it follows that // is the distance which the top face of the piston valve must lie below the top face of the valve chest when the valve is vertically central in the valve chest in relation to the SEC. 168] SLIDE VALVES AND THEIR SETTING 129 ports. Now lay off on the valve templet below / a distance JK, which is equal to IJ. Cut the templet off square at K and it will be complete and of correct length. Arrange The Templets On The Engine Valve Chest. Bend a piece of strap iron to form a support, G, (Fig. 180) for the steam-port templet. Drill the short leg of the support to accommodate one of the valve-chest studs and drill the long leg to take three round-head wood screws. Replace and reconnect the valve in the chest. Secure the steam-port templet to the valve chest as shown in Fig. 180, with the "H" end of the steam-port templet exactly on a horizontal line with the top face of the steam chest. Now place the valve templet alongside of the steam-port templet (Fig. 180) with the lower end, K, of the valve templet resting on the upper face of the valve. The end K should always, when the tem- plets are in use, rest on the upper end of the valve. Now, if the templets have been accurately made they will visibly reproduce, outside of the steam chest, the invisible events which are occurring within it. To Use The Templets For Valve Setting, it is merely necessary to follow the directions of Table 167 and measure the valve events which occur from the templets instead of measuring them directly from the actual valve and ports. After the valve has once been set correctly, it may be desirable to label and retain the templets for future use. But, if the proper trammel is made and center-punch reference marks are spotted on the valve stem as described in other examples, the use of the templet for resetting will be unnecessary. 168. Setting A Slide Valve For Equal Cut-Offs has definite limitations. For instance, a valve designed for a nominal cut-off of, say, %o stroke could not give satisfactory operation if set for f or % o cut-off at each end. In setting for equal cut-offs, one must not attempt to depart very far from the nominal cut-off for which the engine was designed. The following procedure is intended to give a practical means for setting slide valves for equal cut-offs which will give satis- factory operation. (1) Set valve for proper equal leads by Table 167. (2) Scribe a mark, A, (Fig. 182) at some convenient place on crosshead. (3) Place engine on crank-end dead center. (4) Scribe a mark, B, on the crosshead guide opposite A on the crosshead. (5) Turn engine slowly in direction it is to run until the valve just closes the crank-end cylinder port to live steam. (6) Scribe a mark, C, on the crosshead guide opposite A on the crosshead. (7) Turn engine to head-end dead center. 130 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 (8) Scribe a mark, D, on the crosshead guide opposite A on the crosshead. (9) Scribe another mark, E, making DE = EC. (10) Turn engine in direction it is to run until A stands opposite E on the guide. (11) Change effective valve-stem length sufficiently to half close the cylinder port. (12) Move eccentric on shaft (opposite to engine rotation) to just close the cylinder port. (13) Turn engine in direction it is to run until cut-off again takes place at the crank end. (14) If A is not opposite C, repeat steps (6) to (13). (15) Check valve setting with an indicator (Sec. 175). NOTE. SETTING FOR EQUAL CUT-OFFS Is A CUT-AND-TRY ADJUST- MENT, it being necessary usually to repeat steps (6) to (13) several times before the adjustments are correct. Crosshead on Head -End Dead Center, Connecting -Frame FIG. 182. Method of marking crosshead guides for setting valve for equal cut-offs. 169. The General Procedure In Setting A Slide Valve For An Intermediate Between Equal Leads And Equal Cut-Offs differs from that for equal leads (Sec. 167) only in that the adjustment is made for definite unequal leads. The lead at the head end is made a little less, and that at the crank end a little more, than the value recommended in Sec. 165. The dif- ference between the leads at the two ends should be approxi- mately ^{Q in. for each foot of stroke. The result of this difference is to eliminate the lead at the head end (make it zero) and, at the crank end to double the value given in Sec. 165. The Ridgway Engine Co. recommends, for engines of 14 in. stroke and smaller that the lead should measure ^2 m - more at the crank than at the head end and for larger engines J/16 in. more at the crank than at the head end. The pro- cedure therefore becomes: SEC. 170] SLIDE VALVES AND THEIR SETTING 131 (1) Establish dead centers (Sec. 153). (2) Remove valve-chest cover. (3) If engine has shaft governor, it may be necessary to block the gov- ernor to its normal operating position (See Sec. 174). (4) With indirect valve, remove the valve and measure it. If necessary make templet (Sec. 157). (5) With indirect valve, measure valve seat and, if necessary make templet (Sec 157). (6) Replace valve on seat. (7) Set engine on head-end dead center. (8) Rotate eccentric on shaft, in direction engine is to run, until the lead at head end is, say, M in. (9) Measure accurately the lead at this end. Call it L\. (10) Fasten eccentric to shaft. (11) Turn engine to crank-end dead center. (12) Measure lead at crank end. Call it L 2 . (13) Change lead at this end so that L 2 LI = K = the proper differ- ence between the leads at the two ends. Make the adjustment by chang- ing the valve-stem length. (14) Shift eccentric to attain the required lead at this (crank) end. (15) Replace valve-chest cover. (16) Check setting with indicator (Sec. 175). NOTE. WHEN VALVES ARE THUS SET FOR UNEQUAL LEADS THE RESULTING INDICATOR DIAGRAMS WILL SHOW admission occurring too early at the crank end and too late at the head end. This must be tolerated because it is a consequence of the valve setting. Should the engine, however, appear to "pound" at the crank end, the eccentric must be turned backward on the shaft or the valve-stem length must be changed until the pounding stops. 170. Multiported Valves Are Set by following the same general rules as outlined from Sec. 167 to Sec. 169. Multiported valves are generally so designed that cut-off and the other events occur at each valve port at the same time. For example, Fig. 183 shows that head-end admis- l B^ SJ ^^^/J^rT ^TT 11 ji < Port 'c.E. Cylinder sion will occur at the same time Port past edges A and B. Obviously FIG. IBS. A multiported slide valve rf ,i i at the point of head-end admission. cut-off must occur at these edges at the same time. Therefore the setting of valves of this type requires no special explanation. Each particular valve 132 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 should be examined for peculiarities. Templets may be made of the valve and the seat to facilitate future setting. 171. A Method Of Setting Any Slide Valve Without Remov- ing The Steam-Chest Cover (Power, Nov. 15, 1921) is described below. This applies to plain D, piston, balanced, and multiported slide valves in fact to any slide valve. However the method can be used effectively only for engines which have little or no valve leakage; this restricts it, largely, to relatively-new or to recently-overhauled engines. EXPLANATION. // there is a rocker for transmitting motion of the eccentric to the valve rod, for the best valve setting the length of the eccentric rod should be so adjusted that the rocker will swing approxi- mately as far to one side as to the other of that position in which it would be at right angles to the valve rod. After the length of the eccentric rod has been thus adjusted, the valve setting is completed by adjusting the valve rod to such length that one end of the valve will travel over the opening edge of its steam port as much as the other end of the valve will travel over the opening edge of its port and then with the engine on a center, setting the eccentric to that position which will give the valve the desired amount of lead. How this may be done is explained below. // the valve-rod length cannot be adjusted outside of the stuffing box, it will be necessary for good valve setting to remove the steam-chest cover for that purpose. But where the rocker would be thrown only slightly out of perpendicular to the valve rod by adjusting the length of the eccen- tric rod, then a fair valve setting can be effected by simply adjusting the length of the eccentric rod for equalizing the travel of the valve without opening the steam chest. Or in case there is no rocker, the equalization of valve travel can be effected by adjusting either the length of the valve rod or the length of the eccentric rod, without removing the steam-chest cover. For testing the equalization of valve travel without opening the steam chest: Place the engine on a center, make a mark on the guide to corre- spond with a mark on the crosshead. Temporarily fasten the eccentric on the shaft in that position which will just permit steam to be blown through the port at the same end. Then, turn the flywheel forward to the position where, by opening the throttle valve, very little steam is shown by the pet cock to be admitted to the other end of the cylinder. Make a mark on the guide to correspond with the mark on the crosshead. Also make another mark with the engine on dead center at the same end of the cylinder. Also make a mark on the guide halfway between the marks last made on the guide. Then turn the engine wheel to such a position that the mark on the crosshead will be opposite to this middle mark. Adjust the length of the valve rod or eccentric rod so steam will be just admitted on the same end. SEC. 172] SLIDE VALVES AND THEIR SETTING 133 Next turn the engine forward toward the other center until the mark on the crosshead comes the same distance from the end of the stroke as the middle mark is from the other end. If steam is just admitted the travel has been equalized. If not, turn the engine to the position where steam is just admitted. Make another mark on the guide halfway between the position where steam was admitted and the position where it should have been admitted. With the crosshead set at this middle mark, readjust the valve-rod or eccentric-rod length until steam is admitted at that end of the cylinder. Now set the valve for the desired amount of lead. With the valve travel thus equalized, place the engine on the head-end center. Turn the eccen- tric forward on the shaft, and set the eccentric to the position at which steam is just admitted to the head end of the cylinder. Then make a mark on the valve rod exactly 1 in. out from the end of the stuffing-box gland. Shift the eccentric as much farther forward on the shaft as may be necessary to shift the mark made on the valve rod by a distance equal to the desired amount of lead. 172. Setting A Riding Cut-Off Valve Mechanism must, since it contains two valves, be accomplished in two steps, (1) THE MAIN VALVE Is SET for equal leads by the method of Table 167 or as follows : Rotate the eccentric from one extreme position to the other to see that both cylinder ports are opened to the same extent. If they are not, adjust (Table 167) the valve-stem effective length until they are. Whether they open exactly to their total width is not important. Then put the engine crank on the head-end dead center and have the eccentric rotated, in the direction in which the engine is to run, until the head-end cylinder port begins opening and is open by the amoun t of the lead (usually ^2 in.). This may often be determined by observing the cylinder port through the port in the main valve. Then fasten the eccentric securely to the shaft. The valves of a piston-valve engine must be set by an indirect method, such as that which is described in the following example. (2) SETTING THE CUT-OFF VALVE is dependent upon whether the cut- off valve is (a) hand-adjustable, (6) governor-operated, (c) neither hand- adjustable nor governor-operated. In any one of these three constructions the first step is to adjust the valve-stem length. To do this, place the main valve in its mid-travel position and turn the cut-off eccentric. The cut-off valve should travel equal distances beyond the two ports of the main valve. If it does not do this, adjust the effective valve-stem length until it does. (a) // the cut-off valve is hand-adjustable: Make marks A and D (Fig. 182) on the crosshead and guide to represent the head end of the stroke. With the engine still on head-end dead center, place the cut-off eccentric on its crank-end center (Sec. 154) and fasten it there by tightening its set screws. Now measure two-thirds stroke, DE, from the head-end 134 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 mark D on the crosshead guide and make another mark, E, on the guide. Turn the engine in the direction it is to run to bring the crosshead mark A to this last-made mark, E, on the guide. Then adjust the position of the cut-off valve on its stem (by the hand wheel, Fig. 184) until it just closes the head-end port of the main valve. This completes the setting. (6) // the cut-off valve is governor-operated: With the governor connected up and its weights resting at their inner positions, turn the flywheel until cut-off occurs and measure the fraction of stroke at which this occurs. Do this for the forward and return strokes. The fractions should be equal if the valve stems are of proper length. If the fractions are unequal they may be equalized by changing the effective length of the cut-off valve stem. Then, the governor springs should be disconnected and the weights blocked out against their stops. Turning the flywheel now should not cause the cut-off valve to uncover the ports of the main valve at any position during the revolution. ^-Adjusting Handwhee/ Riding Cut-Off .Left-Hand Thread Fio. 184. Section of a Meyer riding-cut-off valve. (c) // the cut-off valve is neither hand-adjustable nor governor-operated: Place the engine on head-end dead center and the cut-off eccentric on its crank-end center and fasten it there, just as in (a). Now turn the engine ahead for % stroke (or whatever fraction of stroke at which cut-off is desired) of the crosshead, as in (a). Now loosen the cut-off eccentric and shift it ahead (in the direction the crank is to turn) until it closes the head-end port in the main valve. Then fasten the eccentric securely. The setting is thus completed. The following example illustrates the application of the preceding rules to the setting of a riding-cut-off piston-valve engine's valves. EXAMPLE. SETTING THE VALVES OF A SHAFT-GOVERNED PISTON- RIDING-CUT-OFF-VALVE ENGINE for selected equal leads. This is based on the directions in an article in Southern Engineer for December, 1919. An indirect method (Sec. 156) must be employed. While the detail procedure herein outlined is riot exactly the same as that specified in the general directions of Sec. 172 above, the result which is attained is the same. SEC. 172] SLIDE VALVES AND THEIR SETTING 135 These directions relate specifically to an engine of " Buckeye" con- struction, the valve and cylinder arrangement of which is shown in Fig. 185. There are two piston valves, Vi and V 2 (Fig. 185) one working within the other. The working edges of neither are visible when one is setting the valves. The cylindrical end portions, E, of the main valve, Fi, form two smaller valve chests for the cut-off valve. The two cup-like ends of the main valve are retained in correct relation by three rods, R, which tie the ends together. The hollow main-valve stem, M, is screwed into that main-valve head which lies nearest the crank. The cut-off-valve stem, C, slides longitudinally within the main- valve stem. Stationary Valve- ..Main Chesf Liner .' Valve Riding Cut- Off Valve. -Cylinder Head FIG. 185. Piston-type riding-cut-off valve. (Longitudinal section through cylinder and valve chest of "Buckeye" simple engine.) Prepare To Set The Valve. Remove the valve-chest cover. Disconnect the valve rods from the rocker shafts. Remove the valves and place them on a bench. Now, since the valve ports are invisible when the valves are in the valve chest, templets (Sec. 157) must be made whereby the invisible events which occur inside the valve chest will be reproduced outside of it, where the events, thus reproduced, will be visible. Make The Steam-Port Templet. First, make a wooden measuring rod (R, Fig. 186); it should be of smoothed clear pine, about 1 in. wide % in. thick and somewhat longer than the steam chest. Cut one end to the shape which is shown at the right in Fig. 186. To take the measure- ments for the steam-port templet, place the shaped end of the rod against the inner steam-port edge as shown. Then, with a knife blade, mark the width of the outer port with two fine lines, X and Y (Fig. 186). Remove the rod from the chest and mark the width of the other steam port on the rod : Measure the width between X and Y and lay off this width from the shaped end of the rod, as shown at Z in Fig. 187. Cut a smoothed clear 136 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 pine branch board, S, (Fig. 187) for a steam-port templet. It'^may be % in. thick, 4 in. wide and about the length of the valve-chest. Lay the rod on the board and transfer the locations of the ports from the rod to the board, as shown in Fig. 187. Draw pencil "hatch" lines along the length of the board which does not represent the steam ports. Stationary Liner { Or Bushing 'Wooden "-Head- End ''--.. Measuring Steam Port Rod Crank- End Steam Port' FIG. 186. Using measuring rod for determining steam-port locations and widths. Wooden 'Measuring Rod , z Is 'Pencil Hatch " ~ -Marks Indicating Lines Drawn Port Locations \ On Templet And Widths, lf } Steam-Port Templet (Q Wooden- Piece) FIG. 187. Transferring steam-port locations and widths to the steam-port templet. Make The Main-Valve Templet Cut apiece, M(Fig. 188), of smoothed clear pine % in. by 2 in. and somewhat longer than the main valve. Hold M edgewise against the main valve and mark, with knife cuts, the locations of the valve ports and the valve ends, as shown in Fig. 188. Now, if the main-valve templet is placed on the steam-port templet, (Fig. 189) the exact relative positions of the two sets of ports will be shown. The portions of M which represent metal should be pencil hatched as suggested in Fig. 189. Riding Cui-Off-Valve Cut-Off- Valve Rod* ,.- Main Valve Main-Va/ve Rod* \ 'Port -Main-Valve LocationMarks . Templet ^Valve-Length Location Marks FIG. 188. Transferring the length of the main valve and the valve-port widths and locations to the main-valve templet. .Marks Indicating Ends Of Main Valve*. ; Main-Valve Port Locations*, \ 'Hatch L ines ' { 5team-Port ''Steam- Drawn On Board Marks Port In Pencil Templet FIG. 189. Main- valve templet and steam-port templet in correct mid- travel positions showing the relations between the ports in each. Spot Cut-Off-Valve-Position Marks On The Cut-Off-Valve Rod thus: Slide the cut-off valve inside of the main valve until the left end of the cut-off valve just closes the port, P (Fig. 190). Make a trammel gage, T. of steel wire. Spot a center-punch mark, C, on the main-valve stem. Place one point of T in C and under the opposite point of T spot another center-punch mark, C", on the cut-off-valve stem. Now, slide the cut-off valve to the right within the main valve until the right end of the cut-off SEC. 172] SLIDE VALVES AND THEIR SETTING 137 valve just closes the other main-valve port, Q. With the punch and gage spot the corresponding mark, D, on the cut-off valve stem. Obviously, when one end of the gage, T, is in C and the cut-off valve is shifted until the other gage end lies in either D or C", the corresponding port in the main valve will have just been closed. Arrange The Templets In Position For Setting The Valve. Replace both valves in the valve chest. Arrange two saw horses or a bench to support the steam-port templet (Fig. 191) in line with and at the same elevation as the bottom of the valve chest. Place the main-valve templet edge- .-Ri'ding-Cut-Off Valve Valve Trammel Cut-Off Gage- Val FIG. 190. Center-punch marks and gage for adjusting the cut-off-valve stem and the cut-off valve. wise (Fig. 191) on the steam-port templet. Provide a metal strap, H, and so fasten it with screws to the main-valve templet that the projecting end of the strap just touches the left end of the main valve, when all are in the positions shown in Fig. 191 : That is, have the main-valve eccentric, turned to such a position that the left end of the main valve is in line with the head-end steam port edge as shown at Q in Fig. 191. Now shift longitudinally the steam-port templet until marks M and N are in line. Secure the steam-port templet in this position to the bench or horses, with nails driven part way in. The two templets should now accurately represent the relative positions of the main valve and the steam ports Main - Valve Metal Templet-- . Strip Valve Chest- N' G'' Steam-Port 1* Templet'"' Main Valve'' FIG. 191. Templets arranged at end of valve chest ready for setting the valves. When the main valve and the main-valve templet with it is moved back and forth in its seat the results are reproduced by the templets. Adjust The Effective Lengths Of The Eccentric Rods So That The Valves, When At The Ends Of Their Travels, Will Open The Head-End And The Crank-End Ports By Equal Amounts. Since the cut-off valve should be adjusted with reference to the main valve, the main valve should be adjusted first. Adjust The Main-Valve Eccentric Rod To Correct Effective Length. Turn the main eccentric to one dead-center position (Fig. 165) and 138 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 measure from the templets (Fig. 191) the distance that the edge of the corresponding valve has over-ridden the edge of its steam port, or, instead, the distance that the valve should move to entirely open the port. Then, turn the eccentric to the opposite dead-center position (Fig. 163) and note the relative location of the valve edge and port edge in this position. If, in both positions, the valve either opens the ports by the same amount or over-rides the ports by the same amount, the head-end and crank-end travels are equal and the main-eccentric-rod effective length is correct. If this eccentric-rod effective length is not correct, it may be adjusted to correct length as directed in Table 167. Adjust The Cut-Off-Valve Eccentric Rod To Correct Effective Length; proceed thus: Place the main valve in its mid- travel position (Fig. 189) as indicated by the templets. Secure it in this position by clamping the main-rod stuffing-box gland. Rotate the governor wheel until the cut-off eccentric is on its head-end (Fig. 163) dead center. Then with one point of the gage, T (Fig. 190), in center-punch mark, C, measure the distance of the other gage point from the punch mark, C", on the cut-off valve stem. Now, retain one point of the gage in C and have the cut-off eccentric turned to the crank-end dead-center (Fig. 165) position. Note the dis- tance the gage point is from D. If these two distances are equal, the cut-off-eccentric-rod effective length is correct. If it is not of correct length, adjust it to correct length as directed in Table 167. Set The Main-Valve Eccentric For Selected Equal Leads. Loosen the stuffing-box gland which clamped the main-valve stem. Turn the engine crank to its head-end dead-center position and rotate the main-valve eccentric to its head-end center position, Fig. 163. [When a direct valve gear (one which does not employ levers which change the direction of the valve-stem movement from that of the eccentric-rod movement) and a piston valve is employed, the valve on opening its port for the admission of steam moves in a direction opposite to the direction of motion of the piston. The main-valve gear of the Buckeye engine is "direct."] Therefore if the crank is to run "over" the eccentric should be turned in the opposite direction, or under, until the port at the head end of the cylinder remains open only by the extent of the selected lead. The proper lead may be determined as explained under "Selected Lead" in Sec. 165; it should on engines of this type seldom exceed Me in. This lead, in any case, is measured as the distance between the lines F and G in Figs. 189 and 191 on the templets. After it has been thus set for the selected lead, secure the main eccentric to the shaft. The main valve should now be properly set. To check the lead at the opposite end to insure accuracy, turn the engine crank to the opposite dead center and measure the lead which shows with this position. If the lead is not the amount selected and is not the same at both ends, it will be necessary to change the eccentric rod effective length and the angle of advance as directed in Table 167, until the lead is the amount selected and is the same at both ends. SEC. 172] SLIDE VALVES AND THEIR SETTING 139 Set The Cut-Off Valve Eccentric. -Turn the engine shaft, starting at the head-end dead center, in the engine's running direction until the main valve, the eccentric of which is now properly secured to the engine shaft, just closes the port in the valve seat. This is the cut-off point for the main valve. Loosen the governor wheel from the engine shaft. Now, starting with the cut-off eccentric or the governor wheel at the eccen- tric's head-end dead center position, turn it in the engine's running direction, until the cut-off valve just closes the port in the main valve. This position is determined by placing one point of T (Fig. 190) in C and shifting the cut-off eccentric until the mark, C', lies under the other gage-point as shown in Fig. 190. The full part of the cut-off eccentric should now project from the shaft on the same side and in approximately the same direction as does the crank itself. Secure the cut-off eccentric '^Engine Cylinder Trammel Cut-Off-Valve Center-Punch 3 'Main-Va/ve ,-'' Center- Punch 'Main- Marks Valve Rod FIG. 192. Punch marks to insure future rapid setting of the main valve. (governor wheel), as thus set, to the engine shaft. Both main and cut-off valves should now be properly set. Spot Identifying Marks On the Main-Valve Stem To Facilitate Its Future Rapid Setting. Make another trammel gage, as T 2 in Fig. 192. Place the engine crank on dead center again. Spot a center-punch mark, V, on the steam-chest head. Place the straight point of T z in V and spot a center-punch mark, E, on the main valve stem under the other point of T z . Turn the crank to the opposite dead-center position and spot another center punch mark, under the extending gage point, at H. It is evident that, when, at any future time, the main-valve stem is brought into the position shown in Fig. 192 and as determined with T 2 , the main valve will have just opened the port to the extent of the selected lead. Hence, by employing T 2 and the marks H and E, the main valve may be readjusted without removing it or even the valve-chest cover. Bisect the distance between H and E and spot another punch mark at the point of bisection, 7. Now, if, in the future, 7 is brought under the extending 140 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 gage-point, then the main valve will occupy its mid- travel position; this position must be determined in adjusting the cut-off-valve eccentric rod effective length, as before directed. Replace the valve-chest cover and move the engine crank from "dead center" and the job is finished. Preserve The Trammel Gages. Drill a small hole through each gage. Tag them respectively "main valve" and "cut-off valve." Tie them together and lay them away in a safe place. The wooden templets, which were employed in setting the valves, need never again be used. 173. To Reverse The Direction Of Rotation Of A Slide- Valve Engine : For a throttling governed engine, place the engine in the head-end dead-center position. The lead or lag of the eccentric will then indicate the direction of rotation: With outside-admission valves (Sec. 136) the crank pin always, if there is no eccentric-rod reversing rocker, follows the eccentric. With inside-admission valves (Sec. 136) the eccentric always follows the crank. Loosen the eccentric and turn it about the shaft so that it leads, on lags behind, the crank pin for the new direction of rotation by the same angle as it lagged behind, or led, the crank pin for the old direction of rotation. The lead of the valve will be the same as before. In fact, an often convenient method of reversing the direction of rotation is, the engine being on dead center, to measure the observed lead and then shift the eccentric around the shaft, which will pull over the valve, until exactly the same lead is shown at the same-end steam port. Then secure the eccentric in its new position and the job is completed. NOTE. IP A REVERSING ROCKER Is USED IN THE ECCENTRIC GEAR, the eccentric must be placed on the shaft exactly on the opposite side from that which it would occupy if no reversing rocker were employed. That is, with outside-admission valves, the eccentric will follow the crank; with inside-admission valves, the crank will follow the eccentric. With this in mind, the above rules may be followed for reversing the rotational direction of engines with reversing rockers. 174. How Governors Affect Slide-Valve Setting. (1) Throt- tling governors have no bearing on the valve motion and, there- fore, need no special attention. Valves on engines having throttling governors have the same motion, irrespective of the engine load. (2) Variable-cut-off governors, shaft governors for example, change the motion of the valves with changes in engine-load and, therefore, require consideration when adjust- SEC. 174] SLIDE VALVES AND THEIR SETTING 141 ments are being made. These governors may change (a) the valve travel, (6) the angle of advance, (c) both the valve travel and the angle of advance. With such governors the eccentric is almost always fixed to the governor and forms a part of it. It is, therefore, not adjustable on the shaft. The valve-stem length should be adjusted for equality of leads (Sec. 167) or for a slightly larger lead at the crank than at the head end (Sec. 169). If the eccentric must be shifted to obtain satisfactory operation, it is usually necessary to cut a Governor Blocked In Full-Load Running Position .Excess ive- Speed >sif/on Fia. 193. Shaft governor blocked in full-load running position for adjusting valve. new flywheel key way into the shaft. Whenever adjustment of the eccentric is made, it should be made only when the governor is " blocked" (Fig. 193) into the position which it occupies when running under full load or that fraction of full load at which the engine is most often used. Generally, three-fourths to full load position is used. The valve may then be set by the methods of Sec. 167 to Sec. 169. See also preceding Sec. 164. NOTE. To FIND THE FULL-LOAD RUNNING POSITION OF A SHAFT GOVERNOR, of a type which changes the valve travel, run the engine under a constant full load at the proper speed. Then, with a scale, measure the valve-stem travel. Now stop the engine and so block the governor (Fig. 193) that the same valve travel occurs, when the engine is turned over by hand, as that which occurred when the engine was running. 142 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 I -First Set 175. The Steam-Engine Indicator Is Often Used In Valve- Setting Operations (Figs. 194 to 202). See Div. 3 for a pre- liminary discussion of the application of the indicator in valve setting. The indicator may be used simply to check the setting of valves, which have already been set by measure- ment, or it may be used to set the valves approximately when it is inconvenient to remove the valve chest cover. There are two fundamental principles which should be observed when using the indicator for valve setting: (1) The angle of ad- vance, or position of the eccen- tric with respect to the crank, determines the timing of the events. (2) The length of the valve stem, or position of the valve on the valve stem, deter- mines the relative sizes (areas) of the cards from each end of the cylinder with respect to each other. A valve stem of incor- rect length will produce an effect on the crank-end card opposite from that which it produces on the head-end card. In other words, if the crank-end card is found to be increasing in size with each change of length of the valve stem, it will also be found that the head-end card is correspondingly decreasing in size. Shifting the eccentric, however, will produce the same effects on both the head-end and crank-end diagrams. H-Second Set HI- Final Sst FIG. 194. Typical successive cards taken from an engine while setting the valves with an indicator. EXAMPLE. The First Set of cards, 7 (Fig. 194), taken from an engine which needs valve adjustment, indicate two things: (1) The head-end and crank-end cards are not the same size; therefore the valve-stem length must be adjusted. (2) All events, admission, release, etc., are late, and there- fore the eccentric must be shifted on the crank shaft. Since the head-end card is the smaller, the valve stem should be shortened to allow more steam to flow into the head-end of the cylinder and thus increase the size of the head-end card. Since all events are late it is necessary to increase SEC. 175] SLIDE VALVES AND THEIR SETTING 143 Lengthen Valve Stem FIG. 195. Illustrating defective slide- valve setting valve stem too short (outside-admission valve). Lengthen Valve Stem. Move Eccentric Ahead FIG. 196. Illustrating defective slide- valve setting valve stem too short. (Outside-admission valve.) Events Occurring Late Move Eccentric Ahead FIG. 197. Illustrating incorrect an- gular advance events occurring late. (Outside-admission valve.) Events Occurring Early Move Eccentric Back FIG. 198. Illustrating incorrect an- gular advance events occurring early. (Outside-admission valve.) Incorrect Length of Valve Stem. Eccentric Improperly Located H.E. Lengthen Valve Stem. Move Eccentric Forward FIG. 199. Illustrating defective valve setting valve stem too short and eccentric too far back. (Outside-admission valve.) Incorrect Length of Valve Stem. Eccentric Improperly Located Shorten Valve Stem. Move Eccentric Back FIG. 200. Illustrating defective valve setting valve stem too long and eccen- tric too far ahead. (Outside-admission valve.) Events Occurring Early Move Eccentric Back FIG. 201. Illustrating incorrect an- gular advance events occurring early. (Outside-admission valve.) Events Occurring Late Move Eccentric Aheacf FIG. 202. Illustrating incorrect an- gular advance events occurring late. (Outside-admission valve.) 144 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 4 the angle of advance, or shift the eccentric ahead a trifle to cause the events to come earlier. The Second Set of cards, II (Fig. 194), taken after the above adjust- ments have been made, show that the length of valve-stem is now correct but that the eccentric has been shifted too far ahead and that all events are occurring too early. The eccentric should therefore be shifted backward about half the amount by which it was originally shifted forward. The Final Set of cards, III (Fig. 194), indicate that the valve is now functioning properly and that further adjustments are unnecessary. 176. Various Defects Of Slide-Valve Settings, As Deter- mined By The Steam Engine Indicator, And Their Remedies are shown in Figs. 195 to 202. See also Sec. 112 in Div. 3 for further information relating to this subject. Much time will be saved if each set of cards which is taken is studied very carefully before resetting the valve. It sometimes happens that successive cards will show only slight changes in the valve setting. It should also be noted that the various changes recommended to correct the defective valve settings in Figs. 195 to 202 are only for outside-admission slide valves. If inside-admission slide valves are to be considered, adjust- ments different from those recommended in these illustrations should be made; see note following Table 159. QUESTIONS ON DIVISION 4 1. What are the outstanding features of slide valves? On what classes of engines are they used? 2. What is meant by valve setting? 3. What are valve diagrams and what is their use? 4. Enumerate the functions of a slide valve? 5. What are the positions of the valve on its seat and of the piston in the cylinder at admission, cut-off, release, and compression for each end of the cylinder? Draw a sketch for each position. 6. Explain, with a sketch, outside-admission and inside-admission slide valves. 7. Enumerate the advantages and disadvantages of plain D-slide valves. 8. What are the advantages and disadvantages of piston slide valves. 9. Do inside-admission valves have any advantage over outside-admission valves? 10. Draw a sketch to explain the principle of balancing a flat slide valve. What is the purpose? 11. Summarize the advantages and disadvantages of balanced slide-valves. 12. Discuss the merits of multiporting a valve. Are multiported valves balanced? 13. Explain the principle and purpose of the riding- cut-off valve. Give its advan- tages and disadvantages. 14. Define valve lap. Draw sketches to differentiate between steam, exhaust, inside and outside lap. 15. With inside-admission valves, what other name can be given to the outside lap? To the inside lap? SEC. 176] SLIDE VALVES AND THEIR SETTING 145 16. What is meant by inside clearance? What class of slide valves may have inside clearance? What does it accomplish? 17. Should valve lap ever be changed? If so, when and how? 18. What are the purposes of fitting a valve with lap? 19. Draw a sketch to define lead. Explain fully its purpose. 20. What is the usual operating mechanism for a slide valve? 21. Explain the similarity of an eccentric to a crank. Is there any difference? 22. Define eccentricity, eccentric circle, throw, valve travel. 23. What is the usual relation of valve travel to eccentricity? 24. Define the angle of advance. Upon what does it depend? 25. Explain the relative positions on the shafts of eccentrics for inside- and outside- admission valves. 26. With a sketch, illustrate connecting-rod angularity. How does it affect (1) the piston velocity, (2) the valve events? 27. Discuss angularity of the eccentric rod. 28. Define dead center and tell why, in valve-setting, it must be accurately established. Give the usual method of establishing dead centers. 29. How can one compensate for lost motion in establishing dead centers? 30. What are the two general methods of setting steam-engine valves? What are the advantages and limitations of each? 31. Draw a sketch and with it explain the indirect-measurement method of ascertaining valve operation. 32. Explain the use of templets in valve setting. 33. With sketches describe how an eccentric can be placed exactly on "center." 34. What are the possible adjustments of a slide-valve operating mechanism? 35. How should the valve be set on a new engine? On an old engine? 36. For what three operating conditions may slide valves be set? What are the advantages of each condition? 37. How could you proceed in setting a slide valve for equal leads? 38. Give the principal steps in setting a valve for equal cut-offs. Is this a direct procedure? Has it any limitations? 39. What is the reason for sometimes setting a slide valve for unequal leads and how is it done? 40. Does setting for unequal leads provide an ideal indicator diagram? Why? 41. Does the setting of multiported valves involve any more operations than that of single-ported valves? Why? 42. How would you set the main valve of a riding-cut-off engine? 43. Tell how to set the riding-cut-off valve of an engine on which a hand-wheel adjustment exists. How far ahead of the crank should the eccentric be placed? 44. What is the procedure in setting a riding-cut-off valve which is controlled by a shaft governor? 45. How is the riding-cut-off valve set when it is neither hand-adjustable nor governor- operated? 46. Does a shaft governor affect the procedure in valve setting ? Why ? 47. Is it generally possible to set a shaft-governed engine for any desired condition? Why? 48. How do throttling governors affect valve setting? 49. How may one find the full-load running position of a shaft governor? 50. How do the angle of advance and effective length of valve stem, if incorrect, distort an indicator diagram? 51. What would be the procedure in rectifying the diagrams shown in Fig. 101? 52. Describe the valves and valve-operating mechanism of the Mclntosh & Seymour engine. 10 DIVISION 5 CORLISS AND POPPET VALVES AND THEIR SETTING 177. The Reasons For Employing Corliss Or Poppet Valves are: (l) These valves are suited to engines which require small clearances, Sec. 305; these valves can be located very near to the place where steam enters or leaves the cylinder and usually have but a very limited movement. (2) They are well adapted where a quick opening and closing of the valves is necessary especially where a quick closing of the valve at cut-off is essential. (3) By reason of their limited movement, these valves are subjected to little friction; the mechanical losses (Sec. 11) of such engines are, therefore, small and the valves will operate a long time without showing signs of wear. NOTE. ENGINES WITH CORLISS AND POPPET VALVES ARE USUALLY MUCH MORE EFFICIENT (see Div. 10) than are engines with slide valves, but to provide the increased efficiency the engines must have a greater number of parts and cost much more to construct. They are therefore used chiefly when the saving due to their efficiency more than offsets their high initial cost. 178. The Advantages Of Corliss Valves (see Div. 2 for definition) are: (1) The valves may be made to move slowly and but little when they are opened or closed. (2) The valves move rapidly while opening or closing, especially where detach- ing valves are used. (3) The valves may be located very near to where the steam is to be admitted to or exhausted from the cylinder. (4) The valve events admission, cut-off, release, and compres- sion are independently adjustable, and only cut-off need be varied to meet the requirements of different engine loads. (5) Steam is exhausted from the cylinder through separate valves from those through which the steam is admitted. Thus, the cooler exhaust steam does not sweep over and cool the admis- sion valves; see Sec. 274. 179. Typical Designs Of Corliss Valves are shown in Figs. 203 to 206, and 233. Features which distinguish good design may be enumerated thus: (1) The valves should never extend 146 SEC. 179] CORLISS AND POPPET VALVES 147 into the displacement volume; that is, there should be no danger, even if the valve were stopped in any position, of the piston striking it and causing damage. (2) The valves should, in all positions, be supported on the seat throughout their entire length; that is, there should be no tendency for the steam acting on one side of the valve Edge. ,5tiffening ' \ Bridges Cylinder , Head "'Exhaust.' Valve FIG. 203. Corliss valves (positively-operated) in cylin- der head of the "Ideal" Cor- liss-valve engine. **-Slot For Valve Gear Engagement FIG. 204. Corliss admission valve of the "Ideal" Corliss-valve engine. Admission Valve I- Hamilton Type Valve H - Ty pe Frequently Used FIG. 205. Detaching Corliss-engine admission valves (Hooven, Owens, Rentschler Company. Valve V\ is supported its full length at all times. Valve Vz, when open, is supported only at its ends or by the bridges which may cause it to spring. V\ weighs somewhat less than Vi. The cylinder clearance is somewhat less with Vi than with F2.) ,Cap Piston Ring-. .-Piston Exhaust Valve I- Hamilton Exhaust Valve Type of Exhaust Valve Frequently Used FIG. 206. Detaching Corliss-engine exhaust valves. (Hooven, Owens, Rentschler Co. In the Hamilton cgnstruction, Vi, the valve does not rock into the cylinder space, where, should the valve gear break, it might wreck the engine.) to bend it and thus possibly cause uneven wear of its seat. 148 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 SEC. 180] CORLISS AND POPPET VALVES 149 (3) With multiported valves, the number of edges past which leakage might occur should be a minimum. (4) The total pro- jected area against which steam may act to force the valve against its seat should be a minimum, so as to reduce the force causing friction at the valve. 180. Positively-Operated Corliss-Valve Mechanisms are illustrated in Figs. 38, 207, 208, 209, and 235. The admission valves in these mechanisms are usually operated through a wrist plate (Fig. 38) or through a system of separate levers and links for each valve: these levers may be located at the valve l-Central Position II- Extreme Position FIG. 208. Showing linkwork inside of gear case of Ridgway four-valve engine. (Fig. 209) or alongside the crosshead guides (Fig. 207), and they may be enclosed in a dust-proof case or they may be exposed. The valves may, however, be driven by rods attached directly to a rocker arm as are the exhaust valves in Fig. 209. The exhaust valves are usually driven from a separate wrist plate or directly from a rocker arm, although they are sometimes driven by a system of levers and links such as that shown for the admission valves in Fig. 209. 181. The Advantages And Disadvantages Of Positively- Operated Corliss-Valve Engines are, in general, those stated in Sec. 178. The following additions should be noted: (1) Being positively-operated, the valves may be operated at higher 150 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 speeds than can the detaching Corliss valves. This means that, with a given size of cylinder, a positively-operated-valve engine may operate at a higher speed and hence can develop more power and can operate satisfactorialy with a smaller flywheel than can an engine which has detaching valves. (2) The operation of the valves is practically noiseless. Detach- ing Corliss engines make considerable noise as the dash pots close. (3) Shaft governors are more applicable to positively- Oil Trouqh J 1 f . d:i | |3 -j;j| Base Fia. 209. Valve gear of Ames four-valve non-releasing Corliss engines. (Ames Iron Works.) operated than to detaching valves. This means that the speed regulation will, generally speaking, be better with posi- tively-operated valves. (4) For long-stroke, slow-speed engines especially, positively-operated valves do not give as quick cut-off as do the detaching valves. It follows from the above that positively-operated Corliss valves are best suited for short-stroke, medium- and high-speed engines where close regulation of speed is desired. They provide a relatively compact, efficient, and noiseless type of engine for this service. SEC. 181] CORLISS AND POPPET VALVES 151 152 STEAM ENGINE PRINCIPLES AND PRACTICE [Dnr. 5 182. Detaching (Releasing, Or Drop-Cut-Off) Corliss- Valve Mechanisms (see Sec. 50 for definition) are illustrated in Figs. 210 to 212. The valve stem, S, Fig. 211, is extended from the cylinder through a bracket or bonnet and has keyed to it the steam-valve arm (D, Fig. 212). The hub of the steam- .Bonnet Governor Cam Rod--. Knock-Off Lever-^ Bel I I {Crank. \ ' xt>? Earliest Cut-Off-. Knock-Off Lever-. \ Knock-Off Cam-.^ Spring-. '' Latest Cut-Off Governor Rod-. Steam- Valve Arm FIG. 211. Part-side view of typical Corliss-valve releasing mechanism. /_.. -Safety Cam ''Steam-Valve Arm Rod FIG. 212. Front view of typical Corliss-valve releasing mechanism. valve arm forms a shaft upon which a bell crank, B, Fig. 212, and a knock-off lever, E, are mounted so as to turn freely. B is connected at one end to the steam-valve rod (K, Fig. 210) ; and carries at its other end a latch or hook (C, Fig. 212) which is pivoted at A. The steam-valve arm, D, has, attached to it, Safety Cam-' Steam Arm - - 1' Dash-Pot Rod-^, I-Lcntch Raising Valve H- Latch Released FIG. 213. The Reynolds trip gear for Corliss engines. a dash-pot rod (Z), Fig. 210) which leads to a dash pot, X. The operation of this releasing mechanism or trip gear is explained below: EXPLANATION. Suppose the bell crank to be turned, by the steam- valve rod, in the direction indicated in Figs. 212 and 213. The latch, C, SEC. 183] CORLISS AND POPPET VALVES 153 engages a projection or catch plate, P, on the steam-valve arm, D, and raises D, rotating it about its axis and opening the valve. The dash-pot rod is also raised, forming a partial vacuum in the dash pot. Arms B and D thus turn together as one, until the inner arm of the latch strikes the knock-off cam on the lever, E, which remains stationary. When the latch arm does strike the knock-off cam lever B still moving as indi- cated the latch is rotated about its pivot at A and the catch plate on D is released from the hook, C. The air pressure above the dash-pot piston immediately forces it down, drawing arm D with it and closing the valve. 183. Advantages And Disadvantages Of Detaching-Corliss- Valve Engines are, generally, as given in Sec. 178, and in addition, the following: (1) Cut-off occurs very rapidly irrespec- tive of the engine speed or load. This makes these valves satisfactory for slow-speed, long-stroke engines, of which class all very large engines necessarily must be. (2) The valves cannot be operated at high speed because, at high speeds, the valves tend to act sluggishly and sometimes do not open. (3) The valve mechanism is noisy as compared to that of positively-operated Corliss valves. From the above it is evident that the detaching-Corliss-valve mechanism is particularly and well suited to large low-speed, long-stroke engines. 184. The Elements Of A Detaching-Corliss-Valve Mechan- ism are, besides the releasing or trip gear described in Sec. 182, the following: (1) An eccentric, E, Fig. 210, for imparting motion to the valve gear. (2) A wrist plate, W, which receives the motion of the eccentric and imparts it to (3) the valve rods, K and L, which in turn move the bell cranks, B, Fig. 212, and the exhaust-valve arms. Since the distance from the eccentric to the wrist plate is long, the connection between them is made up of (4) an eccentric rod, P, Fig. 210, and (5) a reach rod, Q, both supported on a (6) rocker arm, R, which relieves the wrist plate and eccentric of considerable weight. The knock-off levers, E, Fig. 212, are held in place by (7) governor rods, H, Fig. 210, which are controlled through a bell- crank lever, B, by the (8) governor drop rod, 0. (9) The dash pot rod, D, Fig. 210, connects the steam valve arm, D, Fig. 212, with the (10) dash pot piston in X, Fig. 210. NOTE. DETACHING-CORLISS-VALVE ENGINES FREQUENTLY HAVE Two ECCENTRICS and then, of course, they also have two eccentric rods, 154 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 two rocker arms, two reach rods, and (usually) two wrist plates. The reason for using two eccentrics is explained in Sec. 185. Furthermore, engines of certain makes depart somewhat from the exact mechanism described above but these are special constrictions which are so designed for some specific purpose and usually differ very little from that here described. 185. The Features Of Single- And Double-Eccentric Detaching-Corliss- Valve Mechanisms are: (1) When a single eccentric drives both the steam and the exhaust valves, the range of cut-off is limited to about one-third the piston stroke. The reason for this is explained below. (2) In order to obtain a greater range of cut-off, separate eccentrics are employed, one to drive the exhaust valves, the other to drive the steam valves. With two eccentrics, the admission and exhaust valves can be adjusted independently, and steam may be cut off anywhere, nearly to the end of the stroke. EXPLANATION. WHY, WITH A SINGLE ECCENTRIC, THE CUT-OFF RANGE Is LIMITED To ABOUT ONE-THIRD STROKE may be explained thus: After an eccentric, in rotating, reaches the extreme of its throw or its "center" position (Sec. 154), all of the motions which it compels are reversed. Now, in a Corliss trip gear, the catch plate is released if released at all while the wrist plate pulls on the bell crank. Also, the wrist plate ceases to pull on a bell crank when its direction of rotation is reversed; that is, when the eccentric from which the wrist plate derives its motion reaches its center position. Therefore, the catch plate is released if released at all before the eccentric reaches the extreme of its throw. Now, considering the eccentric motion with reference to the exhaust valves, which it also operates through the wrist plate it is evident that each exhaust valve has its greatest opening when the wrist plate, and hence the eccentric, is in its extreme position. It is also evident that the exhaust valve opens and closes at equal time intervals before and after it has its greatest opening. Therefore, since release must occur before the end of a forward stroke and since compression (exhaust valve closure) must occur befoVe the end of a return stroke, it is evident that the greatest opening of the exhaust valve, and hence the extreme throw of the eccentric, must occur before the middle of the return stroke. It follows, then, that the eccentric must occupy its other extreme position before the middle of the forward stroke. Now, since the steam valves if released at all must be released before the eccentric reaches its extreme position, it follows that they must be released before one-half stroke is completed. It follows from the above that, to obtain as large a cut-off range as possible with a single-eccentric mechanism, both release and exhaust valve SEC. 186] CORLISS AND POPPET VALVES 155 closure must occur late. These conditions might be satisfactory for a very slow rotative speed; but, for higher speed, earlier release and more compression would surely be required. These latter conditions can only be obtained by moving the eccentric forward on the shaft, and this in turn cuts down the cut-off range. The practical cut-off range with a single-eccentric Corliss-valve mechanism is therefore about one-third stroke. 186. Typical Designs Of Corliss-Valve Detaching Mechan- isms Or Trip Gears are shown in Figs. 211, 212, and 214 to Governor Valve Toe Bracket- . - -Rod To Governor Toe Collar "7-Governor- Toe Collar Knock-Off Lever 'Safety Cam lir-^l .-Latch -Latch Plates Steam Valve Rod FIG. 214. Gravity trip gear of Hamilton Corliss engines. 221. The Reynolds trip gear, as shown in Figs. 211, 212 and 220, is probably the oldest design and most widely used. It relies upon a spring to cause engagement of the hook and catch plate. Because springs sometimes break, some manufacturers have designed trip gears in which engagement is effected by gravity (Figs. 214 and 219). Other manufacturers employ positive knock-off cams (Figs. 215 and 216) which have an added advantage of being adapted to somewhat faster opera- tion than either spring- or gravity-opposed cams. 187. Dash Pots For Detaching Corliss Valves (Fig. 222) are constructed differently by almost every manufacturer. The 156 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 Governor-. -Safety Device \Wrist Plate FIG. 215. Nordberg long-range valve gear and governor. (The main lever, A, is supported by a bracket on the governor at point P about which it is caused to swing by the knock-off eccentric rod, E. At the bottom end of this lever is hung the three- armed lever, K, the two vertical ends of which are connected to the knock-off cams and the horizontal arm is connected by the drop rod to the governor at point Pz. The drop rod is parallel to A. It is obvious that since this parallelogram is oscillated by the knock-off eccentric drive rod, its sides must remain parallel; therefore, the lever, K, always moves in a position parallel to itself. Should, however, a change of load occur, the governor then lifts or lowers the point, Pz, thus changing the angularity of lever K and changing the center of oscillation of the cams and the point of cut-off.) .-BellCmnk .-Catch Plate ' . Bonnet Cam Dash- Pot Rod - FIG. 216. Patent long range Corliss trip gear. (Nordberg Mfg. Co.) Bonnet Bell Crank Dash-Pot Rod FIG. 217. Corliss-valve trip gear as used on Vilter engines., ^ (Vilter Mfg. Co.) SEC. 187] CORLISS AND POPPET VALVES 157 primary function of the dash pot is, of course, to provide a means for quickly closing the admission or steam valve when the catch plate is released from the hook. A dash pot which was designed to produce only this effect might, however, cause much noise when the plunger struck the bottom of the cylinder. To overcome this objectionable feature, dash pots are usually equipped with a secondary piston which must force air from a cylinder as it descends. By properly restrict- . Go vernor Rod ^^ Knock-Off : 'Lever Si-earn Valve Arm- Knock-Off Bar-, Knock- Off Cam-- Latch Latch Pivot Point-' Catch Plate Bell f , Crank' ' FIG. 218. Vilter Corliss-engine trip gear showing knock-off bar. Steam- Valve Rod FIG. 219. Gravity trip gear of Murray Corliss engines. (Murray Iron Works Co.) ing the opening through which the air is expelled, a very effect- ive cushion can thus be provided. EXPLANATION. As explained in Sec. 182, when the dash pot is lifted through rod, R (Fig. 222), a partial vacuum is created beneath the piston, P. Also, air is drawn in through the hole, H, into the lower portion of cylinder C. When the dash-pot rod is released, the air pressure from above forces down the plunger, which must now displace the entrapped air from C. The passage of air from C is restricted by the valve, V, which can so be adjusted as to produce in C the desired cushioning. NOTE. THE TRIP GEAR SHOULD PROVIDE A MEANS FOR CLOSING THE STEAM VALVE IF THE DASH POT DOES NOT FUNCTION. With the Reynolds gear, the inside of the hook C, Fig. 213, accomplishes this result by forcing down the dash-pot rod. With the mechanisms of Figs. 217 and 219, the steam valve is positively closed by the pin A. 158 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 SEC. 188] CORLISS AND POPPET VALVES 159 188. The Advantages And Disadvantages Of Poppet Valves (see Sec. 51 for definition) are: (1) They are very well suited to use with superheated steam; because they are small and very symmetrical in form, they are not distorted by temperature changes. (2) A large valve opening is effected with only a small valve movement; thus, little work is required to move the valve in opening it. (3) The valve does not slide on its seat, but lifts from the seat; thus, there is no wear between the two and the valve is not likely to leak. (4) The clearance can be small as with Corliss valves; thus, clearance losses are kept small. (5) Bonnet- .- Knock-Off Cam Governor Rod- Drop Rod- , Cylinder, Cushion ;' Space \ Adjusting Valve. Plunger^ Plug' 'Suction Space FIG. 221. Nordberg standard Corliss valve gear. FIG. 222. Corliss-valve dash pot. (Murray Iron Works, Burlington, Iowa.) Poppet-valve operating mechanisms are usually complex; being more complicated than the mechanisms for any other type. of valve, they are usually also more expensive. The use of poppet valves in steam engines is comparatively recent practice. Many new forms of valve-operating mechanisms are being made but whether all of these mechanisms are mechanically good remains yet to be seen. (6) Poppet valves are nearly balanced because they expose only a small unbal- anced area to steam pressure; they are, thus, easily lifted from their seats. The slight unbalance is really desirable as the steam pressure holds the valves against their seats and thus prevents leakage. The use of poppet valves is certain to continue, however, and increase as time goes on and as facili- ties for the production of superheated steam improve. 160 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 NOTE. POPPET VALVES SHOULD BE So LOCATED IN THE ENGINE CYLINDER THAT WATER CANNOT STAND ON THEIR SEATS when the engine is not running. If water is permitted to collect on the valve seats, it soon corrodes them and causes leakage. The slightest leak affords a place for steam to blow through and wear a larger leak. 189. Single And Double-Beat Poppet Valves (Figs. 40 and 41) are, respectively, those (Fig. 40) which are solid and close Dash-pot Piston - Thermometer FIG. 223. Longitudinal section through cylinder of Vilter poppet-valve engine. (Vilter Mfg. Co.) against one ring or a seat, and those (Fig. 41) which are made hollow and close against two rings or seats, one above the other. Single-beat poppet valves are analogous to simple slide valves in that they are forced against their seats by the difference of the pressures above and below the valve, and in that when open they offer but one passage through which the steam can flow; Double-beat poppet valves are analogous SEC. 190] CORLISS AND POPPET VALVES 161 to balanced, double-ported slide valves in that the difference of the pressures above and below the valve acts only on a por- tion of the valve's projected cross-sectional area, and in that, when open, the steam may flow under the outer edge and through the hollow center of the valve. 190. Typical Designs Of Poppet- Valve Mechanisms are illustrated in Figs. 41, 42, 223 to 227, and 242. In general, it may be stated that the poppet valve is given its motion by an oscillating cam (Figs. 41, 42, 224 and 246) or a reciprocating Cam Lever, Operated From Eccentric On Crank Shaft Double-beat Admission Valve Exhaust Pipe-' FIG. 224. Longitudinal section through cylinder of Skinner "Universal Una-flow" engine, showing valve-operating mechanisms. cam (Figs. 227 and 242) which in turn derives its motion from an eccentric. The eccentric may be on the main or crank shaft of the engine or it may be on a lay-shaft which lies alongside of and parallel to the longitudinal axis of the cylinder and which derives its motion through miter or helical gears from the crank shaft. The cam which operates the valve may be a positive one that is, it may compel the closure as well as the opening of the valve or it may simply open the valve against a spring which later closes the valve. The spring, if one is used, should be located where the high- 11 162 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 Distance Between Tram Marks In Inches, Is Stamped On Rod. Admission Valve .Peep Hole Roller Rod T . xhaust Ring-.. Admission Valve. FIG. 225. Longitudinal section through cylinder of "Ames controlled-compression una-flow" engine. Governor Rod-. ^ FIG. 226. Poppet-valve operating mechanism of Vilter engines. (Note that this engine employs the usual double-eccentric Corliss-valve trip gear for operating the poppet valves.) SEC; 191] CORLISS AND POPPET VALVES 163 .Cam -Rod, Operated '. from Eccentric temperature steam will not flow over it and thereby heat it. A spring which is subjected to high temperature is apt to rapidly lose its temper. 191. In Setting The Valves Of A Corliss- Or Poppet-Valve Engine, the first thing to do is, if possible, to get the manu- facturer's instructions and recommendations as to the lap and lead. If this information can- not be. obtained, the valve- setting may be done as directed in the following sections. Good values of steam lap, exhaust lap, and steam lead for Corliss engines are given in Table 193. 192. The Directions For Set- ting Valves Of Single -Eccentric Detaching-Corliss-Valve E n - gines are: 1. ESTABLISH MARKS, if this was not previously done.. The necessary marks are: (a) Three marks C, B, and D, Fig. 228 on the wrist-plate support, to denote the central and extreme positions of the wrist plate. (6) A mark, A, on the wrist-plate hub, which is used with B, C and D. (c) A mark or marks (S, Fig. 229) on . . FIG. 227. Detail of poppet-valve mechan- the end of each steam and exhaust ism on head en d of Chuse uniflow engine, valve the mark to denote the position of the valve's working or cutting edge, (d) A mark or marks (T, Fig. 229) at the end of each valve seat to indicate the position of the working edge of the seat. The mark A (Fig. 228) is made at any convenient point on the wrist- plate hub, usually on. the top as shown. Then, with the wrist plate in its vertical position (Fig. 230) that is, with the reach-rod pin directly in vertical line with the center of the wrist plate mark B is located on the support opposite A which is on the wrist plate, as shown in Fig. 228. Marks C and D are located later as described under (4). To make marks S and T, remove the back bonnets (the plates over the valve openings on the opposite side of the cylinder from the wrist plate). Remove the valves successively from their seats and with a straight-edge along the working edges (Fig. 231) scribe marks at the ends. These marks can then be cut lightly with a cold chisel as shown in Fig. 229. 2. ADJUST THE LENGTHS OF THE STEAM AND EXHAUST VALVE RODS 164 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 (K and L, Figs. 210 and 232). To do this, unhook the reach rod, Q, from the wrist plate and set the wrist plate in its central position, that is, with mark A opposite mark B, Fig. 228. Clamp the wrist plate in this posi- tion by placing a sheet of paper between it and the washer, L (Fig. 228), and tightening the retaining nut. Remove the back bonnets, as above directed, if this was not previously done. Now adjust the lengths of the Corliss Valve Encf ^ .Cutting / of ,.--' Edge ; Valve FIG. 228.- Plan view of Corliss wrist plate showing marks used in setting valves. FIG. 229. Showing marks on Corliss valve and seat whereby the relation of the cutting edges can be judged. steam valve rods, K, so that the valves have a little lap as shown on Fig. 233. These rods are nearly always made with right and left-hand threads at opposite ends to facilitate adjustment. The lap, measured between S and T (Fig. 233), will range from He to Y in. for small engines and from ^ to % in. for larger engines; see also Table 193. Then adjust Reach Rod-. FIG. 230. Plumbing wrist plate and rocker arm. Steel \ Scribe Straight-Edge'- Hark *"' FIG. 231. Showing method of making mark on end of a Corliss valve. the lengths of the exhaust valve rods, L, Figs. 210 and 232, so that the valves will just coincide, or in other words so that the marks E and F, Fig. 233, are in line with each other. Some engineers prefer a slight amount of lap at the exhaust ports (see Table 193), others prefer a slight opening of the exhaust ports when the wrist plate is central; under these conditions the marks E and F cannot be in line. The distance between SEC. 192] CORLISS AND POPPET VALVES 165 these lines will be equal to the desired amount of opening or lap. For small engines the opening of the exhaust valves may be He in. and for FIG. 232. Valve side of Fulton Corliss engine cylinder. (Fulton Iron Works Co., St. Louis.) FIQ. 233. Back view of cylinder of Fig. 232 with valves shown in section. large engines it may be up to %6 in.; but in any case, the amount of this opening must be less than the lap of the steam valves, otherwise there will be danger of steam blowing through without doing work. When rods 166 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 K and L have been adjusted, the paper may be removed from the wrist plate and the reach rod fastened to it. 3. ADJUST THE LENGTH OF THE REACH ROD (Q, Figs. 210 and 232). To do this, loosen the set screws which hold the eccentric to the shaft and turn the eccentric on the shaft or, without loosening the eccentric, turn the flywheel until the rocker arm (R, Fig. 210) stands exactly vertical if the flywheel is turned, have someone watch the clearance at the upper ends of the dash-pot rods (see instruction 9). Use a plumb line, employing the same method as shown for the wrist plate in Fig. 230, to establish the vertical position. Fasten the eccentric temporarily to the shaft with a set screw. With the rocker arm, R, vertical, adjust the length of the reach rod, Q, so that the wrist plate also stands vertical or central that is, with mark A opposite mark B (Fig. 228). 4. ADJUST THE LENGTH OF THE ECCENTRIC ROD (P, Fig. 210). Again loosen the eccentric set screws and turn the eccentric around on the shaft or simply turn the flywheel at the same time watching (or having someone watch) the movement of the mark A, Fig. 228, with respect to B. If marks C and D are already on the wrist-plate hub, A should move exactly from C to D. If no marks C and D exist, A should move equal distances to both sides of B. If A does not move as specified, adjust the length of the eccentric rod, P (Fig. 210), until it does. If there were no marks C and D (Fig. 228), they can now be established for future use, at each of the extreme positions of A. 5. SET THE ECCENTRIC ON THE SHAFT. Place the engine on one of its dead centers (Sec. 153). Rotate the eccentric on the shaft in the direc- tion the engine is to run until the admission valve nearest the piston opens by the desired lead. Lead for Corliss engines may be taken as J-^4 to 23 34 X60 1^2 3^ Ke 3^4 16 X36 X Ha Me 2>3 36 X66 H H K 2 3% 18 X40 H y 32 Me 2% 40 X66 Ke H y* 3% 20 X42 H H* Me 2 42 X 60 Ke %4 y* 3^i 22 X44 1H2 Hfs Me 2^ 44 X 60 K %4 Ke 4 24 X48 Ke Ha Me 2H 46 X66 H %4 Ke 4 26 X 50 Ke H* Me 2H 48 X 66 H 4 Ke 4 1 Distance of piston from end of stroke. 2 These values are for single-eccentric engines. Double-eccentric engines are usually set for negative steam lap (open port) of one-fourth the full port-opening. 170 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 P^ S i jg .22 ^C CD EH 8fi i * s bfl O 9 CJ C3 ^ _G d o I 3^ S 2 > * c ^ o ^ cc 4-^ Ci ^ ^j CO b G JM '^5 h 2 ^ o b O 1 4 1 3 1 W 1 1 -1 1 i | fe b 03 e r "iC O ^- CD cc i 5 " i J J 1 1-s i 1 CO | o w a 03 J i ^73 b .2 i 5C cS 1 3 ol 1 3 2 c3 b fe b o fl ^J flj 3 j 03 4 03 5 o3 b C 73 2 b O b 1 2 o | 3 03 3 1 73 73 CO b b b 4J cS 'c T^ 05 b ;~ 3 ;3 b E a w * H 3 3 1 5 (3 o3 o3 w 1 o3 6 .dvanced I 73 0) ngthened ortened ngthened ortened ngthened ortened 4i I < | -M 3 1 i > J j 05 2 ^ | ( 1 o t ~T i i I i 1 a } i SEC. 194] CORLISS AND POPPET VALVES 171 2 k a T3 C o3 -^ 02 w H-5 ' 2 u h K 40 w 5 ' S ; h ; . -2 c o3 49 J a s s_ T^ \ 1 h3 w ^ 1 1 1 1 S-H I (M M . h .2 1 1 5 1 p | bfl p | j 1 03 03 M I T3 S3 TJ o3 ^ P -d ~ S C3 c3 d S * S c w 0) a w 3 o qj .S b i 1 s d r I 1 I I O 1 > H lo 3 g o O i 0) o> ^ .p X ^ o * ! a { S 1 3 .SP .-S _p 05 bC ^ 172 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 195. In Setting Valves Of Double -Eccentric Detaching- Corliss-Valve Engines the same processes can be used as given in Sec. 192 for single-eccentric engines with the following differences: The steam and exhaust valves, since they are actuated from separate wrist plates, are set for lap when their respective wrist plates are central. The steam valves are, however, set for negative lap; see Table 193. The rocker arms must be set vertical when the respective wrist plates are vertical. The exhaust eccentric can be set to give com- pression as specified in Table 193. The steam eccentric is separately set to give the desired lead. When setting the steam eccentric for lead, the style of wrist plate which operates the steam valves determines whether the eccentric should be moved in the same direction as the crank or in the opposite direction. Similarly, an inspection of the valve gear must be made to determine in which direction to turn the eccentric when adjusting the exhaust valves at the point of closure or compression. If the exhaust wrist plate is moved by an attachment above its point of support, as with the steam valves, the eccentric must be moved in the direction in which the engine is to run, and the position of the exhaust eccentric will be nearly that of the steam eccentric. If the point of attachment is below the point of support (Fig. 220) , the eccen- tric must be moved in the opposite direction to that in which the engine is to run. 196. Do Not Try To Lengthen The Cut-Off Of A Corliss Engine. Many engineers have lost employment for attempt- ing this. In order to make an engine carry more load, it may seem necessary to adjust some rods to lengthen the cut- off (make it later). It is true that this will cause an engine to operate at a slightly higher speed; but, unless great care is taken, one is apt to make the operation of the engine unsafe in case the load were suddenly thrown off of the engine. That is, unless the upper governor collar is raised sufficiently to allow it to rise and thus prevent the admission valves from opening, there is danger, when the load is taken off, that the engine might run away. Also, changing the cut-off by changing rod lengths might prevent the safety cams from coming into operation, if the governor belt should break or run off its pulley. Hence : SEC. 197] CORLISS AND POPPET VALVES 173 197. To Make A Corliss Engine Carry More Load one of only three things should be attempted: (1) Increase the steam pressure if the engine is safe for higher pressure. (2) Reduce the back pressure. (3) Increase the engine speed as directed in Div. 6. 198. In Setting Positively-Operated Corliss Valves And Poppet Valves, if manufacturers' instructions are not at hand or attainable, a greater deal is left to the ingeniousness of the engineer. This must necessarily be, because of the many different forms of operating mechanism which these valves employ. The instructions for several engines are given in following sections and may be studied as a guide in so far as the principles which are given may be readily applied to different engines. 199. The Directions For Setting The Valves Of Ball (Posi- tively-Operated) Corliss Engines, Fig. 235 (Erie Ball Engine Co.), are: An indicator should always be used in setting the valves of these engines, as without its use only a rough approximation can be made. If it is absolutely necessary to set them without an indicator, the first thing to do is to put the governor eccentric in the shortest travel and block it there. This is very important, as it is impossible to set the valves correctly without doing so. To put the eccentric in its shortest travel, bring the center of the eccentric in line with the center of the suspension pin and the center of the shaft. The governor should then be nearly against the stop which limits its movement in that direction. With the governor blocked in this position, turn the engine until the admission valve at the crank end moves as far toward opening as it will. It should not open the port at all, but should lack 3^2 to He in. of coming line and line. If it does not, it will be necessary to adjust the length of the reach rod, between the rocker arm and the cylinder, until the valve lacks at least ^2 in. of coming line and line. Then, turn the engine to head-end dead center and adjust the link connecting the two gear cases, so that the admission valve at the head end also lacks ^2 to He in. of opening. This will complete the setting of the admission valves as far as it can be done without an indicator. Upon taking cards it will probably be found that slight changes will be advantageous. With regard to the exhaust valves; if the cylinder is less than 19 in. bore, it will have a link connecting the cranks of the two exhaust valves. If the cylinder is less than 19 in. bore, this link should be the same length, center to center, as the distance apart of the two valve spindles. For engines having 19 in. or larger bore (Fig. 235), where the exhaust valves are operated from a wrist plate, the short links connecting the 174 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 valve cranks to the wrist plate should he adjusted to such a length that, when the wrist plate is turned to bring the centers of the two link pins and the center of the wrist-plate pin in a straight line, the valve will cover the exhaust ports with equal lap on each side of the ports. Next, roll the engine over by hand and note whether one exhaust valve opens wider than the other. If it does, adjust the length of the reach rod until both valves open equal amounts. Then adjust the position of the eccentric on the shaft so as to have compression begin at the desired distance from the end of the stroke. If an indicator is used, try to adjust so that the compression will run up to about one-half the throttle pressure. Steam Rocker Arm- .-Front Exhaust Bonnet 'Exhaust- Valve Link Rods " Rocker- Exhaust Eccentric Rod''' Arm Bracket '' E- Elevation FIG. 235. Plan and valve-gear side elevation of Ball four-valve (Corliss) engine with exhaust wrist plate. (Erie Ball Engine Co.) It is best to have a little more compression at the head end than at the crank end, as the piston travels faster at the head end and it requires more compression there to cushion it properly. The proper amount of compression is the amount which makes the engine run most smoothly, and the only way of determining it is by experiment after the engine is in service. In adjusting the admission valves by the indicator, set them so the cards will be practically alike at no load slightly higher on the head end if anything and so the initial pressure shown by the cards at no load will not be over half of the throttle pressure. When this is done the governor will automatically take care of the other loads. At an early SEC. 200] CORLISS AND POPPET VALVES 175 cut-off there will be, and should be, considerable wire drawing. Do not try to prevent this, as it is right to have it that way, and it is necessary for the best economy. 200. The Directions For Setting Valves Of The Fleming- Harrisburg Four-Valve Engine (Harrisburg Foundry and Machine Works) are: Disconnect the reach rods and locate the dead centers of the engine. After the centers have been located, turn the engine until the steam-valve rocker arm stands plumb. Now adjust the reach rods from it to the valve arms so that the bell cranks are inclined slightly from the vertical center line passing through the valve stems, toward the head end as shown in Fig. 236, where the amount of inclination is indicated at A and A\. The amount of this inclination of the steam- valve bell cranks varies for different cylinder sizes and is as stated in Table 201. Next, turn the engine until the exhaust-valve rocker arm stands plumb and adjust the reach rods from it to the exhaust-valve FIG. 236. Diagram of levers arms so that these incline from each other of Fleming-Harrisburg four- each to its own end of the cylinder by valve engines (The dimensions the amount shown in co.umn B of Table 201. "' * to, For the high-pressure cylinder of a tandem- compound engine the exhaust-valve arms are turned upward instead of down; this, however, does not change the angle of inclination, these arms being set at the inclination specified in the table, and away from each other as before. For very large low-pressure cylinders, where bell cranks are used on the exhaust valves, these also are set at the inclination specified in this table except that they incline toward each other. To make the eccentric rods of proper length, adjust them so that the rocker arms will travel equally on both sides of their neutral vertical positions. The valves should next be set in the proper relation to the valve arms before clamping the arms to the stems, and forcing the set screws into place. To do this, place the engine on its head-end dead center and disconnect the springs from the governor. If the governor has been adjusted for proper engine speed measure the length of each spring before disconnecting it so that, when the springs are replaced, the initial tension can be restored. With the springs removed, block the governor in the position of least travel, that is, against the outer stops; remove the valve cover-plates and note the marking of the valves and ports (Figs. 237 and 238). This marking will be found on the ends of the valves and at the ends of the cylinder ports, the steam edges and exhaust edges all being marked S. 176 STEAM ENGINE PRINCIPLES AND PRACTICE [Dw. 5 Now, on simple engines and on the high-pressure cylinders of compound engines, set the head-end steam valves so as to overlap the port edges, S, by about He in., which may be termed negative lead. Then clamp this I , Steam Supply \- ii Flancie Steam Chest Flange'' \ FIG. 237. Exterior outline of Harrisburg four-valve engine. valve arm on the stem and turn the engine in the direction in which it will run to the crank-end center. Set the crank-end steam valve with about ^2 in. lap or negative lead and clamp the valve arm on the stem. To Open FIG. 238. Vertical section through cylinder and valves of Harrisburg four-valve engine. This negative lead is especially necessary for condensing engines, to prevent the engine from running away when the load is thrown off. The ports usually do not open to steam at all with the governor blocked in this SEC. 200] CORLISS AND POPPET VALVES 177 position, and positively must not open more than enough to admit sufficient steam to overcome the friction of the engine. The blocking of the governor should now be changed. Fix it in such a position as will give about H cut-off. To do this, the point of cut-off should be located on the guides by making marks on the lower guide in line with the mark on the crosshead shoe for each dead-center position, and dividing the distance between them into three equal parts. Now turn the engine over until the mark on the crosshead shoe is in line with the point on the guide corresponding to H cut-off for the head end and block the governor so that the valve is line and line at the steam edge. Next, turn the engine over until the valve shows the cut-off on the crank end. It will be noted that the crosshead has not traveled the full Yz stroke, as indicated by the crosshead and guide marks, by from % to 1 in., depending on the size of the engine. An adjustment of the valves can be made, which will lessen this amount, but it will increase the differ- ence in lead between the two ends. Hence, this adjustment must be made to the best advantage, lead and cut-off considered. It will be noted that lead materially increases for later points of cut-off and tends to make the engine pound if too great. The exhaust valves may be properly set by turning the engine over to bring the valve arms and rocker arms into their neutral positions. With the engine in this neutral position, adjust the head-end exhaust valve with about y\ G in. lap and the crank-end exhaust valve with Y in. lap. Now, for determining trial compression make a mark on the guides measuring from each dead-center mark: For the high-pressure cylinder of a com- pound engine the mark should be about 1^ in- from each end of the stroke. For a simple engine or the low-pressure cylinder of a compound engine the mark should be about 3 in. from the end of the stroke. These measurements will increase for engines having 24 in. or larger stroke. Now clamp the two exhaust valves on the valve stems, and turn the engine over in the direction in which it will run until the crosshead mark coincides with the head-end mark just made on the guides. This will bring the crank pin below the center line of the engine, and the piston in position for compression at the head end of the cylinder. With the crosshead still in this position, turn the eccentric around on the shaft until the valve and port edges (S, Fig. 237) coincide for the head-end valve. This valve is now in proper relation to the crank for compression and the eccentric set screw should be set down on the shaft. The engine should now be turned over until the crosshead mark coincides with the crank- end compression mark on the guide, when the two edges S of the crank- end exhaust valve and seat should coincide. If they do not, loosen the valve stem in the arm and turn the valve so that these two marks do coincide and fasten it again. This valve is also now right for compres- sion. With the setting just described, the crank-end exhaust port should be about one-half open when the engine is on head-end dead center. This should also be true for the head-end valve when the engine is turned on the crank-end center. 12 178 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 In valve setting, always (Sec. 153) turn the engine over in the direction it runs, never turning it past a desired point and then back to it, as the lost motion will prevent accurate adjustment. When turning an engine over on which the rods have not been adjusted, care should be taken to insure against jamming of the valve gear; that is, forcing it beyond its normal travel in one direction and straining it, due to the rods being too long or too short. 201. Table Showing Advance Of Steam And Exhaust Valve Arms On Harrisburg Four-Valve Engines. Dimensions are all in inches and refer to Fig. 236. Cylinder Advance steam valve bell cranks Advance ex- haust valve arm, sizes A A, B 9 -10^ KG Ke 11 -14> H* % 15 -17 IH H 1714-20 H % K 19M-S4^ IK H H 25 -29 iH i y 8 30 -343^ IH i 7 /8 35 -40^ IH IH IH 46 -56 m IH iK 202. Directions For Setting Valves Of Ridgway Four-Valve Engines. All engines are set in the shop to dimensions shown in Table 203 which apply to Figs. 239 and 240. They are then set by indicator and reference marks are made on all eccentric and valve rods. These marks are 3 in. apart on small engines and 4 in. apart on large engines. All arms are marked with a chisel so that if at any time they have moved it will be possible to return them to their original location. To set the valves: Use the marks if possible. If marks are not visible, set to the dimensions of Table 203. Then use an indicator to perfect the setting; see Sec. 112 and Sec. 175. Table 204 shows the results of adjustments to the simple and cross compound engines. Table 205 shows the results of adjustments to the four-valve tandem compound engines. SEC. 203] CORLISS AND POPPET VALVES 179 203. Table Of Dimensions For Setting Ridgway Simple Four-Valve Engines. The steam valves are set with the gov- ernor bar blocked against the outer stop, thus: When crank is on head-end dead center, set head-end valve with J^2 m - lead. When crank is on crank-end dead center, set crank-end valve with Jf 6 i n - lead. Set exhaust valves and eccentric to . . FIG. 239. Showing the following dimensions which apply to me thod of locating ex- Figs. 239 and 240. haust eccentric on shaft of Ridgway engine. Head-End Steam Valve Crank-End Steam Valve t I A ll_) ^Center Linf Of Gear Box C r^ Valves Move To Open To Eccentrics- Crank-End Exhaust Valve FIG. 240. Diagram of valve gearing of Ridgway simple four-valve engine. Compression Length between centers of valve rods T f ' of ex- Bed Stroke Head Crank Steam valve rods Exhaust valve rods haust eccentric on shaft C ) X L D 12-14 w 4" 2'-10K" 2'-5H" 2'- 9^" 17^" 2" F 14-16 5" W 3'- 2K" 2'- 6^^ 3'- W \*w 2" H 16-18 5H" 5" 3'- 7H" 2'- 9>i/' 3'- 6^' 19%" 3" J 18-20 BH" 6" 3'-ll^" 2'-H^" 3'-llH' 22" 3J^' K 22-24 7" 6H' 4'- 3^" 2'-H^". 4'-. 3>i' 22" 3>i' L 20-22-24 7" 7" 4'- 8H" 3'- 5^"' 4'- 7^' 2'-2H" 3^' M 26-28 8" 7M" 5'- 0^" 3'- 5^ 4'-ll%' 2'-2K" 3^' N 24-26-28 m" 8" 5'- 5^" 4'-0" 5'- 4" 2'-5K" 4H' 30-32 9" w 5'- 9H" 4'-0" 5'- 8" 2'-5M" 4M' P 28-30-32 W 9" Q 34-36 10" 9K" 204. Table Of Results Of Adjustments To Ridgway Simple And Cross Compound Four-Valve Engines. The letters referred to are shown on Fig. 240. 180 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 Steam valves Adjustment Head end Crank end Admission Cut-off Admission Cut-off Turn stem A in arm B counter- clockwise or shorten rod C. Earlier or more lead Later Unchanged Unchanged Turn stem E in arm F clockwise or lengthen rod D. Unchanged Unchanged Earlier or more lead Later Lengthen reach rod M or turn shaft O in arm P counter- clockwise. Earlier or more lead Later Later or less lead Earlier Exhaust valves Adjustment Head end Crank end Release Compres- sion Release Compres- sion Turn stem G in arm H clockwise or shorten rod K. Earlier Later Unchanged Unchanged Turn stem L in arm J clockwise or shorten rod L. Unchanged Unchanged Earlier Later Shorten reach rod N Earlier Later Later Earlier Earlier Turn exhaust eccentric around shaft in direction of rotation .... Earlier Earlier Earlier H.R Cylinder Head- End Steam Valve Crank-End Steam \b/ve L. P. Cylinder Head-End Steam Valve Crank- End Steam Valve I ToL.P Eccentric Head-End Exhaust Valve Valve Head- End Exhaust Crank- End Exhaust Valve Valve FIG. 241. Diagram of valve gearing of Ridgway tandem-compound four-valve engine. SEC. 205 J CORLISS AND POPPET VALVES 181 205. Table Of Results Of Adjustments To Ridgway Tandem Compound Four -Valve Engines. The letters referred to are shown on Fig. 241. High-pressure steam valves Adjustment Head end Crank end Admission Cut-off Admission Cut-off Turn stem A in arm B counter- clockwise or shorten rod C. Earlier or more lead Later Unchanged Unchanged Turn stem E in arm F clockwise or shorten rod D. Unchanged Unchanged Earlier or more lead Later Lengthen reach rod M or turn shaft O in arm P counterclock- wise. Earlier or more lead Later Later or less lead Earlier Low-pressure steam valves Adjustment Head end Crank end Admission Cut-off Admission Cut-off Turn stem A in arm B counter- clockwise or shorten rod C. Earlier or more lead Later Unchanged Unchanged Turn stem E in arm F clockwise or shorten rod Z>. Unchanged Unchanged Earlier or more lead Later Lengthen reach rod N or turn shaft Q in arm R counterclock- wise. Earlier or more lead Later Later or less lead Earlier Turn low-pressure eccentric around shaft in direction of rotation. Earlier or more lead Earlier Earlier or more lead Earlier 182 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 High-pressure exhaust valves Adjustment Head end Crank end Release Compres- sion Release Compres- sion Turn stem G in arm" H clockwise or shorten rod K. Earlier Later Unchanged Unchanged Turn stem L in arm J counter- clockwise or lengthen rod L. Unchanged Unchanged Earlier Later Shorten reach rod N . Earlier Later Later Earlier Turn low- pressure eccentric around shaft in direction of rotation. Earlier Earlier Earlier Earlier Low-pressure exhaust valves Adjustment Head end Crank end Release Compres- sion Release Compres- sion Turn stem G in arm H clockwise or shorten rod K. Earlier Later Unchanged Unchanged Turn stem L in arm J counter- clockwise or shorten rod S. Unchanged Unchanged Earlier Later Shorten reach rod N. Earlier Later Later Earlier Turn low-pressure eccentric around shaft in direction of rotation. Earlier Earlier Earlier Earlier 206. The Directions For Setting Poppet Valves On Ames "Una -flow" Engines (Ames Iron Works) are: The valve gear should be assembled and set according to the tram marks, M, found on the rods and rod heads as shown in Fig. 225. The proper distance, in inches, between punch marks on the rod and head will be found stamped on the rod. If, for any reason, the marks cannot be found, a preliminary setting of SEC. 206] CORLISS AND POPPET VALVES 183 the valves can be made as follows and the final setting made after an indicator has been used on the engine. (See Fig. 245 for illustration of complete engine.) Spring-Tension j_ Screw '^Bonnet Cap , 1. Two- VALVE TYPE, straight una-flow. (a) MAIN VALVES. Connect the eccentric rod to the rocker arm and adjust the length of the rod so that the rocker travels equal distances to both sides of the vertical when the engine is turned over by hand. Then adjust the valve stems (F, Fig. 242) so that there will be about Kooo in. space between the flat part of the cams and the rollers in the roller rods. This space can be measured with a thickness gage in- serted through the peephole opening in the side of the bonnet. This space will increase after the engine has been warmed by the high-temperature steam and should be about "Kooo m - when the engine is in normal opera- tion. Next, connect the reach rod, R (Fig. 225), to the crank-end roller rod, C, and adjust the length of the reach rod so that, with the engine on crank-end dead center, the roller, Q (Fig. 242) in the crank-end roller rod just touches the cam, M. Then, with the engine on head-end dead 'Adjust Clearance Here FIG. 242. Section through bonnet and valve of Ames uniflow engine. center, adjust the ball rods, B, over the cylinder, so that the roller in the head-end roller rod just touches the cam as at the crank end. With the engine running under normal load, take indicator diagrams and then make whatever adjustments seem necessary to make the diagram as desired. In making these adjustments, give attention first to the crank-end valve. Then, after that is properly adjusted, set the head-end valve. The effects of adjustments of the reach and ball rods are given in Table 207. Bear in mind that the valve motion is very sensitive to adjustment and that very little change in rod length is required to make a very material change in the indicator diagrams. In most cases, the lead will show later and the admission line will not be as good at the head end as at the crank end, and if there is any difference in the compression it will show highest at the head end. Care should be exercised when increasing the lead on the valves, while the engine is carrying load, not to increase it to such an extent that the governor will lose control of the engine's speed when operating at friction load or no load. This condition may occur if the rollers are adjusted so far under the cams with the engine carrying a load that, when the load is thrown off and the governor is on its minimum travel, the rollers may still be contacting with the cams and lifting the valves slightly. Steam would thus be admitted to the cylinder causing the governor to 184 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 lose control of the engine at friction or light load. If this occurs it is only necessary to decrease the lead to such an extent that, with the maximum steam pressure, the governor will control the engine at friction load. Typical indicator diagrams are shown in Fig. 243.-/. If the engine is to operate sometimes condensing and sometimes non- condensing, the valves should be set for condensing operation, as a con- densing engine will not operate satisfactorily with as much lead when I- Indicator Diagrams From Una-Flow Engine Non-Condensing [- Indicator Diagrams From Control led-Compression Una-Flow All Diagrams Taken Non-Condensing Diagram Shows Late Admission On The Head-End Diagram ShowslateAdmiss On The Crank- End Diagram Shows Late Admission On The Crank- End Correct Non- Condensing Diagram Diagram Shows Crank-End Exhaust Valve Closes Too Early Causing High Compression On Crank-End Correct Condensing Diagram Diagram Shows Head-End Exhaust Valve Closes Too Early Causing High Compression On Head-End A Correct Diagram FIG. 243. Typical indicator diagrams from Ames "una-flow" engines. operating condensing as it will when operating non-condensing, due to the action of the vacuum in addition to the very early admission of steam. (6) AUTOMATIC BY-PASS VALVES (Fig. 244). All engines built for condensing operation are furnished with by-pass valves which are auto- matically controlled by the pressure in the exhaust pipe or exhaust belt of the engine. The object of the by-pass valves is to automatically increase the volumetric clearance of the engine in case of loss of vacuum or in case the vacuum falls below a predetermined point, also to auto- matically decrease the clearance when the vacuum is restored or raised SEC. 206] CORLISS AND POPPET VALVES 185 above the predetermined point. The additional clearance space is within the cylinder head at the bottom. The by-pass valve opens or closes communication between the cylinder and this additional clearance volume. The valve of Fig. 244 does not operate with each stroke of the engine but only when the vacuum changes through the predetermined point. The vacuum acts upon a piston, P (Fig. 244), which is within a cylinder, C, and thus allows the atmospheric pressure from above to force the piston downward against a spring, thus drawing down the valve and closing it. If the vacuum falls below the predetermined point, the spring forces the piston upward and opens the valve. By adjusting the tension on the spring, the valve can be made to operate at any desired point within By-Pass Valve This Hole Is For l/enf.. .-' Ana 'Should 'y'' Be Left Open To Atmosphere Pi pels Connected To Central Exhaust Be'* Washer- Screw For Adjusting t Tension On Spring'' -By-Pass --Valve Cage By-Fbss-Va/ve Piston I -By- Pass-Valve Cylinder C "Spring Forces Valve From Seat When Vacuum Falls Be/ow a Predeter- mined Point When Vacuum On Piston Overcomes Tension On Spring The Valve Closes FIG. 244. Section through automatic by-pass valve of Ames "una-flow" engine. reasonable limits. When operating at a vacuum of 24 to 26 in. of mer- cury, the spring should be adjusted to operate at 15 to 18 in. vacuum. These valves should be removed at least once every six months and examined to insure that they are not gummed or corroded. 2. FOUR- VALVE TYPE, controlled-compression una-flow. The steam valves are set exactly as on the two-valve type. If no marks are avail- able for setting the eccentric, it should be so located that the center line of the keyway is, in rotation, 52 to 53 degrees back of the crank pin, except on 34 to 36-in. stroke engines, for which engines the center line of the keyway should lead the crank pin in rotation by approximately 127 to 128 degrees. Then adjust the eccentric rod, E (Fig. 245), so that the exhaust rocker arm, R, will travel equal distances to both sides of the vertical. 186 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 Remove the covers on the opposite side of the cage from the rocker lever. This will allow full view of the cams, Q (Fig. 225). The roller in the small crosshead on the exhaust valve stem should be adjusted, through the small rectangular opening on the side of the cage, so that there will be about Mooo in. space between the cam and roller, at a point on the round part of the cam just before the lifting part comes into con- tact with the roller. The smaller this space is kept, the more quiet will be the operation of the valves; but, to insure proper closing of the valves, some clearance must be provided. Turn the engine over in direction of rotation until it is on dead center (Sec. 153) and make a mark on the side of the crosshead shoe and a similar mark on the crosshead guide directly in line with the one on the crosshead shoe. Turn the engine to the other dead center and mark the guide at that end in the same way. This will provide for conveniently measuring Oil Supply Tank And Filter ,Va/ve Cages* ,-Steam-va/ve / Throttle ^ Reach Rod . _JH*L : Valve Sub-base-'' Exhaust Rocker-arm 'Exhaust- valve Cages' FIG. 245. Governor and valve-gear side of Ames "controlled compression una-flow" engine. (Ames Iron Works.) the distance the piston may be from the end of its stroke. Turn the engine over until the piston is 1 in. from head-end center and the crank pin below the engine's center line. In this position adjust the exhaust reach rod, (Fig. 245) Q, so that the cam in the crank-end cage is just touching the roller. Turn the engine to within 1 in. of crank-end dead center and adjust the exhaust valve rod, V, so that the cam in the head-end cage is barely touching its roller. Further adjustments may be made, after the engine is running, from the indicator diagrams. In making adjustments on the reach rod and valve rod, it should be remembered that the exhaust valves open as their small levers move toward the ends of the cylinder except on 34-in. and 36-in. stroke engines where they open when the levers move toward the center of the cylinder. The effects of adjustments are given in Table 207 and typical indicator diagrams are shown in Fig. 243.-/7. SEC. 207] CORLISS AND POPPET VALVES 187 f> s-i ^H !n >j S S3 S ^ ^3 o ^ ^ T, | ^ H 1 | . fe . r^ c* O ^a Ja ^ a 3 i o bC "cl nission 1 ~S o3 G G J a PP 1 la > 1 02 d 1 1 a 02 G O ^H fc ^ ^G a) S a D .1 - .. PI ji Ja^a 'a 3 > g i ^3 02 i " ^ 03 o 1 a 1 S) b QQ o a G ^ F-I O O X a $ 1 a -a G Q Q G^ 03 Q) S'S S 2 ^ ^ o o> > rH o* ' w w o " i3 o* ^ *'*' *6 "** +. i _= 5 1 f *!*! t*lj 2 ^ 2 J 1 s J30cu>^-J^g c5 oj b.^3-i-="cj- J ^ 1 1 ? S 3 g. ^ , ^ K) 1 ^ > (., cS ^ o3 5P G bfi S "a G .g '3 II Il1.s1- s illl -S M "Sb O G O G 'G Si 2 be +-> be ^> -43 I.4l4-*i^ 1 11| ill 11 ^Cj fl,> r p^ QJ 188 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 208. In Setting The Valves Of A Chuse Condensing Uniflow Engine, Figs. 227 and 391, proceed as follows (Chuse Engine and Manufacturing Company) : First loosen the lock-ring nut on the ball-and-socket joint on the crank-end roller slide. This will permit dropping down the reach rod which extends from the rocker arm to the roller slide, so that the slides can be moved back and forth by hand. Next, remove the covers or caps from the camheads. This will uncover the upper ends of the cam cross- heads, to which the cams are fastened. It will also uncover the upper side of the slides, in which the rollers are located. Then push one of the slides just far enough so that the roller will be under the thin end of the cam. Observe carefully that the proper clearance exists between the roller and the cam at this point by introducing between them a piece of an indicator card or a Kooo-in. thickness gage. If the cam is too low, so that a paper will not enter, raise the cam crosshead by loosening the locknut on the valve stem at the lower end of the cam crosshead and then screwing out the valve stem slightly just enough to provide the necessary clearance between the cam and the roller. Then tighten the locknut and again try the clearance. Too much space between the cam and the roller will cause the roller to strike too hard against the incline of the cam, thereby producing noisy running. It is also well to lift up the cam crosshead and valve and release them to insure that the valve is solidly on its seat. After adjusting both crank- end and head-end valves in this manner, the cam heads should be replaced. Be sure that the springs are in their proper positions before tightening down the cap screws on these covers. Then connect the reach rod to the roller slide again and place the engine on the exact crank-end dead center. With the engine on crank-end dead center, lengthen or shorten the reach rod until the roller lifts the crank-end valve ^2 in. This lift can best be measured with a small inside caliper by setting it to the distance between the upper end of the stem sleeve and the under side of the locknut on the valve stem. After the crank-end valve has been set in this manner, turn the engine over to the exact head-end dead center. Increase or decrease the distance between the slides, by lengthening or shortening the rod which connects the two slides, until the head-end valve is lifted just ^62 in., as was the crank-end valve before. This completes the valve setting so far as it can be done by measurement. The final setting is made after taking indicator diagrams; see Sec. 112.^ 209. The Directions For Setting Valves Of "Lentz" Poppet-Valve Engines (Erie City Iron Works) are: The setting of all valves except those which are controlled by the governor is left to the operating engineer, insofar as there are no rigid rules laid down by the manufacturers. An approxi- SEC. 2101 CORLISS AND POPPET VALVES 189 mate setting can be made by measurement as directed below the final setting can then be made from indicator diagrams. See Fig. 383 for illustration of complete engine. 1. STEAM VALVES. The steam valves which are under the governor's control have their eccentric driving block (D, Fig. 246) keyed to the lay-shaft, L. The correct setting can be checked as follows: Turn the lay-shaft until the eccentric rod stands at right angles to the driving block, D, as shown in Fig. 246. If the governor is now opened and closed from minimum to maximum position, the cam lever should show a hardly perceptible motion. This is the correct position for the lead, and the valve spindle must be so adjusted that the roller just touches the curve of the cam and that with the least motion of the side shaft, the .-Roller Guide ' .-Steam- Cam :' Lever Exhaust Eccentric Steam Eccentric '' Governor Ring I'Eleva-tion Lay Shaft :-Plan --Steam Eccentric Strap FIG. 246. High-pressure steam-valve gear of "Lentz" engine. (Erie City Iron Works.) valve lift commences. In case the steam valves ever have to be taken out, the correct position in which to replace them may be determined as follows: It will be noticed that there is a small center-punch mark in the valve stem, S, and one in the roller guide, R. When, at the factory, the valve is properly located, these marks are exactly 2 in. apart. To replace the valve it is only necessary to set a pair of dividers to 2 in. and adjust the length of the valve spindle until these marks are just 2 in. apart. If the engine has been in operation* several years, this dimension may be slightly different on account of natural wear on the roller and cam. The final position may then be determined by turning the valve stem a minute fraction of a turn until a position is found where the cam will engage the roller with an easy and smooth effect without jar and noise. All other eccentrics being clamped to the shaft, they can be easily turned in any direction. By turning the low-pressure steam eccentric forward, the lead is increased and cut-off made later; and vice versa when turning in the opposite direction. By "forward" is meant in the direc- tion of rotation of the side shaft, and by backward, against the rotation 100 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 5 of the side shaft. When shortening the eccentric rods on the steam valves, lead is increased and cut-off made later, and vice versa when lengthened. 2. EXHAUST VALVES. When turning the exhaust eccentric forward, release and compression are made earlier, and vice versa when turned backward. 3. VALVE SPRINGS. Valve springs should be so adjusted as to keep the roller and cam in contact without throwing unneessary load on the valve gear. 210. The Directions For Setting Valves Of Vilter Poppet- Valve Engines (Fig 226) are : Since, on these engines, the valve- operating mechanism comprises the same essential parts as does that of a double-eccentric Corliss-valve engine the setting of the valves is almost the same as given in Sec. 195 for the latter. In the following directions only those adjustments which differ essentially from the setting of Corliss valves are treated in detail. ADJUST THE ECCENTRIC RODS AND REACH RODS, as for a double eccen- tric Corliss engine, so that the rocker arms and wrist plates travel equal distances to both sides of their central positions. ADJUST THE STEAM VALVE RODS so that when the steam poppet valve is on its seat and the steam wrist plate is in its extreme position there is about 26 in. clearance at the latch for hooking in. SET THE STEAM ECCENTRIC by setting the engine on dead center and rotating the eccentric on the shaft in the direction the engine is to run until the steam valve which is nearest the piston has ^2 in. lead or opening. Then tighten the eccentric, to the shaft. ADJUST THE GOVERNOR RODS, with the governor blocked about 1 in. above the automatic safety stop or block (Fig. 440), so that cut-off occurs in equal fractions of the forward and return strokes. This is done by adjusting the rods connecting the knock-off levers of the head-end steam valves with those of the crank-end steam valves. Then, with the governor resting on the safety stop, adjust the governor rods from the governor to the crank-end valves so that cut-off takes place when the steam wrist plate has nearly reached the end of its travel. Cut-off can be observed by watching for the spring-loaded dash-pot piston to drop down. ADJUST THE EXHAUST VALVE RODS so that, with the exhaust wrist plate in its central position, the exhaust cams only touch the steel rollers on the exhaust-valve stems. The cams should not, in this position, lift the valves from their seats. SET THE EXHAUST ECCENTRIC so that it travels about 60 deg. behind the crank. In order to increase the compression and provide earlier release, move the exhaust eccentric toward the crank or in the direction of rotation. Later compression and release are provided by turning the SEC. 210] CORLISS AND POPPET VALVES 191 exhaust eccentric in a direction the reverse of that in which the engine runs. MAKE FINAL ADJUSTMENTS FROM INDICATOR DIAGRAMS as with all other engines; see Sees. 112 and 175. QUESTIONS ON DIVISION 5 1. State briefly the reasons for employing Corliss or poppet valves. 2. Under what conditions might it not be advisable to use an engine with Corliss or poppet valves? Why? 3. What are the distinct advantages of Corliss valves? 4. What features distinguish a well-designed Corliss valve? 5. Explain with a sketch the operating mechanisms used with positively-operated Corliss valves. What variations are there? 6. State the advantages and disadvantages of positively-operated Corliss valves. To what kinds of engines are they best suited? 7. Illustrate with a sketch and explain the operation of the usual detaching Corliss- valve releasing mechanism. 8. Describe, with a sketch, the entire valve-operating mechanism of a detaching Corliss-valve engine. 9. What are the advantages and disadvantages of detaching Corliss valves? 10. Why are two eccentrics sometimes employed with Corliss valves? Explain fully the limitations of using only one eccentric. 11. What is the cut-off range of a single-eccentric Corliss engine? 12. Into what three classes may trip gears be divided? What are the merits of each class? 13. What is the principal function of a dash pot in connection with a trip gear? What secondary function has the dash pot? 14. What provision should be made in the valve mechanism to prevent inoperation of the engine in the event that a dash pot ceases to function? 15. What are the principal advantages and disadvantages of poppet valves? 16. What is likely to cause leaking of poppet valves? 17. Explain, with slide valve analogies, the difference between single and double-beat poppet valves. 18. Explain, with sketches, the operation of as many different poppet-valve operating mechanisms as you can. 19. Take the sketch made in answering Question 8 and explain the adjustment of every part thereon which can be adjusted. 20. What marks are necessary in setting Corliss valves? Show a sketch. If these marks did not appear on an engine, how would you establish them? 21. How does the valve-setting of double-eccentric Corliss engines differ from that of single-eccentric engines? 22. Is it advisable to try to lengthen the cut-off of a Corliss engine? Why? 23. How may a Corliss engine be made to deliver more power? 24. Can marks be used to advantage in setting positively-operated Corliss valves? 25. In the absence of manufacturer's instructions, how would you attempt to set the valves of a positively-operated Corliss-valve engine which has a shaft governor, has its steam valves operated from a gear box at the side of the frame, and has its exhaust valves driven from a wrist plate? How if the steam valve gearing were located immedi- ately at the valve bonnet? 26. How would you set the admission valves of a uniflow engine which are operated by overhead reciprocating cams driven by a shaft governor? 27. How would you set poppet exhaust valves which are operated by cams which are rotated by connectors to an eccentric on the main shaft? 28. Describe the setting of poppet valves which are operated from a lay shaft. 29. Explain the construction and valve setting of a Corliss-gear poppet-valve mechanism. 30. Explain how you would make adjustments to correct the faults which are revealed by Figs. 102 and 103. DIVISION 6 FLY-BALL STEAM-ENGINE GOVERNORS, PRINCIPLES AND ADJUSTMENT 211. A Steam -Engine Governor (Fig. 247; see also Sec. 74 and Fig. 52), as commonly used in connection with a stationary steam engine, is a device for keeping the speed of the engine reasonably constant. A properly operating gover- 5 1 earn Hook- i Spring. Spindle ,. Top- Governor Safety - Sfop.p Governor Dash- FIG. 247. Governor for Corliss engine. (Harding and Willard, MECHANICAL EQUIP- MENT OF BUILDINGS.) nor "may be regarded as a permanent watchman, overlooking the 'engine/ with an observant eye. If more power is required, it (the governor) drops, apparently of its own account and lets the engine take more steam ; and, as the load decreases, it rises and reduces the amount of steam to suit. We owe this 192 SEC. 212J FLY-BALL STEAM-ENGINE GOVERNORS 193 device to the genius of James Watt." (From IL Hamkens, STEAM ENGINE TROUBLES.) The principle of Watt's pendu- lum or fly-ball governor is still widely used but has been modi- fied to meet modern conditions. NOTE. A GOVERNOR Is NOT NECESSARY UNDER SOME CONDITIONS (Graph B, Fig. 248), such as in marine engine service, because the work done by such an engine increases rapidly with the engine speed. There 100 90 ^80 o: * 10 " 50 "40 a- 30 tO 70 10 4 s 'Governed Engine > fum fim 7 f / \ A ^Ur igbverne nqine r K/na Ac> 1 Whlct ->x/mafe/i ~f/onar/ eeci, id / Wo -f Loan Apprt - Propoi TheSp airi 7 Is Sf 1 /B 1 70 40 60 60 IOO \7Q I40 IfcO Load In Per Cent Of Full Load FIG. 248. Graphs showing speed variation with load of governed and ungoverned engines. FIG. 249. Simple pendulum or Governor. "Watt's" is then a resultant constant speed for any amount of steam which may be admitted to the engine. But in most stationary-engine service (constant-speed service) the load may vary greatly and the engine, if not governed nor regulated by hand, would slow down, whenever the load happened to increase; or "run away" whenever the loads were diminished. Hence, for such service a governor is necessary. 212. The Two Principal Kinds Of Steam-Engine Governors (see Sec. 74) are: (1) Fly-ball governors, which are discussed in this division. (2) Shaft governors, which are discussed in Div. 7. A fly-ball governor (Figs. 247, 249 and 250)' is one which depends for its action (Fig. 252) on the centrifugal force 13 194 STE'AM ENGINE PRINCIPLES AND PRACTICE [Div. 6 developed in two or more weights which are rotated about a (usually) vertical spindle which is provided for the purpose. Increased rotational speed. causes the weights to shift radially from the spindle axis and thereby move some part which regu- lates the amount of steam admitted to the engine (Sec. 74). 213. Two Forces Are Em- ployed By Steam-Engine Gov- ernors For Detecting Variations In Engine Speed : (1) Centrifugal force. (2) Inertia or tangential inertia. Centrifugal force is ordinarily the only force em- ployed in fly-ball governors for f x\ \\ L Jnert/a Forces-, \\ ^c^ x \- % r*\n L~'D/reci-ion \ Of \Ro~fation / '/' ^p^v .' Cenlr/petaf \ . Force' / ^ b I-Top View M .Centrifugal \ Force ^C-_ . N n- Side View FIG. 250. Governor employing hori- zontal tension spring. (Hamkens, STEAM ENGINE TROUBLES.) FIG. 251. Showing forces developed by a revolving governor weight. detecting speed variations. Inertia is employed, as will be explained in Div. 7, in shaft governors. Note, however, that inertia and centrifugal force are both employed in such gover- nors never inertia alone. Centrifugal force is the tendency of a rotating body to move away from its axis of rotation. In governor design, this force is opposed by a centripetal force SEC. 214] FLY-BALL STEAM-ENGINE GOVERNORS 195 which is introduced by means of arms, weights, springs or other mechanism. A centripetal force is one which opposes a centrifugal force ; for equilibrium the centripetal force must be exactly equal and opposite to the centrifugal force. EXPLANATION. Consider (Fig. 251) a ball, B, which is pivoted at M and rotating about a vertical spindle, S. There is a centrifugal force, C, tending to make the ball move out radially from the spindle, S. The ball is prevented from so moving by a spring, N, which exerts a centri- petal force, P, just equal to the centrifugal force. If the ball is started suddenly, it tends to "hang back" and exerts a force, /, due to its inertia. If the ball is stopped suddenly, it tends to continue moving and exerts a force, /', also due to inertia. 214. All Fly-Ball Governors Permit Some Variation In Engine Speed. It has been found impractical to endeavor to maintain the speed of an engine exactly constant. It will be noted from subsequent descriptions of governor operation that the governor does not change its position until a change in speed occurs; hence, it is evident that a speed change is neces- sary to cause a governor to operate. There is, moreover, when an engine is properly governed, a definite speed corre- sponding to each load, that is, the speed varies with the load. The graph A (Fig. 248) is characteristic of this sort of per- formance. The speed variation from no load to overloads may be made very small if so desired. Variation in speed of 5 per cent, over the working range of the engine is often permissible. Variations as low as 1 per cent, of the mean engine speed may be obtained under favorable conditions. 215. There Are Two Principal Methods Used With Fly- Ball Governors For Controlling The Steam Admitted To An Engine : (1) By throttling (Figs. 252 and 253) or reducing the pressure in the steam chest of the engine by partly closing a valve in the live-steam line. With this method, the governor (Fig. 254) is not part of the valve-operating mechanism. This method of governing is used chiefly with simple slide- valve engines. (2) By varying the cut-off. Under this condi- tion, the governor (Figs. 247, 255, and 256) is part of the valve gear. This method of governing is employed chiefly with Corliss and poppet-valve engines. 196 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 EXPLANATION. Fig. 253 shows the effect on the indicator diagram of a slide-valve engine of a throttling governor such as that of Fig. 254. The line, A , represents the admission and expansion with a large governor- valve opening. B and C correspond to smaller governor-valve openings at lighter loads. It will be noted from the way in which the admission Governor /n No~ Load Posit ion I-Full-Load, Governor Valve Open ///////////////////////// -No-Load, Governor Valve Nearly Closed Fia. 252. Diagram illustrating method of governing by throttling, matic construction shown above is never used.) (The diagram- lines slope from points R, S and T, that there is considerable throttling (wire drawing or pressure drop due to friction) of the steam in the governor valve. This throttling results in loss in effective steam pressure (Sec. 14) and consequent poor economy especially at light loads. Fig. 256 shows the effect of a cut-off governor such as that shown in Fig. 247, on the Atmospheric Pressure FIG. 253. Indicator diagrams at various loads taken from an engine governed by throttling. indicator diagrams of a Corliss engine. The cut-off occurs at A, B t C and D (Fig. 256) at various loads. The engine performance here shown is much superior to that in Fig. 253. The admission lines are nearly horizontal indicating that there is, at all loads, but little steam friction in the valves. SEC. 215] FLY-BALL STEAM-ENGINE GOVERNORS 197 'Oil Governor Here Hemispherical Weigtrfs- Weight- Carrying Spindle-. Spring Adjust men t For D/fferenf Speeds Spring For Closing Thrott WhenSafefy Lever /s Dropped FIG. 254. Erie pump governor. (This governor is used on pumping engines where, besides limiting the maximum engine speed, it must control the engine speed to meet the demands of the pump. That is, if less pumping is required, the governor diminishes the engine speed. Thus, it will control the engine at speeds of 80 to 320 r.p.m., depending upon the demand. If the belt breaks, the idler, 7, drops allowing the valve to be closed by the spring, S, through the safety latch, M, and lever, L.) 198 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 216. A Steam -Engine Governor Should Be Designed And Maintained For The Greatest Possible Safety And Reliability. A "safety stop" should be provided in every case. Belt- G over nor In Full-Load Position. Knock-Off Block Js Con1rv/ fed By Governor ,' Governor- Sleeve Controls Lever Supply I-Full-Lodd Position; Cut-Off Has Not Occured At One- Fourth Stroke Steam Supply Crank Operates Va/ve Through Linkage E- No-Load Position; Cut-Off Occurs Before One-Fourth Stroke FIG. 255. Diagram illustrating method of governing by varying the cut-off. (The "knock-off" principle illustrated above is employed extensively in the Corliss governing mechanism; but the diagrammatic simplified construction shown above is never used.) driven governors are commonly provided with safety idlers (7, Figs. 254 and 257) so that, if the belt breaks, the idler will drop and shut the governor valve. Corliss governors (Fig. 247) A B Atmospheric Pressure?* _ k"Zero Pressure FIG. 256. Indicator diagrams taken at various loads from engine governed by changing cut-off. are provided with safety knock-off cams, C, so that, in case the governor drive fails and the balls drop, the intake valves will admit no steam to the engine. Various arrangements SEC. 216] FLY-BALL STEAM-ENGINE GOVERNORS 199 (Fig. 258) are provided for holding the governor out of the safety position while starting the engine. Whatever arrange- ment is used, it must be so designed that it will fall out of the way automatically as soon as the governor lifts (Fig. 258). The engineer's memory should not be trusted to remove the starting cam or lever. Pins (P, Fig. 259), which must be removed by hand after starting, should not be tolerated. FIG. 257. Elevation of Pickering governor showing safety idler feature. NOTE. MANY ENGINES AND POWER PLANTS HAVE BEEN WRECKED DUE To GOVERNOR FAILURES. If the governor does not shut off nearly all the steam when the load is taken off the engine, the engine speed may become great enough to burst the flywheel by centrifugal force. Some- times a "secondary safety stop" (Fig. 260) is installed in addition to the one with which the governor is regularly equipped. 200 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 NOTE. AN ENGINE, WHICH lp EQUIPPED WITH A SAFETY DEVICE, MAY STOP WHEN AN EXCESSIVELY HEAVY LOAD Is THROWN ON IT (W. H. Wakeman in Power}. In almost all makes of Corliss engine -Load Or Counterpoise Weight (Starting Lever ) Position When Starting Position When Running FIG. 258. Showing starting lever, L, which falls out of position when the governor lifts. .-Drop Rod From Governor Governor 'o/umn Pin-' Governor CoJumn'' FIG. 259. Showing unsatisfactory pin arrangement for holding Corliss governor in starting position. This arrangement is unsafe. governors there is the "safety pin" on which the weights are brought to rest when the mechanism is not in action. Or instead a "safety collar" may be used. Both of these devices prevent the mechanism from falling Primary (Throttling) Governor*-*^ ,Steam Line fo Engine .-Belt- Wheef Rim Governor Belt Pulley-- Trip Rod ' Throttle Valve " ~70 Engine '^Centrifugal Tripping Device FIG. 260. Detail of the design of trigger device for secondary speed control on Chandler & Taylor variable-speed engines. (If speed becomes excessive, T is thrown outward by centrifugal force, compressing S. Thereby C is tripped which releases R. Then W falls down and closes V which shuts off steam to the engine.) so low that no steam will be admitted. These pins, or collars, are so placed that, when it is at rest, the engine will get steam. When the engine is in full operation, the pin is removed or the collar so turned that, SEC. 217] FLY-BALL STEAM-ENGINE GOVERNORS 201 should the belt or gear break, the governor mechanism will drop so low as to cut off all steam and a shut-down results. In plants where heavy and changing loads are handled, it is not uncommon for a sudden load to be imposed on the engine, which is so great as to make the mechanism drop low enough to shut off steam, if the operator has attended to his duty of removing the pin or setting the safety collar after starting up. The result is a shut-down. This may confuse the inexperienced operator until he knows the cause. Always look at the "safety" when an unusual shut- down occurs. NOTE. SOME GOVERNOR PULLEYS ARE SECURED To THE SHAFT WITH A SET-SCREW WHICH MAY COME LOOSE, or a key may work loose. The pulley may hold just enough to slowly rotate the governor but not suffi- ciently to bring it up to speed. The result will be a runaway engine. An oily or slack governor belt may also cause this. 217. Only The Best And Safest Materials And Methods Should Be Used In The Construction Of Governor Mechanisms. 5houfcferect I-Straight Key - Taper Key FIG. 261. Showing methods of securing governor pulleys. FIG. 262. Showing a method of curing a governor lever. The cost of these materials and methods is comparatively small, whereas the damage done, if the governor fails, may be very large. Governor belts should be of the best grade and be so sewed and cemented as to be practically endless. They should be of even weight and not wide enough to rub on the flanges of the governor pulleys. Governor pulleys should preferably be of metal and secured with more than a single set-screw. Pulley faces and belts should be kept free of oil which might cause slipping. Recommended fastenings for governor pulleys and levers are shown in Figs. 261 and 262. 218. Dangers Due To The Binding Of A Governor Mechan- ism Should Be Carefully Avoided. The pivots of governor 202 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 rods should have sufficient end play (E, Fig. 263) to prevent binding caused by slight frame movements or by grit getting between the end faces. The governor, if new or if it has been Spindle 'Collar Pivot Pin 'Counterpoise -Yoke FIG. 263. Showing proper end-play for FIG. 264. A collar which limits the lift governor-rod pivots. of a fly-ball governor should never be allowed to get too low. out of use for some time, should be moved by hand before starting to insure that it does not bind. Collars (C, Fig. 264) must not limit the movement of the governor so as to prevent Casing JL; -Spindle FIG. 265. Enclosed-spring governor. (From Hamkens, STEAM ENGINE TROUBLES.) its completely shutting off the steam supply. Enclosed parts (such as dash-pots, Sec. 230, and enclosed springs, Fig. 265) should be inspected regularly. Oil should occasion- ally be drained from dash-pots and the pots refilled with clean SEC. 219] FLY-BALL STEAM-ENGINE GOVERNORS 203 oil. The pots should be kept well filled with oil as pocketed air is likely to cause dangerous racing. 219. Various Terms Used To Describe The Performance Of A Governor may be defined as follows : (1) By sensitiveness is meant the ability of a governor to substantially vary the amount of steam admitted to the engine in response to slight changes in engine speed. Sensitiveness is not an exact term (see below). (2) By powerfulness of a governor is meant the force which the rotating parts of the governor are capable of exerting on the governor rods or other steam-controlling mechanism when a variation in speed occurs. If a governor is to be very sensitive, and very powerful, it must be very large or run at a high speed. (3) Promptness is the ability of the governor to respond quickly to load changes. A very prompt governor is one which requires only a fraction of a second to adjust itself to a considerable change in load. (4) Sluggishness is the opposite of promptness. A governor which requires a half minute or more to adjust itself to a new load is relatively ''sluggish.'' To be very prompt, a fly-ball governor must not be heavy. (5) Coefficient of regulation, also called regulation, coefficient of speed regulation, speed variation or fluctuation, is the variation in speed which the governor permits from no load to full load expressed as a percentage of the full-load speed. The coefficient of regula- tion is an exact mathematical measure of sensitiveness. Expressing this relation by a formula: (25) M r = ^P^' (decimal) Wherein: M r = the regulation coefficient, expressed deci- mally. N n = speed of the engine at no load, in revolutions per minute. N/ = speed of the engine at full load, in revolu- tions per minute. EXAMPLE. An engine manufacturer guarantees a regulation coefficient of 1.5 per cent, for his engine equipped with a certain governor. The engine makes 178 r.p.m. at no load and 175.7 r.p.m. at full load. Is it within the guarantee? SOLUTION. By For. (1) the coefficient of regula- tion, Mr = (N n - N f }/Nf = (178 - 175.7) -r- 175.7 = 0.0141 = 1.41 per cent. The engine is within the guarantee. 204 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 NOTE. IN CONDUCTING REGULATION GUARANTEE TESTS, it is usually understood that the change from no load to full load is to be made gradually. But "specifications should clearly state the method to be employed in determining the speed variation and basis upon which the calculations are to be made. This is particularly important when the unit is supplying both a lighting and rapidly fluctuating motor load, as in this case the instantaneous variation of speed must be limited to a small margin to prevent 'blinking' of the lights. For high-speed direct- connected units the U. S. Treasury Department specifies that the maxi- mum variation in speed for a slow change in load from no load to full load or vice versa shall not exceed 1^ per cent, of the speed at full or normal load, and that for sudden change in load the maximum variation shall not exceed 2 per cent." (From Harding and Willard, MECHANICAL EQUIPMENT OF BUILDINGS.) 220. Some Descriptive Terms Applied To Fly-Ball Gover- nors which should be understood are: (1) A stable or static governor is one which occupies a definite position at a definite speed. A governor is stable when the resistance to motion (centripetal force) changes faster, as the balls assume different positions, than does the centrifugal force which the balls develop. (2) An unstable or astatic governor is one in which a slight increase or decrease in speed will cause it to move to one or the other extreme position. If the restraining (or centri- petal) force changes more slowly than the centrifugal force, a governor is unstable. (3) A neutral or isochronous governor is one which, at a certain speed, assumes, indifferently, any position throughout its range. If the centrifugal force and the centripetal force change at the same rate, the governor is neutral or isochronous. NOTE. AN UNSTABLE GOVERNOR Is QUITE USELESS FOR ENGINEER- ING PURPOSES. Such a governor would always be either in full-load position or shut off entirely. Governors are frequently called "isochron- ous" (which means equal speed) when they are not truly so. A truly isochronous governor would also be useless for engineering because it would change in position as much for a slight change in load as it would for a large one. The aim in governor design should be to make the governor stable but very nearly neutral, that is, to make it as nearly isochronous as is feasible. Such a governor gives smaller speed variation than does a very stable governor. 221. The Action Of Centrifugal Force In Actuating A Governor is considered in Sees. 222 and 224. While a knowl- SEC. 222] FLY-BALL STEAM-ENGINE GOVERNORS 205 edge of these principles is of interest to the practical man, it is not probable that he will ever have to apply them in adjusting or maintaining an engine governor. However, a knowledge of these principles and their application is essential to the governor designer. 222. To Compute The Centrifugal Force Developed In A Revolving Governor Weight, use the following formula: (26) F c = 0.000,028,5Wr;]V 2 (pounds) Wherein: F c the centrifugal force, in pounds, developed by the weight. W = the weight of the governor ball, in pounds. 2Lb. Arms Of Different Lengths --T* -Pivot Yoke. Spindle-. . inks -Sleeve Neglect The Weight Of The Levers, Links, And Sleeve FIG. 266. How much tension is there in the spring? Different Weights FIG. 267. Showing constant height to which governor balls will rise at a certain speed. N = the speed of the governor, in revolutions per minute. Ti = the radius from the center of gravity of the weight to the axis of rotation (center of the spindle), in inches. EXAMPLE. Assume that the balls of the governor (Fig. 266) weigh 2 Ib. each and are 10 in. from the center of the spindle when they are revolving at 250 r.p.m. What centrifugal force will they exert on the spring under these conditions? SOLUTION. By For. (26), the centrifugal force in each ball equals the tension on the spring, or: F c = 0.000,028,5Wr,-#2 = 0.000,028,5 X 2 X 10 X (250) 2 = 35.6 Ib. 223. The Theoretical Vertical Distance Between The Center Of The Balls And The Pivot Of The Arms In A Simple Pendu- lum Governor Depends On The Angular Speed And Is Inde- pendent Of All Other Factors. Assume that three balls, BI, B 2 and 3 (Fig. 267), of different weights are suspended by arms of different lengths and caused to make the same number of revolutions per minute about a common spindle, S. The vertical height, H, will be the same for all three regardless of the 206 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 weights of the balls and lengths of the arms. The statements of this section are true only for an ideal governor mechanism which has weightless arms and which has nothing to lift when it operates. If the governor balls must, when they rise, lift a weight other than their own then they will not rise as far as they would rise if unweighted. See Sec. 225 for effects of weighting. 224. To Compute The Theoretical Height To Which The Balls Of An Ideal Simple Pendulum Governor Will Rise At A Given Speed, use the following formula: (27) L t , = (inches) Simple Pendulum Governor Loaded Governor /^ Positions The Load Weighs Times As Much As One Ball ) ;'60r.p.m. "I? 120r.p.m. 'Weight of Arms and Sleeve May be Neglected FIG. 268. How high FIG. 269. Showing theoretical positions of balls of will the balls rise? simple and of loaded governors at different speeds. (Arms are assumed to be weightless. The bails lift nothing but themselves and, if specified, a centrally attached load.) Wherein: L h i = the height, in inches, from the center of gravity of the balls to the pivot of a simple pendulum governor. N = the speed of the governor, in revolutions per minute. EXAMPLE. Compute the height from the center of gravity of the balls to the pivot of the governor balls shown in Fig. 268 when it is revolving at 60 r.p.m.; at 120 r.p.m. SOLUTION. By For. (27), the height, Lhi = 35,200/N 2 = 35,200 ^- 3,600 = 9.8 in. at 60 r.p.m. L hi = 35,200 H- 14,400 = 2.44 in. at 120 r.p.m. NOTE. THE SIMPLE PENDULUM GOVERNOR MUST RUN AT Low SPEEDS since the balls would fly out to a nearly horizontal position at high speeds SEC. 225] FLY-BALL STEAM-ENGINE GOVERNORS 207 I -Loaded Watt H- Porter .-Spm and would then change very little in position while the speed varied greatly ; that this is true is evident from the preceding example. Fig. 269 shows the theoretical angular positions of a simple-pendulum-governor arm at different speeds. The practical speed limit for simple-pendulum governors is about 125 r.p.m. while speeds of 600 r.p.m. and over are used in spring-loaded fly-ball steam engine governors. Actual governor balls do not ordinarily rise as high as indicated by Fig. 269 because of the restraining gravitational forces of the mechanisms or weights which must be lifted by the balls. 225. Nearly All Modern Fly-Ball Governors Are Weight- Or Spring-Loaded. Hence they will not rise to the theoretical heights given by For. (27.) Watt's unloaded governor (Fig. 249) was satisfactory for slow-speed engines which did not require close speed regulation, but for most mod- ern requirements, it is unsatisfac- tory. Fig. 270 shows various methods of applying a weight load, W, or counterpoise to a fly-ball governor. In all of these methods the weight is so arranged that it will slide on the spindle and revolve with the spindle and balls. The Weight, in all Cases, Opposes the FIG. 270. Various arrange- , , ,. , , , n ments used in applying a weight tendency of the balls to fly apart. ] oa d or counterpoise to a gover- These arrangements give more accu- nor ^ = weight or counterpoise, rate regulation than can be obtained with an unloaded governor because, with them, a small change in engine speed can be made to cause a large change in gov- ernor position (Fig. 269). 226. The Advantages Of The Spring- Or Weight-Loaded Governor Over The Simple Pendulum Governor may be enumerated as follows: (1) It increases the range of speed between maximum and minimum governor positions (2) It affords closer regulation by increasing the vertical move- ment (Fig. 269) for a given change in speed. (3) It decreases the sluggishness of the governor by making it possible to employ light-weight balls. (4) It increases the sensitiveness of the governor by furnishing an effective means of offsetting frictional resistances. The governor is made more powerful 208 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 and, thus, more easily overcomes frictional resistances in its own mechanism. 227. The Following Formula Expresses The Relation, For A Porter Governor, Between Speed, Height, And Weights Of Balls And Counterpoise. This formula assumes that the four arms of the governor are of equal length. w + Wi w 35,200 (28) L hi = ^ X ~~- (inches) Wherein: Lhi = the height (Lhi, Fig. 271) from the center of, the balls to the intersection of the arm and spindle axes, in inches. W = the weight of one of the two balls, in pounds. Wi = the weight of the central load or counterpoise, in pounds. N = the speed of the governor, in revolutions per minute. EXAMPLE. What does the counterpoise of a Porter governor (Fig. 271) weigh if the balls weigh 8.3 Ib. each and the height is 13 in. at 325 r.p.m. ? SOLUTION. Substituting in For. (28), there results: 13 = [(8.3 + Wi) *- 8.3] X 35,200 -* (325) 2 , from which Wi + 8.3 = 323.7 or W l = 315 Ib. NOTE. THE RELATIONS OF FORCES, WEIGHTS AND SPEEDS IN FLY-BALL GOVERNORS are indi- cated in the following items. The matters of rates of increase and decrease of centrifugal and centripetal forces in governors of various types in various positions will not be discussed in detail Porter ^J in this book since they involve higher mathe- Governor TT . . ,, matics and are of interest principally to governor 325 a r.p.m. designers. Also the methods of analyzing the FIG. 271. How much forces in a governor (as used in the above ex- does the central load or ample) will not be explained for somewhat the counterpoise weigh/ same reason. (1) The lifting forces exerted by governor balls in a loaded governor are usually many times greater than the weights of the balls. (2) The centrifugal force of the balls is proportional to the weight of the balls, to the distance of the balls from the spindle and to the square of the speed; see For. (26). (3) The faster a given set of governor balls revolves, the greater must be the load applied to balance them. (4) The greater the load for a given set of balls, the more powerful (Sec. 219) the governor, provided it goes fast enough to lift the load. (5) Other things being equal, a high-speed heavily-loaded governor is more prompt and more sensitive than a low-speed one. SEC. 228] FLY-BALL STEAM ENGINE GOVERNORS 209 (6) All weight-loaded gover- nors of the types shown in Fig. 270 are stable except the cross- arm type which may be so de- signed as to be unstable or astatic. Extra attachments may be added to any gov- ernor so as to lessen or increase its stability. (7) Governors of the types shown in Fig. 270 become less powerful and sensitive as their arms approach nearly-horizontal positions. (8) The smaller the speed regu- lation, the less powerful will be a given set of governor weights or balls revolving at a given speed. 228. Spring-Loaded Gov- ernors May Secure Close Regulation And Are, In General, More Prompt Than Weight-Loaded Gov- ernors. The inertia of a spring is negligible and so only the inertia of the weights and arms need be Main Compression Spring Knife 'Edge Driving Gear Bearing Spindle- FIG. 272. Spring arrangement used in the Gardner throttling governor. 14 FIG. 273. General arrangement of No. 7 open Tolle governor. (Vilter Mfg. Co., Milwaukee, Wis.) 210 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 overcome when a spring-loaded governor changes position. With a given governor design, a stiffcr spring slightly com- pressed gives a more stable and prompt (but less sensitive) governor than does a weaker (more flexible) spring more heavily compressed. A spring-loaded governor is usually stable because the resistance of a spring rapidly increases as the force on it is increased. Figs. 257, 265, 272, and 273 show various arrangements by which spring loads may be applied to fly-ball governors. 229. A Governor Which Has Small Speed Regulation Must Be Provided With Some Means Of Preventing "Hunt- c , f '- ^ h^ \ J * ^ :.:' D y -Li '//* /r C//C n II ^ \ 1 O i D A TT Much Mechanical Friction~ TTT ->< B 3 i 2 / A t 111 Proper Fluid //"/c tion FIG. 05 10 15 20 25 30 35 40 45 Time In Seconds 274. Showing characteristic "Hunting" graphs of governors. 'P/vof Support FIG. 275. Non-adjustable governor dash-pot filled with oil. ing." A governor hunts when, in changing from one load to another, it has a tendency to go too far due to the momen- tum of its parts. EXPLANATION. Fig. 274-7 shows the "hunting" of a very free-moving governor when the load changes suddenly. Assume that the governor was steady in position A A' for a certain load and that the load changes so that the governor should, for equilibrium, assume some new position B'B. The governor responds but the momentum of its parts carries it past the proper position to C and then back to D. This action may SEC. 230] FLY-BALL STEAM-ENGINE GOVERNORS 211 Piston cause the engine to pull unevenly and the "hunting" may then be further increased. Graph // shows the effect of much mechanical friction on the governor action. The governor then hunts very violently and in "jerks " but the action may be very uncertain and cause much variation in engine speed. Graph III shows the effect of fluid friction introduced by means of a properly adjusted dash-pot (Figs. 275 and 276). The governor tends to follow graph / (Fig. 274) but the fluid friction in the dash-pot prevents its so doing. The governor soon comes to rest at E. Fluid friction prevents rapid movement but offers practically no resistance to very slow motion. This friction therefore prevents "hunting" and sudden move- ments but does not materially decrease the accuracy of the the governor. 230. A Dash-Pot Or Gagpot (Figs. 275 and 276) is usually used to limit the rate at which a cut-off governor may move. The valve of a throttling governor has a stabilizing (or damp- ing) effect so that a dash-pot is not ordinarily necessary with governors of the throttling type. The dash-pot consists (Fig. 276) of a cylinder C filled with oil; a piston P, and rod R and means such as pipe B for allowing oil to flow around the piston at the proper rate. Simple non-adjustable dash-pots (Fig. 275) have holes for allowing oil to pass through the piston. Movable plates are sometimes placed over these holes and controlled by a nut on the piston rod. A pet-cock is usually provided for draining and a hole for filling. If the dash-pot piston rod is directly connected to a lever, as in Fig. 250, the dash-pot cylinder should be so mounted on a pivot such as L (Fig. 276) that it will always line up with the lever pivot as the lever swings. If the rod is connected through a spring (Fig. 277), or if the piston is designed as shown in Fig. 288, the cylinder may be rigidly mounted. NOTE. THE SIZE OF DASH-POT REQUIRED FOR A GOVERNOR varies with the load conditions. Ten square inches per 100 engine horse power is ordinarily ample where the dash-pot stroke is about equal to its bore. Common machine oil is usually used in dash pots. It may be ''Mounting Lug FIG. 276. Dash-pot ad- justable by valve, V, on outside. 212 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 thinned with kerosine if too thick. Cylinder oil or glycerine may be used if a thicker liquid is required. Spring Dash-Pof Connection Motor- Contra/ fed Counterpoise-, P _ -Rocker-Arm and Rods for ' Osc/J 'Idling Knock-Off Cams FIG. 277. Nordberg governor showing spring-connected dash-pot rod. (If the safety idler, I, drops due to failure of the belt, the weights, W, will be released and the pivot, C, will be dropped. This will operate the rods, R, S and T, so as to stop the engine. When the engine is driving an a.c. generator, the motor, M, is, when synchronizing the generator with another generator, so controlled by the operator at the electrical switch- board that the weight, P, is shifted to such a position that the engine speed is changed to the proper one to permit synchronizing. After the machines have been synchronized, the load may be properly divided between the two engines by the operation of M. 231. Governors May Be Adjusted To Change Engine Speed In Several Ways. (1) Weight may be added or removed. Provision is often made for adding or removing weight (Figs. 277, 278 and 279). A weight may sometimes be adjusted in or out on a lever arm (W, Fig. 280). Increasing SEC. 231] FLY-BALL STEAM-ENGINE GOVERNORS 213 Shot For Varying Weigh t Of Loact-- HoIeFor Putting In Shot Hole For Removing Shot-. the leverage or the weight, where the weight opposes the rise of the governor, increases the engine and governor speed and vice versa. To compute even approximately the amount of weight which should be added or deducted in any given case usually involves complicated calculations and a knowledge of the weights of each of the moving parts of the governor; see note under Sec. 227. Hence, in practice, the most direct method of finding the necessary amount of weight is by trial. (2) Increasing or decreasing spring tension or adding an extra spring changes the engine speed. Most spring-loaded governors (Figs. 254, 265 and 273) have adjust- ments for this purpose. When they do not, an extra spring (Fig. 281) may be added. Increasing the spring tension increases en- gine speed. (3) A take-up adjust- ment may be provided in the governor mechanism (Figs. 282 and 283). Increasing the effec- tive length of the linkage in such adjustments ordinarily decreases the engine speed. In increasing the engine speed by this method when a Corliss governor is used, make sure that the governor will shut off completely after the adjustment is made. The collar on the governor spindle may have to be raised to permit this. It is dangerous to make the cut-off later for a given governor position without testing afterward to make sure the governor will shut off. (4) Increasing the weight of the balls of a loaded governor decreases the engine speed. (5) The pulley or gear sizes may be changed to drive the governor at a different speed relative to the engine speed. That is, the governor continues to rotate at its original speed but the engine speed is either increased or decreased. Starting Lever-' FIG. 278. Governor which may be adjusted for different speeds by adding or removing weight (shot). (Murray Iron Works Co., Burlington, Iowa.) 214 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. G Counterpoise Weight May Be Increased With Shot--. Removable Weight For Speed Adjustment FIG. 279. General arrangement of high-speed loaded Watt governor No. 2. (Viller Mfg. Co., Milwaukee, Wis.) SEC. 231] FLY-BALL STEAM-ENGINE GOVERNORS 215 If the governor driving pulley on the engine shaft is increased in size, the engine speed will be proportionally decreased. If Sleeve. Increases Speed in This Posit/on* E-Side View FIG. 280. Showing weight which may be adjusted on lever to change the engine speed which is maintained by the governor. 'V//////////////////////// FIG. 281. Extra spring added to vary the governed speed of an engine. FIG. 282. Showing speed adjustment provided in governor linkage. the driven pulley or gear is increased in size, the speed of the engine will be proportionally increased and vice versa. 216 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 Operaf/na Spindle-- Does Not Revolve Guide 'Spind/e 'Stationary) NOTE. THE SENSITIVENESS OF A GOVERNOR Is OFTEN CHANGED ALSO WHEN THE SPEED Is CHANGED. Increasing the weight or spring tension has a tendency to make the governor more sensitive. Many . paper-mill engine governors are provided with double cone pulley drives so that the engine speed may be increased to 4 or 5 times the minimum speed by shifting the drive on the cones. Engines equipped with such gov- ernors are called variable speed engines. NOTE. THE SPEED AT WHICH ENGINE GOVERNORS SHOULD OP- ERATE Is SOMETIMES STAMPED ON THE GOVERNORS by the manufac- turer of the engine. If it is not so stamped the correct operating speed should be ascertained from the manufacturer or by test be- fore one attempts to change the engine speed. EXAMPLE . An engine (Fig. 284-7) which has a governor- driving pulley, P, 9 in. in diameter and a driven pulley, D, 12 in. in diameter is operating satisfactorily at 75 r.p.m. What change should be made in the governor drive so that the engine will operate at 65 r.p.m.? SOLUTION. For satisfactory op- eration, the governor should oper- ate at the same speed the same r.p.m. of the governor and its pulley as before. With the en- gine speed decreased, the same governor speed may be maintained by changing either pulley P or pulley D; or by changing both pulleys P and D, and using new ones of properly selected diam- eters. If pulley P is changed, its new diameter should be 9 X 75 -5- 65 = 10.3 in. If pulley D is changed, the diameter for a 65-r.p.m. engine speed should be 12 X 65 * 75 = 10.4 in. as shown in Fig. 284-77. With the decrease in engine speed, there will have to be a very slight FIG. 283. Vertical section of Pickering gov ernor showing methods of adjustment. SEC. 231] FLY-BALL STEAM-ENGINE GOVERNORS 217 decrease in the valve opening to maintain the lower speed, but this change in valve opening may, usually, be effected by an adjustment in the Link~\ Counterpoise Governor- . .Governor Driving p / Pulley; 9"Diam. ,- Engine Shaft /TT/////////////////////////////////////////////////'//////^////////'///// I-Old Drive (Engine Speed 75 r.p.m.) *~~Adjustable .Weight D/'am. 10.4 D/am.~.J Q fl-New Drive (Engine Speed 65r.p.m.) FIG. 284. Example changing governor-drive pulleys for a new engine-speed. governor linkage. With the engine speed increased, the procedure would be the reverse of that just described. JJ Teeth^ Governor 75 Teeth.. 36 Teeth. JO* ) ^wv^" Shaft- I-New Gearing .-Bevel ' 5/7,v/- ^ u '' (Je^rj .Governor- Drive Gears'^/* Shaff 72 Teeth -^f: n-Old Gearing Miter Gears-- FIG. 285. Example changing either spur- or bevel-gear sizes for new engine-speed. EXAMPLE. If the governor in the preceding example had been gear driven (Fig. 285), the change in speed might have been made by changing 218 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 either the bevel gears, E and F, or the straight spur gears, A and B. In either case, assuming that the distance between the meshing gear centers must remain fixed, the two gears which mesh must both be changed. Assume that the gears, A and B, are 4 diametral pitch (that is, 4 teeth per inch of diameter) and have 36 and 72 teeth respectively. The pitch diameter of A is then 9 in. and that of B 18 in. The distance between centers must remain the same since the crank shaft and pinion shaft are both fixed. This distance is, in this case, (9 -5- 2) + (18 -f- 2) = 13.5 in. But for the change in speed required, the ratio must be changed in the proportion of 75 to 65 or it must now be 2 X 75 -5- 65 = 2.301. If the same pitch is to be used, the total number of teeth in both gears must remain the same (108 teeth). The requirements for the new gears are then expressed by the equations: M -ft- = 2.301 and M + N = 108 Where M is the number of teeth in the new pulley, B', and N is the number of teeth in the new pulley A' '. Solving, by the simultaneous equation method, M = 75.3 and N = 32.7. Taking the nearest whole number of teeth which will give the required pitch diameters, there results : 33 and 75 for the required number of teeth. If the change is to be made in the bevel gears, a new pair must be designed or selected which will provide the desired ratio and Jhe proper shaft alignments. EXAMPLE. Certain of the other means described in the above section for changing the speed of the engine of Fig. 284 are: (1) // the counter- poise, C, is made lighter it will decrease the speed of both the engine and governor; if it is made heavier, it will increase the speed of both engine and governor. (2) Changing the weight W has the same effect as changing C because the rod which supports W is connected to the spindle which carries C. Changing the weight, W, provides a convenient method of temporarily changing the speed of the engine. Thus, if a machine is being started which requires considerable power and which would normally slow down the overloaded engine, a weight of sufficient amount may be added to W to maintain, for the time being, the engine speed constant. Then, when the load of the machine is discontinued, the extra weight may be removed from W. This, as compared with the modern speed regulating devices is a crude expedient; but in emergencies it may prove serviceable. (3) // the weight, D, is shifted backward or forward on its lever, it will change slightly the speed of the engine. (4) Some governors have at L a link of adjustable length whereby the engine speed may be changed; see "Caution" below. (5) The effective length of the cam rod, R, may be increased or decreased to change the engine speed. Caution: But neither this plan nor the one just preceding it should, ordinarily, be adopted. Changes in L may affect the sensitiveness of the governor mechanism. Careless adjustment of either L or R may prevent the realization of a very short cut-off and thereby cause trouble racing if all of the engine's load is suddenly thrown off. SEC. 232] FLY-BALL STEAM-ENGINE GOVERNORS 219 232. Governors May Be Adjusted For Greater Or Less Speed Regulation but such adjustments should, whenever possible, be referred to the manufacturer. The inexperienced engineer is cautioned against making radical adjustments of this sort. (1) Weight-loaded governors will give closer regulation if their speed is increased and enough dead weight added to bring the engine speed back to its original value. Conversely, if the speed is decreased and the dead weight lessened, there will be more variation in speed. (2) If a weaker spring is substituted in a spring-loaded governor and this 'I H-rH ..-Hanctwheet Various Holes for Connecting Governor Drop Rod FIG. 286. Showing adjustable governor levers. (Lever, J, is adjusted by changing the rod pivot from one hole to another. Lever // is adjusted by means of a hand wheel, H, and lead screw, L.) spring is compressed more so as to exert the same force, the regulation will be closer because a lesser change in pressure in the spring will then be required to produce the same amount of movement. (3) The radius of a governor lever (Fig. 286) may be so adjusted that the same valve movement is accom- plished with less governor movement. NOTE. AFTER MAKING ANY OF THE ABOVE ADJUSTMENTS FOR CLOSER SPEED REGULATION, there may be trouble with the governor hunting and the dash-pot resistance may have to be increased and per- haps a spring inserted in the dash-pot rod (Fig. 277) mechanism. 233. Some Governors May Be Adjusted For Greater Or Less Promptness, but these adjustments should ordinarily 220 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 6 be left to the governor designer and manufacturer. (1) Inertia effect may be introduced to secure quicker response but such a change ordinarily requires complete re-design of the governor. (2) Spring load may sometimes be substituted for part of the weight load in a weight-loaded governor. The spring is lighter and may change position more quickly than a weight. (3) A spring may sometimes, if not already used, be inserted in the dash-pot rod (Fig. 277). This spring allows the governor to assume its new position at once and Piston Rod Sleeve Support For , - Drop Rod End From Governor Of Chain U-Governor Co/umn 4- Valve Control Rods FIG. 287. Chain recommended as substi- tute for the dash-pot for greater promptness. (C. E. Bascom in Power, June 29, 1915.) "Piston Curved To Prevent B/nd/ng FIG. 288. Spring inserted in dash-pot to retard the governor movement near the no-load po- sition. Caution: If this device is used, the engine must be watched to insure that it will not race at light loads. the dash-pot adjusts itself later. (4) A hanging chain (Fig. 287) has been recommended as a substitute for a dash-pot where greater promptness is desired. (5) A lighter oil or larger opening in the dash-pot gives greater promptness. A heavier oil or smaller opening in the dash-pot gives slower action less promptness. (6) A spring may be inserted in the dash-pot, as shown in Fig. 288, if the engine is too prompt near no load. SEC. 234] FLY-BALL STEAM-ENGINE GOVERNORS 221 ifc OP 3 p o> o IT o ts o g s >, 'i' s g ,te ft I'fl * 5"3 0~ ,M ^3 tn ^ 9 5 ft pj c -2 o .. s-i'5b ^^ +a fel S3S 0) "** P 1 c ^ >J" J3 yi II cc'" O M * J O ft s^ 1 C ^^ o 2 S3 o , S3 >IS3a 1 0-2 S3 "to o '-S 3 S *-2 M '| -i ^.S^ ^ M M -S S III. h" Jill 1 G J!ii c o'Sb c C 'So a H llll W3 Js ft .2*2 1 s ^S|E o 1 OJ T3 T5 s S^j ^ S S ^ a;2 o_> o^ 'Bo 0_> S"3 0) TO ^^ > 83^ 0> I Ol r3 11 II iall'S 11 li IH " o* o a C 3t o O ft 0) ol2l "i^^ s O > /T* 1*11.3 Load and sp o'C o> Governor m sensitive, i gine spe may be 1 same Governor m likely to hu Govern driven slo\ and less hei ily loaded Governor 1 sensitive, i gine spe may be 1 same Governor m stable n S-g 03 3 ^g g 3 ' Change weigl for spring Substitul weight load : all or part spring load Governor mo sluggish 3l llsl Governor mo prompt "3 II S" S3 ll S3 -^ o> G S3 ill 'gJ2 ^o "oo fe O'S'g "** o o 'S "^"M ^ S 0) M ^8 |g i ^l| c ^ ft t- QQ O ll G 'Sb G H ^1 1 Q a 'Sb a H 51S1 |lfl M a 1 1J| 01 d fll 1sl oo 1 a S IL 83 C o-"S o o~^ g o3^3 o S * o ^ 1 |^ G 3.2 S S3 -a M *** S "'& - ^ ;^ J* -> o-S 1 83 3^ Jg hoGt^ oo |ll! "'a P*- 2 ^> ^ M |goft-i fllli i i^S| s i.S | g i fc'* il q^ 1) fs^S i| S (U >> S rS ^ C; C8 3 OH 3 ill Jl bill Q.S ft S c'S i 1 j 5 S- .-' ' C M 8C c3 ^ P s For example, shaft governors may be stable, unstable, may allow racing, may hunt, may require dash-pots or may give too much speed regulation for very much the same reasons as were explained under fly-ball governors. Shaft governors, however, do not permit of as many adjustments as do fly-ball governors. Shaft governors cannot ordinarily be adjusted while in motion. The two principal methods of adjustment, as will be explained, are varying the weights and varying the spring tension (Sec. 255). NOTE. THE FORCES REQUIRED FOR SHAFT GOVERNING are ordinarily much greater than those required for governing by the methods explained in Div. 6. In shaft governing, the eccentric must be held by the governor in a certain position for each load it must be held there with sufficient firmness that the valve-gear friction will not displace it. This necessi- tates the exertion of a relatively considerable force. Also, the forces which the governor must exert depend on the valve gear and its reaction to the governor and eccentric motion. It is therefore impossible to exactly analyze the forces in a shaft governor by considering only the governor itself. They must be considered in connection with the valve gear which the governor operates. A shaft governor must be specially designed as a part of the engine on which it is to operate. 244. Shaft Governors Employ For Their Operation Forces Of Two Kinds: (1) Centrifugal force, Sec. 213. (2) Inertia, Sec. 213. In this respect they differ from fly-ball governors 230 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 Flu- Whee! which employ centrifugal force only. How these forces are utilized in shaft-governor operation is explained in the succeed- ing sections. 245. Centrifugal Force Effects The Permanent Control In Shaft Governors. Fig. 293 illustrates an imaginary shaft governor which employs only centrifugal force for its operation. In all shaft governors there is a weight (W, Fig. 293) supported by an arm or arranged to slide in guides, G, which are connected to a revolving flywheel, F, so that the centrifugal force tends to throw the weight away from the center, C, of the wheel. A spring, S, is employed to count- eract the effect of centrifugal force and is so arranged as to restore the weights to normal position when the engine comes to rest. In the governor shown in Fig. 293 the centrifugal force tends to throw W outward and toward the circumference of the wheel, whereas the spring tends to draw W inward. The spring thus counteracts the centrifugal force, holding the governor in such position as to maintain an almost uniform speed. When W is forced in toward the center it increases the eccen- tricity of the crank pin (Sec. 148) and when it is forced away from the center it decreases the eccentricity. NOTE. By properly proportioning and arranging the weights and the spring, it is possible to make a shaft governor of this centrifugal class so that its parts will move directly proportionally to any change in speed of the engine. But for reasons given in Sec. 248 the force of inertia is also employed in all modern commercial shaft governors. NOTE. No GOVERNOR EMPLOYING CENTRIFUGAL FORCE As A REGU- LATING MEANS CAN OPERATE WITHOUT SOME CHANGE IN THE ENGINE SPEED As THE LOAD ON THE ENGINE CHANGES. In Div. 6, it was stated that no change in governor position occurred until a change in speed had taken place. This statement is equally true of shaft governors in spite of certain manufacturers' claims to the contrary. However, FIG. 293. Showing imaginary shaft governor which operates by centrifugal force only. (This imaginary construe- rpvolvinff tion is never used in actual governors.) SEC. 246] SHAFT STEAM-ENGINE GOVERNORS 231 Direction Of ' Revo/ uf ion with shaft governors the difference between the no-load and full-load speeds may be less than one revolution in 300 speed regulation of ^ of 1 per cent. Such a small speed variation would be difficult to detect with a revolution counter. If an engine is operating at no load and the load is suddenly thrown on, the engine may, due to the inertia effect (see Sec. 213) of the governor, attain, in accelerating, a speed greater than the no-load speed before the governor reaches equilibrium. But this extra speed is only temporary. For normal operation, the engine must run a little slower at full load than at no load. 246. Inertia Forces Effect Temporary Control In A Shaft Governor. The principle of inertia is employed in shaft governors for preventing sudden changes in speed in somewhat the same way as it is employed in fly- wheels. The inertia governor may thus be considered a sort of auxiliary flywheel which acts through the valves of the engine instead of acting directly on the crank shaft. The principle of inertia is one of Sir Isaac Newton's laws of mo- tion. It may be stated as ap- plied to revolving; governor parts FIG. 294. Imaginary shaft gover- thUS : A body at rest tends tO nor which would be affected by in- remain at rest; and when revolv- ertia only - (This Construction is never used.) ing, tends to continue revolving at a uniform speed. Fig. 294 shows an imaginary shaft governor which would operate by inertia only. The weighted bar, WW, is pivoted at its center of gravity, G. Since the bar is so pivoted, it has no tendency to revolve on its pivot due to centrifugal force. It is held loosely in place by springs and kept from extreme rotation by the stops, BB. Now, if the flywheel, F, is suddenly started in the direction indicated, the weighted bar will, due to its inertia, tend to "hang back." It will rotate, relative to the flywheel, so that the valve-operating crank pin, P, will be brought nearer the center of the shaft, C, which is equivalent to decreasing the eccentricity, Sec. 148. This movement will decrease the valve travel and the speed of the engine will thus be checked. A governor of this sort would prevent sudden changes in engine 232 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 Direction Of ( F/ywhee/ Rotation speed but it would allow any amount of gradual engine-speed change. Consequently, for a shaft governor which is to maintain some definite engine speed, centrifugal force (Sec. 213) must also be employed. 247. A Shaft Governor Secures Prompt Action And Close Regulation By Combining Centrifugal Force And Inertia. The elementary governor bar, IW, of Fig. 295 is so arranged that its mass is affected by both centrifugal force and inertia. The governor bar is pivoted at M (not at its center of gravity) and carries a large " centrifu- gal" weight, W, and a smaller ' ' inertia ' ; weight, I . The whole bar, however, is acted upon by both centrifugal force and in- ertia. It is prevented from rotating excessively by the stops, B. The center of gravity of the bar is at G. The bar carries also the valve-operating crank pin, P, which operates the valves of the engine through the valve rod and valve stem. Assume that the flywheel is being started in the direction of arrow R. As the flywheel speed increases, the center of gravity tends to move outward as indicated by the arrow T, but is restrained by the spring. If the speed of the flywheel increases suddenly, the weights, due to their inertia, tend to rotate in the direction indicated at S, against the spring tension. This movement will bring the pin, P, closer to the center, C, and the travel of the valve will thus be reduced. With a reduced valve-travel, the engine will be unable to further increase its speed. After the speed becomes uniform at its higher value, the weights will exert no inertia effect. Inertia will, therefore, no longer keep the governor in its new position but an increased centrifugal force will then have been developed (Sec. 213) due to the increased speed. This force will maintain the governor bar in the new position. If the speed slackens, the above-described processes FIG. 295. Diagram of governor of the "Rites" type. (This arrangement is the most widely used of any shaft governor arrangement but the dis- tances shown above are exaggerated.) SEC. 248] SHAFT STEAM-ENGINE GOVERNORS 233 will be reversed, the spring operating, after the speed is uniform and inertia is no longer effective, to retain the bar in its low-speed position. The hunting of a shaft governor which actually occurs before it attains its final condition of equilib- rium for the given load is similar to that described for fly- ball governors in Sec. 229. It is not therefore treated in this explanation. 248. Why Shaft Governors Employ Both Centrifugal Force And Inertia in order to secure prompt action may be explained as follows: A shaft governor, due to the considerable force which it must exert to keep the eccentric in position against the friction of the valve and valve gear, must be relatively heavy that is, it must be many times heavier for a given service than a fly-ball governor. As explained in Div. 6, a governor which is very heavy is correspondingly slow or sluggish if only centrifugal force is used. Hence, it is obvious that, with heavy weight arms, to insure the prompt action which is essential for close speed regulation, a shaft governor must employ some force other than centrifugal force. Hence nearly all shaft governors are so designed that the inertia of the weights will assist the governor in changing position. By thus employing inertia, a shaft governor obtains more prompt action than is ordinarily possible with a fly-ball governor. The speed regulation of a good shaft governor is within less than 1 per cent, regardless of whether the change in load is made slowly or suddenly. Furthermore the governing action is so prompt that a well-designed shaft governor will attain its new position for a changed load within 1 or 2 revolutions, which may represent but a fraction of a second. 249. How A Shaft Governor Controls The Speed Of An Engine may be understood by referring to Figs. 296, 297 and 298. The governor shown is arranged to vary the valve travel without changing the angular advance of the eccentric materially. EXPLANATION. The governor is shown in Fig. 296 in full-load position. The valve-operating crank-pin, P, which is carried on the governor bar, travels in a large circle, E, giving a maximum valve travel. The engine steam port, A, has therefore a large opening at quarter stroke and cut-off occurs late. If the load is suddenly thrown off the engine, the 234 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 governor will assume the new position shown in Fig. 297, explained in Sec. 247, and the crank pin then travels in a smaller circle, E' (Fig. 297). The travel of the crank pin is now but little more than sufficient to . - Direction Of Ro tat ion Governor Arm. j Equal . Arms. FIG. 296. Method of governing with shaft governor and slide valve. (Takes steam for nearly full stroke.) ,' Direct ion Of Rotation Governor -' -Steam m Supply FIG. 297. Method of governing with shaft governor and slide valve. (Cut-off at about one-fourth stroke.) .-Direct/on Of Rotation Governor Rocker ^Arm : ''Arm ?uaf rmsj Steam FIG. 298. Method of governing with shaft governor and slide valve. (Steam cut off entirely.) uncover the admission port at A', and cut-off occurs a little past quarter stroke. Less steam will now be admitted to the engine and the engine speed will be prevented from further increasing. With the arrangement SEC. 250] SHAFT STEAM-ENGINE GOVERNORS 235 shown, compression occurs earlier in Fig. 297 than in Fig. 296. This also helps to cause the engine to develop less power if the governor position is changed as described above. The extreme position of the governor is shown in Fig. 298, where the throw of the eccentric is less than the steam lap of the valve so that the steam is shut off from the cylinder entirely. NOTE. The engine shown in Figs. 296 to 298 runs "under." If the governor arm and spring were reversed in position (turned over from left to right) the engine would run "over." 250. Reversing An Automatic Engine should be avoided whenever possible. The engine has probably been nicely adjusted before it left the factory and it is usually difficult for the inexperienced person to re-adjust the wheel correctly. NOTE. To REVERSE A TROY AUTOMATIC ENGINE, do not disturb the valve nor remove the flywheel from the engine shaft. Remove the governor arm (Fig. 299) and reverse it on the pin turn out the side which was against the wheel. Then re-key it to the pin using the other an- gle key- way which is provided in the pin. The stops, drag spring and coil spring must be carefully reversed in position, restoring the original conditions as nearly as possible. Be sure that the stops do not prevent the governor from shutting off but do prevent it from straining any of the mechanism. Be sure that the friction of the drag spring or other parts has not been made excessive by the change. The wheel must then be re-balanced as explained in the note of the following section. 251. The Balance Of A Shaft Governor And Its Flywheel are important features of design. If the moving parts of a governor have no tendency to rotate about their pivots, due to gravity, when the governor is at rest, the governor itself is said to be in balance. If a governor is not in balance, it will, when the engine is running slowly, tend to deflect first one way and then another. A governor flywheel is in balance if its center of gravity lies in the axis about which it revolves. If the flywheel is not balanced it will, when the engine is running, produce a centrifugal force acting at its center of gravity. This centrifugal force will produce undue pressures in the main bearings and excessive bending stresses in the crank shaft. The balance of a governor flywheel may or may not, depending on its construction, be destroyed as the weights assume different positions at various engine speeds. A governor flywheel is in continual balance when, as the weights 236 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 I- Enlarged tnd View Of Shaft ^Orease Spot \5haft Center -Scribed Circle Off Center deflect with centrifugal force, its balance is not destroyed. If a governor flywheel is not in continual balance, it will, theoretically, be out of balance at some governor position. But the flywheel may be balanced for a certain position of its weights by bolting weights, W (Fig. 299), at the proper points to the flywheel rim. It is possible for a governor itself to be in balance without the flywheel being balanced for any or all positions of the weights. Ex- amples of various degrees of gov- ernor and flywheel balance are given in the following section. NOTE. IF THE FLYWHEEL HAS BECOME UNBALANCED due to revers- ing the engine or other alterations, the balance may be restored as follows : First find the direction of the un- balanced force. To do this, smear grease or chalk or some other material on the end of the shaft near the center, as shown in /, Fig. 299, so that a scribed line will show on it. Arrange a block, box or chair so as to support or steady a scriber near the shaft center and, while the engine is running, scribe a small circle on the end of the shaft. If the center of the scribed circle is not in the center of the shaft, the flywheel is out of balance. Weight must then be added to the flywheel rim at a point located by drawing a line from the shaft center through the center of the scribed circle and extending this line to the rim. The amount of the balancing weight which is required may be found by first sticking a lump of putty or clay to the rim and making another scribed circle. When the right amount of clay to insure balance is found in this way, select a piece of metal of the same weight as the clay. Bolt the metal to the flywheel rim with a counter- sunk machine bolt. 252. Shaft Governors May Be Classified With Respect To The Arrangement of Weights Employed as follows: (1) Balanced governors with two weights and their flywheels in continual balance, as shown in Figs. 300 and 301. (2) Balanced Governors with a single weight and their flywheels not in continual balance (Fig. 302) . (3) Governors with a single arm which carries H-Weights For Restoring Balance To Flywheel Fia. 299. Illustrating a method of balancing a flywheel. (Governor wheel of a Troy automatic engine.) SEC. 252] SHAFT STEAM-ENGINE GOVERNORS 237 Direct ion Of Rotation --, inertia weight, centrifugal weight and eccentric (Fig. 303); the governor and its wheel being nearly balanced in all posi- tions. The action of governors of this type was explained in Sec. 247. (4) Governors having two arms or an arm and a weight, the governor and its wheel being nearly balanced in all positions (Figs. 291 and 304). Gov- ernors of all of the above classes can be so operated that the regulation is either assisted or retarded by in- ertia and can be connected to a rotating or a swinging eccentric as desired. In mOSt Of the governors here FIQ. SOO. Shaft governor which employs described, the inertia aSSistS two weights. (Governor balanced and fly- . wheel in continual balance.) the regulation. See Table 254 for manufacturers of engines which employ governors of the various kinds. Spring "Tension Adjustment Weight Direction of Rotation^ Leaf EXAMPLES. Figs. 300 and 301 show governors of Class 1 having two weights, W, in balance. The eccentric (Fig. 300) is mounted on a plate, G, pivoted at P and is connected to weight levers, WE, by connecting rods in such a manner that the action of centrifugal force, in throwing the weights WW outward, causes the center, R, of the eccentric to swing toward the center, 0, of the shaft. The springs pivoted at K act against the centrifugal force and hold the weights in a certain position for each speed. The dash-pot simply restrains the motion when too rapid and tends to prevent racing and hunting. Fig. 302 is an illustration of a shaft governor the flywheel of which is not in continual balance (Class 2) . Although this governor has but a single weight, B, its parts are nevertheless balanced. Its ad- vantages over governors of Class 1 are a lesser number of working parts, simpler construction and less friction. An example of a governor of this class the Robb- Armstrong-Sweet gover- nor (Fig. 309) (see Table 254). Flywheel'' FIG. 301. "Hard- wick" shaft governor as used on the Erie engine. 238 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 Fig. 303 shows a governor of Class 3 which has a nearly balanced single arm. This governor is of the Rites type, which is extensively used in the United States, and is designed to take full advantage of inertia. ^Direct/on Of tat/on FIG. 302. Shaft governor employing a single weight, B, balanced by the eccentric, P. (The flywheel balance depends on the position of B.) D/rec-f/'onOf..-- Rotation - ' Stop-' Drag Spring FIG. 303. Rites governor. (This governor is not in balance nor is its wheel but the flywheel may be balanced with extra weights on the rim; and the governor may, by friction, be prevented from knocking at low speeds so that satisfactory results may never- theless be obtained.) Fig. 291 is an example of a governor of Class 4. The advantage claimed for it by the manufacturers is close regulation without the use of a dash-pot to prevent hunting. SEC. 253] SHAFT STEAM-ENGINE GOVERNORS 239 NOTE. Some parts of the following text is based on material from SHAFT GOVERNORS by Hubert E. Collins; other parts are based on data from instruction books of the various engine manufacturers. 253. The Two Methods Whereby The Engine Valves May Be Controlled By A Shaft Governor Through The Eccentric Or The Valve-Operating Crank Phi, either of which may be employed in any given governor, are as follows: (1) The eccentric is rotated or twisted around the shaft. Thereby the Centrifugal Adjustable We/gthf^ Aafj'usfab/e Spring Tens/on^ /nerfia Weights '' FIG. 304. Chuse Engine Mfg. Co., governor. (This governor is used on non-releasing Corliss-valve engines to control the position of the eccentric which operates the admission valves only. The exhaust- valve-operating eccentric remains fixed in position.) angular advance is changed without change of eccentricity or throw. (2) The eccentric is mounted on a disc or plate which is swung by the governor action across the center of the shaft. Thereby the throw and angular advance of the eccen- tric are both changed, the object in the design being to have the lead of the valve change but slightly with different governor positions. With either of the above classes of valve gear, the governor may employ any of the weight arrangements specified in Sec. 252. It follows that the weight arrangement of a governor does not determine its method of valve control. NOTE. A SHAFT GOVERNOR OF ANY TYPE MAY USE A CRANK PIN IN PLACE OF AN ECCENTRIC. When the governor is at the end of the shaft, a crank pin is usually used. When the shaft continues on through the 240 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 governor, an eccentric, which is properly slotted to permit movement to or from the shaft center is ordinarily employed. EXPLANATION. The Buckeye governor of Fig. 316 is an example of Class 1. The eccentric, C, has two ears which are connected by links to the ends of the levers, M. As the weights, A, are thrown out by centrifugal force, the eccentric is rotated in the direction indicated. Its angular advance is thus increased. The Fitchburg governor of Fig. 320 is an example of Class 2; the eccentric, A, is so arranged that its throw and angular advance are both varied, see Sees. 148 and 151, giving a practically constant valve lead. 254. Table Showing Classification Of Shaft Governors. Manufacturer Governor name Fig. No. Class by weight arrange- ment, Sec. 252 Class by eccentric arrange- ment, Sec. 253 Ames Iron Works Robb- Armstrong- Brownell Co Sweet Rites 310 306 2 3 2 2 Buckeye Engine Co Chandler & Taylor Chuse Engine Mfg. Co. . Erie Ball Engine Co., Ball engine. Erie Engine Works, Erie engine Buckeye Armstrong Chuse Robb-Armstrong- Sweet Hard wick 316 311 304 301 1 2 4 2 1 1 2 2 2 2 Fitchburg Fitchburg 320 1 2 Harrisburg i Fleming 314 1 2 Hooven-Owens-Rentch- ler Co., Hamilton en- gine Special* 321 1 1 A. L. Ide & Sons, Ideal engine Liddell Co | Rites 1 Armstrong Rites 312 306 3 2 3 2 2 2 Nordberg Special* 3 2 Ridgway Rites 308 3 2 Skinner Skinner 291 4 2 Trov Rites 307 3 2 * These two governors are not shaft governors according to the defini- tion in Sec. 242, but are in a class by themselves. They are very similar to shaft governors, however, and because of their importance are here included. SEC. 255] SHAFT STEAM-ENGINE GOVERNORS 241 256. Some Effects Of Weight Or Spring Adjustment On Shaft-Governor Operation may be stated as follows: The sensitiveness of shaft governors and the speed at which they will regulate depend principally on the following conditions: (1) Tension of springs. (2) The distance from the point where the springs are attached to the weight or lever pivot. (3) The sensitiveness of the springs that is, the distance they will deflect for a given increase in force. (4) The angle at which the spring acts to the direction which the governor arm or weight tends to move. (5) The mass of the weight which produces centrifugal force. (6) The distance of the center of gravity of the weight from the fulcrum. (7) The angle between the direction in which the weight tends to move and that in which it is free to move. Substituting a heavier spring, increasing the spring leverage, or shifting the spring more in line with the direction in which the movable end of the spring moves, makes the governor less sensitive. Increasing the centrifugal weight and at the same time adjusting the spring so as to give the same speed makes the governor more sensitive in fact, the governor may thus be made unstable. Small changes in speed may be made by changing the centrifugal weight or spring tension (whichever is recommended by the manufacturer) without any other apparent effects. 242 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 11 S T ^ 1 I ' 3 JS fi S aJ -f X 1 a .a 1 33 .* _M j-J 93 aJ 'S 1 03 A .s "fi a 02 13 ^ ^ o III S & X 1 I If III i 1 ii jg 13 * '73 J | 1 > -** c8 a> -*> .SP 'S 1 jj ^ - _ -t v 03 ^ bC a 'S > C3 ? i I S o g *S > Q * - B 1 j s "S d d o 1 1 Jl 0> |j a 1 a 9 a 11 1 1 O o3 _0 1 a co 2 i ' | 1 > fcn *M ^ a> 08 .1 S o S a M s 93 rH "^ ^ 0) 93 g S | 1 * W 3 > 5 " a> "3 ~" ^ c c | 1 '- w y s 4) III c^ " " 1 1 1 " ,s CO 1 * 8 t 1 j 1 s 93 a PLH a (_, a 8 '5 ^ bo a a u a ^ o o o o> 1 -8 a> I 1 1 Ja H W S 1C to fe o e c o O u ' 3 e ^s o o 1 1 !-l a O , 2 c s -s SEC. 257] SHAFT STEAM-ENGINE GOVERNORS 243 257. Some Troubles Which May Be Encountered In Operating Any Shaft Governor and their remedies are as follows: (1) The governor is sluggish. Sluggishness in shaft governors usually results from one of two causes. Either there is too much friction or the governor is too nearly neutral (isochronous) to be stable. The friction may be in the dash- pot or anywhere in the mechanism as explained in the following section. If the dash-pot resists the movement of the governor too much, a larger hole in the piston or larger valve opening or a lighter oil will remedy the trouble. If the governor has been adjusted for very close regulation, it may lack the power to change its position promptly. The remedy (Table 256) is to increase the weight and use a stronger spring so that the original speed is obtained or to increase the spring leverage where means of so doing is provided. Governors of the Robb-Armstrong-Sweet type (Sec. 263) may be sluggish when adjusted for too much regulation. (2) The governor hunts. This may be due to very close regulation with a free-moving governor. It may usually, under these conditions, be corrected by introducing more friction by means of a drag spring or preferably a dash-pot. If good action cannot be secured in this way, the governor should be adjusted for larger regulation as explained above.- (3) The engine speeds up or races. The spring may be entirely too tight or too stiff for the desired speed. The weights may be much too light or, in the Rites type (Sec. 260), too nearly balanced about the weight pivot. Under these conditions, adjust the weight and spring for the desired speed. NOTE. RACING Is MOST FREQUENTLY CAUSED BY FRICTION of parts or other local troubles. There is, however, a noticeable difference between racing caused by over-sensitiveness or too weak springs and that caused by friction. When it is caused by spring tension alone, the changes in speed will be rapid, even, and within a certain range. When caused by friction, the weights will stick in their inner position until the speed developed is so high as to throw them out; or, when the engine is above speed, they will stick where they are until the speed is reduced enough for the springs to draw them back again. Such changes are usually accompanied by noise when the change takes place. 244 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 258. Most Troubles With Shaft Governors Are Due To Some Part Of The Mechanism Sticking or not moving freely. All of the well-known makes of modern shaft governors, regardless of their class, are thoroughly adjusted, tested, regulated, and set by their makers usually before they are shipped from the factory. Hence, when they are delivered to the operating engineer, they should regulate within the guaranteed speed range. The difficulties which arise after the governors have been in service for an extended period usually are due to wear or to an accidental cause, and usually can be remedied readily. After a governor has been perfected and has run satisfactorily, there is no reason why it cannot be restored to its original condition. Often the trouble is a slight one, so small as to be overlooked. Connecting Strap Valve ' FIG. 305. Sweet governor, operating gridiron valve. EXAMPLES. An engineer may, with a spanner wrench, give the valve- rod gland a half turn to tighten it up; this may cause the engine to run away. An engine having a Sweet governor (Fig. 305) may race if a single very small grain of gravel, G, gets between the band which connects the spring and the weight arm and the weight arm itself. Again, a cap which pinches on one of the fulcrum-pins or a slight burr on a valve-rod has caused trouble in a governor. The slightest thing should not be overlooked. Dry pins often cause trouble. Hence a governor should be oiled as regularly as any other part of the engine. About once a month, when the engine is operating continually in a dirty atmosphere, all pins and bearings should be taken apart and cleaned. When a search for trouble begins, nothing should be neglected from the governor eccentric to the farthest edge of the valve in the valve SEC. 259] SHAFT STEAM-ENGINE GOVERNORS 245 chest. Disconnect the eccentric rods from the governor eccentric and remove or release the spring or springs from the weight arm or arms. Then move the weight arms in and out from inner to outer positions. Most of the shaft governors on engines from 5 h.p. to 1,000 h.p. are so counterbalanced that, when thus dismantled, one man should with the smaller engines be able to easily move the parts in and out with one hand. On the larger engines, he should be able to do this with both hands but he should never use a bar of any kind. If the weight arms do not move with sufficient freedom to permit this, the trouble is probably caused by dry or cut pins, pinching caps, bent rods or links which make the pins bind, pinching or dry eccentric straps, or the eccentric binding (in some instances between a bearing and governor-wheel hub). Or sometimes gummed oil and grit cause it. If the governor is free and in perfect condition, disconnect the valves from the rockers or valve-rod slides, as the case may be. Then look for dry surface of pins or bearings or slides, bent rods and other like condi- tions. This done, see that the valve stems are straight and true, and in line with their connections; also that their bearings do not bind and are not dry. See whether they are burred or are worn so small in the stuffing box that the packing when pulled tight binds the stems. Note whether the packing is old and dry. Look into the steam chest. See if the valve is set properly and if it leaks or if the pressure-plate binds. Often an engineer forgets that proper valve setting (see Div. 4) is as essential as it is to have the governor free and well lubricated. NOTE. GREASES AND LUBRICANTS WHICH DRY OUT AND LEAVE DEPOSITS SHOULD BE CAREFULLY AVOIDED FOR SHAFT GOVERNORS. A thin grease, the consistency of vaseline, is preferable for the roller bearings and pins. Cylinder oil is satisfactory for the smaller pivots. The roller bearings should preferably be examined, cleaned and oiled monthly. 259. In Adjusting Shaft Governors, the engineer should first make sure that the main pin or pins and their bushings are free and properly lubricated, and that the valve is properly set and runs freely. If the arm is heavy enough to drive the valve, see whether the desired governing effect can be produced by adjusting the spring. Avoid adding unnecessary weights and the consequent overstraining of springs, bushings and pins. NOTE. IT MAY BE NECESSARY To ADJUST THE SHAFT GOVERNOR WITH No OTHER DATA THAN THAT WHICH BECOMES AVAILABLE FROM WATCHING THE ELECTRICAL SWITCHBOARD METERS, while the engine is running in service. The proper remedy for the apparent fault may be 246 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 applied on the occasion of the next shut-down. It may take an hour's careful watching of the switchboard instruments to determine the real action of the governor. The only certain procedure is to wait for the load to so change that the symptom for which one is watching will be shown. That is, the load should remain constant long enough to give the engine time to attain a constant speed. The observations should be repeated until the exact constant speeds under several different loads are ascertained. NOTE. A COMMON CAUSE OF COMPLAINT WITH SHAFT GOVERNORS Is HAMMERING of the weighted arm on the stops in starting or shutting down the engine. This can often be overcome on a Rites type governor by moving the attached weights and noting whether hammering is increased of diminished. Usually the proper change is to add weight on the spring side of the arm and to increase the spring tension, though it may be necessary to add weight at both ends. It is a peculiar fact that friction in the valve gear operates to help the governor spring so that an engine may be speeded up several revolutions by excessively tight valve-stem packing or any similarly acting cause. It is well to look over the valve motion as a possible cause of any unaccountable change of speed. If a brake or drag spring is used on the governor the friction may be increased to prevent hammering; but if it is set up too tightly, it may cause continual changes of speed through its action in checking the governor arm as it swings out or in, and so prevent the arm from floating gradually to the proper position. 260. The Rites Governor Is Used By A Number Of Different Engine Manufacturers: see Table 254. The action of this governor was explained in Sec. 247. In practice, as the load increases, this governor usually changes not only the throw of the eccentric but also its angular advance. Thus, the points of compression and cut-off are advanced but the lead remains practically constant. The movement of the governor is much exaggerated in Figs. 295 to 298. The actual layout is shown in Fig. 306. The Rites governor as used on the Troy vertical engine is shown in Fig. 307, and on the Ridgway engine in Fig. 308. 261. Rites Governors Are Sometimes Provided With Dash- Pots Or Drag Springs For Limiting The Rate Of Movement. The dash-pot, G (Fig. 308), is filled with oil for side-crank engines and with air for center-crank engines. A plug having an opening of proper size is inserted in the bottom of the air-filled pot to regulate the rate of movement. A by-pass and valve are provided for regulating some oil dash-pots. SEC. 261] SHAFT STEAM-ENGINE GOVERNORS 247 Others are controlled by holes in the pistons (Sec. 230). Air dash-pots are more likely to give trouble from sticking with Inert/a Direction (Weight^ Of Rotation Direction Of Rotation Center Of Gravity Weight A Governor ***--., Vafve-Rod Pin- Center Of Gravity Weight B "Imaginary Line Joining Centers Of Gravity FIG. 306. Lay-out of Rites gover- nor. (The locations of the centers of gravity in A and B may be shifted by adding movable weights to or remov- ing movable weights from them, or by shifting the position of the movable weights.) Running _.. Over - ' ' FIG. 307. Governor of the Troy vertical engine. (Rites type.) Adjustable ' Weight FIG. 308. Governor of the ridgway automatic engine. (Rites type.) dirt than are oil dash-pots and should therefore be closely watched and lubricated with cylinder oil. Dash-pots may be adjusted for greater or less promptness as explained in Sec. 248 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 233, Div. 6. The drag spring, S (Fig. 307) , introduces mechan- ical friction to prevent too much movement of the governor. There is ordinarily sufficient vibration of the engine to prevent such springs from making the governor bind when in the wrong position. 262. Some Special Adjustments Of The Rites Governor (Fig. 306) are as follows: (1) Shifting the movable weights, which are frequently provided, from W to X or from Y to Z increases the weight leverage; see Table 256. (2) Shifting movable weights from B to A increases the centrifugal weight. Removing weights from positions B, W or Y has an effect similar to that of adding them at Z, A or X. Shifting the spring pivot, S, farther from the governor pivot, G, decreases the sensitiveness. 263. The Robb -Armstrong-Sweet Governor, which is used by many manufacturers (see Table 254), is shown in .Direction Of FIG. 309. Simple Robb-Armstrong-Sweet governor. Figs. 309 to 313. This governor is placed in the second class in Sees. 252 and 253. The weight, W, is fastened directly to the spring, S, which is secured to the flywheel rim, F, or spoke. The tension on the spring is changed by taking up or slackening the tension-studs, B. The eccentric arm, A, is pivoted at P, moving the eccentric or eccentric pin, R, which changes the travel of the valve and the point of cut-off. The arm, A, is actuated by the spring by means of one link, L, one end of which can be changed in its position by shifting the pin into any one of the series of holes shown. SEC. 264] SHAFT STEAM-ENGINE GOVERNORS 249 NOTE. I N ADJUSTING ROBB-ARMSTRONG-SWEET GOVERNORS: To increase the speed, give more tension on the spring. To decrease the speed, give less tension on the spring. To get closer regulation and sensitiveness, move the pin, E, in the eccentric lever closer to the shaft center. To Slot For Adjusting For Different Sensitiveness Spring Tension Adjustment For Different Speeds 'ccentric Rod FIG. 310. Governor of the Ames engines. (Robb-Armstrong-Sweet type.) Fia. 311. Governor of Chandler & Taylor engine. (Armstrong type.) make more stable and sluggish, and prevent racing, move the pin, E, closer to the rim of the wheel. No change of weight is provided for, as the above-suggested adjustments are considered by the makers to be sufficient to cover all requirements. Weight f/y wheel- Pivot Pi Adjusting Bolt - 'heel FIG. 312. Side view of shaft governor of the "Ideal" Corliss-valve engine. Counter- balance Weight Bosses For Governor Attachment FIG. 313. Sectional elevation of "Ideal" Corliss- valve engine shaft with governor mechanism removed. 264. The Principal Adjustments Of The Fleming-Harris- burg Engine Governor (Fig. 314) in their recommended order are: (1) For greater or less speed, increase or decrease the weights, W, in the centrifugal (larger) weight pockets, keeping 250 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 them equal in the two larger weight pockets. (2) If more speed adjustment is required, vary the spring tension. (3) For more sensitiveness, shift the traversing blocks, B, in the Traverse Block Fid. 314. Fleming-Harrisburg centrally balanced centrifugal inertia governor. This shows a right-hand governor, engine running over. slots farther from the centrifugal weights. For less sensitive- ness more stability shift the blocks closer to the centrifugal weights. Direction Of Rotation FIG. 315. American-Ball engine governor. 265. The American-Ball Engine Governor (Fig. 315) is of class 4, Sec. 252. The advantage of the two springs, D and C, is that there is little bowing outward of the springs with cen- SEC. 266] SHAFT STEAM-ENGINE GOVERNORS 251 trifugal force with this spring arrangement. If spring C is slackened, and spring D tightened, the governor will be more sensitive. If both are tightened at once by nut F, the speed will be increased. 266. The Buckeye Governor (Fig. 316)) has several unique features. It controls only the cut-off eccentric. The Buckeye engine is fitted with a fixed eccentric which controls the other Tension FIG. 316. Buckeye engine governor. (Employs two weights in gravity balance changes only angle of advance.) steam events namely, release, compression and admission. The governor changes only the point of cut-off. This governor changes only the angular advance of the eccentric. The travel of the valve therefore remains constant. An advantage claimed for this method of governing is that the valve which has a constant travel wears the valve seat evenly. If the valve travel is less under light than under heavy loads, shoulders may be worn on the seat at the ends of the valve travel when the engine is running under light load. The valve will then strike these shoulders when an extra load is put on the engine. 252 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 EXPLANATION. The weights, A (Fig. 316), are mounted on weight arms, M, which are pivoted at N. The links, B, connect the weight- arm ends to the ears of the eccentric, C. When the weights, A, are moved outward by centrifugal force against the tension of springs, F, the eccentric may be turned a maximum of 90 deg. around the shaft as a center. Springs, F ' , are fastened to arms, M, by means of spring clips, D, which may be adjusted on the arms to increase the leverage of the spring and thereby increase its effective strength. The outer ends of the springs are connected to the rim of the flywheel by tension screws, S, by which the tension of the springs may be varied. The auxiliary leaf springs, P, act against the spring studs, T, and have the effect of increasing the spring tension near the minimum-speed position. The rollers, G, prevent the springs from bowing outward due to centrifugal force, at speeds of 250 r.p.m. or more. NOTE. SOME SPECIAL TROUBLES OF THE BUCKEYE GOVERNOR AND THEIR REMEDIES are; see Fig. 316. Auxiliary springs, P, too weak. The performance when these springs are too weak will be the same in kind as though they were absent entirely, though more moderate in degree. On starting, the engine will run above its proper speed before the levers, M, will expand. Then they will fly out violently. Stable regulation will be possible only with loads so light as to regulate at one-fourth stroke cut- off or earlier. That is, stable regula- tion can be obtained only with loads such as require the levers to act solely in the outer half of their range of movement. At heavier loads, the governor will race continually. The effective strength of the auxiliaries may be increased by lengthening the spring stud as from V to X (Fig. 317). Auxiliary springs, P, too strong. On starting up, the levers will move out at noticeably less than rated speed and expand gradually as the speed increases till the limit of the follow of the auxiliary springs is reached. Then, if they are much too strong, the expanding movement will tempo- rarily cease until normal speed is reached, when they will finish their expansion with proper promptness. The regulation will be the same as in the previous case when the load was too light to bring the auxiliary springs into action. But, with heavier loads, the speed will be slow in proportion to the undue strength of the springs. At maximum load, that is, just sufficient load to bring the levers to their inner stops, the speed will be reduced to about what was required to start them out. In all of the foregoing cases, the tension of the main springs was assumed to be what it should be with the auxiliaries at their best adjustment. That tension of the main springs which may be carried, without racing at any load, is always less than will be required when auxiliary springs are applied. FIG. 317. Adjustable spring stud for auxiliary springs of Buckeye governor. SEC. 267] SHAFT STEAM-ENGINE GOVERNORS 253 267. The Mclntosh & Seymour Engine Governor (Figs. 318 and 319) is itself balanced and its flywheel is in continual balance. Like the Buckeye governor, it controls a cut-off FIG. 318. Mclntosh & Seymour engine governor fully deflected. (No-load position.) eccentric only by varying its angle of advance. The weights, C, are deflected outward by centrifugal force against the tension of the leaf springs, A. The governor may be adjusted Direction Of FIG. 319. Mclntosh & Seymour engine governor at rest. for greater spring tension at B and for greater centrifugal weight by adding lead weights to the pockets, C. The manu- facture of this engine and governor has been discontinued. 254 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 268. The Fitchburg Governor (Fig. 320) employs two weights, HH, which are balanced with the other governor parts, and moves the eccentric in a straight line, thereby varying its throw. For the larger engines, the governor is mounted within a wheel-like casting, called a governor case, which is clamped to the engine shaft. NOTE. IN SETTING THE FITCHBURG GOVERNOR, the location of the governor case, K (or flywheel when the governor is mounted within a flywheel), is determined by placing the engine on one dead center and rolling the case around the shaft until the offset, 0, of the eccentric Direction Of Rotation^ FIG. 320. Fitchburg governor. (The legend "Crank Pin" means that the crank pin is located in the position indicated by the arrow. The crank pin is not shown.) is on the opposite side of the shaft from the crank-pin. Then roll K carefully into such a position that when (with the springs removed) the eccentric, A, is thrown back and forth across the shaft, no end motion is given to the valve rod. At this place tighten the governor case firmly upon the shaft. Turn the engine to the opposite dead center, and again move the eccentric back and forth across the shaft. If there is at this end any end motion to the valve rod, change the position of the governor case on the shaft enough to make the motion just half as much, then fasten the governor case firmly in this final position by drilling into the shaft for the point of the set screw and then tightening the clamp-bolts to place solidly. Put in the springs, C, and tighten them until the engine operates at the proper speed. Be sure to tighten up the springs that go through the counterbalance which hangs nearest the pin B (when the governor is at rest) about three-fourths of an inch more than the springs on the other side. SEC. 269] SHAFT STEAM-ENGINE GOVERNORS 255 NOTE. WHEN IT Is DESIRED To CHANGE THE DIRECTION OF ROTA- TION OF A FITCHBURG ENGINE, a new eccentric must be procured from the makers and put on in place of the one on the governor. The ends of the links which connect the weight arms must be changed on the counter- balance weight- arm end, to the holes opposite to those which they occupied when the old eccentric was used. 269. The Governing Mechanism Of The Hamilton Uniflow Engine is shown in Figs. 321 to 323. Centrifugal force is developed in two flat curved weights, W (Fig. 322), which are Wedge For Raising Spring-Adjustment FIG. 321. Longitudinal section of governor of the Hamilton uniflow poppet-valve engine. pivoted at P. These deflect outward, rotating the eccentric mounting, E, through the geared sectors, G. The rotation of the eccentric is opposed by the spring S, through the arm, A (Fig. 323). The tension on the spring, S, may be adjusted when the governor is at rest by the screw, N. This tension may also be adjusted when the engine is running by means of the handwheel, L (Fig. 321). This wheel is mounted on a screw-threaded sleeve which forces the wedge, R, against the screw, N, when L is turned. The movement of N is com- municated to spring S, through the spring-mounting lever, M. 256 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 7 By thus changing the spring tension, the speed at which the governor controls the engine may be changed. Direction Of Rotation .Weight R Direction Of Dotation -. FIG. 322. Hamilton uniflow-engine governor showing weights and eccen- tric-rotating sectors. FIG. 323. Hamilton uniflow-engine governor showing screw for spring- tension speed adjustment. 270. Setting The Valves Of An Automatic Engine consists mainly in adjusting the length of the valve stem. Shaft governors are nearly always keyed to the shaft and so the position of the governor is fixed and determines the position Direction Of Rotation FIG. 324. Showing governor blocked in extreme short-travel position. of the eccentric. If it is desired to change a shaft governor for greater or less equal lead (see Sec. 174) a new keyway must be cut. The valve travel of an automatic engine usually varies with the load and is determined by adjustment of the governor. Directions for valve setting are given in Div. 4. SEC. 270] SHAFT STEAM-ENGINE GOVERNORS 257 Fig. 324 illustrates the method of blocking a flywheel governor when the valves are being set. QUESTIONS ON DIVISION 7 1. What is a shaft governor? An automatic engine? 2. How does the governing action of a shaft governor and slide valve differ in economy from that of a throttling governor? From that of a fly-ball-governed Corliss releasing gear? 3. Why must a shaft governor exert more force for a given service than must a fly-ball governor? 4. Explain by a sketch the action of a shaft governor which is affected by centrifugal force alone. Why must some speed change occur in order that a centrifugal governor may operate? 5. What is the principle of inertia? How is it employed in shaft governors? Why cannot inertia be used in a shaft governor as the only governing force? 6. Explain how inertia and centrifugal force come into play in inertia governors. Why is it more necessary to employ inertia in shaft governors than in fly-ball governors? 7. What difficulties are encountered in reversing shaft-governed engines? Why must the flywheel usually be rebalanced after a governor has been reversed? 8. When is a shaft governor said to be balanced? Its flywheel? When in continual balance? 9. Explain how the balance of a flywheel may be restored. 10. Name four classes of governor weight arrangement and name a manufacturer of governors of each class. 11. What are the two methods of valve control through the eccentric? Name a governor which uses each method. 12. Which of the above methods of valve control is largely used with simple slide- valve automatic engines? 13. What are the principal methods of changing the speed of a shaft-governed engine? 14. How may the sensitiveness of a governor be decreased when there is no means of changing the spring leverage? 15. What is one cause of excessive hunting of a shaft governor? Of sluggishness? Of racing? Give one remedy for each. 16. What is the most common source of trouble with shaft governors? How may this trouble be located in the various parts of the governor mechanism? 17. What lubricant is satisfactory for governor roller bearings? For smaller governor pivots? 18. How may data be obtained, in steam-engine-driven electric-power generating stations, for governor adjustment? 19. What causes a governor to hammer against the stops when starting or stopping? How may this trouble be sometimes corrected in a Rites governor? 20. Explain by a sketch the effects of shifting weights from one part of a Rites gov- ernor to another. 21. Name two adjustments of the Robb-Armstrong-Sewet governor. 22. Name three adjustments of the Fleming governor. 23. What is the advantage of the spring arrangement of the American-Ball engine governor? How may this arrangement be used to vary the sensitiveness of the governor? 24. Explain the action of the auxiliary springs of the Buckeye governor. What is the bad effect if they are too weak? What if they are too strong? How may their effective strength be increased? 25. What is the governor case of a Fitchburg engine? Explain how to set the governor case on the shaft. 26. Explain a simple method of setting the slide valve of an automatic engine. 17 DIVISION 8 COMPOUND AND MULTI-EXPANSION ENGINES 271. Compound And Multi-Expansion Engines (Fig. 325) are widely used where the nature of the load requires the use of reciprocating engines and where better economies are desired than can be obtained with simple engines. Compound engines range in capacity mainly from 50 to 4,000 h.p. For mar- ine service and for driving machinery in mills, compound and multi-expansion engines find extensive application. For electric power generation, the turbine is gradually replacing the compound engine because of the turbine's lower first cost and more compact form; and, under many conditions (Sec. 299), its better economies. Also the use of the turbine for marine service is increasing. Where fuel is very cheap, as in a saw-mill, or where there is use for the exhaust steam for heat- ing or industrial purposes, a simple engine is usually preferred to a compound one because of its lower first cost; the economy of the engine then being a secondary consideration. NOTE. FOR DEFINITION OF THE COMPOUND ENGINE and classification with respect to cylinder arrangement, see Sees. 34 to 40. 272. The Compound Engine Usually Operates Through Large Temperature And Pressure Ranges. The temperature or pressure range of an engine is understood to mean the differ- ence between the highest and lowest temperatures or pressures of the steam within the engine cylinders. Compound engines are commonly operated condensing at 150 to 200 Ib. per sq. in. boiler pressure and sometimes, if the valves are properly designed, on superheated steam. Nothing is gained by using a compound engine for service where the temperature and pressure range is small. That is, for a boiler pressure of 100 Ib. per sq. in. and a back pressure of 5 Ib. per sq. in. gage, the economies of the simple and compound engines would be so 258 SEC. 272] COMPOUND ENGINES 259 260 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 nearly equal that the additional first cost of the compound engine would, probably, not be justified. "In general" (Gebhardt), "compounding increases the steam economy at rated load 10 to 25 per cent, for non-condensing and from 15 to 40 per cent, for condensing operation." At fractional loads the saving in steam due to compounding is smaller; in fact, a compound engine may, at light load, use more steam than a simple engine would use at the same load. NOTE. THE SAVING SHOWN BY THE COMPOUND ENGINE OVER THE SIMPLE ENGINE Is GREATER AT HIGHER BOILER PRESSURES. A certain triple expansion condensing engine is credited with a consumption of but 11.23 Ib. of saturated steam per i.h.p. hr. at 257 Ib. per sq. in. pressure; whereas the consumption of simple non-condensing, single-valve engines is usually about 30 to 35 Ib. of steam per i.h.p. hr. 273. The Principal Advantages Of The Compound Or Multi -Expansion Engine Over The Simple Engine having the same total ratio of expansion (see note below) and power out- put may be enumerated as follows; each is discussed in a succeeding section: (1) Reduced cylinder condensation because of the lesser temperature range in each cylinder (Sec. 274). (2) Reduced leakage loss partly due to the lesser pressure differ- ence in the two ends or each cylinder. That is, the "net pressure" on each piston is reduced by compounding (Sec. 275). (3) Higher mechanical efficiency because the ratio of the maximum to the mean effective pressure in each of the cylin- ders is greatly reduced. This ratio is usually from 40 to 70 per cent, of what it would be vvere the same total ratio of expansion employed in a simple engine (Sec. 276). (4) More even torque when cross compound engines are used with their cranks set at 90 deg. or 120 deg. apart (Sec. 277). The important disadvantages of the compound or multi-expansion engine are its greater first cost, its greater complexity and the large amount of room which it requires. NOTE. THE RATIO OF EXPANSION is the final volume of the steam at release divided by its original volume at cut-off. In a compound engine, the final volume at release is in the low-pressure cylinder and the original volume at cut-off is in the high-pressure cylinder. NOTE. TORQUE is the stress on a body which tends to cause it or causes it to turn. Torque is conveniently measured in pound inches. SEC. 274] COMPOUND ENGINES 261 A pound inch of torque is exerted by a force of one pound acting at a radius of one inch. The torque exerted in Fig. 326 by the connecting rod on the crank shaft is 500 X 14 = 7,000 Ib. in. EXAMPLE. Assume that a compound engine has a high-pressure cylinder clearance of 6 per cent, and a displacement volume of 2.9 cu. ft., and cuts off at 0.32 of its stroke. The low-pressure cylinder has a dis- placement and clearance volume of 11.8 cu. ft. total. What is the ratio of expansion? The boiler pressure is 176 Ib. per sq. in. abs. Assuming that release occurs at the end of the stroke what is the pressure at release in the low-pressure cylinder? Assume that the .expansion is hyperbolic that is, the absolute pressure varies inversely as the volume. SOLUTION. The volume of the steam at cut-off is 0.32 of the displacement volume plus the clearance. That is, (0.32 X 2.9) + (0.06 X 2.9) = 1.103 cu. ft. Then the ratio of expansion = 11.8 -7- 1.102 = 10.7. If the absolute pres- sure varies inversely as the volume, the FIG. 326. Illustrating torque or final pressure at 10.7 times the original turnin s moment exerted in an en- volume is 176 + 10.7 = 16.4 Ib. per sq. in. abs. The final pressure at release is always somewhat different in practice than the value thus calculated. 274. How The Compound Engine Avoids Excessive Cylinder Condensation When Employing Large Temperature And Pressure Ranges may be understood by reference to Figs. 327, 328 and 329. The phenomena of cylinder condensation is described below. As explained in the author's PRACTICAL HEAT under "Gas And Vapor Cycles," the larger the steam temperature and pressure range through which the engine operates, the greater will be its possible thermal efficiency provided the steam is used economically. But, if a simple single-valve engine were used with a large temperature range, there would be so much cylinder condensation that the high possible efficiency would not be even approximately realized. If an engine cylinder is properly lagged (insulated), there is little cylinder condensation due to radiation it is nearly all due to the behavior of the steam during the stroke as explained below. EXPLANATION. In the single-valve engine (Fig. 327) the steam ports, H, are alternately filled with live steam and exhaust steam. (The 262 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 following temperatures are taken from a steam table.) The exhaust steam at 120 deg. fahr. 26.5 in. of mercury vacuum must pass out Live Steam Is Coo led Through Slide" Valve Wa/f By Exhaust Steam Steani Live Steam Leaks Jnfef [Directly Into Exhaust -y^A^ Exhaust:^ '-Piston.' ";.. ^/ '?.. t ' Some High -Temperature 5team Remains In '-" Exhaust Ports '".,-' -" 'So/??? Exhaust Steam Left In The Clearance Space ! Temperature Range = 3 58- 1 20" = 238" FIG. 327. Showing live steam and exhaust steam in contact with parts of a single- valve engine. (The engine is assumed to operate condensing at 150 Ib. per sq. in. and 26.5 in. of mercury vacuum.) through the same ports through which the live steam enters at 358 deg. fahr. 135 Ib. per sq. in. gage pressure. It is evident that the walls of Steam Inlet- Cylinder Wall Being Heated By Live Steam Cylinder Wall Being Coo/ed By Exhaust Steam Exhaust , '-Exhaust Va/ve f> en Temperature Range = 358- 120= 236 FIG. 328. Showing live steam and exhaust steam in contact with cylinder walls in a simple four-valve engine. the ports as well as those of the cylinder are alternately heated and cooled. They are heated by the live steam which then condenses on them, and cooled by the re-evaporation of this condensed steam when the pressure SEC. 274] COMPOUND ENGINES 263 is lowered. Some of the steam, by thus condensing and re-evaporating- passes through the cylinder without doing work. In the simple four- valve engine (Fig. 328), the steam alternately heats and c'ools the cylinder walls but the valves and ports remain at a fairly constant temperature. Thus the four-valve engine avoids some of the cylinder condensation which takes place in the single-valve engine because the steam passages and the valves themselves are not heated and cooled. Furthermore, the exhaust steam in the clearance space of the simple engines of Figs. 327 and 328 mixes with the incoming live steam, and thus, condenses a portion of the live steam. In the compound engine (Fig. 329), the exhaust from the low-pressure cylinder, L, does not come in contact at all with the same parts as does the live steam (at boiler pressure) . There is, nevertheless, some cylinder con- densation in the compound engine due to the temperature difference Steam Supply - . .j 150 Ib. per _. Low- Pressure - " Cylinder 25 1 b. per sq./rt. abs.'' Temperature Range 358"- 241 "=117 Fine*/ Exhaust-' *'"/? '/A per scj. In. abs. Tempera'ture Range = 240- 120= 120 FIG. 329. Showing temperatures in various parts of a compound engine. (The arrangement shown is, in general, that of a Woolf-tandem compound engine.) between the incoming and issuing steam in each cylinder. But, because of the lower temperature range in each cylinder, the total condensation is considerably less in the compound engine than in either the single- or four-valve simple engine. It will therefore be evident from a study of the above explanation and of Figs. 327 to 329 that compounding reduces the temperature range in each compound-engine cylinder to approximately one-half of that of a simple engine in which the total temperature range is the same. Similar reasoning will disclose how the temperature range per cyliner may be further reduced by employing three or four cylinders as is done in triple- or quadruple-expansion engines. With a reduction in the temperature range per cylinder, the total cylinder condensation is reduced correspondingly. NOTE. THE SURFACES OF THE ENGINE CYLINDER WITH WHICH STEAM, AT VARIOUS TEMPERATURES, CONTACTS assume, at different 264 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 instants, very nearly the temperature of the steam at those instants. When a change in steam temperature occurs, the depth to which such a change in temperature will penetrate the cylinder walls will be propor- tional to the time during which the walls are exposed to the steam at the new temperature. Thus, if a steam stroke is performed in less time, there will be less cylinder condensation. Therefore, the losses due to cylinder condensation decrease as the engine speed increases. Attempts have been made to line cylinder heads with low-heat-conducting materials to prevent cylinder condensation. These materials have all proved to be of insufficient mechanical strength and, therefore, have not been widely used. 275. Why Leakage Past The Piston And Valves Is Less In A Compound Engine Than In An Equivalent Simple Engine may be understood by referring to Figs. 328 and 329. The maximum difference between the pressures on the two sides of the piston and valves in the high-pressure cylinder (Fig. 329) is 150 25 = 125 Ib. per sq. in.; and, in the low-pressure cylinder the difference is 25 1.7 = 23.3 Ib. per sq. in. Now, in the simple engine (Fig. 328) the pressure difference is 150 1.7 = 148.3 Ib. per sq. in. The pressure difference is not much less in the high-pressure cylinder than it is in the simple engine, but the high-pressure cylinder is much smaller for the same power output and the volume of leakage is there- fore correspondingly small. Also the steam which leaks past the high-pressure piston is effective in doing work in the low-pressure cylinder. 276. The Mechanical Efficiency Of A Compound Engine Is Ordinarily Greater Than That Of An Equivalent Simple Engine in spite of the greater number of bearings and moving parts of the compound engine. The simple engine, to obtain the same total ratio of expansion as the compound engine, must cut off earlier in its stroke. Fig. 330 shows theoretical engine indicator diagrams. / shows the simple engine diagram. II shows the combined diagrams (Sec. 281) from the highl- and low-pressure cylinders of a compound engine. The mean effective pressures P 2 and P 3 in the compound-engine cylinders are large fractions of the corresponding maximum pressures in the two cylinders. In the simple engine, the mean effective pressure Pi is only a small part of the maximum pressure, PQ. The two diagrams show the same total ratio of expansion but SEC. 277] COMPOUND ENGINES 265 the ratio of expansion (see example under Sec. 273) in the simple engine is 15 whereas that in the compound-engine high-pressure cylinder is only 5. That is, the engine would do the maximum work for which it was designed during only about }{$ of the stroke in the simple engine and for J of the stroke in the compound engine. The low-pressure cylinder, due to its later cut-off, does its maximum amount of work during half of its stroke. This better distribution of the driving force results in better mechanical efficiency. Zero Vo/ume Or \ Clearance Line \ Receiver Pressure -.. % Atmospheric L_ -^ ; Pressure Total Vacuum^ ar " High-Pressure Cylinder \ ^ .'Mean Effective Pressure ;*' High-Pressure ;' Terminal Drop \ Low-Pressure Cylinder } Mean Effective Pressure ^ I- Simple Engine Diagram FIG. 330. Ideal indicator diagrams of compound engine and equivalent simple engine. - Combined Diagrams Of Compound Engine 277. How The Turning Moment Or Torque Is Made More Even In Compound Engines Of Different Designs may be seen by referring to Figs. 331 to 333. The turning moment of a tandem-compound engine (Fig. 331) is only little more even or regular than that of an equivalent simple engine, although the later cut-off of the compound engine gives a longer maxi- mum turning moment. The torque developed by such an engine is shown graphically in Fig. 331. But, if the high and low-pressure cylinders operate cranks at 90 deg. with each other (as is common in cross-compound engines) the points of maximum torque in the two cylinders will occur 90 deg. apart as shown in Fig. 332. The driving moment on the shaft will then be much more regular and the necessary flywheel size will thus be greatly reduced. If a triple-expansion engine has its three cranks set at 120 deg., the resulting torque 266 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 45 90 135 180 225" 210" Angular Position Of Crank 315 360 FIG. 331. Graph showing variation of torque with angular position of crank for tandem-compound engine. High-Pressure Dead Centers -> 45 90 135" 180" 225 Angular Position Of Crank 210 315 360 FIG. 332. Graph showing variation in torque with angular position of crank in a cross- compound engine with cranks at 90 deg. . - - -High- Pressure Deaa" Centers - \ / _ -Mean Torque \ -High -Press. \ Cu 30" GO 90 120" 150 180 210 240 270 300 330 360 Angular Position Of Crank FIG. 333j Graph showing variation of torque with angular position of cranks of a triple-expansion engine having three cranks set at 120 deg. SEC. 278] COMPOUND ENGINES 267 graph will be that shown in Fig. 333. An almost uniform turning moment will result. 278. Compound Engines May Be Classified With Respect To The Method Of Transfer Of Steam From One Cylinder To Another as follows: (1) Woolf -compound engines (Fig. 334) in which the high-pressure cylinder exhausts directly into the low-pressure cylinder. The cylinders of engines of this class are usually arranged in tandem (Fig. 329) but may also have separate cranks set at an angle of 180 deg. as in Fig. 334. (2) Receiver-compound engines (Fig. 335) in which the steam is Fia. 334. Woolf-compound marine engine. The high-pressure cylinder exhausts directly through the piston valve into the low-pressure cylinder. (For complete details of this engine see Fig. 524.) delivered from the high-pressure cylinder to a receiver and thence to the low-pressure cylinder. All cross-compound engines having cranks at 90 deg. and triple-expansion engines with cranks at 120 deg. are of the receiver-compound type. The reason for this is that, with these cylinder arrangements, the high-pressure cylinder does not exhaust at the proper time to supply the low-pressure cylinder with steam. A receiver, A, Figs. 335 and 336, is therefore employed to store, during the intervals between events, the steam from the high- pressure cylinder so that it will be available for supplying the low-pressure cylinder. The receiver may be in the form of a 268 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. i i . ~ T] - 500 /6v., 60-Cycle Flywheel - -->^ \\ ^^ ,,-T' Alternator Regular Governor Small Safety Valve' 17-6 C.ToC.- I-Plan View 2-6 f Receiver-*. --9-0' Exhaust To Condenser 9-0" Safety Valve n-End Elevation FIQ. 335. Fulton Iron Works Co. cross-compound, 18 and 36 by 48 in. engine driving alternator. (Steam is admitted to the high-pressure cylinder at B. Jt is exhausted through C to A where it is reheated. Thence it flows through D to G and is exhausted through // to the condenser. The speed governor, N, is mounted on the low- pressure cylinder, and controls the valves of both cylinders by means of rods, R and S. The over-speed governor, M , prevents the high-pressure valves from picking up when the engine speed exceeds a pre-determined value.) SEC. 279] COMPOUND ENGINES 269 separate chamber or it may be merely an enlarged pipe con- necting the cylinders or an enlarged low-pressure steam chest. Steam Outlet * To Low-Pressure Cylinder Manhole Cover- FIG. 336. Diagram of a combined live- steam reheater and receiver for a 18 and 32 by 42 in. cross-compound engine. (Fulton Iron Works Co. design. This corresponds to receiver, A, Fig. 335.) NOTE. THE VOLUME OF A RE- CEIVER should be at least 1 to 1.5 times the high-pressure cylinder volume for a cross-compound engine with cranks at 90 deg. Receivers having volumes of 5 or more times that of the high-pres- sure cylinder are sometimes used. For other cylinder arrangements, the receiver may be smaller. Small receiver volumes result in irregular high-pressure exhaust lines, such as those shown at AB in Figs. 337 and 338. Receivers should be provided with pop safety valves to prevent damage in case the receiver pressure rises due to a failure of the low-pressure admission valves to function prop- erly. A drain (S, Fig. 339) should always be provided from every receiver to remove condensed steam. The pressure gage used on a receiver should be of the com- pound or combination type and should read vacuum and pressure as high as the boiler pressure. A by-pass should be provided for admitting live steam to the com- pound-engine receiver. This assures that, if the high-pressure crank is on dead center, the low- pressure cylinder may be used to start the engine. The by-pass also permits " warming up " the receiver and low-pressure cylinder before starting the engine. 279. Reheaters Or Interheaters (Fig. 336) are frequently used with compound and usually with triple-expansion engines. A reheater or interheater is a device for heating the steam which is discharged from the high-pressure or inter- mediate cylinder of an engine before it enters the next lower- 270 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 pressure cylinder. Reheaters are usually built in the receiver or take the place of the receiver. The heating may be done with live steam or with furnace gases. With compound Variable iure X Receiver Back Pressure Due \ Pressure \JoL.RCu-f-Off .Compression Practically No Receiver Volume FIG. 337. Actual indicator dia- grams showing decrease in receiver- pressure in a Woolf tandem-com- pound engine during high-pressure exhaust stroke. Atmospheric Line. ''Increase Of Low / Back Pressure Pressure f Due To Closed Low-Pressure . Little Receiver Volume Steam Valve FIG. 338. Actual indicator diagrams from cross-compound engine showing variation in receiver pressure during exhaust. engines, a reheater usually does not improve the total thermal efficiency of the engine materially, where the heating is done with live steam, unless the receiver-pressure steam is, by Live-Sfeam {Supply H-PCylinde. (130-lb. Jacketing-Sfeam Pipes"----, Trap-' FIG. 339. Arrangement of receivers and drains on a triple-expansion pumping engine. (H. P. = high pressure cylinder; I. P. = intermediate pressure; L. P. = low pressure. A, B and C are cylinder-jacketing steam pipes. D and E carry live steam for the combined reheaters and receivers. reheating, superheated about 100 deg. fahr. or more. Re- heaters always improve the quality of the low-pressure steam materially and so make the low-pressure cylinder easier to SEC. 280] COMPOUND ENGINES 271 operate. That is, with steam of greater quality, the operation and lubrication are more positive. Reheaters in which furnace gases are used increase engine economy considerably. Such a reheater is used on the Buckeye-mobile (Fig. 395). 280. The Meanings Of Various Terms Used In Connection With Compound Engines are as follows: The cylinder ratio is the ratio of the displacement volume (Sec. 3) of the low- pressure cylinder to that of the high-pressure cylinder. Where the stroke of the two cylinders is the same, the cylinder ratio may be taken for most purposes as the square of the ratio the diameters. Thus, if the high-pressure cylinder is 10 in. in diameter and the low-pressure cylinder is 20 in. in diameter, the cylinder ratio is (20/10) 2 = 4 or, as sometimes expressed, it is 4 to 1. In computing the exact value of cylinder ratio the volume occupied by the piston rods must be deducted. The total ratio of expansion is the ratio of the final volume of the steam in the low-pressure cylinder to its volume at cut-off in the high-pressure cylinder. Neglecting clearance and, for equal cut-offs in the two cylinders, the total ratio of expansion is the cylinder ratio times the reciprocal of the fraction of stroke completed at high-pressure cut-off. Thus, if cut-off occurs at ^ stroke and the cylinder ratio is 4, the total ratio of expansion is 4 X 3 = 12. Free expansion is the expansion of the steam in the receiver and passages between cylinders. It is measured by the mean difference between the pressure along the exhaust line of the high-pressure cylinder and that along the admission line of the low-pressure cylinder. Terminal drop is the difference between the pressure in the high-pressure cylinder at release and the average receiver pressure. NOTE. THE CYLINDER RATIO IN COMPOUND ENGINES VARIES FROM ABOUT 2 To 1, To ABOUT 8 To 1. With a given percentage of cut-off in the high-pressure cylinder, a larger cylinder ratio results in a larger termi- nal drop. But if a sufficiently early cut-off and a large cylinder ratio are used, the terminal drop may be comparatively small. The economy of the engine will then be high but its power output small in proportion to its weight. If a larger power output is desired at the expense of ec6n- omy, a later cut-off and smaller cylinder ratio are employed. 281. Two Indicator Diagrams From Each Cylinder Of A Compound Engine May Be Combined, if the diagrams 272 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 are taken as specified in Sec. 282 to form a single diagram, Fig. 340. One purpose in so doing is to see how nearly the combined expansion lines, which are thus obtained, conform to the ideal expansion curve or to the saturation line PD (Fig. 340) for the weight of steam which was admitted to the cylinder. Leaking exhaust and admission valves and leaking pistons may thus be detected in the compound engine, in the same manner as explained in Div. 3 for the simple engine. A convenient method of combining diagrams is, by Pressure Scale Of Low- Pressure Original High - Diagram --'" Pressure Card- . w FIG. 340. Method of combining high-pressure and low-pressure diagrams from a tandem-compound engine. H.P. = high-pressure cylinder; L.P. = low-pressure cylinder. a graphic means, to increase the volume scale of the low- pressure diagram to the high-pressure-diagram volume scale and to reduce the pressure scale of the high-pressure diagram to the low-pressure diagram scale. The two diagrams will then have the same volume and pressure scales. This method is explained below. NOTE. INDICATOR DIAGRAMS WHICH ARE To BE COMBINED SHOULD BE TAKEN SIMULTANEOUSLY AND WHEN THE LOAD Is CONSTANT. If the diagrams are taken simultaneously with two indicators while the SEC. 281] COMPOUND ENGINES 273 load is changing, then the combined diagrams may show more steam being delivered to the receiver than is withdrawn from it or vice versa. Where this occurs, the analysis will be misleading. If the two diagrams are taken with one indicator, care should be taken to restore, while taking the second card, exactly the same conditions as obtained for the first card. Furthermore, the conditions should be maintained constant for an interval sufficient to allow the receiver pressure to assume its normal value before either diagram is taken. Combining cards which were taken under different or under changing conditions is a frequent source of erroneous conclusions. EXPLANATION. Two lines, OX and OY (Fig. 340), are drawn at right angles, as shown, on a large sheet of paper. A scale of pressures is laid off on OY equal to the spring scale of the low-pressure diagram for example, 20 Ib. per in. The low-pressure diagram, LP, is pasted as shown with its clearance line (see example under Sec. 108) coinciding with OY and its total vacuum line with OX. Locate Z, on OX, even with the end of the diagram. Draw WZQ through Z and any convenient point, W. Now paste down the high-pressure diagram, HP, as shown, so that its clearance line falls on OY and that its highest point, K, is correctly located on the spring scale of the low-pressure diagram. Draw RC as shown. Select point T so that OT -f- OZ = (the displacement volume of the low-pressure cylinder and its clearance} -5- (the displacement volume of the high-pressure cylinder and its clearance] or, if the percentage clearances in both cylinders are the same, then OT -T- OZ = the cylinder ratio. Draw TB at right angles to OX to intersect WQ. Draw BA through B parallel to OX. Then as many points as desired may be transferred to locate the new low-pressure diagram: Thus, to transfer point M, draw MMi, draw WMiM 2 and project M and M 2 to Ms', Ms is the required point. Draw, if not already drawn, the atmospheric lines, RS and RiSi. Draw SiRV and project K to V. Then to transfer any point, N, draw NNi and draw VNiN* and project N and 7V 2 to Ns. N 3 is the required point on the new high-pressure diagram. To draw the saturation curve, calculate from test results the weight of steam used per stroke at the load at which the diagrams were taken. That is : Weight of steam per stroke = (weight of steam used during test) -T- (number of strokes during test). Add to this weight, the weight of steam trapped at compression in the high-pressure cylinder, assuming the steam to be dry. Then find, by using a steam table, the volumes occupied by this total weight of saturated steam at various pressures and plot the volumes and corresponding pressures on the diagram. NOTE. THE LOW-PRESSURE EXPANSION LINE OF A COMBINED INDICATOR DIAGRAM is nearly always farther measured horizontally or along the volume axis from the saturation graph than is the high- pressure expansion line. This is partly due to the fact that steam is pres- ent in the high-pressure cylinder which is not discharged to the receiver but is retained as cushion steam. If, now, the weight of steam retained 18 274 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 in the low-pressure cylinder as cushion steam were the same as that retained in the high-pressure cylinder, the two expansion lines might follow one smooth curve. But, since the weight of steam retained in the low-pressure cylinder is less than that retained in the high-pressure cylin- der, the total weight of steam in the low-pressure cylinder is less than in the high-pressure cylinder. Therefore, its volume will be less. That the low pressure expansion line is farther from the saturation graph than is the high-pressure expansion line is also because part of the steam is condensed in the high-pressure cylinder and upon being admitted to the low-pressure cylinder still more of it is condensed. When an interheater or reheater (Sec. 279) is used, the low-pressure expansion line is much nearer the saturation graph. Giving the low-pressure cylinder later cut-off does not, as might be expected, extend the low-pressure expansion line. This is because giving later cut-off in the low-pressure cylinder gives a lower receiver pressure. NOTE. COMPOUND-ENGINE INDICATOR CARDS MAY ALSO BE COM- BINED To SHOW THE SIMULTANEOUS CONDITIONS IN BOTH CYLINDERS as suggested in Figs. 337 and 338. For this purpose the volume hori- zontal scales need not be changed. The pressure scales are replotted to a common scale and the simultaneous events for each card are plotted above one another vertically. The line AB shows the receiver pressure. The line CD shows the pressure of the steam as admitted to the low- pressure cylinder. The vertical distance at any point between AB and CD shows the pressure drop through the receiver. Hence, such cards are useful in studying receiver pressures and drop. 282. A "Mean Indicator Diagram" Must Be Drawn, If Unlike Indicator Diagrams Are Obtained From The Head And Crank Ends Of Either Engine Cylinder, before the dia- grams from the two cylinders can, properly, be combined. This is because some of the steam which passed through the crank end of the high-pressure cylinder will pass through the head end of the low-pressure cylinder if the valves are not adjusted symmetrically as shown by a balanced indicator card. A graphic method of drawing a mean card for an engine cylinder is as follows : EXPLANATION. The indicator diagrams, 7 and II (Fig. 341), are ruled with vertical equally spaced lines as shown. The clearance lines M and atmospheric or total vacuum lines (whichever is most convenient) WZ are also drawn. A reference line XY is then drawn and vertical lines are drawn as shown twice as far apart as those in / and II. The sum of the clearances, WA and CZ, are laid out at XA , and the clearance line XX i is drawn. Now to transfer any point 5, and its corresponding SEC. 283] COMPOUND ENGINES 275 point, D, to the mean diagram, lay out, with a pair of dividers or other means, the distance Ai-Di equal to the sum of AB and CD. It will be noted that both the pressure scale and volume scale of the diagram are doubled by this operation. -Head-End FIG. 341. Illustrating method of drawing a mean indicator diagram from head-end and crank-end indicator diagrams. 283. The Indicated Horse Power Of Compound Engines may be computed by computing the power of each cylinder and adding the results. The method for computing the horse power of a simple engine was explained in Sec. 123. Each cylinder of a multi-expansion engine may be considered as a simple engine in computing indicated horse power. The cylinder area, the mean effective pressure, and spring scale are ordinarily different in the different cylinders. Therefore little is ordinarily gained by computing the power of the two cylinders together. However, if the diagrams have been carefully combined, as explained in the preceding section, the resulting diagram may be treated as a single diagram in computing indicated horse power. 276 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 284. The Receiver Pressure Usually Varies Somewhat During The Stroke of the engine. In Woolf-compound engines (Fig 334) the back pressure on the high-pressure cylinder is a maximum at high-pressure release but falls off rapidly due to the fact that the low-pressure-cylinder volume increases faster than the high-pressure-cylinder volume decreases. This effect is apparent in most tandem-compound engines but is much less if a receiver is used. The high- pressure exhaust line (AB, Fig. 338), which also represents the receiver pressure, of a cross-compound-engine diagram usually curves down at its ends due to the low-pressure cylinder admit- ting steam at the ends of but not in the middle of the high- pressure stroke. 285. With Compound Engines, The Correct Receiver Pressure Must Be Maintained To Insure Economical Opera- tion. A radically wrong receiver pressure causes most of the work to be done in one cylinder and the engine then gives little better economies than would a simple engine. But even when the receiver pressure is varied within apparently reasonable limits, there may be a difference of 10 per cent, or more in the steam consumed by the engine per indicated horse power hour due to these receiver pressure differences. The receiver pressure recommended by one manufacturer for non-condensing compound engines is about 30 Ib. per sq. in. gage and for condensing operation, about 1520 Ib. per sq. in. gage. 286. To Find The Best Receiver Pressure For Any Receiver- Compound Or Multi -Expansion Engine, find the receiver pressure at which the net work done in the cylinders is equal. This can be accomplished by taking successive indicator cards at the same load from each cylinder and varying the receiver pressure. Then the power (see Sec. 123) developed by each cylinder with each receiver pressure is determined. The best receiver pressure is, of course, that at which the economy of the engine is maximum. But nearly all compound engines are so designed that the work in the two cylinders is about equal when economy is maximum. Therefore, if the work done by the several cylinders is equal, it may, ordi- narily, be assumed that the receiver pressure is correct. In a SEC. 286] COMPOUND ENGINES 277 .'Pivot Is Stationai Vertically Baft Weight-^ Rod To High-Pressure Valve Control** jrn, V Journal; . . Free To Turn On Shaft Flange For Bo/t/'ng To Frame Handwheel For Regulating } I . Receiver Pressure Governor Pulley,^ Fio. 342. Cross-compound Corliss engine governor, N, Fig. 335 showing receiver- pressure regulation device. (Fulton Iron Works Co. design). This governor is located on the low-pressure cylinder and controls the regular knock-off cams on both cylinders. 278 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 High-pressure Spindle- Valves Sleeve --> Operated by Column ..- /fc// / D , \ *\ u \ \ S.60 \ \ \.--Terminal "45 V \ /-'\ /?/~oo \ N s tS F c \ v x x ^^ in 30 ^'' \ Y X ^ *"^"--^ ^--F, (O I 15 fiT.-rr.-r A A ex i Condenser ^Points Of Low ressure ' Pressure Cut-Off ^Receiver Pressure At Pressure-' Intermediate Load FIQ. 345. Theoretical indicator dia- grams showing effect of Governing high- pressure cylinder only. FIG. 344. Theoretical indicator dia- grams showing variation in receiver pressure due to cut-off governing in both cylinders. The lines FFi, EE\, and AAi represent respectively the different re- ceiver pressures. 289. Where Only The High-Pressure Cylinder Is Governed, the cut-off in the low-pressure cylinder is fixed. The receiver pressure will then vary with the load. The low-pressure- cylinder cut-off should therefore be set at a point which will give the proper receiver pressure under the average load expected. EXPLANATION. Fig. 345 shows theoretical indicator diagrams from a compound engine which is governed by changing the cut-off in the high- pressure cylinder only. The low-pressure cut-off is fixed at LL. When high-pressure cut-off is late as at A, the steam expands only to B before it attains the volume MM of the high-pressure cylinder. This amount of steam at the cut-off volume LL of the low-pressure cylinder exerts a pressure C, which is therefore the receiver pressure at this load. Simi- larly, the receiver pressures P and R are produced when cut-off occurs at D and H. In the diagrams of Fig. 344, cut-off occurs at B, C, and D. The low-pressure cut-off is varied by the governor so as to occur at A\, Ei and F\. This governor action varies the receiver pressure but little and keeps the work in the two cylinders about equal. 280 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 290. Triple- And Quadruple -Expansion Engines Are Rarely Used In Stationary Power Plants except in large existing pumping stations. New pumping stations use turbine-driven centrifugal pumps for large-capacity pumping service. But multi-expansion engines are built extensively for marine service. Fig. 346 shows a typical triple-expansion marine engine. Two low-pressure cylinders, LI and L 2 , are used to Low-Pressure Cylinder-^ Low-Pressure Relief Intermediate Valve Cylinder- 'Valve ^Cylinder Chest^ ' High-Pressure Cylinder FIG. 346. Four-cylinder triple-expansion marine engine. secure proper mechanical balance. The combined indicator diagrams from a quadruple-expansion engine are shown in Fig. 347. 291. To Set The Valves Of A Compound Engine, set the valves of each cylinder separately. The high-pressure valves may be set as explained for simple engines in Divs. 4 and 5. The low-pressure valves should be given more lead than those of the high -pressure cylinder. About Jli6 to %4 in. per foot of stroke is advisable for most compound-engine low-pressure valves. For vertical engines, it is advisable to give little more SEC. 291] COMPOUND ENGINES 281 lead on the bottom than on the top of the cylinder. Where the valves are very quick acting, it may be more convenient to set them in relation to the angular position which the crank assumes at the instant when the admission valve begins to open, rather than to set for lead. On the low-pressure cylinder, the valve should start to open when the crank is 7 to 10 deg. ahead of dead center. This angular lead may, however, be as high as 15 deg. " ~5feam Supply Pressure I f .--HuperJbo/ic I 1 /: ' Expansion Line Condenser Pressure FIG. 347. Combined indicator diagrams from a quadruple expansion engine. QUESTIONS ON DIVISION 8 1. Name two conditions under which compound engines are commonly used. 2. Over what pressure ranges are compound engines commonly operated? When are simple engines almost as economical as compound engines? What saving in steam may be expected from the use of a compound engine operated condensing over the steam consumption of a simple condensing engine? 3. Give the four principal advantages of compound engines. 4. Show by a sketch how the live steam comes in contact with the same parts as does the exhaust steam in a simple engine. Why does not this occur in a compound engine? 5. How do engine speed and the heat conductivity of the cylinder wall affect cylinder condensation? 6. Explain how the loss due to leakage past the cylinder and valves is lessened in a compound engine. 7. Why is the mechanical efficiency of a simple engine employing a large ratio of expansion less than that of an equivalent compound engine? 8. What is torque? How is it measured? Why is the torque very uniform in a triple- expansion engine with cranks at 120 deg.? Which do you consider preferable, a tandem- or a cross-compound engine? Why? 9. How may compound engines be classified with respect to the steam flow? Why is a receiver necessary in a cross-compound engine with cranks set at 90 deg. ? 10. How large should a receiver for a cross-compound engine be? With what acces- sories and pipes should it be equipped? 282 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 8 11. What are two principal kinds of reheaters? 12. What is the cylinder ratio of a compound engine? What is free expansion? Terminal drop? 13. What cylinder ratios are used in compound engines? How is engine economy affected by larger cylinder ratios and earlier cut-off? How does this affect power output? 14. Explain by a sketch how indicator diagrams from high- and low-pressure cylinders of a compound engine may be combined. 15. What causes the low-pressure expansion line of a combined indicator diagram to fall farther from the saturation line than does the high-pressure expansion line? 16. How may the indicated horse power of multi-expansion engines be computed? 17. Explain how the receiver pressure varies during a stroke in a cross-compound engine. 18. How may the correct receiver pressure for an engine be determined by means of a steam engine indicator? 19. Which method of compound-engine governing gives the greatest variations in receiver pressure? Why? 20. How much lead should there be in the valves of a low-pressure cylinder of a com- pound engine? PROBLEMS ON DIVISION 8 1. Approximately what receiver pressure should a compound condensing engine have when taking steam at 150 Ib. per sq. in. gage if the cylinder ratio is 4. 3:1. What should be the receiver pressure for a non-condensing compound engine taking steam at 100 Ib. per sq. in. gage and exhausting at 5 Ib. per sq. in. gage? 2. If the crank arm in a simple engine is 6 in. long and the cylinder diameter is 10 in., what maximum torque can the piston exert on the shaft if the effective pressure on the piston is 150 Ib. per sq. in.? Assume that, when the crank and connecting rod are at right angles to each other, the force on the crank pin is 90 per cent, of that on the piston. 3. If, in a quadruple-expansion engine, the temperature ranges in all cylinders are equal, and if steam is supplied to the engine at 225 Ib. per sq. in. gage and exhausted into a condenser where the vacuum is 28.5 in. of mercury column, what is the temperature range in each cylinder? Barometer = 30 in. 4. A compound engine, which has a cylinder ratio of 4.5: 1 cuts off at 26 per cent, stroke in the high-pressure cylinder. Neglecting clearance, what is its ratio of expansion? If there is 6 per cent, clearance in each cylinder, what is the ratio of expansion? 5. If a compound engine has a stroke of 5 ft., what lead should its low-pressure cylinder admission valves have? DIVISION 9 CONDENSING AND NON-CONDENSING OPERATION 292. By Condensing Operation Of A Steam Engine Is Meant Its Operation In Connection With A Steam Condenser So That A Pressure Considerably Below Atmospheric Pressure Is Maintained In The Engine Exhaust Pipes And Passages. That is, the back pressure on an engine operated condensing Steam at 400 Deg fahr / 95 Deg. Fahr Outlet 'to Dry -Air Pump Outlet to Condensate Pump /nfe FIG. 348. Diagram of uniflow-engine cylinder connected through expansion joint to surface condenser. (Fig. 348) is ordinarily 10 to 14 Ib. per sq. in. below atmos- pheric pressure, while that on one operated non-condensing is usually to 5 Ib. per sq. in. above atmospheric pressure. NOTE. A CONDENSER Is A CHAMBER WHEREIN THE EXHAUST STEAM FROM THE ENGINE Is COOLED AND THEREBY CONDENSED INTO WATER. A partial vacuum, into which the engine (Figs. 349 and 350) exhausts, is thus formed. The subject of condensers is treated quite fully in the author's STEAM POWER PLANT AUXILIARIES AND ACCESSORIES. 283 284 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 9 .-Steam-Supply Pipe .-High -Pressure Cylinder , Low '-Pressure Cylinder Surface Feed- Water (Condenser Heater Discharge^ Tunnel ~ ' 'Wef-Air Boiler- Feed,.' Pump Pump --' Cylinder "'""") Circulating- Tunnel Pump C yl- nc! t er FIG. 349. Surface condenser connected for service with tandem-compound engine. Steam is discharged from low-pressure cylinder, L, through P. The cylinder oil and water are removed by S and collected in R. The steam is condensed in C by water, which is sucked from 7 by W and discharged into D. The air and condensate are re- moved by A, the latter being heated in H and fed back to the boiler by F. (Cochrane Heater Catalogue.) Atmospheric Relief Strainer *-Hot Well FIG. 350. Ejector-jet condenser installed for service with simple Corliss engine. Schutte & Koerting Co. catalogue; water is circulated by P through S and the condenser C. The velocity of the water issuing from jets in C is such that water and air are discharged from the vacuum in C against atmospheric pressure.) SEC. 293] CONDENSING AND NON-CONDENSING 285 293. The Main Purpose In Reducing The Back Pressure On A Steam Engine By Means Of A Condenser Is To Save Steam And Thus Save Coal. That is, an engine will develop a given amount of power from less steam if a condenser is used; or, conversely, it will develop more power on a given amount of steam when a condenser is used. EXPLANATION. Fig. 351 represents an ideal condensing engine indi- cator diagram (Sec. 78) superimposed on a corresponding non-condensing diagram. The steam pressure is represented by line PP'; atmospheric pressure by line A A'; and zero pressure or complete vacuum by VV. Consider first that the same volume of steam, S 2 , is used for both con- densing and non-condensing operation, and that this steam expands as represented by line RS. Then, area PRSB'BP represents the work done FIQ. 351. Ideal indicator cards showing comparative work areas, working pressures, and steam consumptions for condensing and non-condensing operation. by the engine running non-condensing; area PRSC'CP represents that done condensing. The shaded area represents the increased work done when running condensing over that when running non-condensing. PI represents the working pressure range with the condenser as compared to Pa without it. The engine thus develops more power from the same amount of steam when operated condensing. But assume that by an earlier cut-off less steam, Si, is admitted to the cylinder so that the expansion follows the new line MN. Si is assumed to be of such an amount that the work area PMNC'CP is equal to the area PRSB'BP. Then the shaded area is equal to the area MNSR, and the work done by a volume of steam Si with condensing operation is equal to that done by a volume of steam 2 with non-condensing operation. Thus the same amount of work is done by less steam with condensing operation. NOTE. METHODS OF CALCULATING THE PERCENTAGE SAVING OR POWER INCREASE DUE To CONDENSING OPERATION are given in the author's STEAM POWER PLANT AUXILIARIES AND ACCESSORIES. 286 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 9 294. Condensing Operation Is Not Economical For Any Engine When Most Of The Exhaust Steam From The Engine Can Be Profitably Used For Heating Or Industrial Purposes. It is much more economical to use exhaust steam for heating than to condense the exhaust and heat with live (boiler- pressure) steam. When all of the exhaust steam from an engine is used for heating, the engine merely acts as a reducing valve and furnishes power as a sort of by-product. On the other hand, when the exhaust is condensed, much heat is absorbed by the condensing water and is lost. In general, the exhaust from an engine should be condensed only when it cannot be used. Outet To... ' FIG. 352. Low-level jet condenser and condenser pump connected to engine and cooling tower. (Water is pumped by the hot-well pump from H to the top of T, and flows by gravity to W. If the condenser, C, fails to work, V opens and the engine exhausts to the atmosphere through A. The heat absorbed by the water in C is removed by evaporation in T.) NOTE. SINCE CONDENSING OPERATION REQUIRES CONSIDERABLE RELATIVELY COLD WATER, IT Is ONLY FEASIBLE WHERE THERE Is AN ADEQUATE WATER SUPPLY. In practice 25 to 100 Ib. of water are required for each pound of steam condensed. Water for a condenser may be recooled in a cooling tower (Fig. 352) or pond and used repeatedly. 295. Table Showing Average Steam Consumptions Of Various Types Of Engines Operated Condensing And Non- Condensing At Full Load. (Based on data from O. B. Goldman's FINANCIAL ENGINEERING.) SEC. 296] CONDENSING AND NON-CONDENSING 287 Engine Saturated steam at 150 Ib. per sq. in. pressure Superheated steam at the same pressure, 100 deg. fahr. superheat Pounds of steam per i.h.p. hr. Per cent. Pounds of steam per i.h.p. hr. Per cent. Non- cond. Cond. * Saving Non- cond. Cond.* Saving Simple, high-speed, single-valve, 18 in. -stroke Simple, four-valve, 18-in. stroke. . . . Compound 18-in. stroke 27.6 24.1 22.0 20.8 25.7 19.8 14.8 17.1 7 18 33 18 17.0 18.3 12.7 15.0 25 18 * The condensing operation is at 26 in. of mercury vacuum. NOTE. The steam consumptions of the condenser auxiliaries are not included in the above values. The condenser auxiliaries, when steam driven, ordinarily consume about 1 to 6 per cent, as much steam as is consumed by the main engine. 296. Cylinder Condensation Is Of Importance In Determin- ing Whether Condensing Or Non-Condensing Operation Is The More Economical. The efficiency loss due to cylinder con-*- 60 3 55 20 \$3 Condenser Vacuum-?6 In. Pressure -150 Lb. per Sq. In, - - A 10 20 30 40 50 56 Percentage of Stroke at Cut-Off FIG. 353. Graph showing that, with condensing operation of a simple engine, the loss due to cylinder condensation is greater than with non-condensing operation; and that it increases as the cut-off becomes earlier. (The percentage loss is greater in smaller engines. The increased loss due to condensing operation is greater when the steam pressure is less. The values were calculated by a formula by R. C. H. Heck.) densation (Sec. 307) in a simple engine (Figs. 353 and 354) is increased by condensing operation. The live steam in a simple engine is admitted to the space which was recently occupied by steam at condenser pressure. The live steam may have a 288 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 9 temperature 300 deg. fahr. or more above that of the con- denser-pressure steam; see a steam table for temperatures of steam at different pressures. The live steam (as explained in Sec. 274) must heat the cylinder walls to nearly its own temperature. In heating the cylinder walls, the live steam is cooled and thereby partially condensed which results in a heat loss. In compound engines (Div. 8), the difference in 15 20 Back -Pressure, Lb. Per Sq In. Aba. FIG. 354. Graph showing that, as the back pressure on a simple engine is reduced or as the vacuum is increased the loss due to cylinder condensation becomes greater. (Simple engine 18 X 12 in. Steam pressure 100 Ib. per sq. in. gage. Speed 175 r.p.m. Cut-off at 20 per cent, stroke. Calculated by a formula by R. C. H. Heck.) temperature between the incoming and outgoing steam in each cylinder is usually much less than in a simple engine. Uniflow engines (Fig. 348) are so constructed that the cool condenser- pressure steam is exhausted in the center of the cylinder whereas the live steam is admitted at the ends. This prevents, in a measure, the cooling of the cylinder ends by the exhaust steam. Compound and uniflow engines are therefore able to get the benefit of the increased working pressure effected by a condenser without incurring excessive loss due to cylinder condensation. SEC. 297] CONDENSING AND NON-CONDENSING 289 297. The Chief Advantages And Disadvantages Of Con- densing Operation are as follows: CONDENSING NON-CONDENSING Advantages Disadvantages Decreases steam consumption of large engines 20 to 40 per cent. Recovers most of the feed water unless a jet condenser is used with impure water. The recovered feed water is usually 50 deg. fahr. hotter than fresh feed. Increases power output of a given installation or decreases necessary size of installation for given power output. Converts heat, which would other- wise be wasted, into work. Requires more steam. Must use fresh feed water which may be expensive to heat and purify. Requires larger boiler installation. Wastes most of the exhaust steam unless it can be used for heating. Disadvantages Advantages Requires additional equipment, * i.e., condensing, pumping and water recooling equipment. Operation more difficult. No steam available for heating. Difficulty in keeping j oints tight and maintaining additional equipment. Relatively low first cost. Operation relatively simple. Exhaust steam available for heat- ing. Fewer joints to keep tight. * In condensing plants these auxiliaries are often steam driven and their exhaust steam is used to heat the feed water. This arrangement lessens the disadvantages of the extra equipment. 298. The Most Profitable Degree Of Vacuum Is Greater With A Uniflow Engine Than With Simple Or Compound Counterflow Engines. The most profitable degree of vacuum for uniflow engines is the highest vacuum that may be reason- ably maintained. The most profitable degree of vacuum for compound counterflow engines is about 26.5 in. of mercury (or about 88 per cent, of a complete vacuum). Further 19 290 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 9 decrease in back pressure is not warranted for these reasons: (1) The power required by the condenser pumps would rapidly increase. (2) Economy would not materially increase. (3) Leaks become troublesome. (4) Cylinder condensation is very great. NOTE. The subjects of starting, stopping and. maintaining condensers are treated in Div. 13. 299. The Chief Application Of The Condensing Engine Is For Electric Power Plants Which Have A Limited Supply Of Water, And For Driving Slow-Moving Machinery Which Cannot Be Turbine Driven. Large modern power plants are, whenever possible, located on a lake or river or arm of the ocean so that there is an abundant supply of cooling water. Such plants nearly always employ turbines, which operate with a higher vacuum than is profitable with engines, and better economies are thus obtained than with condensing engines. Smaller plants which are not so located may employ condensing engines and re-cool the condensing water in a cooling tower or pond. Since the principal use of the turbine is for driving machinery which permits of high rotative speeds (for example, generators and centrifugal pumps), its applica- tion would not be suited to mills and other plants where direct, belt or rope driving is employed. In such plants the condensing engine is commonly used for steam power genera- tion even though the supply of water is adequate for econom- ical condensing turbine operation. QUESTIONS ON DIVISION 9 1. What is meant by condensing operation? How is it accomplished? 2. Explain by a diagram how more power is developed from the same amount of steam by condensing operation. 3. What saving is effected by condensing operation of large compound engines? What is the proportion of the steam required by the main engine to that used by the condenser auxiliaries? 4. When is the condensing operation of any engine less economical than non-con- densing operation? 5. How does cylinder condensation affect the economies of engines of various kinds when operated condensing? 6. Enumerate the chief advantages and disadvantages of condensing operation. 7. What percentage of a total vacuum is ordinarily profitable in a condenser for a compound engine? 8. Give two conditions under which condensing engines are commonly used. DIVISION 10 STEAM-ENGINE EFFICIENCIES AND HOW TO INCREASE THEM 300. The Steam Engine Converts Into Mechanical Work Only A 'Relatively Small Part Of The Total Heat Supplied To It; see Sec. 6. Under some conditions, the heat which is not converted into work may be usefully employed. Under such conditions as will be explained later, the fact that the engine converts into mechanical work only a small part of the heat energy which it receives becomes of comparatively little consequence. Under other conditions, it is of great commer- cial importance. For example, the steam locomotive seldom converts into mechanical work over 10 per cent, of the total heat supplied to it. The remaining 90 per cent, or more produces no useful effects in the locomotive and represents a total loss. Why a large part of such loss is unavoidable, and how the avoidable parts of it may be reduced, constitute the subject of this division. See also the portions of Div. 12 which relate to efficiency. NOTE. THERE Is No POSSIBLE WAY IN WHICH THE EFFICIENCY OF AN ENGINE, WHICH Is ALREADY INSTALLED UNDER GIVEN OPERATING CONDITIONS AND WHICH Is IN GOOD REPAIR, CAN BE GREATLY INCREASED. If the valves and pistons of an engine have only a negligible leakage (Div. 13) and the engine is properly adjusted (Divs. 4 and 5), cleaned, lagged, and lubricated (Div. 16) the operator has ordinarily no further responsibility for its efficiency. It is sometimes possible, where the design of the engine permits, to change to condensing operation, to superheated steam, or to higher boiler pressure, in order to increase engine efficiency. However, these operating conditions are usually so determined in a plant that they cannot be changed without completely rebuilding the plant. When an engine is first selected it should, therefore, be so chosen that it will give the desired efficiency without its being necessary later to alter other plant equipment. Therefore, the efficiency of an engine, assuming good maintenance and correct application, depends entirely on its design. In general, the efficiency of an existing 291 292 STEAM ENGINE PRINCIPLES AND PRACTICE [Drv. 10 steam-power plant can be improved by giving detail attention to the boiler room rather than to the engine room. It is in the boiler room that a great part of the correctable wastes occur. 301. Why A Large Part Of The Losses In A Steam Engine Are Unavoidable may be understood by a study of the hydrau- lic analogy of Fig. 355. Fall in temperature, representing as it does loss of heat or loss of energy, is compared to fall of water, which represents loss of head or of its potential energy of position. The steam engine, A, can operate non-condensing over only a certain temperature range, just as a water-power er ^ure_ _ _ J/ a terAnbp_Of Cliffy Fait Of Water Compared With Fa// In Tempera ture To Datum Plane evel. I- Engine I- Water Power FIG. 355. Showing analogy between water-power utilized and heat utilized by steam engine. plant can utilize only the hydraulic head of the water fall, B. By adding the condenser, C, an additional range in temperature may be utilized just as the fall in the rapids, D, might be utilized by the water-power plant by means of additional piping. But it is just as impractical to cool to 32 deg. fahr. in the condenser as it is, ordinarily, to pipe water to sea level to utilize the final drop or head to that datum plane. EXPLANATION. At 32 deg. fahr. water is, for steam engineering pur- poses, considered to contain no heat just as water at sea level is con- sidered to have no potential energy. There is a large theoretical tem- perature range to absolute zero ( 460 deg. fahr.) just as there is a large theoretical hydraulic drop from sea level to the center of the earth. But, SEC. 302] STEAM-ENGINE EFFICIENCIES ' 293 to use the temperature range below 32 deg. fahr., mechanical refrigera- tion must be employed; and to use water power below sea level, the water must be pumped back to its original level. In either case, no additional power would be developed. It follows that, although only a small part of the total absolute temperature range (and therefore of the total heat) is useful in the steam engine, the remainder is of such nature that little of it can be utilized. 302. It Is Often Unwise To Increase Engine Economy At The Expense Of Greater Fixed Or Maintenance Charges. Fixed charges are taxes, insurance, the interest on the capital invested and depreciation or the amount of money which must be laid aside yearly to replace the engine when it is no longer useful (see Div. 15). Steam-engine operation is, ordinarily, a commercial undertaking increased fixed or maintenance charges may increase total power plant expense as much as do increased fuel costs due to poor engine .efficiency. There- fore engines are not, necessarily, built or operated with a view to securing the greatest possible thermal efficiency. Instead, they should be built and operated to provide the maximum economy, when all factors of cost are considered. Thus, while higher initial steam temperatures used with larger ratios of expansion and higher vacua increase thermal efficiency, such methods of increasing economy are limited by the other costs involved. In general (see Div. 15), the fixed charges on an engine should be much less than the cost of the fuel ; and the engine maintenance charges should be a small fraction of the total expense of the engine during its life. 303. The Losses In A Steam Engine May Be Divided Into Three Classes (see Div. 1) : (1) Rejection losses or heat which it is not possible for a commercial steam engine to use. Since these rejection losses are largely dependent on the kind of cycle on which the engine operates, their amount will be considered quantitatively in Sees. 314 to 316 under the Rankine cycle. The rejection " losses " are often not lost at all. All of the heat thus rejected is present in the exhaust steam and may fre- quently be used for steam heating. (2) Thermal losses (Sec. 309). These losses nearly always constitute actual losses because the heat thus lost is too widely diffused to be useful. 294 ENGINE PRINCIPLES AND PRACTICE [Div. 10 (3) Mechanical losses (Sec. 310). These losses subtract from the mechanical work which has been derived from the heat; and convert part of the work back into heat in the bearings where it is useless and particularly undesirable. NOTE. IN A STEAM ENGINE, THE PERCENTAGE LOSSES ARE A MINI- MUM AT OR NEAR RATED FULL LOAD (Fig. 356). At a considerable Steam Consumption Lb. Per I. H. R Hr. ""> lx> lO O- 4s c / \ / \ / \ / \ / r s ^ 50 100 150 200 Percentage Of Rated Load I- Non- Condensing b. Of Steam Per I.H.RHr. OJ is U1 i ~ %ti I-Wal . expansion -^\,x J^.g N^^agraHBm^^rk N \ <^%^^ompre55bnWith5mall\\{ V^.vJ M^^%^y?>^ ,-CLearance I__L_ " ~ FIG. 360. Showing how less power is derived from the same amount of steam when the clearance volume is larger. EXPLANATION. Fig. 360-1 shows two superimposed ideal indicator diagrams having expansion lines, MN and MNi. The solid-line diagram has a clearance volume, Cj, of 3 per cent. Compression occurs at A and t.hg_p.uahinn stftam is compressed along line R, to about one-half throttle pressure. The dashed-line diagram has a clearance volume, C 2 , of 15 per cent. Compression then occurs at B and the cushion steam is compressed along line S. The shaded area between lines, R and S, then represents the loss in work due to the larger clearance volume, C 2 . SEC. 306] STEAM-ENGINE EFFICIENCIES 297 The steam is compressed to the same theoretical point, D, on the throttle pressure line so that the amount of steam used, Q, is the same in both diagrams. With the larger clearance, there is a slight gain in work on the expansion line represented by the shaded area, MNN\. This area would be equal to the area RS, if the expansion were carried out to back pressure but, with incomplete expansion, area MNNi is smaller than area RS. Fig. 360-11 shows the difference between the clearance losses in actual Corliss and automatic-engine diagrams. The wire-drawing at W in the automatic-engine diagram nullifies the theoretical gain due to larger clearance shown at N\ in I. 306. Table Showing Typical Values For Clearance In Engines Of Different Types, based partly on data from Marks' MECHANICAL ENGINEERS' HANDBOOK : Engine Clearance as a percentage of the displacement volume High value Low value Flat slide valve at side of cylinder Piston valve at side of cylinder Corliss valves Poppet valves 10 15 8 4 5 7 2 1.5 307. Cylinder Condensation Is The Cause Of Part Of The Rejection And Thermal Losses in a steam engine. The three causes of cylinder condensation are: (1) The natural mixing of the supplied steam with the colder steam in the clearance space. This can be greatly reduced by using high compres- sion pressures. (2) Alternate exposure of the cylinder walls to the live steam and exhaust steam. Condensation due to this cause is partly avoided by compounding and use of the uniflow principle. (3) Radiation of heat through the cylinder walls. This is considered a thermal loss (Sec. 309). NOTE. JACKETING (Fig. 359) PREVENTS SUCH CONDENSATION IN THE CYLINDER PROPER As Is DUE To RADIATION. However, condensa- tion takes place in the jacket, and often exceeds, in amount, the saving due to no condensation in the cylinder proper. Jackets are useful in keeping cylinders warm or warming them up in starting. 308. Where The Exhaust Steam Can Be Economically Used For Heating, the rejection losses are of little consequence. 298 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 10 Many power plants which furnish both power and heat use large, simple slide-valve engines and make few provisions for reducing rejection losses. The power plant may then be 50 to 80 per cent, efficient because the exhaust steam is used for heating. The plant then has no rejection losses only mechanical and thermal losses. The performance of the engine itself is no better under these conditions than if the rejected heat were lost but the expense of the rejected heat cannot, when the exhaust is used, be charged to the engine as it can when the live steam is used, for power only. Losses In The ,.p Piping 1. 4 %'> Losses In Piping 1.1%' Loss By Cooling Of Conctensate 1.1% FIG. 361. Showing heat balance in a power plant in which the engine exhaust is used for heating. EXPLANATION. The advantage of using an engine's exhaust steam for heating where both power and heat are desired may be understood by comparing Fig. 361 with Fig. 362. In Fig. 361, it is shown that, with the exception of boiler losses and small piping losses, PI, nearly all of the heat, HI, imparted to the steam in the boiler appears either as work or as useful heat. In Fig. 362, part of the steam, G 2 , is used directly for heating and the rest,. Ez, for operating a condensing engine. There is then a large heat loss in the condenser. Less power is developed by the Fig. 362 arrangement and less heat is available from the same original supply than is available with the arrangement shown in Fig. 361. Thus it is evident that although the efficiency of an engine may be low, the efficiency SEC. 309] STEAM-ENGINE EFFICIENCIES 299 of the combined power and heating plant in which the engine is used may be very high. Heat Transformed Into Work 5.9% 'Losses By ''Heat Carried Cooling Of Away By Drain Water Water Of 0.7% Condensation 30.2% FIG. 362. Heat balance in a plant operating a condensing engine and using live steam for heating. 309. The Principal Method Of Reducing Thermal Losses is by employing heat insulation or lagging on the cylinder .-Throttle-Valve Body .'Steam Valve Exhaust Valves FIG. 363. Well heat- insulated engine cylinder. (Cooper Corliss engine.) walls. The heat conductivity of the metal parts of an engine cylinder is fairly high and, therefore, if they are exposed to 300 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 10 the steam on one side and the air on the other, they conduct much heat from the steam to the air. A layer of porous non- metalic material such as magnesite, asbestos, or diatomaceous earth (L, Fig. 363) is packed around the cylinder walls to reduce radiation. The transmission of steam from one point to another always involves a thermal loss. The fact that transmitting any form of energy involves a loss is illus- trated by the losses in the electric circuits of Fig. 364. 6.5% Boiler & Chimney Loss zau/fe i Pipe Loss I: I, Rejected In Exhaust i- Loss In Engine Cylinder---- 58.7% Loss In Engine And Generator Line And Transformer Loss Delivered To Lamps Or Motors ......... 7.70% '- Sub-Station Street Railway a6 / ' 1.70% FIG. 364. Showing energy balance (losses and useful energy) in typical electric- energy distribution circuits based on a chart from Power. (The heavy figures represent energy lost or used in British thermal units per pound of coal fed to the furnace based on a coal which has a heating value of 13,543 B.t.u. per pound. The lighter figures indicate percentages of the total heat. The calculations were made on the basis that the generator is supplying power to only one of the three circuits either the machine shop, the street railway, or the street lamps. Should more than one circuit be in use at any time, the energy available for these circuits would still total 9.4 per cent., as shown below the dashed dividing line in the list, but it would be divided among the circuits in use. The diagram does not show the losses which are listed above the dashed dividing line of the list.) 310. The Two Principal Methods Of Reducing Mechanical Losses In An Engine are: (1) Designing the engine so as to minimize pressures on bearing surfaces. (2) Proper lubrica- tion (see Div. 16). Large bearings using thick oil have more friction than do smaller bearings using thinner oil. But, for satisfactory operation, the bearing area and viscosity of the oil must be such that an oil film will always be main- SEC. 311] STEAM-ENGINE EFFICIENCIES 301 tained between the rubbing surfaces. A vertical engine has slightly less friction than a similar horizontal one. Because of their vertical position, the rapidly moving parts that is, the piston and crosshead have little tendency to press against the cylinder and guides. An engine running "under" (Sec. 32) has less friction on the guides than one running "over" because when running under the thrust of the connect- ing rod partially supports the crosshead. Stationary engines are commonly built horizontally (Sec. 25) (because of the simpler balancing and framework) and run "over," in spite 15 50 15 5rake Horse Power FIG. 365. Showing variation in friction horse power with variation in brake horse power developed. of the differences in friction, as a rule (because of the easier maintenance) ; see Div. 13. The frictional losses of all engines increase somewhat with the power which the engine develops as indicated in Fig. 365 which is taken from Gebhardt's STEAM POWER PLANT ENGINEERING. 311. Engine Friction Comprises Principally: (1) Bearing friction. (2) Valve friction. (3) Gland friction. Bearing friction is reduced to a minimum by the use of low-friction combinations of metals. Thus, hard steel running in babbitt metal for main bearings (Fig. 366) and hard steel on bronze bushings for connecting-rod bearings (Fig. 367) are widely used. Piston friction may be reduced by means of low-friction metal inserts (Fig. 368) in the wearing face of the piston. Friction in slide and poppet-valves is reduced by balancing the valves (see Divs. 4 and 5). Gland friction may be re- 302 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 10 duced by using metallic-faced packing (Fig. 369) and other low-friction packings being careful never to have the packing pressed too tightly against its rod. Vertical Wedge For Oil-Cup Hole-. Cast Iron Bearing Quarter FIG. 366. Showing low-friction bab- bitt metal inserted in main bearing. (Erie Ball Engine Co.) Ring Section- FIG. 367. Bronze-bushed connecting- rod bearing. Closed-end type. Low- Friction Metal Rings - . I-Detail Of Rin0 H-Half Cross-Section I-Section Along A.C.B FIG. 368. Piston designed to reduce friction and wear by means of low-friction bull- rings, GG. (The single expansive ring E is used to make a tight contact with the cylinder walls.) 312. Mathematical Methods Of Computing Steam-Engine Efficiencies will be discussed in the remainder of this division. The preceding sections considered, in a general way, the causes of steam-engine losses and the common methods of minimizing them. To calculate the exact effect of changes SEC. 313] STEAM-ENGINE EFFICIENCIES 303 ^Sectional Metallic Packing Ring Forced Or Gravity Oil Feed Ring \ Gasket in operating conditions which were previously mentioned, the mathematical methods which herein follow may be em- ployed. Before proceeding consult the portions of Div. 1 which discuss the relations be- tween heat and work and energy and also those portions of Div. 12 which relate to efficiency. 313. Various Ways In Which The Efficiency Of A Steam Engine Is Commonly Expressed are as follows: (1) Based on indicated horse power, it may be expressed as: (a) Thermal effi- ciency based on indicated horse power, E dti in Fig. 370. (6) Pounds of steam used per indi- cated horse power hour, (c) Pounds of coal burned per indi- cated horse power hour, (d) British thermal units per indicated horse power minute, (e) Thermal efficiency based on indicated horse power compared to the ideal Rankine cycle, also called cylinder efficiency. '* ' Vanadium Cas t Iron 'Springs Hold Rings To Shaft FIG. 369. Piston-rod gland packing having low-friction metal wearing face. (Erie City Iron Works.) ^Efficiency Of The Rankine Cycle Ideal Rankine Cycle Ratio Ratio Gives Mechanical Efficiency ,:: Thermal Efficiency Ratio Gives ~~ Edtb =0ver -AU Efficiency FIG. 370. Chart showing relation between the various engine efficiency standards. (2) Based on brake horse power, it may be expressed as: (a) Over-all thermal efficiency or efficiency based on brake horse power, E d a> in Fig. 370. (b) Pounds of steam per 304 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 10 brake horse power hour, (c) Pounds of coal per brake horse hour, (d) British thermal units per brake horse power hour, (e) British thermal units per kilowatt hour. (/) Pounds of coal per kilowatt hour. (3) Mechanical efficiency, E dm in Fig. 370. NOTE. THE STEAM CONSUMPTION is ordinarily calculated for the engine on a dry-steam basis. Engine manufacturer's performance speci- fications are practically always computed on this basis. The weight of dry steam is the weight of the wet steam multiplied by its quality, expressed decimally. A little water suspended in the steam does not decrease the engine efficiency when the efficiency is computed on a dry- steam basis (See the A.S.M.E. TEST CODE in Sec. 381). But the water, of course, does no work. Hence, when an accurate determination is being made, the presence of the water must be considered and the apparent efficiency decreased accordingly. In any case, the efficiency is proportional to the quality of the steam. NOTE. THE "THEORETICAL EFFICIENCY" DEFINED IN Div. 1 is very nearly equal to the thermal efficiency as shown in Fig. 370. The "theoretical efficiency" in Div. 1 includes a small amount of losses by radiation from the engine whereas the thermal efficiency includes only the net indicated work. The "theoretical efficiency" is not ordinarily computed in power plant testing. 314. The Ideal Rankine Cycle Is Frequently Used In Steam-Engine Testing As A Standard Of Engine Performance. (See note below and also the author's PRACTICAL HEAT.) The ideal Rankine cycle (Sec. 8; also called the Clausius cycle) is the most nearly perfect cycle upon which a commer- cial steam engine can operate. It is, therefore, the logical cycle with which to compare steam-engine performance. A mechanically perfect engine without friction, without clear- ance losses, with perfectly non-conducting cylinder walls, and which expanded the steam from exactly throttle pressure to exactly back pressure, would develop all of the power of the ideal cycle (see Fig. 7) . Since no actual engine can have all of these characteristics, no engine can have as great an efficiency as the ideal Rankine cycle on which it operates. NOTE. A RANKINE CYCLE MAY HAVE CLEARANCE AND STILL BE IDEAL. That is, clearance does not involve a loss, provided compression is so timed that the steam in the clearance space is compressed to throttle SEC. 315] STEAM-ENGINE EFFICIENCIES 305 pressure. Thus I and II (Fig. 371) show ideal performance but III, having terminal drop, T, is less efficient. NOTE. AN ENGINE CYCLE is understood to mean the series of repeat- ing processes which occur in the engine cylinder. The cycle is con- veniently pictured on the indicator diagram, which is thus a cycle diagram. Thus, in a practical steam engine the cycle diagram is com- posed of (as shown in Fig. 88) an admission line, a steam line, an expansion line, a release line, an exhaust line, and a compression line. Moreover, the exact cycle of any particular steam engine is further determined by the pressure variations along each of these lines. I-Oriojinal Ideal Rankine Cycle 315. To Compute The Effi- ciency Of The Ideal Rankine Cycle for any set of operating conditions, use the following formula: H ti (29) E dt (a decimal) Clearance H- Ideal Rankine Cycle With Clearance Loss) M- Modified Rankine Cycle. Terminal Drop Involves Loss T FIG. 371. Showing two forms of Hii- Wherein: E dt = the thermal efficiency of the ideal Rankine cycle, expressed decimally. H t i = the total heat per pound of steam as admitted to the engine. the ideal Rankine c y cle and Codified , ' , Rankine cycle. H t2 = the total heat per pound of steam as exhausted from the engine, assuming that it expands adiabatically from the conditions of H t \. Hi 2 = the heat of liquid at the temperature and pressure at which the steam is exhausted. DERIVATION. In general, thermal efficiency = heat converted into work -f- heat input. The heat converted into work in the ideal Rankine cycle, since there is no thermal loss, is the difference between the heat present in the steam admitted and that present in the steam exhausted or Hti Htz- The heat input is the amount of heat which must be supplied to the water at the exhaust temperature to convert it to steam at the admission temperature and pressure, namely (H t \ Hit). Hence the efficiency = heat converted into work -f- the heat input = (Hti Htz) EXAMPLES. Compare the efficiencies of ideal Rankine cycles under the following conditions: (1) 95 per cent, quality steam at 100 Ib. per 20 306 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 10 sq. in. abs. and 20 Ib. per sq. in. abs. back pressure. (2) Saturated steam at 175 Ib. per sq. in. abs. to 1 Ib. per sq. in. back pressure. (3) Superheated steam at 175 Ib. per sq. in. abs. and 200 deg. fahr. superheat to 1 Ib. per sq. in. abs. back pressure. SOLUTIONS. Find the total heats from a total-heat-entropy chart or temperature-entropy chart such as that found in the author's PRACTICAL HEAT and find the heats of liquids from the steam table. By For. (29), the thermal efficiency, E d t = (H t i H t 0 O5 05 CDCOCCCO>OiCCDCO O CO O5 T}< 05 d O5 d d <** CO ^ T}< ascodoJososooas' o' 06 CO tH O t- d O5 06 co C5O5-HO-*O TK * ^ * OQOO5i-i>OOi-lO * CO coNTfcor-oooco co O 0 M C 13 > xxxxxxxx xx ^*t-o ! XX XX ^ C N \M 00 a j Peabody, Thermodynamics Peabody, Thermodynamics Trans. A.S. M.E., Vol. 14, p. 826 Shop test Elec. World, Sept. 1, 1904, p. 407. Elec. World, Oct. 1, 1904, p. 587. . Eng. Record, July 6, 1901, p. 7. . . Meyer, Steam Power Plants, p. 56 Locomotive Tests, 1904, at Louisiana Exposition Elec. World, Sept., 1904, p. 407. .. s 1 Peabody, Thermodynamics Elec. World, Oct. 1, 1904, p. 587. . Elec. World, Sept. 10, 1904 p. 407 Barrus, Engine Tests, p. 95 : c . c ' J* ' '. : . (^ : : "S ' oT ' ' ;H i I ; 13 08 . ; . ; : " 8 ; jjlllj ||| llfllllllll se^so< S . o 02 ' T I ' t IS ^-^ G >> G ^ B >H Pl5|S 2 i 1 i I tf S 1 * 2 !P!i^|! |*l*1.!*'f'.| 1 1 3 1 & 1 1 J PL, On PH PH PM CO s O ^' u p^ J* Q *- M a I 0) T5 u > 13 > 1 : 00 3 X o X (O t> IN -^ 6 -t $ 00 <0 l>) CM ^H i D i~ CM * 00 Tf< TfH CO CO 1 s CO U3 co o o 1C <* O * 1C X 2 ?M 01 2 O 8 (0 5 o i g O 10 2 o 3 l> o (N CO CM c et t O5 s ^ s c^ IN ;r co o 09 69 1H ** C-l O 5H O ss o o s o CM ?, o co s o o co CM O iO ^1 CO CO ^ X (0 d 1 o co a Barrus, Engine Tests, p. 101 Barrus, Engine Tests, p. 118 Barrus, Engine Tests, p. 88 Peabody, Thermodynamics Corliss, jacketed Poppet valves, jacketed Gridiron valves 1 5 i ^ > i K 1 1 314 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 10 325. Table Showing Economies Of Multi-Expansion En- Kind of engine References Cylinder dimensions Quadruple Nordburg pumping engine, Wildwood, Pa. Eng. News, May 4, 1899, p. 280 29, 49 1- X 42 Triple Allis pumping engine, Chestnut Eng. News, Aug. 23, 1909, 30,56,87 X 66 Hill, Boston. p. 125 Allis pumping engine, Bissel's Point, St. Louis Power, May, 1906, p. 299 34, 62, 94 X 72 Holly pumping engine, Spot Eng. News, Nov. 14, 1901, 22, 41, 62 X 60 Pond, Boston. p. 371. Sulzer mill engine, Augsburg. . . . Zeit. d. V.D.I., May 16, 1896, 29.9, 44.5, 2(51.6) p. 534. X 78.7 Compound, Allis-Chalmers engines, New York Subway Power, Feb., 1906, p. 115 2(42), 2(86) X 60 Cross-compound Corliss, At- lantic Mills, Providence Leavitt puming engine, Louis- ville, Ky. Rice & Sargent Corliss, Amer. Sugar Refinery, Brooklyn. Fleming four-valve. Williams Vertical, New York Navy Yard Am. Elecn., June, 1903, p. 260. Trans. A.S.M.E., Vol. 16, p. 169. Trans. A.S.M.E., Vol. 24, p. 1274. Trans. A. S.M.E., Vol. 25, p. 212. Power Oct , 1903, p 583 . 16, 40 X 48 27, 54 X 120 20, 40 X 42 15, 40H X 27 19, 34 X 30 Tandem-compound Corliss Edison Waterside Sta., N. Y Barrus, Eng. Tests, p. 185 Power, July, 1904, p. 24 18, 44 X 72 43>, 75.3 X 60 Compound, Ball & Wood Co. Corliss, W. Al- bany Sta., N. Y. C. & H. R. R. Willans Willans Ball engines, Chicago Public Library. Westinghouse Marine Skinner cross-compound Buffalo tandem-compound. Reeves vert, cross-compound. . . . Cross-comp'd, 4 slide valves 4-cylinder compound locomo- tive No. 2512 Penna. System. Test by Company Engineers. . . Peabody, Thermodynamics. . . . Peabody, Thermodynamics. . . . Eng. Record, Aug. 6, 1898, p. 206. Power, Aug., 1903 Power, July, 1906 Elec, World, May 23, 1903, p. 897. Eng. Record, July 1, 1905, p. 24 Barrus, Eng. Tests, p. 181 Tests made at Louisiana Ex- position, 1904 21, 41 X 30 10, 14 X 6 10, 14 X 6 12, 20 X 13 17, 27 X 24 16, 27 X 18 12, 18 X 10 12, 20 X 14 17M, 28 X 48 14.2, 23.7 X 25.2 * Combined efficiency of pump and engine. t Cnmhinprt p.ff\r,\p.nr,v nf fincrinp and ETfinerator. SEC. 325] STEAM-ENGINE EFFICIENCIES gines Operating On Saturated Steam. 315 ~~ Oi ^ o S3 a g a ^ o '5 . tfl T3 oj d 43 C fi ^" o oo rt : . 1 a '3 ^ a .2 1 a a 1 1 *- "2 * | o> "C >> u i -o a a a J d 1 * >> a . "8 a "'1 11 . * |i j i 5 o w !& O Pi rt S J | ^ h3 ' rt 2- ** 5' J& i ^ expansion 712.0 200.0 0.9 36.5 35.5 310.8 12.26 186.0 22.8 138 74.2 93.0 expansion 1:3^:8.4 801.0 185.0 0.85 17.2 23.4 155.0 10.33 196.0 21.63 138 70.5 *93.3 1:3.3:7.6 1:3H:8 865.0 464.0 140.0 150.0 1.2 1.05 16.5 24.8 20.8 20.5 157.9 10.59 11.01 201.4 203.4 21.06 20.85 151 142 75.0 70.0 *97.4 *96.5 1:2.2:5.9 1823.0 134.0 1.8 56.2 19.5 122.0 11.33 208.0 20.40 158 76.0 condensing 1:4.2 7365.0 ] 175.0 2.2 75.0 27.9 130.0 11.96 220.0 19.2 159 72.4 t93.0 1:4 500.0 643.0 170.0 0.8 137.0 0.95 80.0 18.6 20.5 24.9 100.0 11.20 12.20 222.0 222.0 19.0 19.0 141 150 63.5 67.6 93.0 1:4 627.0 151.0 0.85 121.0 19.4 121.0 12.10 222.7 19.0 143 64.3 1:7.3 348.0 150.0 2.0 152.0 13.0 126.0 12.33 225.8 18.7 162 71.7 l:3K 340.0 100.0 2.0 150.0 16.5 126.0 12.60 229.0 18.5 175 76.5 1:6.4 6893.0 145.2 1.5 60.3 20.6 116.0 12.70 234.0 18.1 157 67.0 1:6.02 5442.0 185. 0| 1.5 76.3 26.5 116.0 11.93 221.0 19.2 150 68.0 t95.2 non-condensing 1:3.8 1125. C 175.0 Atmos. 120.0 47.0 to ft 17.17 291.0 14.5 229 78.8 1:2.0 39.6 165.0| Atmos. 401.0 42.4 -' - .-'" ' Floor Line ,-Anchor-Plate . Foundation '. wy//JD/wI^ ~28" Exhaust Pipe Hi-Side Elevation FIG. 390. Assembly drawing of a cross-compound Fulton-Corliss steam engine. The cylinders are 36 and 76 in. in diameter. The stroke is 54 in. are generally constructed for non-condensing service. Although most of the used steam is exhausted at the end of the forward stroke through the central exhaust holes in the cylinder wall, more steam is exhausted 330 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 11 SEC. 333] STEAM ENGINES OF MODERN TYPES 331 during the return stroke through auxiliary exhaust valves. Although such an engine is not truly of the uniflow type, its economy (Fig. 392) is generally somewhat better than that of an engine operating on the true counter-flow principle. 333. The Uniflow Engine (Sees. 59 and 434 and Fig. 391), as originally invented, was intended to be operated condensing and to have no exhaust valves. The expanded steam should be exhausted through the central port-holes in the cylinder when these holes are uncovered by the piston. When these holes are again covered by the returning piston, the unex- hausted steam within the cylinder (at condenser pressure of 1 to 2 Ib. per sq. in. abs.) is compressed. Since the compression period is long and the clearance small, the unrejected steam is Lb. Steam Perl.H.P-Hr D Cn o Cn O Not -j-Conct ?ns/ngr hi ( 'onden sing--. \ r: "0 25 50 Ib 100 125 Per Cent Of Rated Load FIG. 392. Steam-consumption curves for a 21 by 22 in. Skinner "Universal Unaflow" engine supplied with saturated steam at 140 Ib. per sq. in. gage. FIG. 393. Actual indicator diagrams from a 20 by 24-in. Chuse condensing uniflow engine at the Holstead Mill and Elevator Co., Holstead, Kan. The operat- ing conditions under which these diagrams were taken are: Steam supplied at 150 Ib. per sq. in. Vacuum in condenser, 23 in. Speed 200 r.p.m. compressed to a high pressure usually the pressure at the throttle. The cylinder heads are jacketed with high tempera- ture steam. Thus the unrejected steam is superheated during its compression. Because of this fact and because the colder exhaust steam does not sweep over the warm surfaces near the heads, cylinder condensation is much less in this engine than in a counter-flow engine. Also it has been found that the ratio of expansions within the cylinder can be varied widely without appreciably affecting the economy. This accounts for the small difference (Fig. 392) in the uniflow steam rates between full load and small fractional loads or large over- loads. Since the normal cut-off is usually about Jf o to J stroke, uniflow engines are capable of large over loads. Fig. 332 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 11 393 shows typical indicator diagrams. With saturated steam at moderate pressure the steam rates are about 12 to 15 Ib. per i.h.p. hr. With higher pressures and superheat still better economy can be obtained. The record, it seems, is reported by Lentz as 5.67 Ib. per i.h.p. hr. with steam at 461 Ib. per sq. in. abs. and superheated by 495 deg. to 1,018 deg. fahr. 334. Non-Condensing Uniflow Engines must, of necessity, be built differently from those which are designed to operate only condensing. Modern uniflow engines are frequently designed so that they may be operated either condensing or non-condensing. A uniflow engine designed solely for condensing operation, if operated non-condensing would compress steam from a pressure of about 15 Ib. per sq. in. abs. instead of from 1 or 2 Ib. The result would be that, if no provision were made to prevent it, the pressure in the engine cylinder would rise during compression to many times the pressure of the incoming steam. To prevent this excessive pressure (which would probably cause rupture of the cylinder) several schemes are employed. (1) The clearance volume may be increased so that a much greater space is provided to store the ^ compressed steam ; engines which Atmospheric Pressure-----.-* .-.':::'.'. \ are to be operated either con- FIG. 394. Actual indicator diagrams . ' . , from a 23 by 28-in. chuse non-condens- densmg or non-condensing are ing uniflow engine at Bridge & Beach equipped with a small clearance Mfg. Co., St. Louis. These diagrams - , , . , . , taken while the operating condi- for Condensing Operation which were tions were: Initial steam pressure, may be Connected by Opening 160 Ib. per sq. in. Exhaust, atmos- , .,, jj-o.- i speed 150 r.p.m. a valve with an additional space to provide the necessary clearance for non-condensing operation the valve may be automatic (Fig. 244) or hand-operated. (2) Auxiliary exhaust valves may be employed to continue the exhaust period during a portion of the return stroke after the main exhaust ports are covered by the piston; these valves may connect into the cylinder at the end (Fig. 486) or into the wall some- where between the center and end of the cylinder (Fig. 224). Typical indicator diagrams from an engine which has SEC. 335] STEAM ENGINES OF MODERN TYPES 333 auxiliary exhaust valves are shown in Fig. 394. Engines of this type which are to be operated either condensing or non-condensing are generally fitted with some means, auto- matic or manual, for keeping the auxiliary valves closed when operating condensing. (3) The admission valves may be lifted from their seats or relief valves set to open when the pressure within the cylinder becomes excessive thus allowing steam to escape from the cylinder. This means of adapting a condensing engine to non-condensing operation is necessary as a safety measure but is wasteful and, therefore, is not employed during regular running. NOTE. THE ECONOMY OP NON-CONDENSING UNIFLOW ENGINES varies somewhat with the design, but with saturated steam at moderate pressures (125 to 150 Ib. per sq. in. gage) steam rates of 18 to 25 Ib. per i.h.p. hr. may be expected at full load. At partial loads and overloads, the steam rates increase more rapidly than for condensing uniflow engines but still not as rapidly as for counterflow engines. Non- condensing uniflow engines have been run at 250 per cent, of their rated load with only a 25 per cent, greater steam rate than at rated full load. The costs of these engines are given in Sec. 338. They may be safely operated on steam at any pressure and temperature so long as effective lubrication can be maintained (see Sec. 430). 335. The "Locomobile" Is A Type Of Steam Engine (Fig. 395) which is built integral with a boiler which supplies its steam. It was first made in Germany under the name "lokomobile." Many of these units have long been in use in Europe but, until recently, few have been used in this country. The engine is mounted above the boiler and the flue gases are used to jacket the cylinders. Steam is usually generated at a high pressure and superheated. The entire unit is so designed that its efficiency can be maintained very high. The loco- mobile type of power plant is manufactured in this country under the name Buckeye-mobile (see Table 337) which is illustrated in Fig. 395. The engine is a tandem-compound with piston valves; the receiver is placed in the flue-gas path and arranged as a reheater. Typical performance graphs are shown in Fig. 396. By reason of its exceptionally good econ- omy, the locomobile is very well suited for small power plants where good boiler water is scarce and where fuel is expensive. 334 STEAM ENGINE PRINCIPLES AND PRACTICE (Div 11 336. Steam-Engine First Cost Is Influenced By Many Factors. In a general way, the cost of an engine depends on its cylinder dimensions and the maximum pressure which the SEC. 336] STEAM ENGINES OF MODERN TYPES 335 cylinder will sustain. But, to establish some relation between cost and the power which the engine will develop that is, to attempt to predict the exact cost of an engine of a certain class and horse power is almost impossible because of the many influencing factors: (1) Initial steam pressure deter- mines the power which an engine will develop an engine of a given size (and cost) will therefore give most power when supplied with steam at the maximum pressure for which it is .24 I" m 12 5,0 ^Z5fl ~ H.P Superheat l.^H--- nl Lb.^eoim Per Hour Lb.CooilPerH.P-Hr. Vaigl O r~J OJ c s % - - Total Pounc -/- ^ * k \ . - 'Lb Tl Steam Tff.H.P X '^ ^ -^ ^ "^ -///: ^ 5/z r^ am H.P HP- ^ *> s x-' Pf '' > ^ ^- v.^. X "^ ^~ r"" --- "~~~ ~- TJ- ^ *^ r ~+-, //I ^r ^//7^ V/T- A ^^ -" & S & g $ TotoilLb.CocilPcrHr Tote #t dToa/ . .,*> - " -- - . . ___ .-4 ' ' ZA( "a-r- /V/ B.t //P- ///:- -- --" ^ ~'4 = ? _. ZA Coal Pe rl.H.P ///: 50 15 100 115 ISO H5 200 225 Indicated Horse Power FIG. 396. Performance graphs of a 150-h.p. Buckeye-mobile. Fuel was Pocahontas run of mine, 14,000 B.t.u. per Ib. (Buckeye Engine Co.) safe. (2) Speed, in revolutions per minute, likewise affects the power output an engine of a given size (and cost) will therefore deliver most power when operated nearest its rated maximum speed. (3) Back pressure likewise affects the power output the lower the back pressure, or if condensing, the greater the vacuum, the greater will be the power output. (4) The service for which the engine is to be used affects the necessary construction engines for driving alternating- current generators must have larger flywheels than those for some other services; engines for direct connection to electric generators usually require longer shafts and different bearing constructions than do those which are to drive by belt or rope; some engines must be designed to operate at variable speeds, some to be readily reversed. (5) Sub-bases are some- times required by the purchaser sometimes they are not. When required, sub-bases must sometimes have special construction. 336 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 11 I | '1 lyf 3^ -"rt" 6 > | * 1 11 J5 : w \ fl "S 1 "i g o o o5 ^ i q c g H > w M CO . fa O << O 1 S E tt "to g M bfl M m K? p +i tH g a a p H M G S H o Sd i 8 S 1 O *O U5 OO (M | 8 8 O g o o H le .0 i et CO I (N J> - ^ ^ 1 1 iO O CO (N | i I | | I 3 i 1 IP i IM CO 14 J ^ > I J | 8 5 Troy Engine & Machine Co., T_,r T> i ik | a i 4 ' 05 < G 2 ^, a g s i ll Brownel Chandle Taylor 6 1 1 TS| 3 g Pi i i Ridgwa Skinner Souther I M-l O 0) SAfB A ^BU JO . n*\a 3 03 l> ^ .i ,^ f i CO CO ni S c *1 *&" ?3 5 jl SEC. 337] STEAM ENGINES OF MODERN TYPES 337 & coco ~ss I-H o 05 ^ (-, ->-> ta_ +^ ag , 0) T3 J 1 g i| S M 1 M e " C I S si 1? Is CS O "' 02 ** tf ** 0* PH ** Tj T3 o ; ; Remark Simple Tandem Cross c "a a "5. a 1 i. a 8 | 3 jo; c zo if s lo Simple Compour | S a c a- V | a S 5 "S i 1 " a a S s g B 2 i o -U -U +3 00 S .j g 02 c M C 'S 02 * | T3 0) 1 1 JJJ 020202 R i | tf cL c S 1 tf 4343 0202 E! ^ 3 S S |? !!! g J ^ 3 g H i 1 -.7 88 8 fN - 02 , CO rHIN At 1 I s - | 50-1200 1 If 8 | 12 1 CO a 5| I "S w 6 O 6 6 6 fl 8 I S w (P 3 1 rt 55 cd rt tf z 1 1 1 O 1 o 1 o 0) 6 3 S3 .i i s 3 1 -2 2 fi W g o ^j 3 a; S OQ o 1 If *.$ 1 1 o 1 1 3 d 02 J3 It c 9^ SHH' 03 g| 43 t o 03 JD C3 03 1 0) 1 1 U K ton Iro 3. a > 1* <= V 4) ^5 ^ '35 O.9 03 V S 02 j . 5 p fe " a fa 73 S M M? 1| 03 3 G 42 rt S s 42 a) E 1 o 1 o i S 43 O P? EH J- 3 3 I 1 I 03 a M H g A-22S -S > ||^ S3AJBA zs *|o2 H I 3 fc SEC. 3371 STEAM ENGINES OF MODERN TYPES 339 >Jf a "B * . feJ9> -' i -r q G S 1 o 1 1 8 '] J | \' f Corliss Corliss 1 PH 1 I 1 I a e 4-Poppet 4-Poppet 2-Poppet 2-Poppet 2-Piston 1 esi PH B O 1 < i i a 4) G 8 | a L > 1 O 1. M 3 03 w 1 J 1 i i f ! M ft g * o O *: t I * O e !*3 i H^ aT o C > i a 2 'Si B h ! o M s ^ i J j* . i e c c a o * W > c ri J^ -1 3 a O_^ t J2 S o Q O a c ^ J s c , i o i 1 : 1 p" * 7^ 1 O I |l CS ; ffi 1 9 c 1 1 i i QQ QQ g QQ i S OQ rt OS 03 QQ 1 ri I Ja i d ^r i 1 I ^ Murray Minor Nordberg o> M .9 Southern h a 3 Hamilton Nordberg | QJ- Hamilton Skinner 1 g Q Harrisbur Nordberg Ridgway Buckeye mobile 3t?;OQ 1 > i Q en a^ s ' c i a 3 PH 1 | o x V c M -S d 340 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 11 NOTE. VARIABLE SPEED AND REVERSING ENGINES arc also manu- factured by many of the engine builders listed in Table 337 but these engines are not listed in the above table. EXPLANATION. TABLE 337, although it was intended to contain the names and descriptions of the principal engines manufactured in this country, must be understood to possibly not include all such engines. Furthermore, the fact that a certain engine is or is not included in this table should not be taken to indicate anything whatever with regard to its merits or quality. 338. Table Of Costs Of Steam Engines Of Different Types. The costs given below must be understood to be merely approximate prices and, because of fluctuations in the market and the factors explained in the preceding section, should be used only in making a preliminary estimate. For a final (or even for a reasonably accurate preliminary) estimate, prices should be obtained from the engine manufacturers. The prices given below are as of January 1, 1922, for engines without special bases and arranged for belt drive from the flywheel. Type of engine Cost of engine per horse power Small engine Large engine Simple slide-valve Compound slide-valve .... $22-44 22-33 25-37 35-45 32-45 $11-16 15-17 9-18 16-25 12-21 Simple four-valve Compound four-valve Uniflow . . QUESTIONS ON DIVISION 11 1. Explain the differences between rotary steam engines and (1 ) reciprocating engines (2) steam turbines. 2. Explain, with a sketch, the operation of a rotary steam engine. What are its short- comings? Is it widely used? 3. What are the usual sizes and rotative speeds of simple single-valve engines? What is their field of service? 4. What steam rate may usually be expected from simple single-valve non-condensing engines at full load? At fractional loads? 5. What is the most advisable cut-off for a simple non- condensing single- valve engine? What is the customary piston speed? 6. What are portable steam engines? What is their field of service? In what sizes are they commonly built? SEC. 338] STEAM ENGINES OF MODERN TYPES 341 7. In what sizes and forms are compound single-valve steam engines commonly manufactured? What is their field of service? 8. What steam consumptions may reasonably be expected of compound single-valve engines when operated non-condensing? When operated condensing? 9. Name a well-known make of riding-cut-off piston-valve engines. In what sizes are they manufactured? 10. What forms of valves are employed in four- valve engines? What types of gov- ernors do they employ? 11. What are the common water rates of simple four-valve engines with Corliss valves? With poppet valves? 12. What is the principle of the uniflow engine? Wherein does it derive its great economy? 13. Name and describe two ways in which a uniflow engine may be constructed so as to satisfactorily operate non-condensing. 14. What safety device is relied on to automatically adapt to non-condensing opera- tion, if the vacuum is destroyed, uniflow engines which are designed primarily to operate condensing? 15. What are the usual steam rates of condensing and non-condensing uniflow engines? What exceptional rate has been reported? 16. Are uniflow engines capable of carrying large overloads? Why? 17. How does the steam consumption per indicated horse power hour of a uniflow engine at fractional and overloads compare with that at full load? In this respect, how does the uniflow engine compare with other engines? 18. What is a locomobile? With a sketch describe its construction. What is its field of service? Why? What water rate may be expected with this unit? 19. What are the principal factors which will influence the cost of a steam engine of any class, for a given power output? 20. Which would you expect to cost more per horse power, a small engine or a large engine? A high-speed engine or a low-speed engine? A high-pressure engine or a low- pressure engine? A condensing engine or a non-condensing engine? An engine to drive an alternating-current generator or one for a mill? 21. State approximate costs of engines of the different classes. DIVISION 12 STEAM-ENGINE TESTING 339. The Purposes Of Testing Steam Engines are to deter- mine any or all of the following: (1) The operating conditions. (2) The mechanical efficiency. (3) The water rate. (4) The thermal efficiency. The purposes of the different types of tests, the apparatus required, the method of procedure, and the calculation of the test results are all discussed in the following sections of this division. 340. The Purpose Of An Operating-Condition Test is to ascertain whether the engine valves are functioning properly and to determine mechanical defects that may exist -within the engine cylinder. Tests of this type involve only the use of steam-engine indicators and correct interpretations of the indicator cards which are obtained in the test (see Div. 3 for discussion of indicators and indicator cards). 341. The Purpose Of A Mechanical -Efficiency Test (see Div. 10) is to determine the energy lost in friction in the various bearing surfaces of the engine. This energy loss is called the friction horse power. The methods of conducting such a test are discussed in Sees. 368 and 369. NOTE. See Div. 3 for discussion and rules for calculation of indicated horse power. Methods of determining the brake horse power are de- scribed in subsequent sections. 342. The Purpose Of A Water -Rate Test is to determine the quantity of steam, and thereby the quantity of heat, used by an engine per indicated or brake horse power. This type of test will therefore provide a suitable basis for comparing one engine with another with respect to steam economy. The methods of conducting a water-rate test are described in Sees. 370 to 373. 343. The Purpose Of A Thermal-Efficiency Test is to classify the various heat losses of an engine according to the manner 342 SEC. 344] STEAM-ENGINE TESTING 343 in which the loss occurs. Thus, the energy loss due to the rub- bing contact of bearings can be found in this type of test and classified as a friction loss. Also, as stated in Sec. 318, the thermal efficiency of an engine is a much better measure of its performance than is its water rate, because the water rate depends upon operating conditions. It is therefore apparent that a thermal efficiency test is valuable to the engine designer and builder in that it presents knowledge essential to the designing and building of efficient engines. Thermal effi- ciency test methods are considered in Sec. 374. NOTE. THE THERMAL EFFICIENCY Is GENERALLY CALCULATED IN WATER-RATE TESTS and is calculated from the results obtained in a water-rate test. 344. The General Procedure In Engine Testing consists of operating the engine for sufficient time and under suitable conditions to determine the amount of (1) heat energy supplied to the engine and the amount of (2) mechanical energy developed and delivered by the engine. The determination of these two fundamental quantities ordinarily involves the collection of data as tabulated below. 345. Table Showing Data Necessary In An Engine Test. Quantity sought Data required Heat input Mechanical energy output (a) Pressure of steam supplied to the engine. (6) Condition (quality or superheat) of steam supplied to the engine. (c) Weight of steam rejected by (or supplied to) the engine. (d) Pressure of steam as it is rejected by the engine. (e) Weight of the drip from each jacket. (J) 1 Temperature of the water entering and leaving the condenser and weight of circulating water. (a) Speed of the engine, in revolutions per minute. (6) Indicator diagrams from each end of each cylinder, (c) The engine'slDrake horse power (dynamometer or electric generator measurement). When a heat-balance (Sec. 12) is to be made. 344 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 346. The Equipment Required For Engine Testing depends upon the type of test being made. In general, the most essential instruments are: (1) Pressure and vacuum gages. (2) Barometers. (3) Thermometers. (4) Steam calorimeters. (5) Steam-engine indicators. (6) Planimeters. (7) Tachometers or revolution counters. (8) Dynamometers, or other load-meas- uring apparatus. (9) Steam condensers for condensing exhaust steam. (10) Scales for weighing the condensed steam. The more important of these instruments will now be described. NOTE. Pressure and vacuum gages, barometers, thermometers, and steam calorimeters are described in the author's PRACTICAL HEAT. Indicators and planimeters have been discussed in Div. 3. 347. A Revolution Counter (Figs. 397 and 399) is an instrument which indicates the number of revolutions made during a period of time by a rotating shaft or wheel. To deter- mine the speed in revolutions per minute with a revolution counter, it is only necessary to divide the total number of revolutions made during the period of time by the time period expressed in minutes. Triangular Rotating ' Disc \ ^Revolution ! Counter ^Counter- Tip Inserted in Center - Bored Hole FIG. 397. Hand revolution counter. FIG. 398. Counting revolutions of an engine with a revolution counter. 348. A Hand Revolution Counter is shown in Fig. 397. It consists of a rotating disk, D, connected through worm gearing to a short triangular-pointed stem, $, which is pro- vided with detachable rubber tips. In counting revolutions (Fig. 398), S (Fig. 397) is inserted in the center-bore of the SEC. 349] STEAM-ENGINE TESTING 345 crank shaft of the engine under test and it thus turns with the shaft causing D to revolve. Simultaneously, the operator looks at his watch to keep an accurate account of the time. Ordinarily the counter is permitted to run for 1 min. The operator, looking at the second hand of his watch, inserts the rubber tip in the center-bore at the start of a minute and removes it at the end of the minute. For each 100 revolutions of S, D makes 1 revolution. In counting, the operator holds his thumb over the small stationary button, A, and " feels" each revolution of the rotating button, B, which is attached to D. The rubber tips are used to prevent slipping at high speeds. This type of revolution counter can be used satis- factorily for speeds up to 1200 r.p.m. 349. A Continuous Revolution Counter (Fig. 399) is gen- erally attached permanently to an engine. The operating arm, A, is usually connected by a lever to some engine part having a limited reciprocating motion. The instrument is essentially a stroke counter constructed to add one to the dial reading for every two strokes of the engine. This type of revo- lution counter may be used satis- factorily on engines having speeds up to 250 or 300 r.p.m. 350. A Tachometer (Figs. 400 and 401) is an instrument which registers -the speed of the shaft under consideration in revolutions per minute, directly and at any in- stant. Thus, the variations in its indications from instant to instant FIG. 399. Continuous revolution will show the different shaft speeds at different instants. Tachometers are most satisfactory for the higher speed ranges such as those which are attained in steam-turbine practice, but they may also be used on high- speed engines. They are manufactured to measure speeds as low as 20 and as high as 20,000 r.p.m. However, because of the unavoidable instantaneous variations in the rotative speeds of steam engines, tachometers are entirely unsuitable for engine-speed measurements lower than, say, 300 r.p.m. 346 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 In fact, some engineers would not use tachometers for measur- ing steam-engine speeds. 351. A Fixed Tachometer (Fig. 400) is fastened permanently to some part of the engine frame and is belted from the pulley, B, to the engine shaft. The mechanism consists of a spring- opposed centrifugal governor, the movement of which directly actuates the pointer, P. 352. A Hand Tachometer (Fig. 401) is a governor-operated device internally geared to allow three distinct speed-range adjustments. Adjustment is accomplished by loosening the TA<- -Removable , Rubber Tip -Speed Range Space Lock Hut -Stand FIG. 400. Fixed tachometer (Schaeffer & FIG. 401. Hand t ac h o me t er. Budenburg Mfg. Co.) (Foxboro Mfg. Co.) locknut, N, and pulling out (or pushing in) the driving stem, S, until the desired speed range is indicated in space R. Then N is tightened. The speed is indicated by the pointer, P, on either the inner or outer graduated circles depending upon the speed range in use. 353. Dynamometers Or Load-Measuring Apparatus are of extreme importance in engine testing and may be divided into two general classes: (1) Absorption dynamometers. (2) Electric generators. These are discussed separately in follow- ing sections. In acceptance or factory tests of engines, it is usually necessary to so "load" the engine that it will operate at its rated-horse-power output and possibly also at other outputs below and above the rated output. The load-measur- ing apparatus provides means whereby this loading can be SEC. 354] STEAM-ENGINE TESTING 347 readily effected and measured whereby the engine can be made to do work at a known rate. 354. Absorption Dynamometers, Or Brakes, are of two general types: (1) The Prony brake type (Figs. 402 to 406), wherein the power is absorbed by friction due to a rubbing contact of solid substances. (2) The fluid-friction type (Fig. 409), wherein the power is absorbed by friction due to the turbulence or viscosity of fluids. 355. The Prony-Brake Absorption Dynamometer (Fig. 402) consists of a steel strap, S, bent to conform to the shape of the Wooden Brake Arm-^ rianged Hi/wheel for Cooling- Wafer Steel Strap... Section Of Pulley Flange- ' FIG. 402. Typical Prony brake. flywheel of the engine under test and to which wooden blocks, B, are fastened as shown. The steel strap is rigidly held at one end, E, to the brake arm, A, on one side of the flywheel and is fastened at its other end to a " take-up" device, T, on the other side of the flywheel. The frictional force exerted by the brake can be adjusted by means of the hand-wheel on the " take-up" device. A portable brake for testing very small machines is shown in Fig. 403. NOTE. COOLING OF THE PRONY BRAKE is sometimes essential to prevent the wooden blocks from burning due to heat generated by their friction on the flywheel rim. Effective cooling can be accomplished by playing a small stream of water upon the inside of the flywheel. Some flywheels and pulleys are flanged as shown in Figs. 402 and 406; the U- shaped space, U, Fig. 402, thus formed can be filled with cooling water. As the water heats and evaporates, it can be replenished. 348 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 NOTE. LUBRICATION OF THE PHONY BRAKE is sometimes necessary to prevent chattering and seizing of the brake shoes. Grease or heavy oil placed between the brake blocks on the face of the flywheel at its top will lessen to a great extent the tendency to seize or chatter. f w/'fh Heads \^" \ Countersunk in the Wood, Hard Maple Blocks ' Prony Wooden Flywheel-Templet Brake Arm in Same Position as For Tesf/nq FIG. 403. A portable Prony brake for testing very small engines. (In testing, E is pulled until the braking effect is sufficient. Then the D reading is subtracted from the C reading. The remainder multiplied by the peripheral speed of A, in feet per minute, gives the foot pounds per minute. This value divided by "33,000" gives the horse power. E. E. Larson in Power, Sept. 13, 1917.) 356. The Use Of A Dynamometer Of The Prony-Brake Type Necessitates The Determination Of Constants called the effective length of brake arm and the tare-weight of the brake. The tare-weight "Wi" is its unbalanced weight due to its unsymmetrical construction. This weight can be found by two methods: (1) Dummy Flywheel Method. A wooden templet, T (Fig. 404), which has the same diameter as the flywheel of the engine which is to be tested, is made. The brake is then tare-weight of a Prony brake using a mounted On this templet aS wooden templet of flywheel. (The shown and Supported On SaW- templet is free to roll on the pipe P.) , ~ , horses, S t by a shaft made of pipe, P, so that the brake arm is in the same horizontal position as for testing. The knife-edge is supported on the stand, B. Then, both the stand and the brake are weighed on the scale, W. Saw -Horse' ' "'Platform Scale FIG. 404. Method of determining SEC. 357] STEAM-ENGINE TESTING 349 This scale reading will be the tare-weight, " Wi," of the brake. (2) Rotation Method. Arrange the brake as shown in Fig. 402 and loosen the blocks on the flywheel until the flywheel turns easily. Turn the flywheel by hand in one direction for one or two revolutions and weigh the brake while turning the flywheel. Turning the flywheel in the opposite direction, weigh again. The average of these two weights (one-half their sum) will be the tare-weight, "Wi," of the brake. The determination of the tare-weight by this method should be made two or three times to insure a fair average. Any stand or pedestal used with the brake, for example, P, Fig. 402, must be weighed with the brake when determining the tare- weight. NOTE. THE EFFECTIVE LENGTH OF THE BRAKE ARM, L f (Fig. 402), is the horizontal distance, in feet, between the vertical center line of the knife-edge and the vertical center line of the flywheel when the brake is in the working position. 357. When Using An Absorption Dynamometer, The Brake Horse Power Is Calculated By The Formula (its deriva- tion is given below) : Wherein: P b h P = brake horse power developed. L f = effec- tive length of brake arm, in feet, as defined in Sec. 356. N = the engine speed, in revolutions per minute. W = the gross load on the scale, in pounds, as indicated by the scale during the test. Wi = the tare-weight of the brake, in pounds, as described in Sec. 356. The term (W - Wi) is frequently called the net-weight of the brake. DERIVATION. Assume that the flywheel is held stationary on a vertical axis, and that the brake arm is pushed around the flywheel (Fig. 405) with a force of (W Wi) pounds. This, obviously, is the force which is required to rotate the brake. The distance through which this force will act in one revolution = the circumference of a circle of radius L/ ft. = 2irL/ ft. Since N = r.p.m., the distance traveled in one minute by the friction sides of the brake blocks will be ZirL/N ft. Hence, since the force (W Wi) acts through the distance of 2irL f N ft. in one minute, the work done per minute will be distance per minute X force 2irLfN (W - Wi) ft. Ib. per minute. Now it is evident that work will be 350 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 performed at the same rate by the flywheel when it is revolving within the stationary brake blocks as when the brake blocks are revolving (pushed) around the stationary flywheel, the speed being the same in both cases. Then, since by definition horse power foot pounds of work done per minute -r- 33,000, it follows that : p Pbhp = 33,000 -- which is the same as for For. (41). EXAMPLE. An engine runs at a speed of 270 r.p.m. and its Prony brake and stand push down with a force of 250 Ib. on a platform scale. If the tare-weight of the brake is 40 Ib. and the effective brake-arm Work =Force x Distance =(W-W,)x2TrLfNnLb. FIG. 405. Illustrating derivation of brake formula. Work in foot pounds = Force in pounds X Distance in feet = (W - Wi) X 2wL/JV. length is 4 ft. 6 in., what brake horse power is developed by the engine? SOLUTION. Substituting in For. (41): P bhp = 2irL f N(W - Wi)/33,000 = 2 X 3.14 X 4.5 X 270(250 - 40) -r 33,000 = 48.6 b.h.p. . 358. A Rope Brake Absorption Dynamometer (Fig. 406) is a form of the Prony brake in which a rope is used instead of wooden blocks to provide frictional resistance. The effective brake-arm length of a rope brake (L/, Fig. 407) is the radius of the flywheel plus the radius of the rope. Those portions of the rope between the flywheel and the rope ends must, in a brake of the type shown in Fig. 406, be vertical. EXPLANATION. Considering the rope (Fig. 407) of a rope brake, with- out the stand, the force due to the frictional resistance of the rope is SEC. 358] STEAM-ENGINE TESTING 351 transmitted to the scale as though it were carried through the center line of the rope end A to the scale. Hence the effective brake-arm length is the horizontal distance from the vertical center line of the flywheel to the Rope Looped Through Platform Scale. Hanged Flywheel^ Side View Front View FIG. 406. Typical rope brake on platform scale, S. Of FIG. 407. Illustrating effective brake- arm of a rope brake. Flywheel, ! Effective Length Of Brake Arm -Hand Wheel FIG. 408. A rope brake. (The effective brake-arm length of this brake is measured between the same points as for a Prony brake. (See Fig. 402.) center line of the rope, or the distance L/. Fig. 408 shows a rope brake of another type, for which the effective length of brake arm is found in the same way as for a wooden-block Prony brake. 352 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 EXAMPLE. A rope brake (Fig. 406) made of 1-in. rope is installed on an engine with a 4-ft. diameter brake wheel. A load of 480 Ib. is balanced on a platform scale when the engine is operating at 200 r.p.m. If the tare-weight of the brake is 80 Ib., what is the brake horse power of the engine? SOLUTION. The effective brake-arm length, L f = (4 + H2)/2 = 2 + % 4 = 2.0417 ft. From For. (41): P bhp = 2irL f N (W - W,)/33,000 = 2 X 3,14 X 2.0417 X 200(480 - 80) -*- 33,000 = 31.15 h.p. 359. The Water Brake Is A Dynamometer Of The Fluid- Friction Type (Fig. 409). The principle of operation of the water brake is similar to that of the centrifugal pump. The chief difference is that the cen- trifugal pump is designed to offer the least possible resist- ance to the passage of water, while the water brake is designed to offer the greatest possible re- sistance. This resistance is in- troduced by cupping the casing and constricting the water- outlet areas. The rotor (im- peller) of the water brake is coupled to and rotates with the shaft of the engine under test. The stationary part is equiva- lent to the brake arm of a Prony brake. To 59 FIG. 409. Illustrating principle of the water brake. EXPLANATION. Water is admitted to the impeller chamber, C, through the hollow shaft, S. This water is then, by centrifugal force, forced out radially through the holes in the impeller to the spaces, R, between the impeller arms. As these arms rotate, the water is thrown into the cups, D, in the stationary casing wherein eddy currents are formed. These eddy currents oppose the rotation of the impeller and thereby cause the knife-edge to press down on the scale. The water eventually finds its way through the small clearances between the impeller and casing to the water outlet. The water pressure in the brake can be adjusted to meet various load conditions by throttling the valves on the water inlet and outlet pipes. The greater the pressure within the casing, the greater the load which it imposes on the scale. NOTE. THE BRAKE HORSE POWER ABSORBED BY A WATER BRAKE is found by For. (41). The effective brake-arm length (L f) Fig. 409) is SEC. 360] STEAM-ENGINE TESTING 353 found as with a Prony brake. The tare-weight of this brake is found by Method 2 in Sec. 356. 360. Electrical Loading Of An Engine (Fig. 410) is accom- plished by coupling or belting an engine to an electric generator of known efficiency (Sec. 362) and measuring the power output of the generator. The generator is connected to a variable electrical load usually a water rheostat whereby the power required of the engine to drive the generator can be varied at the will of the operator. Either an alternating-current (A.C.) or a direct-current (D.C.) generator may be used. Mechanical Load Delivered By Electrical Energy Dissipated As Heat-^ Electrical Power Measuring *~ Instrumentfltattmeterl Engine Under/ Mechanical Load Test " Generator By Belt-/ Of97K.W. FIG. 410. Illustrating principle of electrical loading of an engine (Engine, E, is pulling 147 mechanical h.p. Of this, the electrical load on generator, G, which is indicated on P, and which is dissipated in water rheostat, R, comprises 97 kw. or 130 h.p.) NOTE. WHEN GENERATORS ARE BELTED To ENGINES ALLOWANCE MUST BE MADE FOR SLIPPAGE OF THE BELT. This allowance can be made by the following formula, the derivation of which is given below. (4V P N " di "p fhn^ v***/ -toAp T/ 7 / -*np ^n.p. ) 1\ di Wherein: P&/, p = brake horse power of engine. N" = speed of engine in revolutions per minute, di" = diameter of engine pulley, in inches. N' = speed of generator pulley, in revolutions per minute, di' = diam- eter of generator pulley, in inches. Ph P = horse power input to generator (Sec. 362). DERIVATION. The horse power transmitted by a belt = (the net belt pull the force transmitted in pounds) X (the distance, in feet, through which the force acts in one minute) + 33,000. That is, 1 h.p. = 33,000 ft. Ib. per min. The distance through which the net belt pull acts in one minute is the circumference, in feet, of the pulley over which it runs times the number of revolutions it makes in one minute. That is, if the pulley diameter is expressed in inches, the distance = N" X IT X di" I 12. Hence the horse power transmitted to a belt by its engine pulley can be expressed by the formula: (44) bhp Netbeltpull XN" Xir X di"/(l2 X 33,000) (h.p.) 23 354 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 Transforming this equation for the engine pulley, it becomes: (45) Net bell pvll = 12 X Ob.) If For. (44) represents the brake horse power given to the belt by the engine which drives the belt, similarly the net horse power given to the generator by the belt can be represented by : (46) P hp = Net belt pull X N' X * X di'/(12 X 33,000) (h.p.) From which it follows that, for the generator pulley : j*.\ -m r i 1 t i 77 J- ^ -^N OO.UUv/ /\ XflW /n v (47) Net belt pull = - ^-r (Ib.) irN di Since the net belt pull at the engine is the same as, and equal to, the net belt pull at the generator, Fors. (45) and (47) may be equated, thus: (48) Net belt pull - 12 X ^OMX ^ = ^^j, * ^ Ob.) or transposing and dividing by 12 X 33,000 and multiplying by TT N"d " (49; Pbh P = -5757^*1. (h.p.) Which is the same as For. (43). EXAMPLE. A generator having a 2-ft. diameter pulley was driven by a belt from an engine having a 6-ft. diameter flywheel. If the speed of the engine was 200 r.p.m. at 90 h.p. input to the generator and the speed of the generator was 585 r.p.m. at this load, what was the brake horse power of the engine? SOLUTION. From For. (43): P b h P - (N"di" /N'di'^Php = [(200 X 72) -r- (585 X 24)] X 90 = 92.4 b.h.p. 361. To Determine The Electrical Output Of A Direct- Current Generator (Fig. 411) the procedure is as follows: A voltmeter, E, to measure the -Ammeter difference in electric potential (e.m.f.) between the leads, is connected in parallel with the load; see Sec. 365 for " Water Rheostat." An ammeter, 7, to measure the current flowing through the leads, is inserted generator, GD. Using ammeter, /, and in SCI'ieS with the load. The voltmeter, E. ammeter and the voltmeter are read at the same instant. The power output of the generator in kilowatts is then found by substituting the observed values in the following formula: El (50) P kw = (kw.) SEC. 362] STEAM-ENGINE TESTING 355 Wherein: P kw = the power-output of the generator, in kilo- watts. E = the voltage or e.m.f., in volts, as indicated by the voltmeter. I = the current, in amperes, as read from the ammeter at the same instant the voltmeter is read. - ^'--'Jo Load Direct- Current Genercrf-or< NOTE. A DIRECT-CURRENT WATT- METER MAY BE USED (P, Figs. 410 Fia. 412. Illustrating load-output and 412) instead of a voltmeter and determination with a direct-current an ammeter. It is connected as shown generator, GD, using a direct-current and reads directly the product El wattmeter, P. (Note. Single-phase (For ^0} alternating-current generator load de- terminations may be made as illus- trated if an alternating-current wattmeter 362. TO Find The Horse- i s used instead of a direct-current watt- Power Input To Any Generator meter as shown.) When Its Power Output Is Known (1 h.p. = 0.746 kw.) substitute in the formula: Or since, for direct-current generators', For. (50) : P kw = #7/1000, it is true for direct-current generators that: WT (52) P., = (h.p.) Wherein: P hp = the horse-power input to the generator- E d = the efficiency of the generator at the developed load, expressed decimally. NOTE. THE EFFICIENCY OF A GENERATOR AT ANY LOAD CAN BE READ FROM ITS EFFICIENCY GRAPH. This graph is usually plotted between per cent, load and per cent, efficiency or between amperes load at rated voltage and per cent, efficiency. The graph can be obtained from the manufacturer of the generator by giving the serial number and all other name-plate data relating to the machine. EXAMPLE. A steam engine is coupled to and driving a direct-current generator, G d , Fig. 411. If the voltmeter, E, reads 220 volts, the ammeter 7, 764 amp., and the efficiency of the generator at this load, as shown by its efficiency graph, is 0.90, what is the horse-power input of the engine to the generator? SOLUTION. By For. (52) : P hp = EI/74QE d = 220 X 764 H- (746 X 0.90) = 250 h.p. 363. To Determine The Electrical Load With A Single- Phase, Or Two-Phase, Alternating-Current Generator (Figs. 413 and 414) use an alternating-current wattmeter, P, in each 356 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 phase which will read P fcu , directly for that phase. The total output of a two-phase generator is always the sum of the wattmeter readings for each of the two phases. The horse- power input is found by For. (51). For a single-phase alter- nating-current circuit an alternating-current wattmeter may be connected in the same way (Fig. 412) as is a wattmeter on a two-wire direct-current circuit. iloact .- Alternating Current Wattmeter Two -Or Three-Phctse Alternating Current Generator. Alternating Current Wattmeter 2-Phcrse, Alternating Current FIG. 413. Method of determining FIG. 414. Method of determining power output of a 3-wire, 2-phase alter- power output of a 4-wire, 2-phase, nating-current generator, G. (Note. alternating-current generator, GA. The power of a 3-wire 3 phase, alter- nating-current generator may also be determined as illustrated above.) NOTE. IN A THREE-WIRE TWO-PHASE SYSTEM always be sure that the connections are made as shown in Fig. 413; that is, with a wattmeter current coil in each of two lead wires and the voltage coils of each watt- meter connected to the common return wire. EXAMPLE. If wattmeter PI (Fig. 413) reads 30 kw. and wattmeter P 2 reads 35 kw., what is the horse-power input of the engine to the generator, if the generator efficiency at this load is 0.88? SOLUTION. The total power output of the generator in kilowatts, Pfcu> = the sum of the wattmeter readings = PI + P% = 30 + 35 = 65 kw. The horse power input to the generator from For. (51) is: P/ ip = P Au , /0.746E d = 65 -i- (0.746 X 0.88) = 96 h.p. 364. To Determine The Electrical Load With A Three - Phase Alternating-Current Generator (Fig. 413) two alter- nating-current wattmeters, PI, and P^ are connected in any two of the three phases. The sum of the readings of the two wattmeters will be the total output, P kw , of the generator. To determine the horse-power input to the generator substitute in For. (51). SEC. 365] STEAM-ENGINE TESTING 357 NOTE. IN USING Two WATTMETERS IN A THREE- W IRE, THREE-PHASE ALTERNATING-CURRENT CIRCUIT neither of the meters measures the power in any one of the three phases. With light loading one of the meters will probably give a negative reading, and it is necessary to reverse either its current or potential leads in order that the deflection may be noted. In such cases, the algebraic sums must be taken and not the numerical sums. In other words, if one reads + 500 watts and the other 300 watts, the total power in the circuit will be : 500 300 = 200 watts. As the load comes on, the readings of the instrument which gave a negative deflection will decrease until they drop to zero, and it will then be necessary to again reverse the potential leads on this wattmeter. Thereafter, the readings of both instruments will be positive, and the numerical sum of the two will be the power consumption of the load. 365. Where No Useful Load Is Available, Generator Loading May Be Accomplished Satisfactorily By A Water Rheostat (Fig. 415). Where the power developed by the generator, which furnishes the load, can be conveniently employed for a "useful load" as for electric lighting or heating or for motor-driving other machinery it should, obviously, not be wasted. In many plants the power developed by the test generator can be fed into the main bus, thus relieving the other regular generators of part of their load. But where such procedure is not feasible, it is usual to employ a water rheostat as the most convenient means of dissipating the test- load power. EXPLANATION. The water rheostat shown in Fig. 415 consists of two iron electrodes, P and S, one supported from a rope, R, which passes over a pulley. The other rests upon the bottom of the barrel. The barrel is filled with water, W. Each ^Genemtor\ Wooden Barret Leads Iron flectrocfe electrode is connected to a generator lead. The _, . , _ w , .. . FIG. 415. Water rheostat distance between electrodes may be adjusted to for 2-wire systems. vary the resistance offered by the water to the passage of current. Hence the distance between electrodes determines the load on the generator. For voltages below 1000 volts it is usually necessary to add salt to the rheostat water to decrease its resistance sufficiently that a great enough current will flow. 366. In Determining The Water Rate Of Steam Engines, A Steam Condenser Is Often Employed (Fig. 416). As shown, the steam after being used by the engine is exhausted through 358 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 the exhaust pipe, E, into the condenser, C, where it is con- densed. The condensate (condensed steam) runs out through the condensate pipe. } into the weighing tank, T. In T it is weighed on the scale, S. The procedure when using a steam condenser is taken up in following sections. For descriptions of condensers see the author's STEAM POWER PLANT AUX- ILIARIES AND ACCESSORIES. ,-5team Pressure Ga&e Steam -Valve Pooling Water 'Cooliriy Water Inlet Water Seal-- Tank Ft FIG. 416. Illustrating apparatus used in water-rate test. 367. The Detailed Procedure In Testing An Engine Is usually about as indicated in the paragraphs which follow: 1. Specifically decide the object of the test and keep this in mind, not only during the performance of the test, but also during the prepara- tion of the equipment for conducting the test. 2. Precautions should be taken to insure that the engine and its lubricating system are in condition for continuous running for at least the period of the test without danger of a shut-down for adjustments or repairs. Any interruption of operation during the test period will probably decrease the reliability of the test. 3. The name plate, and other data pertaining to the engine itself and to the equipment and instruments used, should be recorded on the log sheet. 4. All test instruments such as gages, thermometers, tachometers, scales, indicators, reducing motions, etc., should be carefully examined and, in tests where the greatest accuracy is desired, should be calibrated before and after the test (allowances should be made in the test data for any discrepancies in calibration or otherwise that may exist). Great SEC. 368] STEAM-ENGINE TESTING 359 care should be used in attaching test instruments to the engine as inac- curate readings can be obtained from the most accurate instruments when incorrectly installed. 5. The engine should run under test conditions for a sufficient length of time to allow all conditions, such as temperatures, pressures, etc., to become constant before data readings are taken. This is necessary in order that true test conditions be attained prior to recording test data. 6. The first set of readings may be taken after conditions have become constant. The time and all necessary data should be immediately recorded on a data sheet previously arranged. All readings thereafter should be taken at equal time intervals throughout the test. The necessary time interval will depend on the duration of the test and the constancy of the load (see Sec. 375). 7. After the test has been completed the test apparatus should be carefully cleaned and indicators should be oiled to prevent rusting. 8. Computations for test results should then be made and checked for accuracy. See following sections for methods and formulas used in calculating the test results. 9. Finally, graphs should be plotted on ruled or squared paper to visualize the test results. In mechanical efficiency tests there should be plotted such graphs as "mechanical efficiency" against "brake horse power," "speed" against "brake horse power," and "indicated horse power" against "brake horse power." In the water-rate tests there should be plotted such graphs as "total pounds of steam consumed per hour" against "indicated horse power" "water rate" against "indicated horse power," "boiler pressure" against "time," "exhaust pressure" against "time," and "thermal efficiency" against "indicated horse power." 368. In Testing A Simple Engine To Determine Its Mechan- ical Efficiency, it is merely necessary to ascertain: (1) Its brake horse power output with a dynamometer or electric generator; Sees. 353 to 365. (2) Its indicated horse power with steam engine indicators; see Div. 3. Then, as explained in Div. 10, the brake horse power (output) divided by the indicated horse power will be the mechanical efficiency. The apparatus is arranged as shown in Fig. 417. It is usually desirable to ascertain the brake and the indicated horse power at a number of different loads so that the efficiencies at these different loads may be determined. Usually the final data are plotted into a graph: Mechanical Efficiency against Load. NOTE. IT Is USUALLY ADVANTAGEOUS To INCREASE OR DECREASE THE BRAKE HORSE POWER LOAD ON THE ENGINE IN EQUAL STEPS when mechanical efficiency tests are being made. The values of brake horse power which are usually taken are >, J, Y, 1, and 1^ of the full-load 360 STEAM ENGINE PRINCIPLES AND PRACTICE [Div, 12 rating of the engine. This loading permits the plotting of a well-pro- portioned mechanical-efficiency graph. A minimum of three indicator diagrams should be taken from each end of the cylinder for each load in order that an average mean effective pressure (Sec. 122) may be obtained for each load. NOTE. IMMEDIATELY AFTER DIAGRAMS ARE TAKEN, INDICATOR CARDS SHOULD BE MARKED with a symbol designating: (1) From which Platform 5ca/e-, / Prony Brake- Me fa/ Brake Steam Supply P/'pe---^ Steam Supply Pressure Gaae^ Reducing Continuous I Engine Under \ Revolution l>l Exhaust Pressure Gage- 1 ' FIG. 417. Arrangement of apparatus for a mechanical-efficiency test on a simple engine. end of the cylinder they were taken. (2) The speed of the engine. (3) The brake load when taking the card. (4) The time at which the card was taken. This is necessary to forestall errors when computing the test results. 369. Data Which Should Be Recorded On The Data Sheet In A Mechanical-Efficiency Test are: (1) Time. (2) Brake load. (3) Speed. (4) Steam pressure. (5) Exhaust pressure. These data should be shown on the data sheet. (Fig. 418) even if some of them du- plicate data shown on the indicator cards. An accu- rate record of the steam Test No. Time Speed Load on ftSS Remarks FIG. 418. Data (log) sheet for mechanical- efficiency engine test. and exhaust pressures, as indicated by pressure gages, G s and G E , Fig. 417, is usually necessary because the engine perform- ance is directly affected by these pressures. 370. In Testing A Simple Engine To Determine Its Water Rate, it is merely necessary to ascertain : (1) Its indicated horse power with steam engine indicators (Div. 3). (2) Its brake SEC. 870] STEAM-ENGINE TESTING 361 Wafer Supply Valve E Pipe~ Closed-., horse power with a dynamometer or electric generator, Sees. 353 to 365. (3) The rate at which it uses steam by condensing the steam or by measuring the boiler-feed water for a suitable time period. (4) The condition (quality or superheat) of its supply steam with a steam calorimeter or a steam ther- mometer. Then, since the water rate of an engine is usually expressed as the number of pounds of dry steam it uses per indicated (or brake) horse power per hour, the water rate can be readily computed. It is customary to find the water rate of engines at different engine loads (Sec. 368) and then to plot the results into a graph: Water Rate against Load. EXPLANATION. Fig. 416 shows the arrangement of equipment for a water- rate test. A steam condenser, C, is used in this case for condensing the exhaust steam from the engine in order that the condensed steam may be weighed to de- termine the water rate of the engine. A steam-pressure gage, G, and a steam calorimeter, Q, should be placed on the steam-supply pipe, H, so that the quality (Sec. 371) of the steam which is used by the engine may be determined. Sim- ilarly, a pressure gage, B, should be placed between the engine and the con- denser to determine the back pressure in the exhaust pipe, E. NOTE. IN SMALL PLANTS IT Is OFTEN CONVENIENT To WEIGH, OR METER, THE FEED WATER To THE BOILER WHICH SUPPLIES STEAM To THE ENGINE UNDER TEST (Fig. 419) for the determination of its water rate instead of weighing the steam after it has passed through the engine as is shown in Fig. 416. When the boiler-feed method is used, care should be taken to insure that the boiler water level and the boiler steam pressure are the same at the finish of the test as they were at its start. NOTE. IF THE SUPPLY STEAM Is SUPERHEATED, a thermometer should be located in the steam-supply pipe adjacent to the throttle valve in addi- tion to the equipment shown in Fig. 416. This thermometer will indicate Suction Line To Bo!/er feed Pump'"' FIG. 419. Equipment arrange- ment for weighing boiler feed- water. (Two weighing tanks, A and B, are mounted on platform scales above a suction tank, C, from which water is supplied to the boiler-feed pump. By means of the valve arrangement shown, one tank, A, can be filled with water and weighed while the other tank, B, discharges its water into the suction tank, C. The water level in tank, C, should be at the same height at the end of the test as it was at the beginning of the test.) 362 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 the temperature of the supply steam. A knowledge of this temperature is necessary to determine the amount of superheat (see Sec. 426) of the steam. 371. Data Which Should Be Recorded On The Data Sheet In A Water -Rate Test are the same as for a mechanical- efficiency test with the addition of: (1) The temperature of the steam in the steam calorimeter, if the supply steam is wet. (2) The temperature of the supply steam, if it is superheated. (3) The weights of steam used by the engine for each load, as the load is usually applied in increments as explained in Sec. 368. The quality and pressure of the supply steam (or the temperature of the supply steam, if superheated) and the pressure of the exhaust steam are important in water- rate tests as the steam consumption of engines is directly affected by these quantities. NOTE. STEAM QUALITY AND ITS DETERMINATION are discussed in the author's PRACTICAL HEAT. To find the quality of steam with a throttling calorimeter substitute in the following formula, the derivation of which is given in PRACTICAL HEAT: 100[g d2 + C m (T /2 - TV,) - Hi] (53, x p = - (per cent.) n v Wherein : x p = the quality of the steam in the engine supply pipe, in per cent. Hdz = the total heat of dry saturated steam at the pressure existing in the calorimeter, in British thermal units per pound. T f2 = the temperature in the calorimeter, in degrees Fahrenheit. T/ 3 = the temperature of saturated steam at the pressure, which is usually assumed to be the barometric pressure, existing in the calorimeter, in degrees Fahrenheit. HI = the heat of the liquid at the pressure existing in the engine supply pipe, in British thermal units per pound. H v = the latent heat of steam at the pressure existing in the steam supply pipe, in British thermal units per pound. C m = the mean specific heat of superheated steam, in British thermal units per pound per degree Fahren- heit rise in temperature, and which may be considered as equal to 0.46. All of the above properties of steam can be found in any standard steam table. CAUTION. All steam tables are arranged for absolute pressures and not for the gage pressures as indicated by gages. To obtain the absolute pressure in any case, it is only necessary to add the atmospheric pressure (Barometric pressure), expressed in pounds per square inch, to the pressure indicated by the gage. See author's PRACTICAL HEAT for an explanation of this situation. SEC. 372] STEAM-ENGINE TESTING 363 EXAMPLE. In Fig. 420, if the barometric pressure is 14.7 Ib. per sq in., the temperature of the steam in the throttling calorimeter 270 deg. fahr., and the steam pressure is 150 Ib. gage (164.7 Ib. abs.), what is the quality of the steam supplied to the engine? SOLUTION. Substituting in For. (53) : x p = 100[ff d2 + C m (T f i - TVs) Hi\/H v = 100[1150.4 + 0.46(270 - 212) - 338] + 856.8 = 98 per cent. The per cent, of moisture in the steam = 100 98 = 2 per cent. 372. In A Water-Rate Test, It Is Necessary To Express The Weight Of Wet Steam Used By An Engine In Terms Of Weight Of Dry Steam Used as all water rates are expressed in pounds of dry steam per indicated or brake horse power per hour. If the engine being tested is taking wet steam (steam of less than 100 per cent, quality), the weight of dry steam used can be found by substituting in the formula: (54) W sd = x d W sw (Ib. of dry steam) Wherein: W sd = the weight of dry steam used, in pounds. x d = the quality of the steam, expressed decimally. W sw = the weight of wet steam used. 373. The Water Rate Of An Engine Can Be Calculated by the following formula if the water rate is to be based on indicated horse power: (55) W sd i = 5 ^ (Ib. dry steam per i.h.p. hr.) or if the water rate is to be based on brake horse power: (56) W sdb = ~ s ~^r (Ib. dry steam per b.h.p. hr.) A bhp/\th Wherein: W sdi = the water rate based on indicated horse power, in pounds of dry steam per indicated horse power per hour. W ad b = the water rate base on brake horse power, in pounds of dry steam per brake horse power per hour. W kd = the total weight, in pounds, of dry steam consumed during the time t h , in hours. P^ P = the average indicated horse power developed during the time period t h . Pbh P = the average brake horse power developed during the time period 4. EXAMPLE. In Fig. 420 if the engine develops 85 i.h.p. and 2550 Ib. ofsteam are used per hour, what is the water rate of the engine in pounds 364 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 of dry steam per indicated horse power per hour? SOLUTION. In the example under Sec. 371, it was found that the quality of the steam was 98 per cent, or 0.98. From For. (54), the total weight of dry steam used = W sd = x d W sw = 0.98 X 2550 = 2499 Jh. From For. (55), the water rate= W sdi = W sd /Pa P Xt h = 2449 + (85 X 1) = 29.4 Ib. of dry steam per i.h.p. hr. NOTE. THE WATER RATE OF AN ENGINE CAN BE CALCULATED APPROXIMATELY BY MEANS OF INDICATOR CARDS (see Div. 3). This method is often used to check other methods of determining the water rate. Engine Header Supplying 2550 Lb. Of Steam <-3-Phase, /L~C Circuit Calorimeter Thermometer--. . A-C. Wattmeter T f2 =T. '^ Exhaust Pressure 4 Lb. Per Sq. In-' FIG. 420. Illustrating calculation of water rate and thermal efficiency of engine, M, using generator, G. 374. To Determine The Thermal Efficiency Of An Engine, it is necessary to know: (1) The rate at which work is done by an engine (its power output). (2) The rate at which heat is furnished to the engine (its power input.) Both of these are reduced to British thermal units per hour per horse power. Then, as explained in Div. 10, if the value for (1) is divided by that for (2) the thermal efficiency will be the result. The power output is found by measuring the indicated horse power (Div. 3). Sometimes, brake horse power is considered as the power output. The brake horse power is measured with a dynamometer or electric generator (Sees. 353 to 365). The power input is found by ascertaining the water rate of the engine and the heat consumed per pound of steam used (Div. 10). Hence it is obvious that the values necessary for the computation of the thermal efficiency are obtained from 1 the same test data as are required in a water-rate test (Sees. 370 to 373). SEC. 375] STEAM-ENGINE TESTING 365 NOTE. THE THERMAL EFFICIENCY CAN ALSO BE CALCULATED BY FOLLOWING THE TEST CODE OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS which is given in a condensed form in Sec. 381. The TEST CODE is a conveniently arranged form consisting of the logical and successive steps to be taken in the calculation of engine-test results. EXAMPLE. If the back pressure (exhaust pressure) in Fig. 420 is 4 Ib. gage (18.7 Ib. abs.), what is the thermal efficiency of the engine based on indicated horse power? SOLUTION. By For. (32) in Sec. 317, H tl =x d H v + Hi. By For. (31): E dti = 2545/W.i(# - Hit). Now, from Fig. 420: W si = 2550 -=- 85 = 30 Ib. peri.h.p. hr. Therefore, with the results found in the example under Sec. 371 and taking values from a standard steam table, the thermal efficiency = E d = 2545/ W ai [(x d H v + Hi) - Hi,} = 2545 -J- 30[(0.98 X 856.8 + 338) - 192.6] = 0.0854 = 8.54 per cent. = thermal efficiency based on indicated horse power. EXAMPLE. If the supply steam in the preceding example were superheated instead of wet and if the temperature of the steam at the throttle was 435.4 deg. fahr., what would be the thermal efficiency of the engine based on indicated horse power? SOLUTION. From For. (31), the thermal efficiency = E dti = 2545/W si (#, - H i2 ) = 2545 -5- [30 (1,235.9 - 192.6)] = 2545 + 31,299 = 0.0814 = 8.14 per cent. = ther- mal efficiency based on indicated horse power. 375. The Duration Of A Test Depends Upon The Type Of Test Being Made. For a mechanical-efficiency test, sufficient time should be allowed for five or six load increments to be applied. For water-rate tests the TEST CODE of the American Society of Mechanical Engineers specifies : "A test for steam or heat consumption, with substantially constant load, should be continued for such time as may be necessary to obtain a number of successive hourly readings, during which the results are reasonably uniform. For a test involving the measurement of feed- water for this purpose, five hours duration is sufficient. Where a surface condenser is used, and the measurement is that of the water discharged . . . , the duration may be somewhat shorter. In this case successive half-hourly records may be compared and the time correspondingly reduced. When the load varies widely at different times of the day, the duration should be such as to cover the entire period of variation." 376. An Acceptance Test Is A Water -Rate Test on a new engine conducted under the observation of both the purchaser and the seller to determine whether the economy, or pounds of steam per indicated horse power hour (or brake horse power hour), for different loads is as economical as was specified in the purchasing contract (see Sec. 456). 366 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 377. In Testing Compound Engines the same procedure can be followed as described in Sec. 367. In such a test, indicator cards must be taken from both the high- and low-pressure cylinders (see Div. 8). The total indicated horse power of the engine will be the sum of the indicated horse power of the high- and of the low-pressure cylinders. The temperature and pressure of the steam in the receiver should be recorded with the other data. An arrangement of apparatus for testing a compound engine is shown in Fig. 421. Supply Jhermome-ter Steam, ;' Steam Calorimeter / / ,'Tandem-Compound Engine Under Test fan? flandwheel * ' ' -Indicators .Continuous ^^^^Brake. ( Adjustment Platform 5upp/u tfeamror Humps 'Condensate Line Condensate Tank--. Condenser Platform Scale for Weighing \ Circulating Htofer/n/et Steam Cylinder FIG. 421. Arrangement of equipment for determining the water rate of a tandem- compound engine. (Horse power is measured with brake B. Steam used by engine, E, is condensed in C and the condensate weighed in W.) 378. In Testing High-Speed Engines care should be used to determine the speed accurately. The indicators and reducing motion should be examined for lost motion as this may cause a noticeable deformation of the indicator cards. Some simple method (see the note under Sec. 101) should be provided for connecting and disconnecting the indicator cord from the reducing motion, as this is often difficult to do on high-speed engines. The brake load should be applied carefully as a slight inaccuracy in loading may cause a large error in power. 379. The Clearance Volume Is Often Determined In Engine Testing especially to enable the plotting of the theoretical SEC. 379] STEAM-ENGINE TESTING 367 -Bucket expansion curve (Sec. 108). The clearance volume may be found by setting the engine carefully on dead center (Sec. 153) and filling the clearance volume with water from a previously weighed container. The difference in weight of the container before and after filling the clearance space will give the weight of the water in the clearance space. From this, the volume of water in, or the volume of, the clearance space may be calculated. NOTE. ALLOWANCE SHOULD BE MADE FOR LEAKY PISTONS AND VALVES WHEN THE CLEARANCE Is BEING DETERMINED by this method. Data may be obtained (Fig. 422) for the necessary correction in this way: (1) Observe the time and quantity of \ \ ^ater Leaking Past Piston \ \ "Piston at End of Stroke water required to fill the clearance space \ Clearance Space Filled with Water at a uniform rate. (2) Note the quan- "Outlet to indicator cock tity of water required to keep the clear- FlG - 422. Method of determining clear- ance space completely filled for any con- ance volume in an engine c y linder - venient length of time. (3) The clearance volume may then be found by substituting in the following formula: (57) (cu. in.) Wherein: Vi = the clearance volume, in cubic inches. Vn = the volume of water, in cubic inches, originally necessary to fill the clearance space at a uniform rate, t t \ = the time, in seconds, originally required to fill the clearance space with the quantity of water V%\. Vii = the volume of water, in cubic inches, necessary to keep the clearance space com- pletely filled. tsi = the time, in seconds, required for introducing the volume of water F t - 2 . DERIVATION. If no leakage occurred, Vi, the clearance volume, in cubic inches, would be equal to Fi, which is the volume of water, in cubic inches, originally necessary to fill the clearance space at a uniform rate. But if there is leakage, then the volume of water lost through leakage must be determined. It is apparent that during the time t s i, which elapses while the clearance space is filled with Fi, the rate of leakage around the piston begins at zero and finally attains a maximum as the water level reaches the top of and fills the clearance space. It follows that the average rate of leakage during the t s i seconds is (very nearly) one-half of the maximum rate. This maximum rate is found after the clearance volume is full by introducing Viz. The maximum rate is 368 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 Viz -5- t S 2. The average rate during t\ is therefore one-half the maximum = F t -2/2 s2 . The time required to introduce Vu was ti. Therefore: since total leakage during the time = the rate X the time, it follows that, (58) leakage = ~ X t sl (cu. in.) ^1*2 which must be subtracted from Vi i to find the net volume of the clearance space, Vi. Therefore, by subtraction: (59) which is the same as For. (57). EXAMPLE. If it takes 120 sec. to fill the clearance space of an engine having a leaky piston with 30 cu. in. of water, and it takes 10 cu. in. of water to keep the clearance space completely filled for 200 sec., what is the true clearance volume? SOLUTION. By For. (57): the true clearance volume = Vi = Vu - t s iV i2 /2t sZ = 30 - [(120 X 10) -r- (2 X 200)] = 30 - [1200 -5- 400] = 30 - 3 = 27 cu. in. 380. It Sometimes Facilitates The Computation Of Test Results If The Engine And Brake Constants Are Calculated. These constants are the numerical results of certain factors which will occur in test computations several times and if the constants are calculated at the start of the test computations, some time will be saved. The engine constants are obtained from For. (13) of Sec. 121 and will not be discussed here. The brake constant is obtained from For. (41), Sec. 357, which is (60) ft,, - (b.h.p.) Wherein: 2: TT: 33,000; and L/ (effective length of brake arm in feet) are all constant values for each test. The brake constant then is: (61) kb = 00 ^^ (brake constant) oo,UUU The brake horse power formula, For. (41), then becomes: (62) P bhp = k b N(W - Wi) (b.h.p.) Wherein: Pbh P = the brake horse power developed. kb = the brake constant. N = the speed of the engine, in revolutions per minute. W = the gross load on the scale, in pounds. Wi = the tare- weight of the brake, in pounds, as explained in Sec. 356. SEC. 381] STEAM-ENGINE TESTING 369 EXAMPLE. If the effective brake-arm length for an engine is 5 ft., what is the brake constant? SOLUTION. From For. (61) the brake constant = k b = 27rL//33,000 = (2 X 3.14 X 5) + 33,000 = 0.000,953 = the brake constant. EXAMPLE. If, for the above engine, a 600-lb. load is indicated by the platform scale, the tare-weight of the brake is 50 lb., and the speed of the engine is 180 r.p.m., what brake horse power is developed by the engine? SOLUTION. From For. (62), the brake horse power = P bhp = k b N (W - Wi) = 0.000,953 X 180(600 - 50) = 94.3 b.h.p. 381. An Outline Of The American Society Of Mechanical Engineers, Steam -Engine Test Code which will standardize procedure and will promote accuracy and rapidity of calcula- tion follows: DATA AND RESULTS OF STEAM-ENGINE TESTS CODE OF 1915 1. Test of engine located at. To determine Test conducted by DIMENSIONS, ETC. 2. Type of engine . . . . : 3. Rated power of engine , (a) Name of builders (6) Kind of valves (c) Type of governor 4. Diameter of cylinder in. 5. Stroke of piston ft. DATE AND DURATION 6. Date 7. Duration hr. AVERAGE PRESSURES AND TEMPERATURES 8. Pressure in steam pipe near throttle, by gage lb. per sq. in. 9. Barometric pressure in. of mercury. (a) Pressure at boiler, by gage lb. per sq. in. 10. Pressure in receiver, by gage lb. per sq. in. 11. Pressure in exhaust pipe near engine, by gage lb. per sq. in. 12. Temperature of steam near throttle .deg. 13. Temperature of steam in exhaust pipe near engine deg. QUALITY OF STEAM 14. Percentage of moisture in steam near throttle or number of degrees of superheat per cent, or deg. 14 370 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 TOTAL QUANTITIES 15. Total water fed to boiler Ib. 16. Total condensed steam from surface condenser (corrected for con- denser leakage) Ib. 17. Total dry steam consumed (Item 15 or 16 less moisture in steam). .Ib. HOURLY QUANTITIES 18. Total water fed to boilers or drawn from surface condenser per hour Ib. 19. Total dry steam consumed for all purposes per hour (Item 17 -r- Item 7) Ib. 20. Dry steam consumed per hour for all purposes foreign to the main engine Ib. 21. Dry steam consumed by engine per hour (Item 19 Item 20) Ib. HOURLY HEAT DATA 22. Heat units consumed per hour [Item 21 X (total heat of steam per pound at pressure of Item 8 minus heat in 1 Ib. of water at tem- perature of Item 13)] B.t.u. INDICATOR DIAGRAMS 23. Commercial cut-off in per cent, of stroke per cent. 24. Initial pressure above atmosphere Ib. per sq. in. 25. Back pressure at lowest point above or below atmosphere Ib. per sq. in. SPEED 26. Revolutions per minute r.p.m. (a) Variation of speed between no load and full load per cent. POWER 27. Indicated horse power developed i.h.p. 28. Brake horse power b.h.p. 29. Friction of engine (Item 27 Item 28) h.p. ECONOMY RESULTS 30. Dry steam consumed by engine per i.h.p. hr Ib. 31. Dry steam consumed by engine per b.h.p. hr Ib. 32. Heat units consumed by engine per i.h.p. hr. (Item 22 -f- Item 27) B.t.u. 33. Heat units consumed by engine per b.h.p. hr. (Item 22 -r- Item 28) B.t.u. EFFICIENCY RESULTS 34. Thermal efficiency of engine referred to i.h.p. (2546.5 -5- Item 32) X 100 per cent. 35. Thermal efficiency of engine referred to b.h.p. (2546.5 -r- Item 33) X 100 per cent, SAMPLE DIAGRAMS 36. Sample diagrams from each cylinder SEC. 381] STEAM-ENGINE TESTING 371 "NOTE. For an engine driving an electric generator the form should be enlarged to include the electrical data, embracing the average voltage, number of amperes in each phase, number of watts, number of watt hours, average power factor, etc. and the economy results based on the electric output embracing the heat units and steam consumed per electric h.p. hr. and per kw. hr. together with the efficiency of the generator." EDITOR'S NOTE. THE THERMAL EFFICIENCY As FOUND IN THE ABOVE TEST CODE WILL DIFFER BY A SMALL PERCENTAGE FROM THE THERMAL EFFICIENCY As FOUND BY For. (31), Sec. 317. This is due to the fact that in Item 22 of the above code the total heat units consumed by an engine is considered as: XaWi(Bti Hit), while from Fors. (31) and (32), the total heat consumed by an engine = W S i(x d H v + HI) Hiz. Wherein: W s = the weight of wet steam consumed by the engine per indicated horse power hour. x d = the quality of the supply steam expressed decimally. H t i = the total heat in 1 Ib. of steam at the supply pressure, in B.t.u. Hiz = the heat in 1 Ib. of water at exhaust pressure, in B.t.u. HI = the heat in 1 Ib. of water at the supply pressure, in B.t.u. H v = the latent heat of vaporization of 1 Ib. of steam at the supply pressure, in B.t.u. The difference in thermal efficiencies, as found by these two different methods, will generally not amount to more than one-half of 1 per cent. QUESTIONS ON DIVISION 12 1. What are the purposes of testing steam engines? 2. What is meant by the term brake horse power? 3. What is meant by the term total indicated horse power? 4. What is meant by the term friction horse power? 5. What is the mechanical efficiency of an engine? 6. What is the difference between a revolution counter and a tachometer? 7. What are the two general classes of load-measuring apparatus? 8. What is a Prony brake? Draw a sketch and describe one. 9. What is the principle of operation of a fluid-friction-type brake? 10. What is meant by the term effective length of brake arm? Illustrate with a sketch. 11. What is the effective length of brake arm for a rope brake? 12. What is the tare-weight of a brake and how is it determined? 13. How may the electrical loading of engines for testing be accomplished? 14. How is the power output of a three-phase alternating-current generator determined? 15. Illustrate with a sketch how the wattmeter connections should be made for determining the power output of a three-phase, three- wire, alternating-current generator. 16. What is the water rate of a steam engine? 17. How are steam engine water rates usually expressed? 18. What apparatus is necessary in a water-rate test? Draw a sketch and explain. 19. When and how is the steam calorimeter used in engine testing? 20. What is the general procedure in testing an engine? 21. How should the load be applied in engine testing? 22. What data are necessary in a water-rate test of a compound engine? 23. What precautions are necessary in testing high-speed engines? 24. How may the clearance volume of an engine be determined? 372 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 12 PROBLEMS ON DIVISION 12 1. An engine develops 120 brake horse power on an indicated horse power of 133 What is the mechanical efficiency? What is the friction horse power? 2. What is the brake horse power developed by an engine (Fig. 423) at a speed of 220 r.p.m. with a net weight of 250 Ib. on the platform scale, if the effective length of the brake arm is 63 in.? 3. What is the brake constant for a iH-in. rope brake (Fig. 424) on a 6-ft. diameter flywheel? 4. An engine uses 5000 Ib. of steam (97 per cent, quality) per hour when developing 200 h.p. (indicated). What is the water rate of the engine in pounds of dry steam per indicated horse power per hour? Effective Brake Arm Length.^ ( 63-- . -V; t ,-Prony Brake Flywhee,. 6 Ft Diameter, 4 Diameter X Rope flywheel Speed = 220 r.p.m. FIG. 423. What is the brake horse power? FIG. 424. What is the stant? brake con- 5. The engine of Fig. 420 uses 2550 Ib. of steam per. hour. What is its water rate in pounds of dry steam per brake horse power per hour, if the wattmeters read 20.2 kw. and 30.7 kw. as illustrated and the generator efficiency at this load is 90 per cent.? What is the thermal efficiency based on brake horse power? 6. A certain engine develops a total indicated horse power of 200 with steam pressure at 200 Ib. per sq. in. gage and exhaust pressure at 8 Ib. per sq. in. gage. If the quality of the supply steam is 99 per cent, and the mechanical efficiency of the engine is 90 per cent, at this load, what is the thermal efficiency of the engine based on brake horse power when the steam consumption is 42,000 Ib. in a 10-hr 'shift? (Assume barometric pressure is 14.7 Ib. per sq. in.). DIVISION 13 RECIPROCATING-ENGINE MANAGEMENT, OPERA- TION AND REPAIR 382. The Purposes Of Proper Engine Management are: (1) Reliability. (2) Efficiency. Reliability is secured by anticipating all common sources of trouble, such as knocks, hot bearings, clogged condenser passages and all accidents by careful attention while the engine is running; and post- poning the repairs, adjustment and overhauling which will eventually be necessary until a shut-down is convenient. A definite upper limit which the efficiency of an engine cannot exceed is fixed by its design; but the efficiency may be pre- vented from becoming unduly low by avoiding excessive leakage and friction, and by correct adjustment. A skillful operator can, by the sound, detect most troubles in an engine room with which he is familiar. By early detecting and correcting trouble and by regular inspection, an engine may be kept in perfect condition with a minimum of effort. 383. An Important Duty Of An Engineer Is To Become Thoroughly Familiar With The Equipment Which He Is To Operate. The first day which an engineer spends in a new plant or one for which he is to assume responsibility usually provides the best opportunity for a general inspection. Among the parts which it is well to include in such an inspec- tion are: 1. Cylinders. If the cylinder heads have been removed (or if there is time for removing them) see that the piston-rod nuts and bolts of the follower-plate, F (Fig. 425), are tight and well secured. A set screw or lock nut (Fig. 426) is recommended for the piston-rod nuts. Note the condition of the cylinder walls, whether they are scored or pitted. Note also the linear clearance between the piston and cylinder head at the end of the stroke, and mark this distance on the guides for reference. While the cylinder head is off, the amount of piston and valve leakage 373 374 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 may be noted by admitting a little steam to the crank end at crank-end dead center and noting the escape of steam. Use a good gasket coated with graphite in closing the cjdinder. In replacing the cylinder head, be sure that the cylinder walls are free from grit, are well lubricated, and that no tools or other obstructions remain in the cylinder. 2. Valves. If valve chest covers are off (or if there is time for removing SetScrew Flush Nut , , _ _ _ Counferbored I- Flush Nut With Set Screw' Piston 'it Pin. Set Screw \ - Longitudinal Section H-End Partial- Sectional Elevation FIG. 425. Piston construction used in the St. Louis Corliss engine. A taper cotter, K, is used in place of the usual piston-rod nut. (St. Louis Iron and MachineWorks). Common Nut With Set Screw FIG. 426. Showing methods of locking piston-rod nuts. Waste Clamping Bolt-* them) note the condition of the valves. Measure the laps (Sec. 143) for future adjustment and if feasible make templets as described in Sec. 157. Also note the valve action by turning the engine over by hand (if the engine is small) with the cover off. Make sure, in replacing the covers, that the valve chest is clean, the rubbing surfaces well lubricated, and that the gaskets used for the covers are in good condition. Pump valves, if found in poor condition, should be refaced or replaced. 3. Flywheel. Note if the dead centers are marked (Sec. 153) on the flywheel rim for valve setting. If the engine is small, turn it over by hand to see if there is undue fric- tion in its bearings. FIG. 427. Simple split bearing. 4. Bearings. Any bearings or boxes which are dissembled should be examined, cleaned if necessary and adjusted. The condition of all bearings and their oil passages should be ascertained as far as possible. SEC. 383] RECIPROCATING-ENGINE MANAGEMENT 375 Clean out oil holes, put in fresh oil and fill with waste (Fig. 427) if exposed. 5. Stuffing boxes. If the packing appears to be in good condition, oil it and screw up to a reasonable compression. If not, repack (Sec. 415). 6. Auxiliaries. The engineer is usually in charge of some or all of the power plant auxiliaries. For care of these, see the author's STEAM POWER PLANT AUXILIARIES AND ACCESSORIES. Bach Pressure \hlve To Heating Sys tern- .'Steam Separator , Throttle ' Valve Feed-Water Heater Ana" Receiver-:, 'Steam Trap- Feed-Pump Exhaust'' "' Boiler- feed Pump FIG. 428. Auxiliary piping and equipment used in connection with non-condensing steam engine. 7. Pumps. These should be given the same sort of inspection as the engine as far as it is applicable; see STEAM POWER PLANT AUXILIARIES AND ACCESSORIES. 8. Condensers. If the steam-space manhole cover or water-space cover of a surface condenser is removed, note the condition of the tubes inside and out. If the grease is excessive on the outside, the steam space should be filled with water and boiled out. The water in the steam space will issue from any split tubes or leaky tube glands. These should be renewed, repacked or tightened as required. The condition of the sprays and passages of a jet condenser should be ascertained if possible. See the author's STEAM POWER PLANT AUXILIARIES AND ACCESSORIES for further information relating to condenser operation and maintenance. 376 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 9. Piping. Trace out all piping connected with the engine (Figs. 428 and 441) and the auxiliaries. If difficulty is experienced in keeping the piping in mind, sketch diagrams (Fig. 429) may be used, or instead the different systems, i.e., city water, low-pressure steam, condenser water, etc., may be marked with occasional stripes of different colors. The loca- tions of all valves should be care- fully noted. Piping that is rusting rapidly should be cleaned, painted and protected from water if possible. Exposed steam or hot-water piping should be lagged. Exhaust lines to condensers (Fig. 430) and atmosphere and valves, G, for changing from condensing to non-condensing oper- ation should be examined. 10. Drains. Drains both on the engine and piping and the traps used in connection with them should r IG . 429.-Sketch diagram of piping. be noted and tegted to make gure that they are clear. 11. Instruments. The pet cocks on gage glasses should be tested to see if they are clear. It should be noted whether the pressure gages Condenser Cooling- Wafer Cone -.. Supply-. Relief Va/ve --- = ' ' Vacuum /Condensing Engines* Gages-, ^- Exhaust Cuf-Out Valves" 'Exhaust- Sfecrm Header FIG. 430. Showing how several engines, E, may be operated condensing with one barometric condenser. and thermometers work properly. If time permits, they should be tested or calibrated. SEC. 384] RECIPROCATING-ENGINE MANAGEMENT 377 12. Tools. See that tools for oiling and for simple repairs and adjust- ments are in place. 13. Supplies. See that cylinder and engine oil and grease, gasket stock, piston and candle-wicking packing, waste, red lead, graphite, and other supplies are on hand. 384. All Steam Engines Should Be Warmed And Drained Before Starting. The pipe, A (Fig. 431), leading to the engine should be warmed and drained before the throttle, C, is given a large opening. This is to insure that the steam which con- denses in warming the pipe will not run into the engine. To /Stop Valve Cylinder Drain Pipe . ED Drain Line To Live- Steam Trap FIG. 431. ;Steam piping for a simple engine. do this, the drain valve, D, should be opened and stop valve, B, opened a very little. While the pipe, A, is being warmed, the drain valves, E and F, should be opened and the throttle, (7, loosened on its seat to prevent sticking. After the pipe, A, is warmed, the valve, B, may be opened wide; but neither B nor C should be opened suddenly since a sudden large flow of steam through a pipe is likely to draw water from the boiler which may wreck the piping. Then either the throttle, C, or by-pass valve, G, may be opened slightly to warm up the engine. NOTE. LARGE ENGINES MUST BE WARMED UP SLOWLY. In general, the warming up for engines of capacities exceeding 100 h.p. should commence 15 or 20 min. before the engine is to be started. If the fires 378 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 in the boilers are just being started when it is desired to warm the engine, the stop and throttle valves may both be opened so that warm air from the boiler will pass through the cylinders. But the stop and throttle valves should both be nearly closed as soon as the boiler begins to generate steam. NOTE. INDEPENDENT OR CENTRAL LUBRICATORS, Y (Fig. 432), FOR THE GUIDES, CRANK PIN OR OTHER BEARINGS should be started just before the engine is started. The cylinder lubricator, X (Fig. 432), should be started as soon as the engine begins to turn over. FIG. 432. Simple slide-valve automatic engine. (Erie Engine Works.) NOTE. THE TYPE OF GOVERNOR MAKES No DIFFERENCE IN START- ING AND STOPPING SLIDE-VALVE ENGINES because the governor whether throttling or automatic is not in action while the engine is starting or stopping. It comes into play only when the engine is running near the speed for which the governor is set. The methods of handling Corliss-engine governors when starting or stopping the engine are described in Sec. 392. 385. A Non-Condensing Slide-Valve Engine May Be Started as follows: The drain cocks, E and F (Fig. 431), are assumed to be open, the stop valve open, the throttle just off its seat, the lubricators for the bearings started and the engine warmed. Unless there are by-pass warming pipes, MN (Fig. 433), to both ends of the cylinder, the engine should, in warming, be rotated or rocked back and forth to SEC. 386] RECIPROCATING-ENGINE MANAGEMENT 379 By-Fhss Warming Pipes allow steam to enter both ends of the cylinder. The engine is then preferably placed about 20 to 30 deg. past dead center. It is started by quickly opening the throttle enough to carry the engine past its first dead center. After the first dead center has been passed, it may be necessary to again partially close the throttle to prevent the en- gine's speed from becoming ex- cessive. The speed should be kept low at first and be grad- ually brought up to running speed by further opening the throttle valve. The lubricator, X (Fig. 432), should now be started. As soon as the drain cocks, EF (Fig. 431), blow dry steam, they may be closed. 386. The Engineer Should Feel An Engine's Bearings After It Has Been Running A Short Time, say in from 15 min. to 1 hr., depending on the load on the engine. They should not Fingers And Sleeves Out Of The Way, ' FIG. 433. Showing by-pass to both ends of an engine cylinder to facili- tate warming. Path Of Connecting- Rod End,^ 'Posit Ion When -' Running "Over" FIG. 434. Showing method of feel- ing crank-pin bearing. FIG. 435. Feeler for detecting heating of inaccessible bearings. (The behavior of the candle when pushed against a hot bearing may be tested by pushing it against a feed- water or low-pressure steam pipe.) be more than slightly warm. The crank-pin bearing may be felt with the palm of the hand if the path of the moving connect- ing rod end is carefully noted (Fig. 434), but care is necessary 380 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 to avoid being caught or hit by a high-speed rod. If there seems to be too much oil flowing to any of the bearings, the supply may be cut down. If any bearing shows a tendency to heat up to such a temperature that the human hand can- not be held on it, it should be given plenty of oil. About 130 deg. fahr. is a conservative maximum allowable bearing tem- perature. For treatment of hot bearings, see Sees. 412 and 413. NOTE. Where bearings are inaccessible, a feeler (Fig. 435) may be used. A little practice will enable the operator to judge the temperature of an object against which the candle of the feeler is pushed. 387. To Stop A Slide-Valve Non-Condensing Engine, it is only necessary to close the throttle valve. If the engine is to remain idle for some time, the main stop valve should be closed and all the oil feeds shut off. The throttle should be left loosely on its seat so that there will be no trouble in opening it again. If the stop is for a few minutes, the drains, E and F (Fig. 431), should be opened and either the throttle or by-pass valves opened a little to keep the engine warm and drained. If the engine is a hoisting engine operated by signals from some other point, the engineer should stand by for further signals. If the signal to start again is expected in a few seconds, nothing but the throttle and perhaps the reversing gear need ordinarily be touched. If the engine is to be laid up (see Sec. 398) for some time, the drains should be opened and be left open until the engine is started again. NOTE. NON-RELEASING CORLISS-VALVE ENGINES MAY BE STARTED AND STOPPED IN THE SAME WAY As ARE SLIDE-VALVE ENGINES. There is less trouble in draining the cylinders of Corliss-valve engines because the exhaust valves of such engines are so located that the condensed steam drains through them. These engines are therefore not always provided with cylinder drains. In starting the engine, first open the throttle valve sufficiently to permit the engine to "warm up." Then close the throttle and turn the engine over by hand to allow any con- densation to flow from the cylinder. Now open the throttle just enough to allow the engine to run very slowly until it is thoroughly warm. Then by further opening the throttle valve the engine may be slowly brought up to normal speed. 388. A Slide-Valve Condensing Engine Which Has Sepa- rately Operated Condenser Pumps Should Be Started After SEC. 389] RECIPROCATING-ENGINE MANAGEMENT 381 The Pumps Are Started. Where the condenser pumps are driven mechanically from the main engine they start simultane- ously with it. In starting a slide-valve condensing engine, start the circulating and air pumps of the condenser according to directions for starting non-condensing engines (Sec. 385). When there is an average flow of cooling water through the condenser and a few inches of vacuum are produced in it, the engine may be started exactly as described for non- condensing operation. When the cylinder drain valves are open, there will be little vacuum due to the drain valves admitting air. The engine may, of course, be warming up while the condenser is being started. After the engine has been running condensing long enough to give a constant temperature in the condenser, the circulating and air pumps may be adjusted to give the desired condenser pressure and condensate temperature. The condensate temperature should ordinarily be about 100 to 120 deg. fahr! The condenser pressure should be about 26-26.5 in. of mercury vacuum or about 1.5-2 Ib. per sq. in. abs. NOTE. The atmospheric relief valve, G (Fig. 430), must, of course, be closed when starting condensing. If there is a centrifugal condensate pump, it may have to be primed or a valve in the condensate line closed before a vacuum can be established in the condenser. If such a valve is closed, it must be opened again and the pump started as soon as a little condensate accumulates in the condenser. NOTE. To start several engines which have a common exhaust header and condenser (Fig. 430) proceed as follows: Start the engine warming and draining. With the valves in the exhaust lines from the engines closed, start the condenser. Close the drain valves and open the exhaust line valve on each engine just before it is started. 389. Condensers Should Be Started Before Starting The Main Engine And Stopped After The Main Engine Has Been Stopped. If the engine is started first, it will exhaust out the atmospheric outlet and run non-condensing. Similarly, if the condenser is stopped first, the atmospheric relief valve will open and the engine will again run non-condensing. A certain amount of oily water will be then left in the con- denser until it is again used. NOTE. THERE Is ORDINARILY LITTLE DANGER OF THE LOW-PRES- SURE CYLINDER OF THE ENGINE SUCKING WATER FROM THE CON- 382 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 DENSER and causing damage. In a barometric condenser, the tail pipe is of such a length (over 35 ft.) that water cannot be sucked into the exhaust pipe. Ejector-jet condensers and low-level jet condensers (see Figs. 350 and 352) ordinarily employ vacuum breakers which open a valve in the condenser shell if the water level becomes too high. These condensers, moreover, are usually located below the engines and so arranged that if a vacuum does form in the exhaust pipe due to steam remaining therein after the engine has been shut down, no water will be sucked into the cylinder. Nevertheless, condensate pumps and wet-air pumps should always be run long enough after the main engine has been stopped to clear the apparatus of water. 390. Air Leaks Constitute The Most Important Source Of Trouble In Condensing Operation. Leaks may be detected by means of a lighted candle. The flame will be sucked to- ward a condenser leak since in the condenser the pressure is below atmospheric. Leaks may occur at valve-stem and piston-rod stuffing boxes, in pipe joints in fact anywhere in any joint holding the vacuum in the condenser, engine, air pump or piping. The effect of such leaks is either to decrease the vacuum, or to increase the power required by the air pump in maintaining the -vacuum, or both. NOTE. THE UNAVOIDABLE DIFFERENCE BETWEEN THE THEORETIC- ALLY POSSIBLE VACUUM AND THE ACTUAL ATTAINABLE VACUUM Is USUALLY LESS THAN % IN. of mercury in all large condensers #nd is a little more for small condensers. The theoretical vacuum is that corresponding in a table of saturated steam properties to the temperature of the condensate which is withdrawn from the condenser. 391. Steam Engines Are Stopped In Exactly The Same Way Whether Condensing Or Non-Condensing as far as the engines themselves are concerned. The condensing apparatus must also be stopped afterward. If there is a centrifugal circulating pump, located above the water supply, the valves in the circulating-water line should be closed so that the piping will remain full of water and the pump, when again started, will not have to be primed. Before leaving a condens- ing engine, the vacuum should be broken, that is, either the atmospheric relief valve or some other valve should be opened so that atmospheric pressure will be restored in the condenser and piping. NOTE. CHANGING FROM CONDENSING To NON-CONDENSING OPERA- TION is usually an accident due to the condenser becoming heated or air SEC. 392] RECIPROCATING-ENGINE MANAGEMENT 383 bound because of the failure of one of the pumps. If the atmospheric relief valve does not stick, there will be no damage done when this happens. The pressure built up by the engine, when the condenser fails, opens the valve and the engine then exhausts into the atmosphere. (Some uniflow engines will, when the vacuum is destroyed, discharge steam from the cylinder relief valves. This condition should be accepted as a warning that the valves which increase the clearance volume, Sec. 334, should be opened.) To intentionally make the change from con- densing to non-condensing operation, stop the condenser pumps, block open the atmospheric relief valve if desired and close the steam valve in the exhaust line to the condenser. To change back to condensing operation, first make sure that the condenser pumps are working properly arid that there is a good supply of circulating water through the con- denser. Then gradually open the steam inlet valve to the condenser while the atmospheric relief valve is being gradually closed. 392. In Starting A Simple Detaching Corliss-Valve Engine, warm up as described for slide-valve engines. Since the Thumb Screw-. ffl-Enlarged Section X-X Fia. 436. Hook-rod or reach-rod of Corliss engine showing latch for engaging wrist- plate pin. (To permit wrist pin to enter or leave slot, unscrew N until it leaves its seat, then pushing 2V to the left will also slide the latch, L, to the left and open the slot.) exhaust valves of Corliss engines are usually located at the bottom of the cylinder there are often no drain valves or cocks. The steam which condenses in the cylinder drains through the exhaust valves and is removed by a trap in the exhaust line. In warming up a Corliss engine, first unhook the reach rod (or hook rod, Figs. 436 and 437) and close the latch so that the valves may be operated independently of the eccen- tric. By means of the starting lever, L (Fig. 438), which may be inserted in a socket in the wrist plate, alternately lift the 384 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 admission valves so as to admit steam to both ends of the cylinder. At first not enough steam should be admitted to move the engine piston ; later, by rocking the starting lever, the Wr/sf Locking- Screw Handle*. (Attached \ Ridaid/y ToM) FIG. 437. Reach-rod and latch. (This is another construction used for the same purpose as that in Fig. 436. To loosen, first unscrew F then pull out the handle connected to C.) FIQ. 438. Corliss engine starting lever and wrist plate. engine piston may be caused to reciprocate back and forth a part of a stroke. When the engine is thoroughly warm and ready for starting, open the throttle a little more and lift ..Throw Lever L So AS the proper admission valve to start the engine in the desired running direction. That is (Fig. 439), to run To Lift Head End Va/ve- Pin Above Z_A Uk^/ T^U " Ver " ^ ^ ^^ shaft W) "ygl steam to the head end if 'Crank Shaft rn il . i i i the crank pin is above the FIG. 439. Showing how to start a Corliss ^ aft and to thp Prank PnH engine running "over." (For engines with \ wrist plates of a construction different from that if the Crank pin is below the here shown it may be necessary to move the cnaft Tf thp Prank i5 IPVP! lever. L, in the opposite direction from that in bndIT " - 1 which the piston is to move. But for the crank with the shaft, the engine position shown in the above illustration, the j d d te d t head-end admission valve should, in every case, be lifted to start the engine running over, that be barred Or jacked to a COn- is, in the direction indicated by the arrow.) ven ient Starting position. These directions assume a horizontal engine but the same methods may be readily applied to vertical engines. Operate the valves by hand until the engine attains sufficient speed to carry it, by momentum, at least one-half a revolution. Then SEC. 393] RECIPROCATING-ENGINE MANAGEMENT 385 slide (swing or screw according to the construction used) the latch of the reach rod so as to allow the reach-rod pin to be caught and held properly. Then remove the starting lever and return it to its rack and gradually open the throttle wider to bring the engine up to speed. After the engine is running at normal speed and under control of the governor open the throttle valve to its maximum opening. NOTE. IF BY NEGLIGENCE THE GOVERNOR HAS BEEN ALLOWED To FALL To THE SAFETY POSITION, the engine will not start; see Sec. 216. In stopping after the preceding run the gov- ernor should have been brought to rest on the .Governor Sleeve tart cam or block, B (Fig. 440; see also S, ">_ ^^' Fig. 247). If it is not on the cam it must be lifted to the starting position by hand or with a tackle before the engine can be started. After the governor lifts, the start- ing cam should fall out of the way of its own weight. If it does not, it should be so turned that, in case of an accident, the gover- nor may fall to the safety position. NOTE. IN STARTING UNIFLOW OR POP- PET-VALVE ENGINES observe the following instructions. Poppet-valve counterflow en- , FlG ' 4 f;~ S * ar J! ng block . . (or cam) for Corliss engine gines may, in general, be started .as was directed in Sec. 387 for non-releasing Corliss engines. Poppet-valve engines which operate on high-pressure super- heated steam must be very carefully drained as they are warmed because, since the walls must be heated to such a high temperature, condensation during warming will be very rapid. For this reason, such engines should be very slowly started. In starting a uniflow engine, first drain all water from the steam manifold, cylinder heads and exhaust cages. Then close the drains and "crack" the throttle so that these parts may be warmed by the live steam. After ten or fifteen minutes again open all drains. Then turn the engine so that its crank is a little ahead of dead center and open the throttle a little, leaving the drains open for a few minutes so that all water may flow from the engine. Immediately after opening the throttle turn on the oil to all bearings. Allow the engine to run slowly for some minutes while all lubrication may be inspected for proper action. A new engine should be speeded up only in the course of two or three hours and all of its bearings should be left loose so as to peen themselves to a better wearing surface. 393. In Stopping A Detaching Corliss Engine, throw the starting cam or block (5, Fig. 440) of the governor into the 25 386 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 starting position before or immediately after turning off the steam. The governor will then come to rest on the cam and be in proper position for starting again. On some engines the Vilter for example there is a rod, running from the governor starting cam to the throttle valve, which automatically places the starting block in the starting position. 394. In Starting A Compound Corliss Engine, it is neces- sary to warm both cylinders. There is usually a by-pass, P (Fig. 441), or pass-over valve for admitting live steam to the receiver, from which the steam will pass to the low-pressure By-Pass To Receiver $ : g Hiah-Pressure \ \ Cylinder---^ Generator . . Live- - Fly wheel Steam''' Low-Pressure Header Cylinder--^ 'Trap Reservoir for Separator 'Drain From Receiver ''Exhaus t > Header ' 'Drain Line FIG. 441. Some typical piping for a large compound engine. cylinder. Thus this by-passed steam warms both the receiver and the low-pressure cylinder. The low-pressure and high- pressure cylinders may therefore be warmed simultaneously about as explained for simple engines in Sec. 392. The drain, D, on the receiver should be opened if not already so. The by-pass valve in P is given only a slight opening so that a high pressure will not be produced in the receiver. A cross-com- pound engine may usually be started by opening the throttle. If the high-pressure piston is on dead center, open the by- pass valve in P sufficiently to give several pounds receiver pressure; then the low-pressure piston will usually start the engine. If, after opening the valve in P, the engine does not start, then either the cut-off is so early that no admission valve SEC. 395] RECIPROCATING-ENGINE MANAGEMENT 387 is open or there is excessive friction. If no admission valve is open, then one of the admission valves must be opened by lifting its dash-pot piston with a starting lever. If now the engine does not start, there being ample steam pressure and throttle opening, the friction is excessive or it is jammed. A bearing may have seized or the piston become rusted in or jammed in the cylinder. Tandem-compound engines are started just as are simple engines but for them only the high- pressure cylinder valves need be operated by hand. NOTE. IF THERE Is No BY-PASS VALVE ON A COMPOUND ENGINE, steam must be worked into the low-pressure cylinder by working the high-pressure cylinder valves. The low-pressure cylinder does not need to be as warm as the high-pressure cylinder because it will operate at a lower temperature. NOTE. TANDEM-COMPOUND SLIDE-VALVE ENGINES ARE STARTED just as are simple slide-valve engines except that the low-pressure cylinder must also be warmed, drained and oiled. Cross-compound slide-valve engines are started similarly also; but such engines will nearly always start when the throttle and by-pass are opened. The use of the receiver is the same as explained above under compound Corliss engines. 395. Compound And Multi-Expansion Engines Are Stopped As Are Simple Engines, by closing the throttle. The only difference in the starting and stopping of multi-expansion engines is in the greater number of parts to be taken care of. As far as oiling and draining are concerned, each cylinder of a multi-expansion engine may be treated as a simple engine, although there is usually a central force-feed lubricator for multi-expansion engines; Sec. 507. NOTE. CONDENSING OPERATION OF COMPOUND ENGINES requires no special explanation beyond that already given. The low-pressure cylinder is the only one directly affected by the condenser. For more complete directions for condenser maintenance, see the author's STEAM POWER PLANT AUXILIARIES AND ACCESSORIES. 396. Regular Inspection Trips Should Be Made Through A Power Plant At Least Once Each Hour. All equipment for which the engineer is responsible should be examined on such trips. On these inspection trips, listen for unusual sounds and knocks, feel for hot bearings, and look for leaks of all sorts. The oil supply in all oil cups and lubricators should 388 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 be replenished if likely to be necessary before the next trip. See that oil is being fed properly to the cylinders and bearings. Watch the boiler pressure to insure that the fireman is keeping a good steam supply. Note the condenser pressure as an indication of the condenser action. In short, check up every readily observed factor and detail which may influence the operation of the plant. An engineer should not leave the plant during his shift unless it is in charge of a competent assistant because trouble may occur at any instant when power-plant machinery is running. 397. In Cleaning Engines, do not use any emery or abrasive material which may get into the bearings and cause trouble. Various polishing powders which are free from grit are on the market and are preferred for this purpose. An engine should be cleaned immediately after it has been stopped this is the best time. Water will spot the polished parts of engines if it is allowed to stand on them. The polished parts should be left covered with a thin film of oil. The oil will in a damp atmosphere prevent corrosion of the metal. 398. Laying Up An Engine consists in preparing it so that it will not suffer any ill effects from lying idle for a year or more if undisturbed. If the piston and valve rods are steel and soft packing is used, either the rod or the packing must be removed. If not removed the water with which the packing is saturated will corrode the rod. If the engine was supplied with plenty of oil at the end of its last run and was well drained while hot, the cylinder interior will thereby be ordi- narily sufficiently protected. It will not be necessary to remove the head. It is a safe plan to remove slide valves and coat them and their seats with grease. The polished metal parts should be also coated with grease. NOTE. IF AN ENGINE Is To BE IDLE FOR ONLY A FEW DAYS but is not to be laid up, it is advisable to run it for half an hour each day during the period to preserve the oil films on the cylinder walls and on the piston and valve rods. 399. Engines Should Not Ordinarily Need Overhauling More Often Than Once A Year even if they are in con- tinuous service. Engines are more commonly run for several years before being completely overhauled. SEC. 400] RECIPROCATING-ENGINE MANAGEMENT 389 400. Piston Rings Must Sometimes Be Replaced. If exces- sive leakage past the piston is detected (see following note) it is probably due to worn, broken or poorly fitted rings. Loose or broken rings may sometimes be detected by the rattling sound when the engine is running. Broken rings should be replaced as soon as detected to avoid scoring of the cylinder walls by the broken ends. Methods of replacing them will be described in the following sections. NOTE. To TEST FOB VALVE LEAKAGE OF SINGLE-VALVE ENGINES (Power, March 1, 1921) proceed as follows: A general test of tightness can be made by turning the engine over to such a position that the valve covers the ports of both ends of the cylinder at the same time. Then, upon admitting steam at the throttle valve, leakage will be shown by discharge of steam from open cylinder pet cocks or indicator connections, or by escape of steam from the exhaust pipe. The leakage under running conditions can be approximately determined by blocking the flywheel and making tests at different points of stroke of the piston. To test valve leakage of a throttling, D-slide-valve engine at a given point of piston stroke from the crank end of the cylinder, remove the cylinder head and with the piston in the crank end of the cylinder, turn the flywheel in the running direction, and block the wheel when the piston has arrived at the desired point; then gradually admit steam through the throttle and observe whether there is escape of steam from the steam passage of the head end into the cylinder or out of the exhaust pipe. Piston leakage must be corrected before it is attempted to inspect leakage of the valve when it is in position for admission of steam for a piston stroke from the head end of the cylinder, because the crank end of the cylinder cannot be uncovered to distinguish piston leakage from valve leakage. When the piston packing has been made tight and cylinder head replaced, turn the flywheel in the running direction until the piston has arrived at the desired point of stroke from the head end of the cylinder. Then with the wheel blocked, open the throttle a little, and steam escaping from the exhaust pipe, or the cylinder pet cock or indicator connection of the crank end, will indicate the valve leakage. With a single-valve automatic engine, proceed the same as for testing valve leakage of a throttling engine, but with the governor blocked in its average running position, and in positions giving other points of cut-off at which it is desired to test valve leakage. 401. To Replace A Cast-Iron Snap Piston Ring, proceed as follows: The piston, of course, must be removed from the cylinder and, if small, may be held in a vise (Fig. 442). The old ring is first pried out as shown in Fig. 443 by means of a 390 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 file and a strip of sheet iron or piece of hack-saw blade, B. The prying may be continued and other strips, B, inserted until the ring may be slipped off. The groove is now examined and if it appears to be worn out of shape as is groove Removable Copper ,--. * Pktonfbd.-.^ **> - Pl5ton .-Sheet Iron Strip "~ Packing Benc/7- FIG. 442. Piston rod held in vise for con- FIG. 443. Prying end of packing ring venience in replacing snap ring. out of groove. A (Fig. 444) it should be trued up on a lathe so that its sides are flat as are those of groove B. 402. A Piston Ring Must Be Fitted To The Piston Grooves as shown in Fig. 445. If a complete snap ring is on hand, it S/ofes Of Groove -Intact, Due To Snug Fit Of Snap R/'ny Stoles Of Groove . Distorted By Pounding FIG. 444. Illustrating wearing effect FIG. 445. Illustrating fit of snap ring in of poorly fitted snap ring. piston groove. is only necessary to grind it to the correct width and slip it on. If the rings on hand are solid rings (Fig. 446) , it is well to grind or machine them to the correct width before slotting them. SEC. 402] RECIPROCATING-ENGINE MANAGEMENT 391 Since, in time, the piston grooves wear wider, rings which are kept for replacement should be a few thousandths of an inch wider than the grooves and should be ground or machined to fit. If machine tools are available, they should be used. Finishing Nail To Be Driven Below Eotgre Of Ring-. k- Fia. 446. A solid cast-iron FIG. 447. Packing ring fastened down for filing, snap ring. A few thousandths of an inch of metal may, however, be removed with a file. EXPLANATION. The ring may be nailed to a board for filing as shown in Fig. 447. If there is more than about 0.010 in. of metal to be removed, it usually pays to start filing with a flat bastard file (Fig. 448) and finish Cast-Iron Pack, \ I About fig Over ^ Width Of Piston ' Groove FIG. 448. Cast-iron packing ring in position for filing. FIG. 449. Outside caliper for measuring width of cast- iron packing ring. with a fine single cut file. The calipers (Fig. 449) are, for convenience, set at about 1/100 in. over the correct size for the rough filing. When the ring is nearly down to size, it should be finished by testing with a surface plate (Fig. 450). Only one side of the ring should be filed. The other side, being true, should be left undisturbed as a reference plane Octagon Sfeef Scrofpet..^ 392 STEAM ENGINE PRINCIPLES AND PRACTICE [Drv. 13 from which to measure. The surface plate is coated with a thin film of red lead and oil and the ring is wiped clean and rubbed on the plate. (Prussian blue is preferable to red lead but is more expensive.) Where the red lead rubs on the ring, the ring is high and should be further reduced with a file or scraper (Fig. 451). This procedure, if continued until the ring bears evenly on the plate, will insure a true surface on the ring. NOTE. SMALL PISTON RINGS MAY BE GROUND To SIZE by rubbing on a piece of emery cloth tacked to a flat board or glued to a flat plate (Fig. 452). For the most accurate work, a lapping plate (Fig. 453) is used. The grooves in the plate are filled with a lapping compound of .-Lifting Lugs-... ^ True Facing Surface' Fia. 450. Cast-iron face or surface FIG. 451. Cast-iron packing ring in po- plate. sition for scraping to fit. emery and oil. The ring is rubbed over the plate and the compound which runs from the grooves, gets between the ring and the plate and grinds the ring to size. f-Sbts To Be Filled With Oil And Emery ~.^ {Cast-Iron Packing Ri'ny FIG. 452. Cast-iron packing ring ground down on emery cloth. Cast-Iron Pfafe"' Wooden Fro/me--' FIG. 453. A lapping plate. 403. Solid Piston Rings Must Be Cut To Allow Springing Into Place. Common snap rings are often turned eccentric so that they are thinner at one side than at the other. They are cut by means of a hack-saw at their thinnest section as shown in Fig. 454. The length of the segment thus removed SEC. 404] RECIPROCATING-ENGINE MANAGEMENT 393 Scn'beol Lines- 1 Segment Of Ring-- is the difference between the circumference of the ring and that of the cylinder. If the ring is not to be fitted as explained below, the ends should be filed down so that they will be about J^2 m - apart when the ring is in place in the cylinder. The solid rings are usually made about 2 per cent, larger in diameter than the cylinder. Len&th( NOTE. A FINISHED RING MAY BE TESTED FOR FIT in the cylinder before it is sprung onto the piston. A coating of red lead on the cylinder walls will, when the ring is rubbed on it, show what portions of the ring bear on the wall. These portions should be slightly reduced by draw-filing. This operation will cause the ends to sn a p p ac ki n g ring, spring apart so that they will have sufficient play. 404. Worn One-Piece Piston Rings May Be Expanded To Snug Contact With The Cylinder Wall By Peening. This is done by holding the ring on an anvil or heavy face-plate (Fig. 455) and striking its inner surface repeatedly with the peen of a ball-peen hammer. The ring should make solid contact with the surface on which it rests, and each blow of the hammer should be directly above the point of contact. The blows should be comparatively light and of equal intensity. The peening operation should begin at one end of the ring (Fig. 455) and should progress around the inner face to the other end. The hammer blows should not ap- proach either edge of the ring nearer than about % in. 405. The Repair Of Steam-Engine Valves is necessary whenever the valves are so badly worn that steam leakage past them is excessive. The repair always consists FIG. 455. Peening a cast of: (1) Truing up the surface along which iron snap packing ring. .-, 1)n ] 1)f> <* <* pn f (<}\ Mnkinn t~hf> Kroner vtd\j (/LH/Ut/b oc/Cvi/ \i J J.VA. {Jilvv fv\J ltll/\j L/l \JlJ\jt adjustment so that the surfaces are kept together as they should be. These repairs are explained below for the various valves. EXPLANATION. REPAIRING PLAIN D-SLIDE VALVES involves a resur- facing of the valve and its seat. Usually the valve can be finished in a 394 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 shaper or miller, but, if machine tools are not available, it may be scraped to a true surface. A surface plate (Fig. 450) is coated lightly with a red- lead-and-oil mixture and the valve rubbed lightly on it. The high spots of the valve face, which are now marked with red lead, may be scraped off with a scraping tool (see Figs. 451 and 467). (If deep grooves appear in the valve face, the high spots may first be filed off.) Each time the high spots are removed the valve should again be tried on the surface plate, continuing these processes alternately until the entire face of the valve is marked when applied to the surface plate. The valve may, after its face is true, be cleaned and itself coated with red lead. It should then be applied to the valve seat so as to mark the high spots on the seat. These may then be scraped off until a true fit is established between the valve and its seat. Oil grooves may be cut into the valve seat if desired, but they must not extend quite to the working edges of the seat lest they should provide passages for steam to blow through. Plain D-slide valves require no adjustment to keep the surfaces together. The steam pressure outside the valve insures good contact. IN REPAIRING BALANCED SLIDE VALVES, the cover plate and the valve surface which rubs against it must also be fitted as is the valve against its seat. If machine tools are available, the surfaces may be readily machined. Otherwise, all surfaces must be scraped (or filed) to fit as directed above. The cover plate must then be so adjusted that it bears lightly against the valve. In some engines, screws are provided for this adjustment. In others, the cover plate is held from the valve seat by distance pieces which, to provide adjustment, must be filed down. Great care must be exercised in such engines that too much metal is not removed as this would necessitate using shims under the distance pieces. To test the cover-plate adjustment place a piece of thin (tissue) paper between it and valve. If, now, the valve can be moved by hand while pressure is applied to the cover plate (by having an assistant press against it firmly with both hands) the cover plate is too far from the valve. Adjust until, with the paper in place, the valve cannot easily be moved. Then see that, with the paper removed, the valve slides freely. THE REPAIR OF PISTON VALVES usually necessitates the replacement of the valve or its seat, although some piston valves are capable of adjustment. Sometimes, when wear is not excessive, leaks may be stopped by simply refitting the rings in the valve (Sec. 400). If this will not suffice, see if the valve is adjustable. If it is, adjust it so that the wear is compensated for. If the valve is not adjustable, determine whether the wear is: (1) All on the seat. (2) All on the valve. (3) On both the valve and the seat. If either the valve or seat is made of brass, the wear will probably be on the brass part. The brass part can then be removed and replaced with a new piece. (These pieces should be kept on hand.) If the valve and seat are both worn, the seat must be rebored and the valve must be replaced by a larger one. In event of any replacement, the valve and seat should be ground to fit by introducing fine emery powder and oil between them and working them upon each SEC. 406] RECIPROCATING-ENGINE MANAGEMENT 395 Mandre/-. other until, when clean, they slide freely. The emery powder must then be very carefully cleaned out so that it cannot be carried into the cylinder. THE REPAIR OP CORLISS VALVES is most effectively accomplished by boring out the valve seats and procuring from the manufacturer new valves of the proper size to fit the newly formed seat. For reboring the seat, a jig, somewhat similar to that shown in Fig. 464, may be employed. (Engine manufacturers usually have such jigs.) The new valve may then be "ground in" as explained above for piston valves. If reboring is not deemed necessary or advisable, the valves may simply be fitted by marking with red lead and scraping or filing until a tight fit is obtained. THE REPAIR OF POPPET VALVES should scarcely ever be necessary because these valves are not subjected to rubbing action. However, should refitting be necessary, the valve springs and cages may be removed and the seats coated lightly with a mixture of fine emery and oil. The valve may then be placed upon the seat and rotated back and forth through a small angle for two or three minutes. The valve should then be removed, the valve and seat cleaned off, and inspected to see if a clear bright ring is obtained completely around each seat. If the surfaces are not satisfactory, the grinding process should be repeated until they are. It is preferable, in grinding poppet valves, to grind the valves immediately upon shutting down the Distance Piece-. engine and before the valves or seat have a chance to cool off. 406. Re-Babbitting May Be Necessary Where Bearings Have Been Partially Melted Out (Fig. 456), due to heating of the bearings while the engine was in operation. Also the normal running wear in the bearings may necessitate their eventually being re-babbitted. A bearing should preferably be removed from the engine for re-babbiting. The general procedure is to pour melted babbitt metal into the shells of the bearing, one at a time, using a mandrel to form the inner surface of the babbitt. The mandrel is smaller than the shaft so that the surface of the metal may be accurately finished to fit the shaft. Pouring the metal around the shaft is not recommended. When it is done, thick shims should be be used between the halves of the bearing so that the surface Wooden B/ocks' '-Flange Of Manc/re/ FIG. 456. Pouring a main bearing box. 396 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 of the babbitt may be scraped and the play may, when the bearing is assembled for service, be taken up by using a thinner shim. 407. To Dismantle A Quartered Main Bearing (Fig. 457) for re-babbitting, the cap, M , and top shell, S, are first removed and the quarter boxes, Q, are drawn out. Shop marks, A and B, which indicate the proper position of the bottom shell, will generally be found on the end of the shell and on the bearing pedestal. These marks should coincide. Before the bottom shell can be removed, it will generally be necessary Eccentric Slipped From Normal Position. Normal Position Quarter Of Eccentric-. ; \ ''Adjusting Pillow Block-' '. Wedge 'Line Of Square [FIG. 457. A quartered main bearing. '^ Pair Of Jacks FIG. 458. Main shaft jacked up to permit removal of bottom bearing shell. to slip the eccentric and possibly the flywheel along the shaft. The nuts on the outboard bearing may then be slacked off and the shaft raised from the bottom shell with jacks J (Fig. 458), placed under the crank and outer end of the shaft. This will permit the bottom shell to be drawn out. 408. To Re-Babbitt The Boxes Of A Quartered Main Bearing, after the boxes have been taken from the pillow block, the old babbitt metal should first be chipped and pried from the boxes with cape and flat chisels. Each box may then in turn be clamped for babbitting (Figs. 456 and 459) to a mandrel having a diameter about ^{Q in. smaller than the shaft diameter. A piece of iron or steel pipe screwed into a flange (Fig. 460) and finished in the lathe makes an excellent mandrel for this purpose. The wooden blocks, A,B,C and D (Figs. 456 and 459) , should be cut and the clamps SEC. 409] RECIPROCATING-ENGINE MANAGEMENT 397 adjusted as shown. Where the boxes cannot be removed from the engine they may be re-babbitted as shown in Figs. 461 and 462. .flange Of ' Mandrel Double Extra Heavy Iron Pipe*, Cast Iron Shell ./ Of Top Box, Of 'Clamp Main Bearing FIG. 4 5 9. Main-bearing box clamped to babbitting mandrel. FIG. 460. Mandrel for use in main bearings. Cast /ron Flange babbitting NOTE. MAIN BEARING BOXES SHOULD BE BABBITTED WHILE WARM. This will prevent sputtering and blowing of the metal when poured and will facilitate the running of the metal to all parts of the box. Good Gates And Vents For Pour ing Formed By Removing], ^ o W- -4 Moulding ^Sand '' 8 i :': Or .'. CQ ii Tire-.'-' ^ Clay'- ol r iii c c * ^-; s tances~.._ piston rod. With the engine on ap- V Line pra/iei TO Axis-* proximate crank-end dead center ^ 4 79.-Showing how incorrect apply gage B between the piston rod shaft a ii gnme nt may be detected at and the wire line near the Stuffing dead centers by measuring from a line box as Shown in ///. Move the which is Parallel to the cylinder center end, R, of the line, L, horizontally hne * so that B will just touch the rod and line as shown. The wire line should now be parallel to the cylinder axis. The gage, B, is then applied to the rod near the crosshead. If the guides are in line, the distance will be the same as at the stuffing-box. Ordinarily the proper location for the line may be located by measuring from the rod only near the crosshead because the guides are seldom out of line; but it is well to check this condition by a measurement near the stuffing-box. The gage, A, is now applied to the connecting rod, measur- ing to a scribed line, H, above the center of the crank-pin bearing. Mark the position of H on the gage, turn over to head-end dead center and mark the position of H again in the same way. If H falls first on one side of M and then on the other, or is at a different distance from M at the two dead-center positions, the outboard bearing should be shifted to bring the shaft into line. How the difference in distance from the line shows an incorrect shaft alignment may be understood from Fig. 479. If there is a considerable constant difference between H and M, the crank pin is out of line due to the shaft slipping longitudinally. 418. The Normal Wear Of The Main Bearing May Cause The Shaft To Get Out Of Line. As the bearing wears, the shaft sinks continually lower at the crank end. The amount of this wear may be measured by means of a tram or trammel gage, G (Fig. 480) . A center-punch mark is made on the base plate of the engine or the bottom of the crank pin and the long end of the gage inserted therein. The gage should be of such a length that the short end will fall in the center of the shaft 410 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 when the shaft position is correct. The amount of movement from this position may then be readily detected. When the shaft gets considerably lower .than its correct position, it may be restored by jacking up and inserting a liner under the lower shell of the bearing. Engine FIG. 480. Showing a method of gaging the wear of a main bearing. 419. A Table Describing The Principal Causes Of Engine Knocks And Their Remedies is given on the opposite page. CAUTION. Do NOT TIGHTEN ANY BEARING To STOP A KNOCK UNLESS IT Is KNOWN THAT THE PARTICULAR BEARING Is LOOSE and is causing the knock. If a bearing which is already in good condition is tightened to stop a knock which is caused by something else, the bearing will be likely to heat and will have to be carefully readjusted. If a certain bearing is thought to be the cause of the knock but there is some uncer- tainty, tightening the bearing may be tried but the original position of the bolts should be carefully noted; and, if the tightening does not diminish the knock, the original condition should be restored. NOTE. THE APPARENT LOCATION OF A KNOCK Is OFTEN DECEPTIVE due to the fact that the sound travels along the engine frame. It requires experience to locate a. knock with any certainty. Nearly all knocks occur at the ends of the stroke, bearing knocks occurring just as the direction is reversed at each end. Cylinder knocks due to water or deposits in the cylinder are more likely to occur at one end only. A violent knock just after an adjustment may be due to interference such as the piston striking the cylinder head after a careless connecting-rod bearing adjustment. NOTE. BY FAR THE COMMONEST CAUSES OF KNOCKS ARE WATER IN THE CYLINDER AND LOOSE BEARINGS. Remedies for these should therefore be tried first unless the cause is known to be some other. If the knock persists after this, the other remedies should be tried in order of their probability somewhat as given in the table. SEC. 419] RECIPROCATING-ENGINE MANAGEMENT 411 Jt ^ 1 o B O - ^x^ 1 1| o XI 03 b s oj O 1 | IS q^ 1 03 I 1 d d 'a 1 T3 ft .2 2 1 it _d S I ^> o 1 I ."2 ' II bO Xt fcJD d a fi 03 S I 0) ii o d 1 M a bO M I 'S ^ '3 M M ti Q - 1 I I 5 "S 1 J ^ CO t -ft Is I 1 '3 bC "3 bfl o 1 f sound o metallic o metallic . metallic o w o o o O ^ ^_( 3 ft M 1 X! "S S "S 3 .1 metalli .1 metalli 11 metalli 1 metalli 2 & 3 S ft E 3 S a E 3 3 a H 03 S a c O Q XI CO 3 Q 3 Q 1 3 Q c3 XI co co I CQ o3 CO 3 Q CO S S bC .2 .1 1 1 a h d d ^ T3 | s g 1 o a 03 o 1 1 1 d o 0) 3 si 3 S 3 I ~ | 5 1 1 1 "S ! 1 Q O s 8 s s O s O "S TJ d d d a TJ d T5 I 'O d "d "S 1 3 3 3 3 3 *3 3 3 3 3 3 co O CO O CO eg eg eg eg eg O CO d 1 o 1 Locatio Cylinder Connecting .2 1 5 Crosshead Connecting Connecting Cylinder lH 1 i Cylinder d 2 O Crosshead 1 | : o o "ft ' 3 . 1 ^ o : ft o> .-g .2 : .d I 3 a o ^ 'I 03 03 o o "a E ; f X5 T) ^ 9 . 'o ft 3 _j 3 o d o 3 S3 S G o o , ^J ^ O OJ sd .2 d O 'i 1 M d o "? XI ^ 1 G -o ^ ' a? ft "C - j_^ W *d *o d ft I d TJ 's aj S 8 d 1 d 2 rs d d I "3 o d o I 1 ol 53 "ft d i J 1 '^1 to M d 'ft -M s 03 I o o 1 | bO 3 d ^ 5 'I o3 j J b O O EH & h J 1 " ^ ^* O 412 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 .-Dash- Pot Rod From Valve Arm 420. The Location Of A Knock Can Often Be Ascertained By Means Of a Sounding Rod. Any light metal rod which is about 2 or 3 ft. long and which has one reasonably smooth end may be used as a sounding rod. One end is placed against the stationary part of the engine where the knock is suspec- ted. The smooth end is placed against the side of the opera- tor's face near his ear. Try several locations in this way. Where the sound is greatest, the knock is probably located. A wooden rod may be used but is not quite as good. 421. When An Engine Runs "Under" (Sec. 32), knocks are likely to occur in the guides. It may be noted (see Fig. 20) that when an engine runs " under," the thrust on the connecting rod tends to lift the crosshead except at dead centers. Therefore the crosshead will ride against the upper guide during the stroke and against the lower one at dead centers. If there is any play be- tween the crosshead and the guides, the crosshead will strike the upper guide and fall to the lower guide at the end of each stroke, thus causing a knock. When the engine runs "over" the crosshead always rides on the lower guide. Engines are more often run " over" for this reason. 422. Troubles Of Dash-Pots For Corliss Releasing Gears are, principally, as follows: In some designs the vacuum created by the lifting of the plunger, L (Fig. 481), is relied on to return the pot to its closed position. The vacuum cylinder may be packed with cup washers or packing rings, P, which must be in good condition to maintain the necessary vacuum. Failure of the vacuum will prevent the admission valves from closing rapidly. A spring may be used temporarily when this occurs. If the valve, V, through which the air is released from the cushion space is open too wide, the dash-pot will slam. If it is not open wide enough, the dash-pot is likely to bounce or not return to rest in time FIG. 481. Showing inverted vacuum dash-pot for Corliss valve gear. SEC. 423] RECIPROCATING-ENGINE MANAGEMENT 413 for the next stroke. Also it may not allow the valves to shut off completely. 423. The Following Information Concerning Each Engine Should Be Ascertained and kept for ready reference so that repair parts may be ordered promptly. A copy of this form, properly filled in, should be framed under glass and mounted near each engine. DATA FORM ENGINE Date when made up Engine No Maker Type Age Kind of engine No. of cylinders Diam Length Thickness Cylinder head thickness Cylinder head bolts, No Size How is cylinder supported Piston, type Area Thickness Construction , Rings, No Width Diam Piston rod diam Length Taper Thread on end of rod at piston Crosshead Follower bolts, No Size Crosshead type Length Height Width Wrist pin, diam Length Shoes, length Thickness Material Method of attaching wrist pin Connecting rod, type Length Diam. min Max Box adjustment Wedge bolts, No Size Crank, type Throw Crank pin diam Length Eccentric rod diam Length Eccentric throw Rocker arms, type Length Travel Pin sizes Bearings, type Length Material in boxes Adjustment Governor type R.p.m How driven What does governor act upon Engine r.p.m Steam pressure Foundation material Floor area What does engine drive 414 STEAM ENGINE PRINCIPLES AND PRACTICE [Div.'lS SEC. 424] RECIPROCATING-ENGINE MANAGEMENT 415 424. Careful Records Should Be Kept of engine performance and other events in the engine room. These records will enable the plant manager to determine the effect of changes which he may make in the methods of operation and will show in what ways improvements in management may be made. The form shown in Fig. 482 may be found useful in keeping such records. QUESTIONS ON DIVISION 13 1. Name three precautions to be taken in replacing a cylinder head. How may piston leakage be judged? 2. Name three conditions which should obtain in a valve chest before the cover is replaced. 3. What, in general, should be done by an engineer in taking charge of an engine room with which he is not familiar? 4. Name some points which should be noted in inspecting condensers? 5. Give two suggestions to aid in remembering power plant piping connections. 6. What conditions of steam and water piping arising from neglect should be corrected? 7. How may traps and water gages be inspected? 8. Name a few supplies which should be kept on hand in an engine room. 9. Make a sketch of piping used in warming up a simple engine and explain its use. 10. When should gravity-feed bearing lubricators be started? Cylinder lubricators? 11. Should the condenser be started before or after starting a condensing engine? Why? 12. After starting an engine when may its drain valves be closed? 13. How is steam worked into both ends of a slide-valve engine which is not provided with by-pass piping? How into the low-pressure cylinder of a compound engine? 14. In stopping the condensing engine, when should the wet-air pump of a low-level jet condenser be stopped? 15. What is the chief source of trouble in condenser operation? How may it be located? 16. Explain how to change from non-condensing to condensing operation. 17. What may cause a condenser to fail and the engine to exhaust through the relief valve? 18. What is the purpose of a governor starting cam on a detaching Corliss engine? A starting lever? A reach-rod latch? 19. How can a detaching Corliss engine be started when the governor is in "safety position"? 20. What difference is there in the starting of a cross- and a tandem-compound engine? 21. What is the danger in using emery powder in cleaning the polished surfaces on an engine? What is the preferable method of cleaning polished work? 22. How may a solid snap piston ring be removed? How may the fit of a worn snap ring be restored? 23. Explain a method of truing up a filed piston ring by using a surface plate. Explain how the fit of a ring in a cylinder may be tested. 24. May a good bearing be ordinarily made by pouring babbitt around a shaft and leaving the bearing surface as it forms? Why? How should oil be distributed over the face of a bearing? Explain with sketches. 25. What is the purpose of a mandrel which is used in babbitting a bearing? How may one be made? In what position is a main bearing preferably babbitted? Why? 26. What is the danger of repeatedly taking up crank-pin bearing wear by moving only one brass? 416 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 27. What should be done when a crank-pin bearing is " brass and brass " and is still too loose? 28. How are simple split bearings adjusted? What clearance should there ordinarily be between an engine journal and its bearing? 29. Name six conditions which will cause bearings to heat. 30. What can be done to stop the heating of a crank-pin bearing without stopping the engine? 31. What should be done when a main bearing starts to heat? 32. Give general directions for handling a badly overheated main bearing. 33. What are some advantages of metallic packing on good rods? 34. How should metallic packing be ordered? How soft packing over % in. wide? 35. What are possible causes of an engine getting out of line? What are the results? 36. In what order should the various alignments of an engine be made in erecting? Explain the procedure using a sketch. 37. If, when erecting an engine, the correct axial center line for the shaft is found not to pass through the center of the outboard bearing, what should be done? 38. How may the alignment of an engine be tested without dismantling it? Explain with a sketch what is indicated if the crank pin is a different distance at the two dead centers from a reference line which is level and which is parallel with the cylinder axis. 39. Name six causes of engine knocks and their remedies. Which are the most common? 40. What danger lies in tightening bearings to stop any knock which occurs in an engine? 41. Why are engines usually run "over"? 42. What happens if the plunger in the dash-pot of a Corliss valve gear leaks exces- sively? What if the cushion air escapes too rapidly? What if it escapes too slowly? 43. Why should engine room records be kept? 44. Explain a method of repairing a plain D-slide valve without machine tools. How are piston valves repaired when the leakage is found to be excessive? Corliss valves? DIVISION 14 USE OF SUPERHEATED STEAM IN ENGINES 425. The Use Of Superheated Steam In Engines Always Results In Some Gain. Actual fuel savings, due to super- heating an engine's steam supply, range from 6 to 20 per cent. Whether the expense of installing and maintaining the superheater (Figs. 483 and 484) is justified can be deter- 18Lb.Of Steam @ 1103 B.TU. 'Per Lb.=19,854 B.J.U. Per I I.H.R:Hr., Delivered By Boiler To Engine 1-14,668 B.T.U. ''.Absorbed By 'Condenser , Superheater 1,156 B.IU. Per Lb,\;_ Engine Heat I- Super heated Steam Plant FIG. 483. Diagram showing theoretical heat transfer calculated for saturated and superheated steam plants. The figures are based on one indicated horsepower hour. Steam pressure = 105 per sq. in. abs. Superheat = 100 deg. fahr. The condenser temperature = 116 deg. fahr. The heats are calculated above this temperature. A typical steam saving due to superheat is assumed. mined only by comparing such expense with the value of the fuel saving which is effected by superheating the steam. This fuel saving in simple engines is about 1 per cent, for each 10 deg. fahr. of superheat. Whether a high initial steam presssure with slight superheat or a low pressure with high superheat 27 417 418 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 14 is the more economical depends on the type and other operat- ing conditions of the engine (Sees. 432-435). NOTE. FOR DEFINITION AND THEORETICAL DISCUSSION OP SUPER- HEATED STEAM, see the author's PRACTICAL HEAT. See also Div. 10. The efficiency of the ideal Rankine cycle is not materially increased by moderate superheat (see Sec. 315). But with superheated steam there is less cylinder condensation and less pressure drop from the boiler to the engine cylinder. Hence, while the use of superheated steam does not materially increase the Rankine- cycle efficiency it does increase the thermal efficiency and hence the Rankine-cycle ratio. S Superheated Steam To Engine .--- Saturated Steam From Boiler - - - FIG. 484. Typical modern superheater installation. (Superheater installed in. boiler set ting.) 426. The Differences Between Superheated And Saturated Steam at the same pressure may be enumerated as follows: 1. Superheated steam is generated first as saturated or wet steam and then further heated in a superheater, practically no water being present, and is thus converted into superheated steam. That is, its temperature is raised above the boiling point at the given pressure. 2. The temperature of superheated steam is greater at the same pressure than that of saturated steam. Saturated steam at a given pressure exists at only one temperature the boiling point at that pressure; but, at this same pressure, superheated steam may have any temperature above the saturated steam temperature. 3. The volume of superheated steam is greater than that of the same weight of saturated steam at the same pressure, that is, its density is less. Steam, in being superheated, expands so that its volume varies roughly as the absolute temperature. The exact volume which it occupies, however, SEC. 427] SUPERHEATED STEAM IN ENGINES 419 must be found from a superheated-steam table or chart. Less weight of superheated steam is therefore required to fill a certain volume and thus for a given amount of work by an engine. This lesser weight of steam requires a lesser condenser and air pump capacity; or, conversely, results in a higher vacuum for a given condenser and air'pump capacity. 4. The total heat per pound of superheated steam is (Fig. 483) greater than that of saturated steam at the same pressure; also superheated steam contains more heat than does saturated steam at the same temperature. . 5. Superheated steam may be cooled somewhat without condensation taking place. Any abstraction of heat from saturated steam causes condensation but the superheat which superheated steam contains, in addition to the heat contained in saturated steam at the same pressure, may all be abstracted from superheated steam before any condensation occurs. 6. Superheated steam, so experiments tend to indicate, decreases more in volume for a given abstraction of heat than does saturated steam. This appears to be the cause of the expansion lines of indicator diagrams, which are taken while using superheated steam, to fall off somewhat more rapidly than they would were saturated steam used under the same conditions. 7. Superheated steam, if brought into contact with a small amount of water, will evaporate all or part of the water; whereas saturated steam will not evaporate any water. Therefore superheated steam never contains any suspended water in the form of fine droplets nor does it carry any water mechanically as does wet steam. 8. Superheated steam has lower heat conductivity than has saturated steam, probably because* there is no moisture in it. Therefore it does not lose heat through the walls of a pipe as readily as does saturated steam. For this reason, it is usually more economical to transmit superheated steam than saturated steam at the same pressure, in spite of the higher temperature of the superheated steam. 9. Superheated steam has less viscosity or fluid friction than has saturated steam. Hence, there is less loss of pressure due to wire-drawing in engine valves when superheated steam is used. A given volume of superheated steam will ordinarily flow through a given pipe line in a given time with less loss in pressure than will the same volume of saturated steam. However, because of the lesser density of the superheated steam, the weight of superheated steam transmitted at a given pressure through a pipe is somewhat less than if the steam were saturated. 427. Valves For Engines Using Highly Superheated Steam are usually of the piston (Fig. 485) or poppet (Fig. 486) types. Locomotive and marine engines which operate on superheated steam usually have piston valves. Stationary engines for highly superheated steam usually have poppet valves. Simple slide valves can only be used for slightly 420 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 14 superheated steam because of their tendency to warp when exposed to the hot dry vapor. The maximum amount of , Exhaust 5team^ Inside admission Exhaust * Packing Gland " Piston' I FIG. 485. Section through cylinder of Erie-Ball piston-valve engine. Auxiliary Exhaust-} Valve Cam- ' Single-Beat Auxiliary Exhaust Vatve- Exhaust Outlet Steam Inlet FIG. 486. Section of poppet-valve engine cylinder of Hamilton uniflow engine. (Hooven Owens, Rentschler Co.) superheat ordinarily used with valves of various types is shown in the following table. SEC. 428] SUPERHEATED STEAM IN ENGINES 421 428. Table Showing Maximum Pressures And Superheats To Which Engine Valves Of The Various Types May Be Subjected. Valve Pressure, Ib. per sq. in. abs. Superheat, deg. fahr. Total temperature, deg. fahr. Flat slide valve 125 50 395 Corliss 200 120 500 Piston f!75 200] Poppet j [250 250 i 170 J 200 570 600 NOTE. GOOD PRACTICE WITH CORLISS VALVES Is To USE MODERATE SUPERHEATS (about 50 deg. fahr.). The first 50 deg. fahr. superheat is the most cheaply obtained and is more beneficial than any other equal increase in superheat. Higher superheats than those indicated in the table are occasionally used but average practice is much lower than the values given. 429. Metals For Valves And Seats Which Are To Be Used With Superheated Steam are cast iron, cast steel, Monel metal and bronze. For safety valves, Monel metal seats and valve feathers are preferred by some manufacturers. Soft brasses cannot be used. Piston valves should, prefer- ably, be cast from the same heats as their seats to insure equal expansion or contraction with change in temperature. Superheated steam has a greater tendency to cut the faces of valves when the valves are " cracked" (nearly closed) than has saturated steam. High-grade cast iron is used for Corliss and poppet valves with superheated steam up to about 550 deg. fahr. It has some tendency to "grow" (suffer a perma- nent increase in size) due to the action of high-temperature steam. Cast steel is used for valve bodies; bronze for piston-valve bushings. 430. Cylinder Oil For Engines Using Superheated Steam must be a high-grade oil which will not decompose at the steam temperature. Highly superheated steam will not con- dense in the cylinder of an engine when operating at full load. A small quantity of the correct heavy-bodied cylinder oil will then furnish efficient lubrication. Friction and high tern- 422 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 14 perature have a tendency to decompose unsuitable oil and form carbonaceous deposits. Therefore only a high-quality cylinder oil should be used. An engine operating under average light-load conditions on highly superheated steam requires a relatively small volume of steam per stroke, which though introduced in the cylinder in a dry condition will, at the end of the stroke, be partially condensed. Also, if the steam is initially only moderately superheated, it will enter the high-pressure cylinder in dry condition, but will cool, and toward the end of the stroke it will partially condense. Under these conditions a medium-bodied high-quality cylinder oil will furish efficient lubrication. A number 2 or number 3 dark straight mineral oil is recommended in Table 482 for most superheated steam conditions. The Vacuum Oil Co. recommends its " Gargoyle cylinder oil 600-W" up to 600 deg. fahr. and " Extra Hecla" for over 600 deg. fahr. total temperature. 431. Operating Engines On Superheated Steam Does Not Nepessarily Involve Any Change In Operating Methods. Engine valves and lubrication systems must be such as to permit the contemplated degree of superheat. Metallic packing (Fig. 369) should always be used with high-pressure superheated steam since soft packings will not stand the high temperatures and pressures. The packing gland should also be independently supplied with oil of a high grade and under pressure. NOTE. OIL Is SUPPLIED To THE CYLINDERS AND VALVES OF COUN- TERFLOW ENGINES EMPLOYING SUPERHEATED STEAM preferably by the atomization method, as explained in Sec. 502. However, oil is some- times admitted through openings into the valve chest. The piston valve of Fig. 485 is supplied with oil through the lining around its central portion. The oil is led through a pipe to the small annular space between the two halves of the lining from which it is carried by the moving valve and later taken away by the steam. Uniflow engines are supplied with cylinder oil as explained in Sec. 434. 432. The Use Of Superheated Steam Partially Obviates The Desirability Of Compounding. As was explained in Sec. 273, the chief purpose in compounding is to decrease cylinder condensation. When superheated steam is used, SEC. 433] SUPERHEATED STEAM IN ENGINES 423 its excess heat prevents any immediate condensation and may keep the steam dry until cut-off. Moreover, the lesser heat conductivity of superheated steam results in a lesser transfer of heat to and from the cylinder walls. Hence it follows that the economy of superheating (Figs. 487 and 488) is not as great in compound and triple-expansion engines as in simple engines. Also the economy of compounding is not as great when superheated steam is used as when the steam is saturated. These facts are evident from the following table: 34 U32 o:30 *2S |26 24 21 I 20 Elfl 16 3 14 i 10 to 8 6 \ \ \ \ Simp/6. ~30%A V 1 ' Non-Conden Bating I sing\ \ ^ ^ \ Sim} X &7S ?%& on-L >af/; ondt rising V \ s ^< Simple Nt >n- 'ensi Cull "^^ Loa 1 ^ ona * "_> ^ \ N / ^% ^ X ^~^ "~~- >- \ ^s ^ ' ^~~ ^ Con Nor -Ful \ pet -Co 1 Lo nd* ^ "~~-~ ider isingr*" *<, va V \ { & Con ndei pou -/sine, ne( r FUI 'Hoc 7d- ; Indicated Horse Power ,40 fcO 80 100 l?0 I40 160 180700 ?ZO Z40J60J80300 15 SO 75 100 115 150 175 700 225 Degrees Superheat FIG. 487. Showing the effect of superheat on a simple 12 by 16-and a compound 10 and 173-^ by 16 in. pis- ton-valve Buckeye engines. (Steam pressure 100-110 Ib. per sq. in. Foster superheater catalogue.) Per Cent. Load On Engine FIG. 488. Graphs showing influence of superheat on water-rate (steam consumption of a 16 by 22-inch "Ideal" Corliss engine. 433. Table Showing Savings Effected In Engines Of Different Classes By Superheating The Supply Steam. (Alexander Bradley, Power, Sept. 2, 1919.) Engine Saving in per cent, due to 100 deg. fahr. superheat at average pressures Steam saving Heat saving Simple engines and compressors 18 13 5 Compound engines and compressors 14 10.5 Triple-expansion engines Single direct-acting pumps 12 22 9.0 16 5 Compound direct-acting pumps 18 13.5 424 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 13 NOTE. Compound and multi-expansion engines benefit more by higher steam pressures than they do by superheat. Consequently the practice is to use relatively high pressures and relatively little superheat with engines of these types. 434. In Uniflow Engines, The Use Of Superheated Steam Is Very Economical (Sec. 333). Uniflow engines are practi- cally always simple engines but are installed where high economies are desired and are commonly operated condensing. Under these conditions, superheated steam is a decided advan- tage and is nearly always used. NOTE. IN LUBRICATING UNIFLOW-ENGINE CYLINDERS, it is better to inject some of the oil at points A and B (Fig. 489), than to mix it all with Steam Supply-. 5-feam . -Aa 'm/s s i on Va I ve Sea t s - Supply- -Oil Leads- Relief Va/ve FIG. 489. Showing recommended points of oil injection in uniflow engine. (Arrows show direction of steam flow.) the steam. Due to the nearly straight path of the steam in a uniflow- engine cylinder, the oil which is mixed with the steam has much less tendency to attach itself to the walls of the cylinder than it has in counter- flow engines. However, when injected at A and B, the oil has a tendency to flow down over the walls. The piston then spreads it over the cylin- der's length. 435. When Superheated Steam Is Used In Compound Or Triple -Expansion Engines, the steam usually becomes satu- rated in the high-pressure cylinder before release. Hence, the steam enters the receiver as wet steam. A reheater (Fig. 336) is frequently used under these conditions to super- heat the steam again before it enters the next lower-pressure cylinder; see the " locomobile" in Fig. 395. SEC. 436] SUPERHEATED STEAM IN ENGINES 425 NOTE. SIMPLE ENGINES ARE PROFITABLY OPERATED AT RELA- TIVELY Low PRESSURES AND HIGH SUPERHEATS. For mechanical reasons high pressures are not desirable in simple engines. But, for high efficiency, the temperature range in a simple engine must be great. By employing high superheats, a large temperature range may be secured without the mechanical difficulties and excessive cylinder con- densation (Fig. 490) which high pressures involve. 5 10 15 20 25 30 35 40 45 Percentage Of Stroke Completed At Cut -Off FIG. 490. Graphs showing effect of superheated steam in decreasing cylinder condensa- tion and leakage in simple engines. (An average of 41 deg. fahr. superheat.) 436. A Table Showing The Advantages And Disadvantages Of Superheated Steam as compared to saturated steam for steam-engine operation is as follows: Advantages Disadvantages Increases engine efficiency. Decreases the amount of oil needed. Requires less weight of steam for a given amount of power. Decreases cylinder condensation and trouble with water in engine cylinder. Decreases radiation and pressure Requires additional equipment. Requires a better grade of oil. Requires high-temperature packing. Where impure feed water is used, dust may be carried from the superheater to the engine. See note below. May cause changes in shape and size of cast-iron parts. NOTE. A FOAMING BOILER MAY GIVE DANGEROUS RESULTS IF THE STEAM Is SUPERHEATED. The foam which leaves the boiler is usually a saturated solution of some mineral which was used as a scale preventive. When this saturated water is evaporated in a superheater, the mineral remains in the superheater as a fine dust. After a quantity of dust accumulates in the superheater, some of it will be carried away with the steam which passes to the engines. As this mineral dust is a very 426 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 14 good abrasive, it becomes very dangerous in that it will probably score the engine cylinder. Foaming of the boilers is, therefore, to be particu- larly avoided when the steam leaving the boiler is later superheated. QUESTIONS ON DIVISION 14 1. What steam saving results from superheating steam for simple engines? 2. What effect has superheat on cylinder condensation? 3. Name six differences between superheated and saturated steam. 4. What is an approximate relation between the temperature of superheated steam and its volume? 5. What types of valves are preferred for highly superheated steam? 6. What effect in the valves of an engine is noticed due to the lesser fluid friction of superheated steam? 7. What is the approximate limit of total temperature for cast-iron valves? 8. What metals are used in valves for superheated steam? 9. What kinds of cylinder oil are recommended for engines using superheated steam? 10. How is oil introduced into a counterflow engine using superheated steam? Into a uniflow engine? 11. What kind of packing should be used for highly superheated steam? 12. What is the relation between compounding and superheating in steam-engine practice? 13. How does superheating lessen the desirability of compounding? 14. When, in general, are high pressures and slight superheats used? When low pres- sures and high superheats? 15. What is the usual condition of the exhaust steam from the high-pressure cylinder of a compound engine using superheated steam? 16. Enumerate the principal advantages of superheated steam for engines. 17. Explain why a foaming boiler is dangerous in a superheated-steam plant. DIVISION 15 SELECTING AN ENGINE 437. The Governing Factor In Selecting An Engine Should Be The Cost Per Unit Of Energy Delivered by the engine. In computing the cost per unit of energy delivered (Sec. 447), all items of expense must be considered. An engine with a very low initial cost may, because of its steam rate, produce power at a much higher cost than a more expensive engine which uses less steam. Conversely, the engine which uses least steam and therefore the least fuel will not, necessarily, produce power more cheaply than a less expensive engine which uses more steam although, erroneously, some engineers consider only the fuel cost. As explained in following sections, there are a large number of elements which enter into the computation of the unit energy cost. The unit energy cost is usually computed over a yearly period, thus : , , n Total expenses per year (bo) Cose per unit of energy = -^ -. , ; ; Energy units developed per year NOTE. THE TOTAL ANNUAL COST OF AN ENGINE, which will supply a given quantity of power throughout the year and under certain condi- tions, is frequently used as the governing factor in selection; but, as explained later, the total annual cost then bears a given ratio to the unit power cost. Thus, it is immaterial whether, under given conditions, the unit energy cost or the total annual cost is taken as the governing factor in engine selection. NOTE. THE PROCEDURE IN SELECTING AN ENGINE FOR A GIVEN SERVICE consists of: (1) A study of requirements and operating conditions Sec. 448, to determine what type or types of engines are best suited for the service. (2) A computation of the unit cost of energy for each engine which is suited for the service and which it is desired to consider. (3) A choice of the engine which affords the least unit energy cost. The sections which immediately follow deal with the calculation of the true unit energy cost. After this are given considerations of service require- ments and more specific rules for engine selection. 427 428 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 438. Various Elements Which Are Factors In Energy Cost And Which Should Be Considered In Computing The Cost Per Unit Of Energy are generally grouped into two classes: (1) The fixed charges, or those elements of cost which are the same whether an engine is operated or idle. The fixed charges, as explained in subsequent sections, comprise interest on invested capital, rentals, insurance, taxes, and depreciation, which is the natural loss of value of the machine as its age increases (Sec. 443). (2) Operating charges, or those elements of cost which are proportional, directly or otherwise, to the energy developed by an engine. The operating charges, as is also explained in subsequent sections, include the cost of all labor involved in the operation of the engine, the costs of all materials which are consumed in its operation, and all costs necessary to keep it in a good operating condition; such as the cost of repairs, replacements, and adjustments. These operating charges are frequently termed attendance, material, and maintenance respectively. NOTE. FIXED CHARGES ARE OFTEN COMPUTED As A LUMP SUM that is, the annual amount of the fixed charges is taken as a certain per- centage of the total first cost. A common percentage for this purpose, which experience shows to be fairly accurate for average conditions, is 15 per cent. Thus, if an engine, installed, costs $10,000, the fixed charges may be taken as 0.15 X $10,000 = $1500 per year. Why 15 per cent, is taken rather than some other value will be evident from a study of the example under Sec. 446 wherein the total of the fixed-charge percentages is 15. 439. Interest is the cost of the capital invested money in any undertaking. Interest is a rental or fee paid for the use of money. A corporation can only obtain money by borrowing from investors who always demand interest (a rental) in payment for use of the money. If the borrowed money is used to purchase an engine, the interest on the invested money is an item of the expense incurred in operating the engine. Now, even if one uses his own money and does not have to borrow in purchasing an engine, interest should nevertheless be charged in when determining the total expenses per year of the engine. One must consider that, if the engine had not been purchased, the money which was used for its SEC. 440] SELECTING AN ENGINE 429 purchase could have been invested, kept on deposit, or loaned so as to draw interest. If the money is invested in an engine it should bring at least the same return. Therefore, for com- parative purposes the interest on the money invested in the engine should always be computed and recognized as an item of expense incident to the ownership of the engine. See example under Sec. 446 for an application of this idea. NOTE. THE ANNUAL INTEREST EXPENSE is determined by the amount of the initial investment and by the current interest rate. The initital investment includes the first cost of the engine, its accessories, founda- tion, and installation together with all transportation charges. The interest rate is usually 6 to 8 per cent, per year. EXAMPLE. If an engine installed complete costs $10,000 and the usual interest rate in the community where it is installed is 6 per cent.; then the annual interest expense of operating the engine = 10,000 X 0.06 = $600 per year and this $600 is just as real an item of the cost of running the engine as is the cost of the oil and waste for it or the cost of the steam which operates it. 440. Rent, As An Item Of Engine Expense, Should Be Charged In Proportion To The Floor Space occupied by an engine whether the building in which the engine is housed is rented or not. The engine and its accessories occupy space which could otherwise be used for some other purpose. The fair rent which this space could command is justly an expense incident to the keeping of the engine. Horizontal engines occupy space about as follows: Over 2000 h.p. 0.5 sq. ft. per h.p.; 500 to 1000 h.p. 1 to 2 sq. ft. per h.p. Small engines 3 to 4 sq. ft. per h.p. NOTE. A PORTION OF THE ADMINISTRATION OR OFFICE EXPENSE OF A PLANT may be charged to an engine, according to its value as compared with that of the rest of the plant. It may, however, be advisable to group the engine administration expense with that of the rest of the power-plant equipment and then, for cost-estimating purposes, to handle this combined item as a single item. 441. Insurance Cost Is An Item Of Engine Expense because it is a direct expenditure for protection against loss by fire or other hazards. The annual cost of insurance against fire loss is small. In a fireproof building it is ordinarily less than 0.5 per cent, annually of the amount of insurance carried. In 430 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 wooden buildings it is somewhat greater. An average value is about 1.5 to 2 per cent. In hazardous locations, such as in a saw mill- where the fire risk is great, it may be impossible to get any insurance. The depreciation rate (Sec. 444) should then be made high enough to cover a possible loss by fire within a few years. 442. Taxes Constitute An Item Of Engine Expense because taxes are the cost of government, including police and fire protection, which is levied on all property in proportion to its assessed value. Tax rates per year are usually 1 to 2 per cent, annually of the assessed value of the property. The assessed value is generally lower by a considerable amount than the first cost. The actual tax rate for any community may be ascertained by consulting the assessor. After the tax rate is determined, the taxes on the engine should be included in its annual expense. Taxes on the real estate on and in which the engine is housed should be taken account of in computing the rental (Sec. 440) and should not be included as a direct engine expense under the heading of taxes. 443. Depreciation is the decrease in value of a thing as it becomes older. Any piece of machinery has a certain useful life. If a thing has a life of 10 years and no scrap value and its original cost is $100, it is evident that (disregarding interest on sinking fund and other refinements) the cost per year of its decrease in value = $100 -5- 10 = $10. From this it is evident that depreciation is a reasonably definite and tangible item in the cost of operating an engine. Depreciation may be due to: (1) Wear and tear; continual use gradually produces wear at all of an engine's bearing surfaces. Eventually it may be impossible to properly adjust the worn parts. The engine will then be useless. (2) Obsolescence; improvements are being made continually in the principles and construc- tion of steam engines. It may therefore be assumed that, even if it were possible to maintain an engine indefinitely in good running order, the engine would eventually have to be replaced by some more efficient engine. As an example of obsolescence may be taken the case of many good steam engines which were in use when the steam turbine was first perfected. In many instances, the engines were so much less efficient than SEC. 444] SELECTING AN ENGINE 431 turbines that, though new, it would have paid to replace them with turbines. (3) Inadequacy; in many plants the demands for power increase to such an extent that it becomes econom- ically wise to discard old but mechanically good engines in favor of larger engines. Customarily, it is not attempted to foretell whether an engine will depreciate because of wear and tear, obsolescence, or inadequacy; but, instead, a useful life is assumed in accordance with the lives which experience^/'' shows to be most common; see following section. NOTE. THE "DEPRECIATION CHARGE" OR "COST" OR THE " ANNUAL DEPRECIATION" is the amount which should be considered as an annual expense incident to the ownership of an engine (or other equipment). It may be found by dividing the first cost of the engine by its useful life in years. It should be understood that annual depreciation charges can be only reasonably accurate estimates or guesses it is impossible to predetermine depreciation exactly. The depreciation charge should actually be paid out that is, it should be placed in a bank or other safe depository. The sum which thus accumulates in the depository is called the sinking fund. At the end of the engine's useful life the sinking fund should equal the first cost of the engine so that the engine may be replaced without borrowing new capital or, if the engine is no longer needed, that the investors may be paid off. To be strictly correct it might seem that, since the sinking fund can be made to draw interest and since at the end of its useful life the engine still has some value (see below), the depreciation charge computed as directed above will provide a sinking fund which will exceed the engine's true deprecia- tion. But, since the life of the engine is not definitely known before- hand, the " straight-line" method of computing the depreciation charge, which is suggested above, is sufficiently accurate for practical purposes. NOTE. THE RESIDUAL VALUE OR SCRAP VALUE OF AN ENGINE is its value at the end of its useful life. Since, at the end of its useful life, an engine has no value as an engine, its residual value is simply the value, as scrap, of the materials of which it is made. The residual value of an engine seldom exceeds 5 per cent, of its first cost. 444. The Usual Depreciation Rates For Steam Engines are determined from their useful lives. Experience shows that the average lives of steam engines are about as follows: High-speed engines 17 years. Medium-speed engines 20 years. Low-speed engines 28 years. EXAMPLE. If the first cost of a medium-speed engine is $8000 what should be its annual depreciation cost? SOLUTION. Since the probable 432 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 100 life of a medium-speed engine is 20 years, the depreciation rate = 100 -5- 20 = 5 per cent. Therefore, the annual depreciation cost = 0.05 X $8000 = $400. 445. The Operating Costs Of An Engine are : (1 ) Maintenance, which comprises the costs of repairs and such replacements of parts as are occasionally necessary. The maintenance cost per year may ordinarily, for estimating purposes, be taken at 2 to 4 per cent, of the first cost of the engine. (2) Materials. These are steam, engine oil, cylinder oil, packings, waste, and miscellaneous supplies. The cost of steam varies greatly with boiler conditions and the price and kind of fuel. With 12,000 B.t.u. coal at $5.00 per ton, the average cost of producing steam in a stoker-fired water-tube boiler plant is about 45 ct. per 1000 Ib. For the same coal in a hand-fired return-tubular plant,the cost would be about 60 ct. per 1000 Ib. In any plant, the cost of steam FIQ. 491. showing average cyi- per pound = (total annual boiler- inder oil consumed per brake 7 \ / 7 / ? horsepower hour by engines of P^ nt expense] = (number of pounds various sizes. of steam generated per year)', see the author's STEAM BOILERS. The cost of cylinder oil may be based on the average cylinder-oil consumptions shown on the graph of Fig. 491. The amount of engine oil used varies greatly with the method of lubrication and the precautions taken for its recovery. It should not greatly exceed the amount of cylinder oil. The cost of the other materials seldom exceeds 10 ct. per h.p. year for a 100-h.p. engine to 2 ct. per h.p. year for a 1000-h.p. engine. In general, the oil and other supplies constitute about 2 to 9 per cent, of the total operating expenses. (3) Attendance. This includes the salaries of operating engineers, oilers, and a portion of the salaries of superintendents and others who devote part of their time to the engine or in supervising its attendants. An operating engineer can, ordinarily, take care of more than one engine; but, where the plant is operated 24 hours per day, three engineers are probably necessary. WO 100 1.000 Brake Horsepower Of Engine SEC. 446] SELECTING AN ENGINE 433 446. The Total Annual Cost Of An Engine is the sum of the annual fixed and operating costs. The meaning of this is illustrated in the following example which gives an economic comparison between engines of two different types which are to be served by an existing boiler plant. EXAMPLE. Compare the annual cost of a poppet-valve engine with that of a slide-valve engine. Both are rated at 200 h.p. and both are operated non-condensing on saturated steam. The poppet-valve engine uses 18 Ib. of steam per i.h.p. hr. at 175 Ib. per sq. in.; the slide-valve engine uses 29 Ib. of steam per i.h.p. hr. at 125 Ib. per sq. in. Assume that the cost of the steam at 175 Ib. per sq. in. is 51 ct. per 1000 Ib., and at 125 Ib. per sq. in. is 50 ct. per 1000 Ib. A stand-by unit is assumed to be necessary in each case. SOLUTION.- Fixed charges: POPPET- SLIDE- POPPET- SLIDE- VALVE VALVE VALVE VALVK First cost of one engine $4,175 $2,225 $ Foundation and installation 625 625 Total first cost. $4,800 $2,850 Interest at 6 per cent. $ 288 $ 171 Depreciation based on an 18-year life at 5.55 per cent. (100 -T- 18 = 5.55 per cent, per year) 266 158 Rent 70 60 Taxes and insurance at 2 per cent 96 57 Total fixed charges 720 446 Doubling this value to include stand-by unit 1,440 892 Operating charges (assuming 700,000 i.h.p. hr. of service per year, that is 200 h.p. delivered 10 hours per day for 350 days) : Steam, 12,600,000 Ib. at 51 ct. per 1000 Ib 6,426 20,300,000 Ib. at 50 ct. per 1000 Ib 10,150 Oil and other supplies 255 255 Attendance 3,150 3,150 Repairs (guess estimate) 115 95 Total operating charges 9,946 13,650 Total annual cost $11,386 14,542 11,386 Annual saving of poppet-over slide-valve engine $ 3,156 28 434 STEAM ENGINE, PRINCIPLES AND PRACTICE [Div. 15 The obvious conclusion is that, for the conditions specified, the poppet- valve engine is the more economical. This is because of its lower steam consumption. If the steam (coal) were cheaper or if the engine were used fewer hours during the year, the difference in the annual costs would be less than $3156 or it might be in favor of the slide-valve engine. It would be possible to decrease the initial investment for the poppet- valve engines by using a cheap engine as a stand-by unit. The standby unit need not, ordinarily, be operated more than a week in each year; hence its steam consumption would be of relatively minor importance. There are, however, many advantages in having both the working and spare engines of the same kind (Sec. 452). 447. The Unit Cost Of The Energy which is generated by an engine is calculated by dividing the total annual cost of an engine by its yearly energy output; see Sec. 437 and also the following example. EXAMPLE. If the engine of the preceding section produces annually 650,000 h.p. hr. of useful mechanical energy, would it be as cheap to buy electrical energy (which can be converted into mechanical with an efficiency of 82 per cent.) for 4 ct. per kw. hr.? SOLUTION. The cost of the purchased mechanical energy (converted electrical energy) is 4 -T- 0.82 = 4.9 ct. per kw. hr. From the engine, the mechanical energy cost = (total annual cost) -r- (number of energy units produced) = $11,386 -T- 650,000 = $0.0175 or 1.75 ct. per h.p. hr. or 1.75 X 1000/746 = 2.35 ct. per kw. hr. Therefore, the engine develops energy at a lower cost than that for which the electrical energy can be bought. 448. Before Endeavoring To Select An Engine For Any Given Service, the following factors should be determined or estimated: (1) Horse power of engine. (2) Speed of engine. (3) Operating conditions, such as the initial state pressure and temperature of the engine's steam supply, whether the engine is to be operated condensing or non-condensing, the boiler capacity, and the cost of fuel. If the engine is to run non- condensing and if exhaust steam is necessary for heating or industrial processes, the quantity of exhaust steam required should also be known. (4) Operating characteristics, such as the load curve (see Sec. 453), the expected life of the engine, and the types of the other engines in the plant. NOTE. IN SELECTING ENGINES FOR A NEW PLANT the operating conditions are not usually determined definitely until after the type of engine which will be used has been selected. Furthermore, the require- ments, as to horse power and exhaust steam required, can frequently be SEC. 449] SELECTING AN ENGINE 435 only estimated. However, in selecting an engine for addition to an existing plant, the requirements and operating conditions are usually better known. 449. In Determining the Proper Horse Power Of A Contem- plated Engine two things should be considered: (1) The maximum or peak load which the engine must carry. As engines cannot economically develop much more than 25 per cent, overload and as it may be expected that the power requirements will usually increase after the engine is in service, the engine selected should have a normal rated capacity at least as great as the peak load which it must carry. (2) The continuity of service which is desired. In some plants the management will not object to an occasional shut-down of the engines for repairs. During the shut-down power may, in some cases, be purchased from another company. In other plants, electric-light plants in particular, there must be no danger of having ever to discontinue any of the power supply. In such plants the units should be so selected that, should the largest unit need repair, the remaining units can carry the entire load which may come on the plant. EXAMPLE. If a power plant has a peak load of 400 h.p., and if shut- downs are permissible, the plant may be equipped with one 400-h.p. engine or two 200-h.p. engines; but, if shut-downs must be avoided, the plant must either have two 400-h.p. engines or three 200-h.p. engines, or some other combination, see Sec. 453. 450. In Determining The Desirable Speed Of A Contem- plated Engine Or Engines, the use to which the engine is to be put should be considered. Generally speaking, elec- tric generators, especially alternating-current generators, are most advantageously driven at high rotative speeds because high-speed generators cost less than do slow-speed gene- rators. High-speed engines may, therefore, be direct-connected to generators whereas slow-speed engines must be belted to or employ larger and more expensive generators. Where engines are not used to drive generators, the service conditions almost automatically determine the most desirable speed. In any case, the desirability of a certain engine speed should be considered along with all other factors. When an engine is belted to its load the ratio of the speeds of the driving to the 436 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 driven pully or vice versa should not exceed 6 to 1; 4 or 5 to 1 is preferable. NOTE. THE SPEED OF AN ENGINE WHICH DRIVES A DIRECT-CON- NECTED ALTERNATING-CURRENT GENERATOR is definitely determined by the desired frequency and the number of field poles of the generator, thus: (64 ) r 9 . - 120 X frequency lOIJ /. p. Trl. ^r; ~7~f* Tl 1 No. of field poles See the author's AMERICAN ELECTRICIANS' HANDBOOK for further informa- tion and table of synchronous speeds for the various frequencies and numbers of field poles. 451. In Considering The Operating Conditions With Reference To The Selection Of A Contemplated Engine Or Engines it should be remembered that: (1) The state of the steam supplied to the engine determines to a degree the kind of valves which the engine may have; see Sec. 428. (2) Exhaust steam requirements, throughout the factory, determine whether a low steam rate is necessary or even desirable. (3) Condens- ing operation is advisable under certain conditions (see Sec. 297), but, in other cases, is not necessary or even desirable. (4) Boiler and condenser capacities determine whether the con- templated engines will necessitate new boilers and condensers and, therefore, additional investment. Sometimes an engine with a small water rate can be installed without any increase in boiler or condenser capacity, whereas a cheaper engine, which would otherwise be satisfactory, would require the purchase of additional equipment because of its higher water rate. (5) Fuel cost determines whether a low-water-rate engine is economically preferable for a given service. Where fuel is very cheap, as in saw mills and coal mines, the higher first cost of an economical engine may not be justified by the small fuel saving. NOTE. IN SELECTING THE PROPER BOILER PRESSURE FOR A NEW PLANT, the soundest plan is to find the unit cost of energy (Sec. 447) for different assumed boiler pressures and the correspondingly different engines and boilers. That pressure is then chosen which provides the least unit cost. Generally speaking, high-pressure boilers are more expensive in fixed and operating costs than are low-pressure boilers. Nevertheless, engines operated on high-pressure steam are always more efficient than those operated on low-pressure steam and, usually, the SEC. 452] SELECTING AN ENGINE 437 9UV 750 o 600 \\\\ Rate 1 Output \ J " j 5 450 I 300 o ISO 1 { 1 * J: A ve/agre/oaaf^4J2 Kw. Y J "^ * 12 2 10 12 fixed charges are less for the engine which is operated on high-pressure steam. The boiler pressure should therefore be as high as is practical with the engine which is best suited to the plant; maximum permissible pressures and superheats for the engines of the different types are given in Table 428. 452. The Operating Characteristics Which Affect The Selection Of An Engine are: (1) The load curve of the plant (Fig. 492). The load curve of the plant is the graph which shows the variation from time to time of the required total engine output. A load curve might be plotted for any par- ticular engine; from this graph can be read the portion of the total time that the engine must carry its rated full load and other fractional loads. These portions of time deter- mine to a large extent whether the engine should have good economy or not. For ex- ample, if an engine is to be operated a great portion of the time at only one-fourth its rated capacity, then it should be selected on the basis of its steam rate at one- fourth load rather than the basis of its full-load steam rate. Likewise, if an engine is to stand idle for a great portion of the time, since its fixed charges continue while it is not in opera- tion, the operating charges may constitute but a small fraction of its total annual cost; hence its water rate is of relatively little importance. (2) The life of the engine. If an engine is to be used continuously, its life will of course be shorter than if it were used but little. However, the life of an engine is fre- quently assumed to be the same regardless of its service because it gradually becomes useless although it may not be wearing out, see Sec. 443. (3) Other engines in the plant. If a plant is already equipped with some engines, additional engines which are to be installed should, unless some other consideration is more important, be of the same make and kind as the older engines. This will insure a better understanding of all engines and, if the new and old engines are exactly alike, 4 6 8 10 12 2 4 fc A. M. P. M. Time FIG. 492. Daily load curve for a 600-kw. electric power plant. 438 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 (65) Load factor = a reduction in the number of repair parts which must be stocked. NOTE. THE "LOAD FACTOK" OF A PLANT may be taken as the ratio of its daily average power output to the maximum load which it must carry. The daily average power output is found by first computing the total daily energy output (kw. hr. or h.p. hr.) and then dividing this value by the number of hours in the day. Stated as an equation: Average power output Maximum power output EXAMPLE. If, in Fig. 492, the average power output is found to be 432 kw., what is the load factor? SOLUTION. Since, in Fig. 492, the maximum load on the plant is 750 kw., load factor = 432/750 = 0.58 or 58 per cent. 453. Engine Sizes Should Be Selected To Suit The Load Curve, where such procedure is economically feasible. Especially in large plants, where a number of engines are required to carry the maximum power output, the engines may be so selected as to size that at no time is any engine operating at a small fraction of its rated load. This can best be illustrated by an example. EXAMPLE. Let graph A, Fig. 493, represent the load curve of a contemplated plant. It is desired to equip the plant with engines to suit the load curve. It is evi- dent that, from midnight to 5 a.m., a 500-h.p. engine will carry the load. It is also evident that, from 8 a.m. to 5 p.m., the load can be carried by engines aggregating 2500 h.p., whereas the maximum load during the day, which occurs in the evening, can be carried by 3000 h.p. of engines. Suppose, FIG. 493. Showing method of operating then, that the plant will be engines to conform to the load curve in a equipped with the following en- T -}^ V s k g r \i Q_ f A 5 T> / t 16 d L jr ve \ .2 7^ C I ' ' ^ inoo \ & I ^ a r > fff Engint > -o K C \ \ 1 - 1 i-z " f 4 6 6 10 12 A. M. 4 fe 6 10 12 R.M. large plant. gines: One 500-h.p., one 1000-h.p., and two 1500-h.p. (one as a stand-by or emergency engine). Then the load can be carried thus: From midnight to 5 a.m. only the 500-h.p. engine need be operated. From 5 a.m. to 8 a.m. only one 1500-h.p. engine will be needed. From 8 a.m. to 5 p.m. one 1500-h.p. and the 1000-h.p. engine can be used. Frem 5 p.m. to 10 p.m. the two 1500- h.p. or one 1500-h.p. together with the two smaller engines will carry the load. From 10 to 11 p.m. one 1500- and the 500-h.p. engine will SEC. 454] SELECTING AN ENGINE 439 suffice: At 11 p.m. the 500-h.p. one can be stopped, the load until midnight being carried by the large engine. Thus, at no time is any engine operated under a small fractional load. Still, the plant can be operated at all times with any unit out of service. 454. The Selection Of An Engine For A Given Service involves a computation of the unit energy costs for those various engines which seem to suit the plant requirements with regard to horse power, speed, operating conditions and plant characteristics, as these requirements are outlined in 0.60 10.50 a: 1 0.40 u w &- 0.30 \n *>0.20 o 010 \ \ ^ Aft end ?nc eCo 5// >erl H./ > Hr ' \ N^ ^ ^ ^ - --. ?=-- ^~. *^-. - "- ~ - r=- _. i 100 200 300 400 500 GOO 100 600 900 1000 Indicated Horse Power FIG. 494. Approximate attendance costs for steam engines. the preceding sections. After the unit energy costs of the various engines have been computed (or their annual costs, see example under Sec. 446), the selection can be readily made. In making rough estimates as to engine cost, the data given in Sec. 338 will be found valuable. The water rates of engines as given in Div. 11 will also be found useful in estimating operating costs. Attendance costs may be taken from Fig. 494 or from a similar graph. 455. A Useful Chart For Selecting An Engine is shown in Fig. 495. Each black space in the chart indicates that the type of engine on that line is not well suited to the condition of its vertical column. A shaded (cross-sectioned) space indicates that the engine type of that line is sometimes used 440 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 for the condition of that vertical column. White spaces FIG. 495. Engine-selection chart. To use, place a strip of paper under the column heading as shown in Fig. 496 and make marks in the proper places under each of the eight headings. Then slide down the paper until a line is found where no black spaces appear before the marks. A line in which no shaded or black spaces appear before the marks will indicate an engine which, if desirable, may be used. A line in which black spaces appear indicates an engine which is not well suited. See also Sec. 455. indicate good practice. Strip Of Paper Chart It is to be remembered that such a chart can only be an aid in selecting an engine and should not be relied upon to give the final choice. The final choice should in all cases be made only after a careful study of unit energy costs for the different engines (Sec. 454) which may be employed for the condition which is under consideration. Fig. 496 shows how to use the chart. 456. Steam-Engine Per- formance Guarantees (Fig. 497) are usually included with the specifications which manu- facturers submit with their price proposals for high-grade engines. The performance guarantees, when written or printed FIG. 496. Illustrating method of using the engine selection chart of Fig. 495. SEC. 456] SELECTING AN ENGINE 441 ALLIS-CHAIMERS MANUFACTURING COMPANY MILWAUKEE. WISCONSIN. U.S.A. SPECIFICATIONS FOR ALLIS-CHALMERS HORIZONTAL SIMPLE CORLISS ENGINE r .......... Uni ted. State. s..M.fg. ? ....Coin.pany.,... . ...... --------------------- .............. ------ .............. These specifications form part of proposal dated ........... J.8n.Uary...ls.i.*.....19.22........ Cylinder diameter 24. inches. .,150... Revolutions per minute Steam pressure at throttle valve 15.Q pounds gauge. Superheat at throttle valve.. ...Za.r.Q. degrees Fah. above temperature of saturated steam. Back pressure at exhaust nozzle. - _ l4 pounds gauge. Vacuum at exhaust nozzle .Non-Condensing ....inches of mercury, ( Be n r nE'er 30 ") Engine to be designed to operate (Condensing or Non-condensing) H.0n-Q.9n49.ns.ing ... Engine to be (Right or Left).... - .JAtt hand. Direction of rotation of wheel (Over or Under) _ Under Direction of drive (Away from or Back by cylinders) Away. Crosshead Pin , diameter 3i inches, length 4.4 _ inches. Crank Pin, diameter. 4.4 inches, length 3.4 inches. Main Bearing, diameter .7 inches, length _ 14.... inches. Back Bearing, diameter...- .7 inches, length... 13 .....inches. Wheel, diameter _ ...ID. feet. Approximate weight .6.9.0.0. pounds. Wheel face .2.1 inches. Type of wheel (Belt, Rope or Square rim) .Belt. __ Wheel to be crowned for belt of following width IS". Wheel to be grooved for _ _ ..ropes inches diameter. .49.00. Weight of heaviest piece of engine, approximately Width and Height of largest piece of engine, approximately ......... ZZ Service (What will the engine drive and how will it be connected ?). ........................... Bfl.lla.d...to.. .Line ..... Shaft ...................... _ .......................... __________ ...... _ ........ . ..... ______________ ....... _ ............ _ ........... . ____ If the engine is to drive an electric generator the following blanks must be filled in. GENERATOR ................................. ............... ...Kilowatts at ......................... % Power Factor (.... ........ ............. K. V. A.) __________ ................. ...Current, ..... ...... - ..... _ ...... ..Cycles, ............ .... . ...... Phase,.. .................... Volts, ...... . ................... R. P. M. Generator will be furnished by ---------------------- ..... ....... - ........... ............. ..... ------ ......... ............... --------------------------------- Exciter will be furnished by_- ................ -------------- ...... - ..... -------- ......... - ......... ---------- ........... - ...... -- ....... - ...... - How is exciter to be driven ......... _ ....... ---- ...... - ................ - ....... ......................................... --- ................. --------------- ....... - .............. STEAM CONSUMPTION This unit when operating under conditions stated on Page S of these specifications will require not to exceed the following pounds of steam per hour: LOAD Full Load .2.5.0...... Three-quarter Load -IB?. One-half Load 1Z.S POUNDS STEAM -I. H. P 21.8 Per1g=3P. I. H. P -I. H. P 2.Q....8 Per ySS-.l. H. P. H. P 22,1 Per S53P.-I. H. P. A tolerance of 2% from figures given must be allowed for errors in obser- vation and measurements. FIG. 497. Manufacturer's typical performance specifications for a simple non-condens- ing Corliss engine. 442 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 ALLIS-CHALM ERS MANUFACTURING COMPANY MILWAUKEE. WISCONSIN. U. S. A. SPECIFICATIONS FOR ALLIS-CHALMERS HORIZONTAL CROSS COMPOUND CORLISS ENGINE For Smith. .^d...jQne.8..ManufctM.r.ing...Cpm.p.anjr.. These specifications form part of proposal dated ...inches, stroke Zf> ...inches, stroke 3.6 High pressure cylinder, diameter 1.6. Low pressure cylinder, diameter ?.? _.. Revolutions per minute 1.20 Steam pressure at throttle valve 150. pounds gauge Superheat at throttle valve .l.P.Q degrees Fah. above temperature of saturated steam. Back pressure at low pressure exhaust nozzle Q.Ond.eaB.itlg pounds gauge. Vacuum at low pressure exhaust nozzle .26 inches of mercury. (**8Si t M ") Engine to be designed to operate (Condensing or Non-condensing) Cond ensing High pressure side to b (Right or Left) .light. hand. Direction of rotation of wheel (Over or Under) :...0.vr. Direction of drive (Away from or Back by cylinders) v Crosshead Pins, diameter 4.B. inches, length 6. inches. Crank Pins, diameter 6 inches, length 5. inches. Main Bearings, diameter .14. inches, length 2.0 inches. Wheel, diameter 14 feet. Approximate weight .2.2000 pounds. Wheel face inches. Type of wheel (Belt, Rope or Square rim) S3uar.e...rim Wheel to be crowned for belt of following width Wheel to be grooved for ropes _ inches diameter. Weight of heaviest piece of engine, approximately 1.PP.P.P ... . pounds (Eeluilv ot .hrl) Width and Height ol largest piece of engine, approximately 48 inches x 48 inches. ....% Power Factor ( 5.P.Q K. V. A.) ...Alternating Current 6p Cycles, 3 Phase 4.8?...,. Volts .1.20 R . P . M . Is parallel operation required X 8 ..? Generator will be furnished by This. .company Exciter will be furnished by This company How is exciter to be driven Belted, to ...pulley, on ...engine .shaft STEAM CONSUMPTION This unit when operating under conditions stated on Page 5 of these specifications will require not to exceed the following pounds of steam per hour: LOAD POUNDS STEAM Full Load .....4PP. < 640 ) K w _ ( L H p) 20 . $ (12 . 8 ; ) p er K w _ ( j H p) Three-quarter Load 3PP (.493.) K . W.-(I. H. P.)....2.!..'.P J.MrlJLper K. W.-(I. H. P.) One-half Load ..... 2 9P 1.350 1 K. W.-( I. H. P.>....?3.:.$ (13.-3 )...Per K . W.-( I. H. P.) NOTE A tolerance of 2% from figures given must be allowed for errors in obser- vation and measurements. * o **" 4) >i SEC. 456] SELECTING AN ENGINE 443 14 16 'Saturated Steam, Condensing: 100 Superheat- Condensing "Til' 25 50 15 100 Per Gent. Of Rated Load 175 Fia. 498. Manufacturer's guar- antees for a uniflow engine which is to operate on steam at 150 Ib. per sq. in. gage, exhausting, when non-condensing, against no back in specification form, constitute what is called a performance specification. In a performance guarantee, a manufacturer will usually agree that, under certain operating conditions, his engine will have certain water rates at full load and at certain fractional loads. The graphs of Fig. 498 represent a manufacturer's guarantees. The purchaser may, in the contract, demand that, if the guarantees are not fulfilled in an acceptance test, either he will not accept the engine or that the price shall be proportionately decreased to pen- alize the manufacturer for failing to meet his guarantee. If a penalty is stipulated, the manufacturer will often demand (and is entitled to) a proportionate bonus or increase P ressure and when condensing into . . a 26-in. vacuum. in price if the acceptance test should show better results than were specified in the guarantee. NOTE. THE ACCEPTANCE TEST may be conducted in the manufac- turer's factory in the presence of the purchaser's representative, or after the engine is erected in the purchaser's plant. If there should be any doubt of obtaining the specified operating conditions during the accept- ance test, the contract may be made to include the basis of correcting the test results to the specified conditions. To insure that the correc- tions will be properly made, manufacturers frequently are required to state their guarantees for a wide variety of operating conditions of which one is certain to approximate the expected conditions of the test. NOTE. To CORRECT TEST RESULTS To STANDARD OR SPECIFIED CONDITIONS see following illustrative example the following approxi- mate rules may be used: (1) For each pound difference in initial pres- sure, correct the steam consumption by from 0.1 to 0.2 per cent. (2) For each 10 deg. of superheat, up to 100 deg. of superheat, correct the steam consumption by 1 per cent. (3) For each inch of vacuum, between 24 and 28 in. of mercury, correct the steam consumption by 0.5 per cent. EXAMPLE. An engine acceptance test shows a steam consumption at Y load of 22 Ib. per i.h.p. hr. The actual operating conditions were: Steam pressure 160 Ib. per sq. in.; superheat 50 deg. fahr.; vacuum 27 in. of mercury. What would be the approximate steam consumption at the same load (^ load) with steam at 175 Ib. per sq. in., superheated 444 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 75 deg. fahr., and with a vacuum of 25 in. of mercury? SOLUTION. Applying a correction of 0.15 per cent, for each pound of pressure: Correction for pressure = 0.15 X (175 - 160) = 2.25 per cent. Super- heat correction = 1 X (75 50) /10 = 2.5 per cent. Vacuum correction = 0.5 X (27 25) = 1 per cent. Now, since steam consumption decreases with increased pressure, higher superheat, and increased vacuum, the net correction 1 2.5 2.25 = 3.75 per cent. Or, the required steam consumption = 22 -(0.0375 X 22) = 21.2 Ib. peri.h.p. hr. 457. Things Which Should Be Specified When Requesting A Quotation On A Steam Engine are as follows: (1) Size give bore and stroke desired or horse power required. (2) Type vertical or horizontal; simple, tandem- or cross-compound; uniflow or counterflow; center crank or side crank; if side cran kj whether right hand or left hand. (3) Speed normal speed or limits between which speed must be varied. (4) Steam pressure (and superheat if any) upon which the engine FIG. 499. Illustrating meaning of "belt is to be Operated. (5) forward" and "belt backward." emOT throttling Or CUt-off. (6) Valve type whether slide, piston, Corliss or poppet. (7) Back pressure or condenser vacuum which will be maintained. (8) Water rates desired at full load and at fractional loads. (9) Speed regulation allowable variation in speed from full load to no load due to sudden or gradual changes in load. (10) Drive whether by belt, rope, or direct-connection. (11) To run over or under. (12) Belt or rope forward or backward (Fig. 499) if for belt or rope drive. (13) Foundation plan if space is restricted specify space limits. (14) Base whether desired or not. (15) Accessories desired with engine electric generator, condenser, lubrication system, foundation anchor bolts, etc. (16) Freight state whether manufacturer shall pay freight. NOTE. IF AN ELECTRIC GENERATOR Is To BE FURNISHED WITH THE ENGINE, the generator should be fully specified. The voltage, load characteristics, number of phases and wires, frequency, method of excita- tion, whether exciter and exciter belt and pulleys are to be furnished, and other electrical accessories which are required should be specified. NOTE. IF A PUMPING ENGINE Is To BE FURNISHED, the capacity, discharge pressure, suction head, and pipe sizes should also be specified- SEC. 457] SELECTING AN ENGINE 445 QUESTIONS ON DIVISION 15 1. What factor should form the basis upon which engines are selected? Define cost per unit of energy. 2. Define fixed charges. Tell what costs are considered as fixed charges? 3. Define operating charges. What costs constitute operating charges? 4. By what approximate rule may fixed charges be computed? What percentage of the first cost are the fixed charges in the example of Sec. 446? 5. Why must interest be considered as a fixed charge? What rate is usually used? 6. Why must rent be always considered as a fixed charge? If a company owns its own power plant building, how is the rental charge justified? 7. How may insurance and tax rates be determined? 8. Explain fully why depreciation must be considered as a fixed charge. What is a sinking fund? 9. What are the customary depreciation rates for steam engines? Explain the use of a sinking fund table. What is the straight line method of computing depreciation? 10. List all the operating costs of a steam engine. Which of these is usually the largest? 11. Define total annual cost. How is it related to the cost per unit of energy? 12. Explain fully how the horse power of a contemplated engine is decided upon. 13. What consideration must be given to engine speed when making a selection? Why? 14. What influence do operating conditions have on the selection of an engine? Explain fully and give the reasons. 15. What operating characteristics must be considered in selecting an engine? How do they affect the unit cost of energy? 16. Explain the use of the chart of Fig. 495 for selecting an engine. Does the chart afford an accurate means for making a wise selection? Why? 17. What are performance guarantees? What is a performance specification? How are they useful? 18. How may performance guarantees be corrected to different operating conditions than those of the test? 19. Write a sample letter requesting a quotation on an engine, giving all information it may be desirable for the manufacturer to know. PROBLEMS ON DIVISION 15 1. An engine has a constant load of 250 h.p. for 10 hours per day and 300 days of the year. If its total cost for the year is $15,000, what is the cost per unit of energy? 1,500 - I 1 1 1 1 V 1 1 ' ~ ' -i 5 Rated Full L oc M -J 1 in * : Actu a 'lo art E i TS 500 > 9 n 24 68 IT 2466 10 12 A. M. P. M. Time FIG. 500. Load curve of plant in Prob. 3. 2. If the engine of Prob. 1 cost $5000, and may be expected to be useful for 28 years, what will be its depreciation charge? 3. A 1000-h.p. non-releasing Corliss-valve engine will cost $10.00 per h.p. including erection, whereas a uniflow engine of the same capacity will cost $13.00 per h.p. The Corliss engine will have the following steam rates: at % load 29.0 Ib. per i.h.p. hr. ; 446 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 15 at K load 23.9 lb.; at H load 23.0 lb.; at full load 23.9 lb. per i.h.p. hr.; at 1M load 24.9 lb. The uniflow steam rates are: at K load 20.3 lb. per i.h.p. hr.; at > load 19.6 lb.; at $i load 19.6 lb.; at full load 20.1 lb.; at l l /i load 21.0 lb. The cost of steam is 50 ct. per 1000 lb. Other operating costs amount to $1.50 per hour of service. The plant is to operate 300 days per year. Fixed charges may be taken at 15 per cent, of the total first cost of the engine. If the load curve of the plant is as shown in Fig. 500, find the unit energy costs for each of the engines. 4. If in Prob. 3 either another uniflow engine or a Corliss engine would be necessary as a stand-by unit which would probably be operated 15 days out of the year, which would it be wise to install? What would be the unit energy cost of the protection against shut-down? DIVISION 16 STEAM-ENGINE LUBRICATION 458. The Purpose Of All Lubrication Is To Reduce Friction. Friction, it is known, causes, enormous financial losses in plants where machinery is employed. These losses, of course cannot be entirely prevented; but, in many cases they can be very greatly reduced by the careful selection and use of lubricants. Before attempting to discuss problems of lubrica- tion it may be well to study the causes and effects of friction in machine or engine bearings. 459. Friction Is A Force Which Resists The Motion of one body or particle over another body or particle with which it is in contact. There are, briefly, three forms of friction: (1) Rolling Friction Between Solids (Fig. 501), as in a ball or roller bearing. (2) Sliding Friction Between Solids (Fig. 502) , as in a plain bearing or between a piston and cylinder. (3) Fluid Friction Between The Particles Of A Fluid (Fig. 503), as with water or steam flowing in currents. 460. Rolling Friction Between Solids Direction of R mn g may be explained by a consideration of the microscopic structure of the solids, Fig. 501. The surfaces of all solids are known to be covered with very small projections and depressions as shown. When one body rests upon the other, these projections interlock partly and prevent motion. Should an . FIG soi.-Magnified sec- tion through small ball or attempt be made, however, to roll the roller in roiling contact with one on the other as shown in Fig. .501, another solid - the upper body will have to be raised slightly as it is rolled over a projection and will then fall again. Its movement, as it rolls along, will consist of a series of rises and falls. The center of the body will travel a zig-zag line as shown. Then, 447 448 STEAM ENGINE PRINCIPLES AND PRACTICE [Drv. 16 too, the rolling body will be slightly ''flattened out" where it touches the other body (as occurs with a partially inflated automobile tire). This flattening out is accompanied by a movement between the particles which compose the body. This movement is again resisted by internal forces between the particles. Hence, this resistance comprises the rolling friction between the bodies. NOTE. "WEAR" Is THE RESULT OF THE BREAKING-OFP OP THE PROJECTIONS, Fig. 501. If only the projections were broken off, one might imagine that eventually the outline of the body would be a smooth curve; but, wherever a projection breaks off, a depression is formed in its place leaving the material adjacent to the original projection so that it forms a new projection. 461. Sliding Friction Between Solids (Fig. 502) is similar to rolling friction. The chief difference between the two is in the number of small projections (on the contact surfaces) which are interlocked. In sliding friction, the areas of the contact surfaces are large, whereas in rolling friction they are usually microscopic. With sliding friction (Fig. 502), as with rolling friction, the two bodies must be separated slightly from one another as they move one upon the other. But in sliding fric- tion this separation is effected against the action of the forces which tend to hold the ?A Motion Of f % . .. ,. __ . . Piece A Fo f ce || bodies together. Now, since the force which tends to slide the bodies one on the FIG. 502. Magnified ,. ,. . ,. section of two solids in other must separate them against the sliding contact without action of forces, it is obvious that it must do work to effect sliding. NOTE. THE FORCE REQUIRED To SLIDE ONE OF THE BODIES ON THE OTHER is the force required to overcome friction. The resistance which one of the bodies opposes to sliding on the other is sliding friction. 462. Fluid Friction Between The Particles Of A Fluid may be explained by a study of the velocity of a fluid when flowing through a pipe (Fig. 503). Actual measurements show that this velocity is not the same at all points in the pipe's cross-section but that it is a maximum at the center and a Motion of Fo Pie ;c. SEC. 463] STEAM-ENGINE LUBRICATION 449 "Direction of flow FIG. 503. Velocity of a fluid in a pipe is not the same at all points in [its cross-section. minimum at the wall. In fact, no accurate measurement can be made exactly at the wall of the pipe and it is very probable that there the velocity would be zero. The velocity at any point on a diameter ab, Fig. 503, is represented graph- ically by the distance from ab to the curve xy. Now, since the velocity is not the same at any two adjacent points on any diameter as ab, it is evident that adjacent particles of the flowing liquid will be moving upon one another. This movement, however, is resisted by internal forces between the particles of the fluid. The total resist- ance comprises the fluid "friction" in the pipe. In other words, fluid friction is the resistance offered by one particle of a fluid to the sliding over it of another particle of the fluid. In general, fluid fric- tion is very much less than sliding or rolling friction. 463. Fluid Friction Replaces Sliding Friction when a fluid is introduced (Fig. 504) between the sliding surfaces of two solids and kept there. The fluid adheres to each solid in suffi- cient quantity to separate the solids and thereby prevent the projections of one from interlocking with those of the other. The fluid then divides some of it moves with one solid and some with the other. The fluid can be thought of in layers which slide upon one another with fluid friction. The amount of fluid friction will depend on the fluid used. The advantage of thus substituting fluid friction for sliding friction between the solids is that the net amount of friction is thereby greatly reduced and "wear" is practically eliminated. 464. The Reason Oils Are Used Between Bearing Surfaces is that they possess the two properties most necessary for a bearing fluid: (1) A bearing fluid must "wet" the surfaces; that is, it must adhere to the surfaces strongly enough that it will of itself divide into layers, some of which will travel with each of the sliding solids. (2) It must "stand up"; that is, its particles must cling together strongly enough that the fluid 29 force rorcc Fio. 504. Magnified section of two solids in sliding contact with lubrication. 450 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 will not be squeezed out under the action of the forces between the solids (Fig. 504) which tend to press the solids together. These properties are respectively termed: (1) Adhesion and (2) cohesion and, together, are called "body." They are present in different oils to varying extents. The significance of "body" in the selection of lubricants for specific purposes is discussed in Sec. 465. EXAMPLE. WATER HAS GREAT ADHERING PROPERTIES but lacks the clinging. Mercury again exceeds in cohesion but lacks adhesion. Hence, neither of these liquids, would make a good lubricant. 465. The "Viscosity" Of A Liquid is a measure of its internal fluid friction or its resistance to flow. A high- viscosity oil is "thick" and flows slowly. A low-viscosity oil is "thin" and flows readily. The viscosity of an oil is usually measured by finding the time required for a certain amount of the oil to flow through a small tube. Besides being a measure of its fluid friction, the viscosity of an oil is, to a certain extent, a measure of its body. See Sec. 472 for a method of measuring viscosity. NOTE. THE VISCOSITY OF AN OIL CHANGES WITH ITS TEMPERATURE, decreasing, for any oil, as the temperature of the oil is raised. It is essential, therefore, that one know the viscosity of an oil at the tem- perature at which it is to be used. 466. Lubricants May Be Grouped Into Three Classes, namely: (1) Solids. (2) Semi-solids. (3) Oils. Each class will be discussed separately, with its uses, in the following sections. 467. Solid Lubricants Are Occasionally Used to smooth out bearing surfaces by filling the small depressions (Fig. 501). Graphite, talc, soapstone, and mica are solids which have lubricating uses. A small percentage of the solid lubricant is usually mixed with a semi-solid lubricant and the mixture is then fed to the bearings. Sometimes solid lubricants are introduced separately to bearings which are also lubricated with oil. Solid lubricants cannot be squeezed from bearings and will, therefore, often keep a bearing cool where no other lubricant will. Experiments have shown that immediately SEC. 468] STEAM-ENGINE LUBRICATION 451 after a temporary application to an oiled bearing, of solid lubricant in powder form, the friction in the bearing is greatly increased, but is reduced after the particles have had time to attach themselves to the rubbing surfaces and form a smooth coating. The virtue of a solid lubricant lies in the effect which it has of filling the depressions in the bearing surfaces themselves. 468. Semi-Solid Lubricants are those which will not flow at ordinary room temperatures. They are commonly known as " greases." They are desirable for lubricating bearings in places where the air is filled with dust and grit, as in rolling, cement, and other similar mills. Greases are also desirable in applications where bearings are subjected to rather high temperatures. Greases have the property of filling bearing cavities and thereby effectively keeping out foreign matter. They may also be used in bearings into which it would be difficult to introduce oils, as in shaft-governor and similar bearings. NOTE. GREASES ARE To BE USED ONLY WHERE THERE Is SOME GOOD REASON FOR NOT USING OIL because the lubricating properties of greases are poor. Unless a grease melts in a bearing it produces consider- able friction. If it does melt it does not lubricate as well as an oil. 469. Oils Are Of Three General Kinds: (1) Mineral oils are distilled from the crude petroleums found in many parts of the world. In the distillation processes a great num- ber of grades of oil are obtained. (2) Fixed (animal and vege- table) oils are obtained by rendering the fatty tissues of animals or by pressing the seeds or fruit of plants. Fixed oils cannot be distilled without decomposition. They are affected more or less by the oxygen in the air which causes them to form solid deposits or varnishes. They also decompose, forming acids which will attack bearing surfaces. They are generally not so easily squeezed from a bearing as are mineral oils, because they possess more adhesion. (3) Compounded oils are mixtures of mineral oils with small percentages of fixed oils. Compounding a mineral oil improves its adhesion and makes it less likely to be washed from the bearing by water (as in an engine cylinder); but it renders the oil more liable 452 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 to gum and cause corrosion and, if the oil is to be used again, makes it harder to separate from entrained water. NOTE. METHODS OF HANDLING OIL BARRELS are shown in Figs. 505 and 506. .To Oil Receptacle liPipe--- ''Connection For Air Hose (I Lb. Pressure) 'Brass Air Pipe Oil Barrel- Fia. 505. Method of emptying a barrel of oil with compressed air. (It is claimed that with this arrangement a barrel of cylinder oil can be emptied in 5 min. and a barrel of engine or other light oil in 3 min. The air pressure should be throttled down and used with considerable caution. Any restriction of the oil discharge or an attempt to force the oil out against a considerable head will result in bursting the barrel. The method can not usually be applied effectively for very heavy oils. It is useful only for oils forced against low heads. (Southern Engineer.) FIG. 506. Arrangement whereby a barrel of oil can be rolled up an inclined plane by one man. 470. Oils Can Be Tested For Certain Properties which may determine whether or not an oil is suited for a particular use. The most important tests are for the following properties SEC. 471] STEAM-ENGINE LUBRICATION 453 of an oil: (1) Specific Gravity. (2) Viscosity. (3) 'Flash and Fire Points. (4) Chill Point. These tests will be discussed in following sections. Besides these a useful test is one to determine the extent to which impurities are present in the oil. Impurities can easily be re- moved by straining the oil through muslin or silk cloth. 471. Its Specific Gravity Indi- cates The Source Of An Oil And The Method Used In Its Re- finement. The specific gravity of an oil is the ratio of its density (at 60 deg. fahr.) to the density of water (at 60 deg. fahr.). It can conveniently be found (Fig. 507) by floating a " specific grav- ity" hydrometer, H, in a jar of the oil and reading the scale, S, of the hydrometer at the level of the oil. The specific gravity of an oil has no direct bearing on its lubricating properties. Oils made from asphaltic-base crudes will generally have a higher specific gravity than oils of a paraffin-base crude. Oils treated by acid will have higher specific gravities than oils treated by filtration. 472. For Measuring Viscosity Of An Oil (Sec. 465), a Say- bolt viscosimeter (Fig. 508) is usually employed. The reser- voir, B, is filled with the oil to be tested until the oil begins to overflow into C, and the temperature of the bath, A, is brought to that at which the measurement is to be made. The stopper, D, is then with- drawn and oil flows from B through the outlet tube, F, into the glass, G. With a stop-watch, time is taken until the -.'-",jV < . :ar "">:' -"A. a a >,.' ' . ^^A/^TV .^.^;^y^--\ : -^'-^-'-:^*':'^ FIG. 520. A typical gravity-circulation lubrication system with filter at the lowest point. oiler (Fig. 522). The chief advantage of the gravity-circula- tion system is that it provides a continuous and generous supply of oil to every bearing. Another advantage is that it lends itself so readily to the use of an oil filter, C (Fig. 520), which insures the supplying of clean oil to the bearings at all times and permits the use of the same oil for an indefinite length of time. New oil need be added only to make up for losses by leakage and evaporation. Any reasonable arrange- ment of filter and overhead tank may be adopted to satisfy building, space and other considerations. 468 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 EXAMPLES. The filter, C, may be so located that the dirty oil from the bearings flows to it by gravity, as in Fig. 520. Or, the filter may be Gravity Ta n k Filtered Oil'' Filtered Oil- Suction Strainers' *p an Discharge FIG. 521. Filtering-and-circulation oil system. (S. F. Bowser & Co., Inc.) situated above A and discharge by gravity into A, in which arrangement the dirty oil is pumped from a collecting basin up to A. A third plan is to locate the filter at any level and pump the oil to and from it by separate Place for Drop -Feed Oiler,. HI- F lush Plug Screw in Top When Drop- Feed Oiler is Not Used I -Exterior View H- Sectioned View FIG. 522. Four-window sight-feed oiler for gravity oiling system. (Richardson- Phenix Co.) pumps. Fig. 521 shows diagrammatically the oil-flow in the system of Fig. 520. Oil filters will be discussed in following sections. Oils for gravity-circulation lubrication systems are specified in Table 483, SEC. 494] STEAM-ENGINE LUBRICATION 469 NOTE. AN INEXPENSIVE GRAVITY-CIRCULATION LUBRICATING SYS- TEM WITH HAND PUMPS is shown in Fig. 523. Tanks A, B, C, and E can have any shape. F and G are hand force-pumps. D is the oil filter. Tanks B and C are simply to hold supply oil for A and D and thereby make continuous pumping unnecessary. 494. The Force-Feed Circu- lation System Of External- Bearing Lubrication, Fig. 524, is one in which oil is supplied to the external bearings by a pump, A } under a pressure of, say, 5 to 15 Ib. per sq. in. The oil is taken from the reservoir, R, in the crank case by A and delivered through pipes, B, to the main bearings. Since the crank shaft is hollow, the oil is led, as shown from the main bearings to the crank pins and eccentric. It is then conducted through pipes, C, to the cross- head pins. Oil which leaves the crosshead splashes onto the guides and thence falls back into the reservoir. An adjust- able relief valve, not shown, permits by-passing some of the oil into the reservoir as it is discharged by the pump. The .,,,,,, . F i a. 523. A simply-constructed Oil-teed tO the bearings Can be gravity-circulation system. (T. G. increased by adjusting the relief Thurston, in The National Engineer, Feb., valve to maintain a higher pres- sure at the pump discharge. As the bearings become worn, a higher pressure is necessary to keep them filled. Also, a light oil will require a higher pressure than a heavy oil. Water, which will find its way into the crank case from the cylin- der, must be drained off at frequent intervals. A scraper 470 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 gland, D, on each piston and valve rod, may be effectively used to keep some of the water out of the crank chamber. See Table 484 for recommended oils for force-feed circulation systems. Low-Pressure Cylinder* High -Pressure Cylinder, ''Oil 'O// ^- Oil Pump Resevoir Level Fia. 524. Compound marine engine with force-feed lubrication. 495. The Relative Merits Of Automatic Lubrication Systems For External Bearings may be briefly stated as follows: (1) Splash-oiling systems are inexpensive in first cost and operate very satisfactorily on engines of speeds of 200 r.p.m. or more. The oil must be periodically renewed but, if filtered, can be used over and over. (2) Gravity circulation systems afford a copius supply of oil to each bearing, are simple and easy to operate, and can be fitted to any engine. The flow of oil to each bearing is known and is readily adjustable. SEC. 496] STEAM-ENGINE LUBRICATION 471 (3) Force-feed circulation systems are very positive that is, the oil supplied to a bearing is more apt, than in the first two systems discussed, to actually enter between the bearing surfaces. On the other hand, the oil-feed to each bearing is unknown, and if, for any reason, a pipe or passage should become clogged this may only be evidenced after serious damage to the bearing. In view of the above, the gravity circulation system is becoming very widely used for modern slow-speed engines, whereas the splash system is in general use on higher-speed engines. 496. Methods Of Supplying Oil To Moving Bearings Of Medium- And Slow-Speed Engines are numerous and are Drop- (Oil Cup 'rank , - -Supported ^WW Floor FIG. 525. "Banjo" crank-pin oiler for side-crank engine. Sight-Feed Drop-Oiler-,^ <- -Crank Disc Weight' "-Crank Pin FIG. 526. Nugent crank-pin oiler. usually such that an engine need not be shut down to adjust the oil feed or, where necessary, to fill the oilers. In the illus- trations which accompany this section, hand-supplied drop- feed oilers are shown. But oil may be conducted to these oil cups by a gravity oiling system if such is available. In the crank-pin oiler (Fig. 525), which is widely used, oil is fed 472 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 from the cup to tube F, which delivers it to the hollow ball D. Tube C is fastened securely to D and to the crank pin, .-Cross head Fe/t Wr'ck (Wipes Oil. from Oiler) 'Ho/low Space (Oil from Drop -Feed Oiler Drips in Here ) Crosshead' Splash Guard' I-SidView H- Section FIG. 527. Method of using wiper cup in oiling crosshead pin . ~,~.,nping Screw (Top Part TMay ^\ be Rotated info r ' any Position and there Clamped) Standard Pipe Threads '' I-Wiper Cup H- Drip Boat FIG. 528. Oil collecting devices. (Sher- wood Mfg. Co.) I- End View H-Side View FIG. 529. Crosshead-pin telescopic oiler. (Richardson-Phenix Co.) B. and rotates with B. Oil, dripping from F to D, is carried through C by centrifugal force and enters B where it lubricates the bearing. A similar device is one (Fig. 526) in which the SEC. 496] S TEA M-ENGINE L UBRICA TION 473 oil cup, instead of being mounted on a rigid support, is held upright by a weighted pendulum to which it is attached; this is not suited to the gravity system. The revolving crank, B, receives oil from tube C and delivers it to the crank pin. The usual method of oiling the crosshead guides (Fig. 527) is to drop oil from the cup, A, onto the upper shoe. Drips from A and from the pin lubricate the lower shoe, being retained by splash guards, D, at each end of the guide. Engine Cylinder - ~Cros$head FIG. 530. Vertical engine equipped with swing joints for supplying oil to crank and crosshead pins. NOTE. ECCENTRICS AND CROSSHEAD PINS ARE FED BY WIPER CUPS OR TELESCOPIC TUBES (Figs. 527, 528 and 529). The wiper cup, C (Fig. 527), supplies the crosshead pin with oil from B. Fig: 528 shows a wiper cup and a drip boat which is used as a wiper cup for feeding oil to eccentrics. Telescopic tubes (Fig. 529) are more effective for cross- head pin and eccentric oiling but are not applicable to crosshead pins of vertical engines. On the other hand, the swing-joint arrangement of Fig. 530 is especially suited to vertical engines. Swing-joint and tele- scopic oilers cannot be used effectively on high-speed engines because of the liability of their becoming disarranged or broken when operating at high speeds. 474 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 497. The Operation Of A Good Oil Purifier Or Filter (Figs. 531, 532 and 533) usually comprises three separate processes : (1) Screening is intended to remove the coarser impurities and relieve the following processes of as much burden as is feasible. (2) Precipitation consists of allowing the finer impurities of higher specific gravity than the oil such as fine metallic wearings and water to settle out from the oil. Precipitation is often accelerated by heating the oil, thus lowering its viscosity and allowing the impurities to pass more freely through it. Separated water should be removed by an auto- matic overflow. (3) Filtration is intended to remove the very finest floating impurities in the oil those which have not been removed in either the screen or the precipitation chamber. NOTE. PASSING THE OIL THROUGH WATER DOES NOT REMOVE IMPURITIES although some engineers try to filter oil in this way. The oil rises through the water in drops from which the impurities cannot be removed no matter how hot the water mav be. ,'lnner Can Filled with Dirfy Oil 498. The Filtering Materials Used In Oil Filters are various. Most small filters employ, as a filtering medium, cotton waste, sawdust, wool, or other loose material, but in large filters cloth is universally used. Even for small filters, cloth in the form of a simple bag is pref- erable to loose material. Loose material, unless well packed, will allow channels FIG. 531. A simply-constructed oil J through which the oil will pass without being filtered. If tightly packed, such material reduces the filter's capacity to possibly 1 or 2 gal. per day. Filter cloth should preferably be arranged so that the impurities will fall away from the cloth as they collect. With horizontal filter surfaces, the oil should flow upward through the cloth which should have a pan under it to prevent the impurities falling on the cloth beneath. Vertical filter surfaces are preferable to those filter. (J. C. Kahl, in^Southern En gineer, Sept., 1910.) SEC. 498J STEAM-ENGINE LUBRICATION 475 horizontal surfaces through which the oil flows downward through the cloth, as the latter are apt to become clogged with impurities. It is also desirable to have the two sides of the Pour Dirty Oil In Here-. Wire-Netting Stralner- 'aste Wire- Netting Strainer^ FIG. 532. A simply-constructed improvised oil filter. (E. Grossenbacher, in Power, Mar. 9, 1920.) filter surface exposed to the same difference in oil pressure at all points. If the oil at the bottom of a filtering surface is 476 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 forced through at a greater pressure than at the top, the cloth at the top will pass less oil than that at the bottom, and, furthermore, impurities may be forced through at the bottom by the greater pressure. In some small niters the oil is filtered by syphoning it through felt strips. NOTE. IMPROVISED OIL FILTERS MAY BE CONSTRUCTED READILY. Fig. 531 shows such a filter which employs felt strips as the filtering material. It gives very satisfactory results as only clean dry oil will Dirty Oil screen Thermometer\\ n 14/\ I / \\Trc H L l^ w.L. Clean Oil Outlet-' FIG. 533. Oil filter. (Richardson-Phenix Co. ) syphon over the top of the inner can. Fig. 532 shows a homemade filter employing a loose filter-material and made of barrel and can parts. In using such a filter care must be taken that the material is closely packed especially at the outer edges and that water does not collect in barrel B to a level higher than the bottom of cone C, as this would permit water to enter the second compartment. 499. Oil Purifiers, Usually Called Filters, Are Manufactured in capacities up to 3800 gal. per min. In the Peterson oil filter (Figs. 533 and 534) oil is poured in and screened at A, and after passing over the heating coils, B, flows down the tube, C, striking deflector, D. From the bottom, the oil SEC. 500] STEAM-ENGINE LUBRICATION 477 flows slowly upward over the several trays, T, gradually losing its water and heavy impurities, and finally passes through G into the filter compartment, shown in Fig. 533. The sepa- rated water flows to the bottom of the precipitation chamber through the funnels around C and through the tube, E. It is automatically discharged through the overflow pipe, P, which is adjustable in height for different oils. In the filtra- tion compartment, H (Fig. 533), the oil flows through the filter Screen --V. ^-Dirty-Oil Inlet Deflector' FIG. 534. Section through precipitation compartment of the oil filter shown in Fig. 533. cloth, which is supported on frames, J, from the outside to the inside. Impurities collect on the filter surfaces and fall to the bottom of H. The clean oil flows from the inside of frames , /, through valves , K, into the clean oil compartment, L. NOTE. As the filter frames, J, are always full of oil, there exists the same difference of pressure between outside and inside of the cloth at all points on the cloth. This pressure is shown by the height of oil in the head gage, R. The clean oil is taken out through pipe M . 500. In A Bowser Oil Filtering Outfit (Fig. 535), dirty oil is introduced and screened at A and collects in the refining and purifying chamber, P, where it is heated by the steam 478 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 coil and then passes up over the trays, B. The oil then over- flows through the regulating valve, E, to the filter bag, C through which it passes to D, the clean oil storage tank. Another Bowser outfit is that shown diagram matically in Fig. 521. The filter cloths in this outfit are placed in the hori- zontal position in the filter pan and allow the oil to pass upward through them. Pans (not shown), between the layers of filter cloth, catch the impurities as they fall from the cloth surface. 501. The Sub ject Of Internal- Bearing Lubrication may be con- veniently treated under three headings. (Internal bearings are defined in Sec. 486.) (1) Nature of the lubricant. Engines oper- Removable Cap - - . Regu/ating Va/ve^ "\ Filtering Removab/e fining And \Chamberand , Stnr/ntr Pur/ fymg Chamber \ Reservoir O/7 Reservoir-- Strainer FIG. 535. Oil filtering outfit. (S. F. Bowser & Co., Inc.) FIG. 536. Typical hand push pump with glass body. (Detroit Lubricator Co.) ating on wet steam require a lubricant which is not readily washed from the cylinder walls. Engines operat- ing on superheated steam require a lubricant which will not carbonize or become too thin at the high superheat tempera- ture; see Fig. 511. (2) Appliance used to feed the lubricant. This can be a hand pump (Fig. 536), a hydrostatic lubricator (Fig. 541), or a mechanical force-feed lubricator (Fig. 544). These appliances will be discussed in following sections. (3) Manner of introducing the lubricant to the bearings, discussed below. 502. The Most Preferable Manner Of Introducing Cylinder Oil is to mix it with the supply steam as the steam approaches SEC. 502] STEAM-ENGINE LUBRICATION 479 the engine. Unless the engine builders recommend some other scheme, the oil should be fed into the steam pipe above the throttle valve and thoroughly atomized before it reaches the cylinder. Feeding the oil through a pipe which does not extend into the interior of the steam pipe is apt to allow the oil to flow down the inner surface of the steam pipe without its being well mixed with the steam. A slotted pipe extending a "spoon-shaped" end well into the steam pipe (Fig. 537) will cause the steam to "spray" the oil through the slots and Cap FIG. 537. Atomizer for internal lubrication of steam engines. (This arrangement may be used with any internal-lubricating apparatus.) FIG. 538. Gravity valve or oil check valve. (MacCord Mfg. Co. Weighted valve A is raised from its seat by oil which enters B and flows out at O. But oil flow in the opposite direction is pre- vented by A.) thus to thoroughly atomize it. A check valve should be placed as shown to insure a steady flow of oil. Some provision should be made that a vacuum in the steam pipe will not draw the oil out of the feed pipe. A gravity valve (Fig. 538) or a suitable spring-loaded check valve will provide this assurance. NOTE. FLAKE GRAPHITE Is SOMETIMES FED To THE VALVES AND CYLINDER, the object being to have the graphite "cake" on to the rubbing surfaces and glaze them, thus reducing the amount of oil neces- sary for good lubrication. Very small quantities of graphite, usually 1 to 3 per cent, by weight of the oil supplied, are fed, generally through 480 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 a separate graphite feeder, Fig. 539, and directly to the steam chest. Some force-feed lubricators will handle a mixture of graphite and oil. A separate graphite feeder is then unnecessary. NOTE. LUBRICATION OF THE STUFFING BOXES is usually accomplished by the oil introduced with the steam. Wherever metallic packing is used, however, it is customary to supply oil directly to the stuffing boxes through separate oil-feed pipes. 503. Feeding Oil To Internal Bearings By Hand is scarcely ever attempted except as a stand-by arrangement for use if the custo- mary method of feeding becomes inoperative. A hand oil pump (Figs. 536 and 540) should, there- fore, be placed on the cylinder oil- supply pipe of every engine and so arranged that it can be brought into service on very short notice. Shut-Off Valve FIG. 539. "Auxiliary" graphite feeder (Lunkenheimer Co.) for attach- ment to steam chest. ^-Standard Pipe Thread FIG. 540. Lever-handle oil pump, heimer Co.) (Lunken- 504. The Principle Of The Hydrostatic Lubricator (Fig. 541) is a simple one. The pipe, A, is connected into the engine steam-supply pipe, 18 in. or more above the lubricator, and is also connected to a condenser, C. In pipe A and in C the steam which enters at A is condensed into water, which, when valve B is open, can flow through pipe D, down into the SEC. 504^ STEAM-ENGINE LUBRICATION 481 bottom of the oil reservoir, E. This incoming water displaces oil which is forced out through pipe F and through the adjust- ing valve, F, which is simply for regulating the feed. The oil then rises through the water in the sight-feed glass, S, and enters the steam pipe, R, through the delivery pipe, L. The gage glass, G, shows the level of the oil in the reservoir. The oil is forced into R only by the column of water in and above C. Feed Adjusting Drain ? Valve cock'' FIG. 541. Hydrostatic lubricator. Nipple-' Coup/ ing > Bushing -,. Drain Cock-... FIG. 542. Hydrostatic lubricator con- structed of pipe fittings. (A. O. Stone, in Power House, Jan. 20, 1920.) The lubricator must be started and stopped with the engine, otherwise it would continue feeding and thereby waste oil. The rate of oil-feed depends on the viscosity of the oil and will, therefore, change with different room temperatures and each time the lubricator is refilled. NOTE. AN EMERGENCY HYDROSTATIC LUBRICATOR READILY MADE OF PIPE FITTINGS is shown in Fig. 542. Regulation of oil-feed is attained by adjustment of the valve, A. It is evident that such a lubricator ; since it has no sight-feed glass, is not at all reliable. It is useful only as an emergency device. To equip this lubricator with a sight glass would 31 482 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 probably involve a cost such that it would be preferable to purchase a manufactured lubricator. 505. The Care And Operation Of Hydrostatic Lubricators are simple. In filling the lubricator valves B and V, Fig. 541, are closed; then drain cock X and plug P are opened. After all water has drained out of E, X is closed and fresh oil is poured into P. In cold weather it may be necessary to heat the oil to sufficiently reduce its viscosity that it will readily flow into the reservoir. Should the condenser, C, by any FIG. 543. Scheme whereby a hand oil pump may be used for filling a hydrostatic lubricator. (W. R. Weiss in Power, Apr. 19, 1921. By connecting the pipe from P to the lubricator at C instead of at the bottom, an arrangement is secured with which the operation of the lubricator need not be stopped to fill it. Pumping oil into the lubricator will then force the water out through the steam pipe whence it will flow to the engine with the supply steam. If the pumping is done slowly, this small amount of water will not harm the engine.) chance be drained of its water, sufficient time must be allowed for it to fill before opening B to the oil. Otherwise, steam would enter the oil and cause " churning" in the sight- feed glass. The only remedy for churning is to completely empty the lubricator, cool it, fill afresh, and wait for the condenser to fill with water. If the sight-feed glass gets smeared with oil, the cause may be that the drops are too SEC. 506] STEAM-ENGINE LUBRICATION 483 large for the bore of the glass tube. This can usually be remedied in one of three ways: (1) Fit a larger diameter glass. (2) Solder a wire on to the nipple (at which the drops form) to guide the oil drops centrally up the tube. (3) Fill the sight- glass with salt water or glycerine. The heavier specific gravity of these liquids will cause the oil to rise in smaller drops which will not touch the glass. NOTE. LEAKAGES OF JOINTS OR PACKING IN HYDROSTATIC LUBRI- CATORS MUST BE AVOIDED, because the lubricators are very sensitive and leaks are sure to interfere with their operation. NOTE. A METHOD OF FILLING A HYDROSTATIC LUBRICATOR WITH A HAND OIL PUMP is shown in Fig. 543, where an additional pet-cock, C, is shown mounted at the top of the gage glass. To refill the lubricator, L, it is first shut off in the usual manner by closing valves B and V. Cocks C and E and valve D are then opened, allowing the water to drain from the lubricator. E is then closed and oil is pumped from P to L, after which D and C are again closed. The lubricator is then ready for service. 506. To Prevent Trouble With Hydrostatic Lubricators it is necessary to use only oil of good quality and to be sure that it is absolutely clean and free of all foreign substances. It is well to strain all of the oil used and to keep it well protected. Sometimes a lubricator cannot work because some of its small passages have become clogged with dirt from the oil. It is good practice to occasionally empty the lubricator and blow steam through it so as to thoroughly clean out any dirt or sedi- ment that may have lodged in the small tubes or passages. NOTE. THE WATER FEED VALVE OF A HYDROSTATIC LUBRICATOR SHOULD BE LEFT OPEN WHEN THE ENGINE Is SHUT DOWN, as during the noon hour, and when the oil regulating valve is closed. The lubricator being connected above the engine throttle valve, steam enters the support arm and heats the oil in the body of the lubricator while the throttle is closed as well as while open. This heat causes the oil in the lubricator to expand. If the water feed valve is left open it acts as a vent, and some of the water in the bottom of the lubricator body will be forced up into the condenser. If the oil regulating valve and water feed are both shut, there will be no outlet for the expanding oil which may then exert such a pressure on the body as to cause it to bulge. 507. Mechanical Force-Feed Lubricators (Figs. 544 and 545) are coming into extensive use for internal lubrication of steam engines. In general, they are preferable to the hydro- 484 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 static lubricators because they are more positive in operation and furthermore they can be arranged to automatically start and stop with the engine. A great number of different kinds Ratchet Wheel-. , Crank , ( Feed- -' I Adjusting ' Screws Connecting Roe/-. Heating / Connection FIG. 544. Exterior view of single-feed, metal-body, force-feed pump. (Hills-McCanna Co.) are on the market. Most of them are very satisfactory. In the one shown (Figs. 544 and 545), the connecting rod, C, Feed- Adjusting Screws FIG. 545. Section through force-feed lubricator. (Hills-McCanna Co.) is driven from some part of the engine which has a reciprocat- ing motion. The rachet wheel, R, transforms this motion into rotation of the crank shaft, S, which again imparts recipro- SEC. 5tf8] STEAM-ENGINE LUBRICATION 485 eating motion to the plunger, A . On the upward stroke of A , oil is drawn up from the reservoir, E, (Fig. 545), through pipe F into the displacement chamber, D. From D it is forced on the downward stroke of A, past the sight glass, G and out through a pipe attached at /, to the engine. Adjustment of feed is accomplished by: (1) Varying the amount of movement of the connecting rod, C. (2) Varying the stroke of the plunger, A, by the screws, J. NOTE. MULTIPLE-FEED MECHANICAL LUBRICATORS are useful for supplying oil to more than one point. In compound engines a multiple- feed lubricator can be employed to furnish a separate supply of oil to each cylinder. A separate feed is also used to feed each stuffing box which is to be oiled. The number of feeds may be sufficient to supply every need of an entire plant with one lubricator, in which event the lubricator is motor- or steam-driven and the feed to each delivery point must be started and stopped by an attendant. NOTE. IN INSTALLING FORCE-FEED LUBRICATORS, the lubricator may be mounted on any convenient place on the engine. The engine builder or engineer will designate the most advantageous location. Installation should be made so that the sight feeds and filler plugs are in full view of the engineer. The ratchet arm can be driven by any reciprocating motion of the engine. Always use pipe free from rust. Before connect- ing up the valve, make sure that the lubricator is clean of all foreign matter and fill the lubricator reservoir with oil. Work the operating lever by hand to fill the oil pipe until it overflows. In this way the oper- ator will know that the pipe line is clear. 508. The Proportional Lubricator Is A Modified Hydro- static Lubricator and is intended to furnish internal lubrication for an entire plant; see Fig. 546. A reducing and enlarging (venturi), section, A, is placed in the main steam pipe from the boiler. The lubricator is installed to deliver oil at the reduced section, A. The condenser, C, however, is connected to the main portion, B, of the steam pipe. As steam flows through the steam pipe, the pressure at A will fall below that at B, due to the velocity of the steam. The greater the velocity of the steam, the greater will be the pressure difference between points A and B. This difference of pressure is utilized, in addition to the difference in specific gravity of the water in C and the oil in F, to force oil from the lubricator through the needle valve, D. Thus, the oil-feed will vary 486 STEAM ENGINE PRINCIPLES AND PRACTICE [Div. 16 with the velocity of the steam in the main pipe. This lubri- cator has the disadvantages of all hydrostatic lubricators and besides, unless the check valve, E, is properly spring- loaded, it may feed oil when no steam is flowing in A. ~Feed-ActJu$ ting Va/ve Sfancf FIG. 546. Meyeringh proportional lubricator. (Oil Well Supply Co., Pittsburgh.) QUESTIONS ON DIVISION 16 1. What is the primary purpose of lubrication? 2. Define friction. 3. Explain rolling friction. 4. Explain sliding friction. 5. Explain fluid friction. 6. What happens when a fluid is introduced between two sliding susfaces? 7. Define body as applied to oils. SEC. 508] STEAM-ENGINE LUBRICATION 487 8. Define viscosity and explain with a sketch how it is measured. 9. What does the viscosity of an oil determine? 10. Does the viscosity of an oil ever change? 11. Explain the use of solid lubricants. 12. Name some substances which are solid lubricants. 13. What are semi-solid lubricants and what are their use? 14. Name three general classifications of oils (classified as to source of supply) and explain the properties of each. , 15. How is the specific gravity of an oil measured and what does it indicate? 16. At what temperatures are oil viscosities usually measured? 17. Define flash point, fire point, and chill point. 18. How are the above points used in the selection of an oil? 19. What are the mechanical conditions of a bearing and how do they affect the choice of an oil? 20. How does the lubricating system which is used in an installation affect the selection of an oil for it? 21. What are deposits in oils caused by? 22. State the principal properties of circulation oils. 23. State the principal properties of cylinder oils. 24. What are the external and internal bearings of a steam engine? 25. Define automatic and non-automatic lubrication of external bearings. 26. Discuss the lubrication of external bearings by hand? 27. Discuss drop-feed lubrication. 28. What is the bottle oiler and how does it function? Explain with a sketch. 29. Describe and, using a sketch, discuss ring-oiled bearings. 30. What are the applications of drop-feed oiling? 31. Describe and discuss splash oiling. 32. Draw a diagram of a gravity-circulation oiling system and discuss its merits. 33. Describe and discuss the force-feed circulation system of bearing lubrication. 34. What are the relative merits of the three systems of Questions 31 to 33? 35. Enumerate the methods of supplying oil to moving engine bearings and describe each. 36. Describe, with a diagrammatic sketch, the operation of a good oil purifier. 37. How should oil flow through cloth filter surfaces? ' 38. How can water be automatically removed from a mixture of oil and water? 39. How should oil be introduced to an engine for its internal-bearing lubrication? 40. How may graphite be introduced to the internal bearings? 41. How are the stuffing boxes lubricated? 42. What is the field of hand oil-pumps? 43. Draw a sketch and with it discuss the principle of the hydrostatic lubricator. 44. Using the sketch of Question 43 show how a hydrostatic lubricator is refilled. 45. What troubles are to be guarded against in using hydrostatic lubricators and how are they avoided? 46. Describe the operation of a mechanical force-feed lubricator. Make a sketch and tell how to install a mechanical force-feed lubricator. 47. What is the principle of the proportional lubricator? APPENDIX SOLUTIONS TO PROBLEMS The Following Solutions To The Problems, which have been presented at the ends of the various divisions throughout the book, are included to assist the student. These solutions should be referred to only after the reader has made an earnest effort to solve, without assistance, the problem which is under consid- eration. If used in this way, these solutions may constitute a material aid. But if the reader refers to this appendix before he has made an honest effort to work out his own solu- tion, then the material in this appendix will, probably, do more harm than good. The Same Symbols And The Same Formulas Are Used in these solutions as those which are employed in the division which precedes the problems which are proposed in the text portions of the book. SOLUTIONS TO PROBLEMS ON DIVISION 1 FUNCTION AND PRINCIPLE OF THE STEAM ENGINE 1. Head-end displacement volume = (10 X 10 X 0.785) X 12 = 942 cu. in. Crank-end displacement volume = 942 - [(1.5 X 1.5 X 0.785) X 12] = 920.8 cu. in. Head-end clearance percentage = 185 * 942 = 0.196 or 19.6 per cent. Crank-end clearance percentage = 180 -r- 920.8 = 0.195 or 19.5 per cent. 2. From steam tables, the total heat of dry saturated steam at 160 Ib. per sq. in. abs. = 1194.5 B.t.u. per Ib. Also, the total heat of steam of 89 per cent, quality at 17 Ib. per sq. in. abs. = 187.5 + (0.89 X 965.6) = 1046.9 B.t.u. per Ib. By For. (1): Theoretical efficiency = (Heat abstracted} -r- (Heat received} = [(Heat received} (Heat rejected}] -r- (Heat received} = [1194.5 - 1046.9[ -f- 1194.5 = 12.3 per cent. 3. Area of piston = 9 X 9 X 0.785 = 63.6 sq. in. Effective pressure = 125 - 4 = 121 Ib. per sq. in. Hence, by For. (3) : W = A ip L /8 P m = 63.6 X 1 X 121 = 7696 ft. Ib. per working stroke. By For. (5): Pap = P m Lf S A ip N a /33,000 = (121 X 1 X 63.6 X 200) -r 33,000 = 46.6 h.p. for each end. Total horse power = 2 X 46.6 = 93.2 h.p. 4. By For. (6): P m = Q.9[K(P g + 14.7) - P a }. Now, from Table 20: 488 SOLUTIONS TO PROBLEMS 489 K = 0.737. Also, P a = 4 + 14.7 = 18.7 Ib. per sq. in. abs. Hence, P m = 0.9[0.737(125 + 14.7) - 18.7] = 75.9 Ib. per sq. in. By For. (5): P ihp = P m L/^ tp AT s /33,000 = (75.9 X 1 X 63.6 X 200) -=- 33,000 = 29.2 h.p. for each end. Total horse power = 2 X 29.2 = 58.4 h.p. SOLUTIONS TO PROBLEMS ON DIVISION 3 INDICATORS AND INDICATOR PRACTICE 1. By the rules of Sec. 84, length of diagram = 4 X 12 -h 13 = 3.69 in. Radius of brumbo pulley = 13 X 3 -5- 12 = 3.25 in. 2. Length of diagram = (diam. smaller pulley -v- diam. larger pulley] X stroke = (2 -f- 18)36 = 4 in. 3. By method of ordinates, mean height crank-end diagram = 1.048 in. mean height, head-end diagram = 1.006 in. 4. By For. (15) mean effective pressure = P m = mean height of diagram X scale of spring. For head-end diagram: P m = 1.006 X 60 = 60.36 Ib. per. sq. in. For crank-end diagram: P m = 1.048 X 60 = 62.88/6. per. sq. in. 5. By For. (13) the h.p. constants are: For head end, k\ = 1.25 X 12 X 12 X 0.7854 1.25 X 113.1 33.000 For crank end, 1 = 244' By F r 33,000 1.25 X (113.1 - 4.9) = 0.004284 = 33,000 1 233' 1.25 X 108.2 33,000 Pihp = P m Nk. 33,000 For head end, X 220 X 233 = 0.0041 , = 60.36 1 = 56.9 &.f>. For crank end, P ihp = 62.88 X 220 X ^h = 56.7 h.p. Total for engine, P ihp = 56.9 + 56.7 = 113.6 h.p. Atmospheric Line- Zero Pressure Line--'' FIG. 547. Solution to Prob. 6. 6. See Fig. 547 which shows the theoretical expansion and compression lines. 7. Expansion and compression curves show that piston and exhaust valves are probably in good order but that there is steam leaking into the crank end during expansion. Admission is early at the head end. The steam lines show a marked slope probably because the engine is under heavy load. 490 APPENDIX 8. By For. (21) the steam rate is 1O VKf) Wu = p ((x 8 + x c )D' ps -(x' s + x c )D" ps ] Ib. per. i.h.p. hr. m The length of the diagrams in Fig. 116 is 3^ in. Values of x g and x' s are found by dividing the distance of a point from the end of the diagram by 3^ in. x c is given in Prob. 6 as 0.15. Pressures at points are taken from the diagrams. Densities are from the steam table. Values of P m were found in Prob. 4. Values of the several terms in the formula are arranged tabularly below. Point R S X Y Distance from end of diagram (in.) . Xq or x' a 3.00 2.80 0.75 0.83 923 862 231 256 Pressure (Ib. per sq. in. abs.) 50 55 21 22 Densitv (Ib. ver cu. ft.).. 0.1175 0.1285 0.0521 0.054 Substituting in For. (21), for head end: 10 yen W ih =- [(0.862 + 0.15)0.1285 -(0.256 + 0.15)0.0545] = 228 [1.012 X 0.1285 - 0.406 X 0.0545] = 228(0.1301 - 0.0221) = 228 X 0.108 = 24.6 Ib. per i.h.p. hr. For crank end : O-923 + 0.15)0.1175 - (0.231 + 0.15)0.0521] = 218.7 [1.073 X 0.1175 - 0.381 X 0.0521] = 218.7(0.1261 - 0.0198) = 218.7 X 0.1063 = 23.25 Ib. per i.h.p. hr . 9. By the rule of Sec. 131 and from the results of Probs. 5 and 8, total steam used per hour = (56.9 X 24.6) + (56.7 X 23.25) = 1399 + 1318 = 2717 Ib. per hr. 10. By planimeter, area of head-end diagram = 3.23 sq. in.; area of crank-end diagram = 3.38 sq. in. By For. (14), head-end P m = 3.23 X 60 3.38 X 60 5-^ = 59.6 Ib. per sq. in. Crank-end P m = 5-^ = 62.4 O.^O O.AO Ib. per sq. in. SOLUTIONS TO PROBLEMS ON DIVISION 6 FLY-BALL STEAM-ENGINE GOVERNORS, PRINCIPLES AND ADJUSTMENT 1. By -For. (25), the coefficient of regulation of the governor, M r = Nn ~ Nf = (201 - 197) -5- 197 = 0.0203 = 2.0 per cent. 2. By For. (27), the height, L hi = = = 4.66 in. SOLUTIONS TO PROBLEMS 491 3. By For. '(26), the centrifugal force, F c = 0.000,028,5Wr,]V 2 = 0.000,028,5 X 6.25 X 4.32 X 500 2 = 192.4 Ib. 4. The governor speed remains constant. The number of revolu- tions of the governor per engine revolution will be proportionally less to allow the additional engine speed. That is, the revolutions will be 3-7 X TT^ =3.1 revolutions per engine revolution. For a decrease in the iZo speed ratio, the size of the driving pulley must be proportionally de- creased, that is, 14 X ^25 = UH in. = the required diameter. W _i_ w Qf) 000 5. Substituting in For. (28), L hi = ^ X -j^~, there results: 16 = --j^- X ^P from which: N* = 28,800 and AT = 170 r.p.m. SOLUTIONS TO PROBLEMS ON DIVISION 8 COMPOUND AND MULTI-EXPANSION ENGINES 1. For the condensing engine, by Sec. 287, the receiver pressure = supply pressure -* cylinder ratio = (150 + 14.7) /4.3 = 38.3 Ib. per sq. in. abs., or 38.3 14.7 = 23.6 Ib. per sq. in. 'gage. For the non-con- densing engine, the receiver pressure = ^supply pressure X back pressure = V(100 + 14.7) X (5 + 14.7) = 47.5 Ib. per sq. in. abs., or 47.5 14.7 = 32.8 Ib. per sq. in. gage. 2. Force on piston = (10 X 10 X 0.785) X 150 = 11,780 Ib. By Sec. 273: Torque = 0:90 X 11,780 X 6 = 63,600 Ib. in. 3. Absolute pressure in condenser = (30 28.5) X 0.491 = 0.74 Ib. per sq. in. From steam tables: steam temperature at 0.74 Ib. per sq. in: abs. = 92 deg. fahr. Steam temperature at (225 + 14.7) = 239.7 Ib. per sq. in. abs. = 397 deg. fahr. Hence, the temperature range in each cylinder = (397 - 92) -=- 4 = 76.2 deg.' fahr. 4. Neglecting clearance, the ratio of expansion = 4.5 -f- 0.26 = 17.3. Considering clearance ratio of expansion = [4.5 +(0.06 X 4.5)] -f- (0.26 + 0.06) = 4.77 -^ 0.32 = 14.9. 6. By Sec. 291, lead = 5 X KG = He in. SOLUTIONS TO PROBLEMS ON DIVISION 10 STEAM-ENGINE EFFICIENCIES AND HOW TO INCREASE THEM 1. By For. (29), the efficiency of the ideal Rankine cycle, _ tin Htz The total heats, H t i and H t2 , are, by a temperature-entropy chart, 1190 492 APPENDIX and 1003 B.t.u. per Ib. The heat of liquid, H t2 = 180 B.t.u. per Ib. Hence, 1190 - 1003 . 10 _ Edt = 1190 - 180 = ' 185 = 18 ' 5 per CmL 2. By For. (30), the Rankine cycle water rate, Wg = 2545 Hti Htz The steam pressure of 150 Ib. per sq. in. gage corresponds to 366 deg. fahr. for saturated steam. The steam, therefore, has 550 366 = 184 deg. fahr. superheat. By the temperature-entropy chart, H t i and H t % = 1295 and 955. Hence, W ' = 1295^955 -"Oft-pr*.?.*. 3. By For. (31), the thermal efficiency, 2545 W.i(H tl - Hi,) By For. (32), the total heat at admission, H n = x d H v + Hi = 0.98 X 853 + 343 = 1179 B.t.u. per Ib. The heat of liquid at exhaust, Hu (from a steam table) = 180 B.t.u. per Ib. Hence, ' ' 138 ' - 180) 4. The actual thermal efficiency of the engine in Prob. 1, by For. (31) = 2545 2545 Edti = W(H n - Hn) = 25(1190 - 180) = - 101 = 1(U ^ *' By For. (34), the Rankine cycle ratio = Actual thermal efficiency _10.1 _ n r t - Efficiency of the ideal Rankine cycle 18.5 5. By For. (35), the mechanical efficiency, E dm = ^ =.-J|| = 88.4 per cent. JTihp 1O 6. By For. (36) the over-all efficiency, 2545 By For. (33), the total heat of the steam admitted, H tl = H d + T n C m = 1196 + 100 X 0.58 = 1254 B.t.u. per Ib. The absolute back pressure = 29.8 27 = 2.8 in. of mercury or 2.8 -i- 2.03 = 1.4 per sq. in. abs. The heat of liquid at this back pres- sure, HIZ = 81 B.t.u. per Ib. Hence the over-all efficiency, E = 17.4(1%?- 81) ' ' 125 - 12 ' 5 Per Cent ' 7. By For. (38), the British thermal units per brake horse power hour = W sb (H tl - Hn) = 17.4(1254 - 81) = 20,400 B.t.u. per b.h.p. hr. or 20,400 ^- 0.746 = 27,300 B.t.u. per kw. hr. SOLUTIONS TO PROBLEMS 493 8. By For. (31), the thermal efficiency, 2545 2545 19(1190 - for the first engine. 13 - 25 per cenL for the second engine. The engine using 18 lb. of steam per indicated horse power hour is, in this case, the more efficient. SOLUTIONS TO PROBLEMS ON DIVISION 12 STEAM-ENGINE TESTING 1. By the rule of Sec. 368, the mechanical efficiency = brake horse power + indicated horse power = 120/133 = 0.903. Friction horse power = indicated horse power brake horse power = 133 120 = 13 h.p. f\ j AT /'TXT' TXT" ~\ 2. By For. (41), the brake horse power = Pbh P = "" f 03 QQQ 2 X 3.14 X 5.25 X 220 X (250) 33,000 ' ' 6Ap ' 3. By For. (61), the brake constant = k b = J r n< { n = OQ nnn ' OO.UUvJ OO.vJUU = 0.000,577. 4. By For. (54), the pounds of dry steam supplied per hour = W*d = z d W sw = 0.97 X 5000 = 4850 lb. From For. (55), the water rate i = 24 ' 25 lb ' dry steam per l ' h ' p ' per hr ' 5. From the example under Sec. 373, it was found that 2499 lb. of dry steam were used per hour. By For. (51), the horse power input to the generator (brake horse power when belt slip is neglected) = Ph P P kw 20.2 + 30.7 0.746E d 0.746 X 0.90 W,d 2499 75.8 h.p. By For. (56), the water rate = = 33.0 lb. of dry steam per b.h.p. per hr. 'bhp A l-h 10'V A 1 Since there are 2550/75.8 or 33.6 lb. of wet steam used per brake horse power per hour the thermal efficiency is, by For. (36) Div. 10, 2545 2545 = dtb ~ W swb [(x d H v + Hi} - Hu 33.6[(0.98 X 856.8 + 338) - 192.6] = 0.0769 = 7.7 per cent, thermal efficiency based on brake 33.6(985.4) horse power. 6. From Sec. 368, the brake horse power = 0.90 X 200 = 180 b.h.p. 494 APPENDIX The weight of wet steam used per hour per brake horse power = 42,000/10 X 180 = 23.3 Ib. By For. (36), the thermal efficiency = p 2545 = . + Hi) - H 12 ] ~ 2545 2545 23.3[(0.99 X 838 + 361.2) - 203] = 23^87^2) = ' 1106 = 1L1 per cent, thermal efficiency based on brake horse power. SOLUTIONS TO PROBLEMS ON DIVISION 16 SELECTING AN ENGINE 1. The energy units developed per year = 10 X 300 X 250 = 750,000 h.p. hr. By For. (63) : Cost per unit of energy = Total expenses per year -5- Energy units developed per year = $15,000 -j- 750,000 = $0.02 per h.p. hr. or 2 ct. per h.p. hr. 2. By Sec. 443, depreciation charge = $5000 -s- 28 = $178.60, 3. DAILY QUANTITIES: HOURS H.P. HR. LB. STEAM, LB. STEAM, LOAD SERVICE CORLISS UNIFLOW IK 3 3,750 93,400 78,700 Rated 1 1,000 23,900 20,100 H 53^ 4,125 95,000 80,900 H 3% 1,750 41,850 34,300 H 12 3,000 87,000 60,900 Totals 24 13,625 341,150 274,900 Cost of steam @ 50 ct. per 1000 Ib $170.58 $137.45 Other operating costs at $1.50 per hr 36.00 36.00 Total daily operating costs $206 . 58 $173 . 45 YEARLY QUANTITIES: Energy units delivered = 300 X 13,625 = '4,087,500 h.p. hr. J300 X 206.58.. ..$61,974 Operating charges, { ^ x m ^ $52jQ35 Fixed charges at 15 per cent 1,500 1,950 Total annual costs $63,474 $53,985 AQ A*7 A. Unit energy costs (per h.p. hr.) = 4 Qgy 500 SO -0155 '53,985 "4,087,500 SOLUTIONS OF PROBLEMS 495 3. From Prob. 3: CORLISS UNIFLOW Daily operating costs $ 206 . 58 $ 173 . 45 Operating costs for 15 days 3,098 . 70 2,601 . 75 Annual Fixed charges 1,500.00 1,950.00 Total annual costs $4,598.70 $4,551 . 75 Therefore, uniflow engine would have smaller annual cost. Energy output in 15 days = 15 X*13,625 = 204,375 h.p. hr. Cost per unit of energy = $4,551.75 -5- 204,375 = $0.0223 per h.p. hr. INDEX PAGE Absorption dynamometers, classifica- tion 347 ACCEPTANCE TEST, definition 365 how conducted . . 443 Adiabatic expansion 16 Admission line, variations, illustra- tion 61 Advance angle 99 Air leaks, .source of trouble in con- densing operation 382 Alignment, engine, method used in erection and re-assembling . . 407 Allis-Chalmers heavy-duty Corliss engine, valve gear, illustra- tion 158 American-Ball engine governor, illus- tration 250 American Injector Company, crank- pin oiler, illustration 463 AMERICAN SOCIETY MECHANICAL ENGINEERS, "Test Code," dry steam basis for com- puting engine efficiency 304 "Test Code" outline 369-371 water-rate test specifications .... 365 American Steam Gage and Valve Company, Thompson indi- cator, illustration 40 AMES "controlled-compression una- flow" engine, illustration. . . 162 engine, Robb-Armstrpng-Sweet governor, illustration 249 four-valve non-releasing Corliss engine, valve gear, illustra- tion 150 "UNA-PLOW" ENGINE directions for setting poppet valves 182-186 effect of valve gear adjust- ments, table 187 AMES IRON WORKS, directions for setting poppet valves on Ames "una-flow" engine 182-186 portable boiler and engine unit, illustration 322 valve gear of Ames four-valve engine, illustration 150 Ammeter, use in determining output of generator 354 Amsler polar planimeter, illustration. 73 ANGLE-compound engine, definition . . 25 of advance, definition 99 ANGULARITY, connecting rod, defini- tion and effects 101 eccentric rod, definition 102 Ashcroft Manufacturing Company, Coffin planimeter, illustra- tion 75 Atmospheric line, indicator card, how drawn 58 AUTOMATIC cut-off governor 228 ENGINE, definition 228 reversing inadvisable ' 235 lubrication systems for external bearings, merits 470 PAGE Automatic Furnace Company, Model Acme engine trunk piston m echanism 35 Auxiliaries, inspection 375 Auxiliary piping and equipment, non- condensing engine, illustra- tion .375 Babbitting, engine bearings :. . . 396 Babbitt recess, method of closing, gating and venting 398 BACK-acting crank-mechanism 34 pressure, purpose of reducing with condenser 285 BALANCED multiported valve 91 SLIDE VALVE, advantages and disadvantages 89 definition 26 repair 394 Ball Engine Company, tandem- compound engine, illustra- tion 24 BALL four-valve Corliss engine, valve-gear, illustration 174 governor, height when revolving . 205 "Banjo" crank-pin oiler, illustration. 471 BEARINGS, adjustment to compen- sate for wear 400 engine, temperature after run- ning short time 379 EXTERNAL, definition 460 drop-feed lubrication 461 lubrication by hand 460 freshly re-babbitted, peening. . . . 397 friction in engines 301 heating, causes 402 high pressure, oil required 455 inaccessible, feeler for detecting heat 380 inspection 374 INTERNAL, definition 460 oil feeding by hand 480 loose, knocks caused by 410 MAIN, see also Main bearing. illustration 302 re-babbitting boxes of 396 mechanical conditions 455 method of scraping high spots, illustration 400 oil, table of uses and viscosities. . . 459 re-babbitting 395 ring-oiled 464 scraping 399 SPLIT, illustration 374 adjustment 401 surfaces, reason for use of oils between 449 wrist-pin or crank-pin, heating . . 403 Bentley, F. W. Jr., sight feed for drop-feed oiler, illustration. 464 BOILER feed-water, equipment for weighing 361 foaming, danger with super- heater 425 PRESSURE, increased, effect on engine efficiency, graph 294 497 498 INDEX PAGE BOILER PRESSURE new plant, how selected 436 stationary power plants, prac- tical limits 295 BOTTLE OILER. 463 illustration 465 Bowser oil filtering outfit, operation . . 477 Bowser, S. F., and Company, Incor- porated, filtering and cir- culation oil system, illustra- tion 468 Bradley, Alexander, on savings effected by superheating supply steam, table 423 BRAKE ARM, effective length, defini- tion 349 rope brake, illustration 351 BRAKE constant, formula for calcula- ting . 368 HORSE POWER calculation when using absorption dynamo- meter, formula 349 absorption by water brake .... 352 computation from indicator diagrams, formula 78 definition 78 thermal efficiency based on formula 310 net-weight 349 tare- weight, definition 348 Brakes, classification 347 Bridge and Beach Manufacturing Company, engine, indicator diagram 332 Brown and Sharpe Company, steel scale with end graduations .. 122 Brumbo pulley, definition 46 Buckeye Engine Company, "Buck- eye-mobile," illustration . . . 334 BUCKEYE ENGINE, effect of superheat graph 423 governor 251 piston-type riding-cut-off valve 135 "BUCKEYE-MOBILE" engine unit, il- lustration 334 performance graphs 335 type of power plant 333 By-pass automatic valves, on condens- ing engines 184 C Calculations, indicator, see Indicator. Cam, oscillating, poppet valve motion given by 161 Center-crank engine, definition 20 CENTRIFUGAL FORCE, definition 194 developed in revolving gover- nor weight, formula .... 205 governor 204 permanent control in shaft governors effected by 230 shaft governor operation 229 Centripetal force, definition 195 Circulation oils, table of properties . . . 456 CHANDLER AND TAYLOR COMPANY, piston valve, illustration .... 27 splash-oiled engine, illustration . . 466 engine, Armstrong governor, illustration 249 variable speed engines, trigger device for secondary speed control 200 Chill point of oil 455 CHUSE ENGINE AND MANUFACTURING COMPANY, condensing uni- flow engine, valve setting. . . 188 PAGE CHUSE ENGINE AND MANUFACTURING COMPANY, Corliss -valve mechanism positively oper- ated, illustration .......... 29 engine indicator diagram ........ 329, 331, 332 governor, illustration ........... uniflow engine, illustration ...... VALVE setting in condensing uni- flow engines .............. stem adjustment, illustration. CLEARANCE, inside, slide valve, defi- nition .................... definition ..................... proper amount between journal and bearing ............... 402 typical values in different type engines, table ............. 297 VOLUME, definition ...... :..-.... 2 determined in engine testing . . effect on engine efficiency ..... Cleveland open-cup tester for flash- and fire-point tests, illustra- tion ...................... Coffin planimeter, illustration ....... Collins, Hubert E., "Shaft Govern- ors," on shaft governor operation ................. COMPOUND ENGINE ............ 258-282 advantages and disadvan- tages .................... 260 application ................... 258 classification according to method of transfer of steam ........ condensing operation ........... correct receiver pressure neces- sary for economical opera- tion ...................... definition .................. ... excessive cylinder condensation avoided by ............... how governed ................. 225 indicated horse power compu- tation ............. . . ..... 275 marine, forced-feed lubrication, illustration... ............ 470 mechanical efficiency greater than that of simple engine . . 264 most profitable degree of vacuum .................. 289 operation through large tem- perature and pressure ranges 258 receiver pressure dependent on cylinder ratio ............ reduced leakage loss, explana tion ..................... saturation line saving greater at higher boiler pressure ................. single valve, uses ............. , stopping ..................... terms used in connection with. testing ....................... 366 torque or turning moment, evenness increased ......... 265 typical piping, illustration ...... 386 use of superheated steam ....... valve setting .................. without by-pass valve, start- ing ...................... COMPRESSION curve, effect of clear- ance volumes on ........... effect of different exhaust pres- sures on .................. 69 Condensation, cylinder, see Cylinder condensation. CONDENSER, barometric, several en- gines operated with ........ 376 239 330 188 Ill 95 2 366 296 454 75 239 267 387 276 23 261 278 264 272 260 323 271 424 280 387 68 INDEX 499 PAGE CONDENSER, definition 283 ejector-jet, Corliss engine, illus- tration 284 inspection. 375 low-level jet, connected to engine, illustration 286 starting and stopping 381 surface, connection to tandem- compound engine, illustra- tion 284 CONDENSING ENGINE, see also Engine, condensing. application 290 definition 36 CONDENSING OPERATION 283-290 adequate water supply neces- sary 286 advantages and disadvantages. . 289 change to non-condensing 382 compound engine 387 definition 283 importance of cylinder con- densation in determining economy 287 methods of calculating power increase due to 285 non-condensing, indicator cards 285 trouble caused by air leaks 382 when not economical 286 CONNECTING ROD, angularity or obliquity, definition 101 bearing, illustration 302 Constants, engine and brake 368 Cooper Corliss engine, heat-insulated cylinder, illustration 299 Cord, indicator, method of arranging, illustration 59 CORLISS cross-compound condensing engine, manufacturer's per- formance specifications 442 detaching valves, dash pots for . . 155 ENGINE, compound, starting .... 386 cut-off, danger of lengthen- ing 172 detaching, stopping 385 effects of valve-gear adjust- ments, table 170-171 ejector-jet condenser, illustra- tion 284 four-valve application 324 governor, starting block 385 hook-rod or reach-rod, illus- tration 383 ideal steam line in 63 indicator card 70 influence of superheat on water-rate, graph 423 load increased 173 leads, laps and trial com- pressions table 169 manufacturer's performance specifications 441 method of governing ^ . . 195 non-releasing, starting and stopping 380 positively-operated, advan- tages and disadvantages .... 149 running over, how started 384 SIMPLE detaching, starting. . . 383 single-eccentric detaching, valve-setting directions 163-169 starting lever and wrist plate, illustration 384 valve setting 163 releasing gear, dash-pot, troubles 412 VALVE... . 146-191 PAGE CORLISS VALVE, advantages 146 dash pot, illustration 159 definition 28 detaching mechanism or trip gear, typical designs 155 engine efficiency increased by . 146 GEAR, illustration 151 inverted vacuum dash-pot, illustration 412 MECHANISM, non-releasing or positively operated, defini- tion ...... 30 positively operated, descrip- tion 149 moderate superheat advisable. 421 reason for employing 146 releasing mechanism, illustra- tion 152 repair 395 typical designs 146 TRIP GEAR, Vilter engine, illus- tration ; .. 156 Nordberg Manufacturing Company, illustration .... 156 COUNTERFLOW ENGINE, definition .... 32 saturated steam operation, economies, table 312-313 using superheated steam, oil supplied by atomization method 422 CRANK-end dead center, definition, illustration . . . 103 MECHANISM, back-acting, illus- tration 34 standard, definition 34 PIN BEARING, heating 403 wedge and shims for adjust- ment illustration 400 PIN OILER, illustration 463 truing up without removing . . . 402 use of in shaft governor in place of eccentric - . 239 Crosby outside-spring indicator, il- lustration 43 CROSS-COMPOUND Corliss engine gov- ernor, receiver-pressure reg- ulation device, illustration . . 277 ENGINE, definition 24 driving alternator, illustration 268 CROSSHEAD shoes, method of adjust- ing, illustration 401 velocity variations during stroke 103 Curved-slot pencil mechanism 43 CUT-OFF, apparent, definition 16 Corliss engine, danger of length- ening 172 valve operating-mechanism, Mc- Intosh and Seymour engine, illustration 94 CYCLE, engine, definition 305 ideal Rankine 7 CYLINDER CONDENSATION, causes and prevention 297 important in determining econ- omy of condensing operation 287 rejection and thermal losses partly caused by 297 CYLINDER diagrams superimposed upon steam-chest diagrams . 64 EFFICIENCY, definition 303, 309 inspection 373 OIL, best method of introducing. 478 compounded with acidless tal- low oil 458 consumption per brake horse- power, graph 432 engines using superheated steam. . . .... 421 500 INDEX PAGE CYLINDER OIL, grades, table 458 properties, table 458 ratio, compound engine, defini- tion 271 D D-SLIDE VALVE, definition 26 disadvantages partially over- come 88 repair 393 DASH-POT, Corliss releasing gears, troubles .....' 412 definition and purpose 211 detaching Corliss valves 155 DEAD CENTER, definition, illustration 103 trammel method of finding, illustration 104 "Design and Construction of Heat Engines," W. E. Ninde, on valve diagrams 84 Design-determined equal leads, defi- nition 114 DETACHING-CORLISS-VALVE engine, advantages and disadvan- tages 153 MECHANISM, elements 153 illustration 30, 152 single-and double-eccentric. 154 Detroit Lubricator Company, hand push pump, illustration 478 DIAGRAM, ideal indicator, illustration 60 INDICATOR, see Indicator diagram. leaky exhaust valve revealed by 66 method of taking 58 DIRECT measurement, valve setting 108 slide valve 87 DISPLACEMENT, slide valve, definition 101 ' " volume, formula 3 DouBLE-acting engine, definition .... 11 beat poppet valve, definition. . . . 160 ECCENTRIC DETACHING CORLIS8- VALVE engine, valve setting. 172 mechanism, features 154 engine, definition 23 flow engine, definition 32 stroke, definition 11 Drains, inspection 376 DROP-cut-off Corliss- valve mechan- ism, illustration 152 PEED lubrication of external bearings 461 oil cup with sight feed, illus- tration 462 oiler, homemade sight feed, illustration 464 Dummy flywheel method, tare- weight of brake found by .... 348 Duplex-compound engine, definition. 24 DYNAMOMETERS, absorption, classifi- cation ' 347 classification 346 fluid-friction type, operation .... 352 Prony brake type, construction and use 347 rope brake absorption type 350 E ECCENTRIC circle 98 crank-end extreme position illus- tration 120 head-end extreme position, illus- tration 120 mechanism, illustration 97 motion derived from 98 rod, angularity, definition 102 setting on center 106 PAGE ECCENTRICITY, definition 98 relation to valve travel 99 EFFICIENCY, heat of liquid basis of calculation 306 steam-engine, how increased 291-317 theoretical, formula 6 ELECTRICAL load, measuring in poly- phase systems 356 loading of engine 353-357 output, direct-current generator, determination 354 ENERGY balance, electric-energy dis- tribution circuits, illustra- tion 300 cost, factors 428 electrical, heat unit equivalent . . 5 mechanical, heat unit equiva- lent 5 ENGINE alignment, method .... 406-408 angle-compound, illustration. ... 25 annual depreciation 431 application of indicator 57 automatic, reversing inadvisable 235 bearings, temperature after run- ning short time 379 center-crank, definition 20 cleaning 388 clearance values, table 297 COMPOUND, see also Compound engine. and multi-expansion 387 four-valve, steam rates 329 single-valve, uses 323 CONDENSING and non-condens- ing, steam consumption, table 286 application 290 definition 36 operation, definition 283 constants, calculation 368 Corliss, see Corliss engine. cost per unit of energy, factors considered in computing ... 428 counterflow or double-flow, defi- nition . 32 cross-compound, illustration .... 24 CYCLE, definition 305 effects of slide valve adjust- ments, table 112 data form 413 depreciation, causes 430 direction of rotation 22 DOUBLE-acting, definition 11 definition 23 duplex-compound, illustration . . 24 ECONOMY, affected by clearance volume 296 vs. maintenance charges 293 with saturated steam, table. . . 316-317 EFFICIENCY BASED ON BRITISH THERMAL UNITS PER kilowatt hour.- 304 brake horse power hour 304 EFFICIENCY BASED ON pounds of coal per brake horse power hour 304 pounds of coal per kilowatt hour 304 EFFICIENCY compared to ideal Rankine cycle 309 factors determining 291 heat of liquid basis of calcula- tion 306 increased by Corliss and Poppet valves 146 mechanical 304 INDEX 501 PAGE ENGINE efficiency, other measures of, formulas 310 standards, chart 303 energy cost in selecting 439 EXPENSE, insurance cost. . 429 rent charged in proportion to floor space 429 taxes 430 factors determining selection .... 434 fitted with pantograph and indi- cators, illustration 47 FIXED charges 428 cut-off, definition 36 four-valve type, construction and use 324 friction 301 getting out of line, definition, causes 405 gridiron-valve, features 91 heat conversion in 5 HiGH-pressure, definition 36 SPEED, definition 36 indicator diagram 62 horizontal, illustration 21 in line 406 inclined, illustration 21 indicator springs selection 55 indicators, see also Indicators .... 40-83 inspection 373-377 knocks, causes and remedies, table 410 laying up 388 left-hand, illustration 21 loading, electrical 353-357 long-stroke, definition 32 Low-pressure, definition 36 speed, definition 36 MECHANICAL efficiency, defini- tion, formula 310 losses, method of reducing ... 300 mechanisms and nomenclature 19-38 MEDiuM-pressure, definition 36 speed, definition 36 modern, constructional, opera- ting and economic charac- teristics 319-340 MULTi-expansion, see also Multi- expansion engine. valve, definition 32 new, valve setting 112 NON-CONDENSING, definition 36 SLIDE-VALVE, starting 378 stopping 380 non-releasing Corliss-valve, starting and stopping 380 old, valve setting 113 operating costs 432 OPERATION conforming to load curve, graph 438 on superheated steam 422 oscillating-cylinder, illustration. 35 out of line, effect on bearings 405 overhauling 388 PERFORMANCE and maintenance, daily record 414 Rankine cycle used as stand- ard in engine testing 304 records, purpose of keeping. . . 415 plan lay-out 406 portable slide-valve, uses 323 proper management purposes . . . 373 quadruple-expansion vertical, il- lustration 25 RECIPROCATING, see also Recipro- cating engine. management, operation and repair 373-415 PAGE ENGINE, residual or scrap value .... 431 riding-cut-off valve type, uses . . . 324 right hand, illustration 21 RUNNING over, definition 22 UNDER, definition 22 knocks in guides 412 saving effected by superheating supply steam, table 423 SELECTION 427-446 chart. 440 determination of speed desired 435 for given service, procedure . . . 427 for new plant 434 governed by cost per unit of energy delivered 427 operating characteristics affecting 437 proper horse power determina- tion 435 with reference to operating conditions 436 SHAFT-GOVERNED piston-valve, setting valve for design- determined equal leads, example 123-125 valve setting 114 short-stroke definition 32 side-crank, definition 20 SIMPLE, definition 22 detaching Corliss-valve, start- ing 383 four-valve, steam rates 328 operation profitable at low pressures and high super- heats 425 SLIDE-VALVE automatic, illus- tration 378 illustration .' . . 2 siNGLE-acting, definition 11 -VALVE, definition 32 test for valve leakage 389 sizes, selected to suit load curve . 438 SLIDE-VALVE condensing start- ing 380 direction of rotation reversed . 140 starting and stopping unaffec- ted by type of governor 378 SPEED for direct-connected gen- erator drive 436 methods of adjustment by governors, illustrations 215 splash-oiled, illustration 465 STEAM, see also Steam engine. function 1 modern types 319-340 superheated steam used in. 417-426 taking steam for full stroke, illustration .- 10 TANDEM-COMPOUND, illustration. 24 slide-valve, starting 387 TESTS, data and results, Ameri- can Society of Mechanical Engineers 369-371 data necessary, table 343 duration 365 results corrected to standard conditions 443 TESTING 342-372 clearance volume determined in 366 equipment 344 for mechanical efficiency 359 procedure 343, 358 thermal efficiency computation. 364 throttling-governed direct- valve , setting valve for selected equal leads example 122 total annual cost 427, 433 502 INDEX PAGE ENGINE, total, steam used per hour 81 TRiPLE-compound, definition. ... 25 expansion, illustration 25 twin-cylinder, illustration 23 types, classification 19 UNIFLOW, construction and opera- tion 331 definition 33 poppet valve, starting 385 UNIT ENERGY COST, COMPUTA- TION, formula 427 example 434 unit, typical, illustration 322 VALVES for use with highly super- heated steam 419 maximum pressures and super- heats, table 421 methods of control by shaft governor 239 VARiABLE-cut-off , definition 37 speed, definition 216 vertical, illustration 20 warming facilitated by by-pass to both ends of cylinder 379 WATER RATE calculation, based on indicated horse power, formula 363 determination by steam con- denser 357 weight of steam used computed from indicator diagram 80 ERIE BALL ENGINE COMPANY, direc- tions for setting Ball Corliss engine valves 173 piston valve engine, illustration . 420 simple balanced-slide-valve en- ' gine, illustration 321 Sweet valve, illustration 90 ERIE CITY IRON WORKS, single-cylin- der Lentz engine, illustra- tion . 326 valve setting directions for Lentz poppet-valve engine.. 188-190 Erie Engine Works, simple slide-valve automatic engine, illustra- tion 378 ERIE governor, Jarecki Manufactur- ing Company, table of sizes. 224 pump governor, illustration 197 EXHAUST line, purpose 67 pressure, effect on compression, graph 69 EXPANSION curve, ideal compound engine 272 free, compound engine, defini- tion 271 larger cylinder necessary for given work output 13 LINE, leaky valves revealed by ... 66 STEAM, form of curve 16 engine 65 theoretical, graph 66 RATIO OF, definition 260 work to heat increased by 13 steam, work done 12 total ratio, compound engine, definition 271 EXTERNAL BEARING, definition 460 lubrication, see Lubrication, exter- nal bearing. External slide valve 87 "Extra Hecla" cylinder oil for use with superheated steam .... 422 Feed-water and steam cycle in power plant, illustration 306 PAGE Feeler, heating of inaccessible bear- ings detected by, illustration 379 Fessenden, C. H., "Valve Gears" 84 FILTER, OIL, illustration from "South- ern Engineer" 474 improvised 476 operation 474 "Power," illustration 475 precipitation compartment, illustration 477 Richardson-Phenix Company, illustration 476 Filtering and circulation oil system, illustration 468 "Financial Engineering," O. B. Gold- man, steam consumption of condensing and non-con- densing engines 286 Fire-point of oil 454 FITCHBURG ENGINE, direct of rotation changed 255 valve mechanism, illustration. . 325 FITCHBURG governor, illustration and operation 254 Fixed-cut-off engine, definition 36 Flash-point of an oil, definition 454 FLEMING-HARRISBURG engine gov- ernor, adjustments 249 four-valve engine, valve-setting directions 175-178 FLY-BALL GOVERNOR, adjustable thrust bearing, illustration. 225 adjustments and their effects, table 221 definition 38, 193 methods for controlling steam . . . 195 neutral or isochronous, defini- tion 204 principles and adjustment . . 192-227 speed variation permitted by .... 195 stable or static, definition 204 unstable or astatic, definition . . . 204 weight- or spring-loaded 207 FLYWHEEL, direction of rotation 22 inspection 374 method of balancing, illustration 236 shaft governor, balance 235 Foaming boiler danger with super- heated steam 425 FORCE-FEED CIRCULATION SYSTEM, advantages and disadvan- tages 471 external-bearing lubrication .... 469 table of oils used 459 FORCE-FEED lubricator, see also Lubricator, force-feed. pump, illustration 484 Foster superheater catalogue effect of superheat, graph 423 FOUR-VALVE ENGINE, construction and use 324 low steam rate 327 FOXBORO MANUFACTURING COM- PANY, continuous revolution counter, illustration 345 hand tachometer, illustration . . . 346 FRICTION, definition 448 fluid, definition . . . 447 horse power, definition 77, 342 SLIDING, definition 448 when replaced by fluid friction 449 rolling, definition 447 FULTON IRON WORKS COMPANY, St. Louis, cross-compound engine, illustration 268 Corliss engine, illustration 165 live-steam reheater and receiver, illustration 269 INDEX 503 PAGE FULTON IRON WORKS COMPANY, receiver-pressure regulation device, illustration 277 Fulton-Corliss cross-compound engine, assembly drawing 329 G 211 Gappot definition and purpose Gardner throttling governor, spring arrangement, illustration . . . 209 "Gargoyle" cylinder oil for use with superheated steam 422 Gear adjustment on governors 278 Gears, Corliss releasing, troubles of dash-pots 412 GEBHARDT "STEAM POWER PLANT ENGINEERING," frictional losses of engines 301 steam engine efficiencies and performance tables. . . . 311-317 GENERATOR, direct-current, determi- nation of electrical output .. 354 efficiency 355 electric, for engine loading 353 horse power input determination, formula 355 loading by water rheostat 357 power output, formula 354 Gland friction in engines 301 Goldman, O. B. "Financial Engi- neering," steam consumption of condensing and non- condensing engines 286 Governing high-pressure cylinder only, effect on receiver pressure 279 GOVERNOR, see also Shaft governor and fly-ball governor. ADJUSTMENT for different speeds by adding or removing weight 213 for promptness and speed regulation 219 to change engine speed 212 American-Ball engine 250 attentions required 225 BELT, requirements 201 oily or slack, danger 201 Buckeye, illustration 251 centrifugal force 204 classification 193 Corliss engine, illustration 192 dash-pot size varying with load conditions 211 definition 192 effect on slide-valve setting 140 enclosed spring, illustration 202 engine, functions 37 Erie pump, illustration 197 failure, engine and power plant wrecks due to 198 Fitchburg type, setting 254 Fleming-Harrisburg centrifugal inertia, illustration 250 FLY-BALL, see also Fly-ball governor 192-227 definition 193 illustration 38 principles and adjustment 192-227 flywheel in balance, explanation. 235 forces for detecting engine speed variations 194 GEAR adjustment 278 example of changing 217 "Hamilton" uniflow poppet- valve engine, illustration . . . 255 horizontal tension spring, illus- tration 194 PAGE GOVERNOR, hunting, definition of term 210 in balance, explanation 235 incorrect application or poor condition, danger 222 lagging during changes in load, causes 223 LEVERS, adjustable, illustration . . 219 method of securing 201 load indicator for 223 Mclntosh and Seymour, illustra- tion 253 MECHANISM, binding, dangers due to 201 construction 201 performance, terms used to describe 203 Porter, relation between speed, height and weights of balls and counterpoise, formula . . 208 position for starting engine 385 pulley, requirements and methods of securing 201 Rites type, Troy vertical engine, illustration 247 Robb-Armstrong-Sweet type, illustration 248 safety and reliability devices .... 198 sensitiveness changing with speed changes 216 SHAFT, see also Shaft governor. full-load running position, how found 141 principles and adjustments. . . 228-257 SIMPLE PENDULUM, angular speed and ball height 205 ball height, formula 206 spring- or weight-loaded, advan- tages over simple pendulum 207 steam-engine, classification 37 THROTTLING, selection 224 table of sizes 224 typical shaft, illustration 37 unstable, useless for engineering purposes 204 vibration, causes 223 weight, revolving, centrifugal force developed formula .... 205 wheel, Troy automatic engine, method of balancing, illus- tration 236 when necessary 193 rod pivots, proper end-play, illustration 202 "Governors and the Governing of Prime Movers," W. Trinks, on racing 222 Graphite, flake, use in valve and cylinder lubrication 479 GRAVITY-CIRCULATION SYSTEM, ad- vantages 470 external-bearing lubrication. . . . 467 GRAVITY oiling system, four-window sight-feed oiler, illustration . . 468 TRIP GEAR, "Hamilton" Corliss engine, illustration 155 Murray Corliss engine, illus- tration 157 valve, MacCord Manufacturing Company, illustration 479 GRIDIRON VALVE, definition 28 engine, features 91 Grpssenbacher, E., oil filter, illustra- tion 475 H HAMILTON Corliss engine, gravity trip gear, illustration 155 504 INDEX PAGE HAMILTON, engine cylinder, detach- ing-poppet admission valve, illustration 32 UNIFLOW ENGINE, governing mechanism 255 poppet-valve engine cylinder, illustration 420 HAMKENS, "STEAM ENGINE TROU- BLES," enclosed-spring gov- ernor illustration 202 governor employing horizontal tension spring illustration . . 194 governors 193 HARDING AND WILLARD, "MECHANI- CAL EQUIPMENT OF BUILD- INGS," Corliss engine gov- ernor, illustration 192 on regulation guarantee tests .... 204 "Hardwick" shaft governor, Erie engine, illustration 237 Harrisburg Foundry and Machine, Works, "Fleming-Harris- burg" engine valve-set- ting.. 175-178 HARRISBURG FOUR-VALVE ENGINE, advance of steam and ex- haust valve arms, table. . . . 178 exterior outline 176 HEAD-END dead center, definition, illustration 103 port opened to extent of lead, illustration 121 HEAT, abstracted 9 as energy 5 BALANCE, explanation 8 high-grade engine, illustration 9 plant with condensing engine using live steam for heating 299 power plant where engine exhaust is used for heating. . 298 conversion in engine, example . . 7 converted into work 9 energy, conversion into mechan- ical work 1 insulation or lagging, thermal losses reduced by 299 mechanical losses 9 rejected, in steam engine 6 thermal losses 9 total, small part converted into mechanical work by steam engine 291 transfer, saturated and super- heated steam plants, diagram 417 unit equivalents in mechanical and electrical energy 5 useful work 9 flow, steam-engine plant, expla- nation 1 insulated engine cylinder, illus- tration 299 HiGH-pressure engine, definition 36 SPEED ENGINE, definition 36 testing 366 HlLLS-McCANNA COMPANY, fqrCC- feed lubricator, illustration. 484 pump, illustration 484 Hirshfeld and Ulbricht, "Steam Power," engine classification 19 Holstead Mill and Elevator Com- any, engine indicator iagram 331 Hook-rod, Corliss engine, illustration 383 HOOVEN, OWENS, RENTSCHLER COM- PANY, Corliss-engine valves, illustration 147 poppet-valve engine cylinder, illustration 420 PAGE Horizontal steam engine, definition . . 20 HORSE POWER, brake, definition 78 computation from indicator diagrams 76 constant, formula 76 definition 14 each end of cylinder, how found 77 FRICTION, definition 77, 342 variation with brake horse power 301 INDICATED, compound engines, computation 275 definition 77 formula for computing 76 input to generator, known out- put, formula 355 of engine, mean effective pres- sure necessary to determine. 70 HUNTING, governor, definition of term 210 graphs of governors 210 shaft governor, cause 243 Hydrometer, use in finding specific gravity of oil 453 HYDROSTATIC LUBRICATOR, see also Lubricator, hydrostatic. illustration 481 Hyperbolic expansion line for steam, graph 65 "IDEAL" CORLISS-VALVE ENGINE, Corliss valve, illustration. 147 shaft governor illustration 249 Ideal Rankine cycle efficiency, form- ula for computing 305 iNCLiNED-plane reducing mechanism . 49 steam engine, definition 20 INDICATED HORSE POWER, definition. 77 thermal efficiency computa- tions based on formula 307 INDICATOR, application to engine 57 cards, condensing and non- condensing operation 285 cock, relief passage 51 connection to cylinder, illustra- tion 51 CORD, connection to crosshead, illustration 48 methods of hooking up 58 Crosby outside-spring, illustra- tion 43 definition 40 DIAGRAMS, actual and theoretical 61 areas found by planimeter .... 73 brake horse power computed from, formula 78 combined, quadruple-expan- sion engine 281 compound and equivalent simple engine 265 engine faults revealed by 69 high-speed engine 62 horse power computed from ... 76 ideal 60 leaky steam-admission valve revealed by 66 MEAN, method of drawing 275 when necessary 274 method of taking 58 steam weight computed from . 80 uses 40 incorrect piping, illustration 52 modern, variation from Watt's . . 42 paper, requirements and place- ment on drum 57 PENCIL mechanism, advantages. 42 INDEX 505 PAGE INDICATOR PENCIL, method of adjust- in? f. 6 , requirements -. 08 piping for 50 practice 40-83 REDUCING, adjustable panto- graph for, illustration 47 MECHANISM, classification 44 when necessary 43 motion, tests before using .... 49 single, for cylinder, disadvan- tages 51 SPRING, adjustment 56 card illustrating test 54 classification 52 for engine, selection 55 periodic tests necessary 53 safe pressures, table 53 scale, formula 54 test 53 two, operated from one reducing mechanism, illustration .... 57 use in valve-setting operations. . 142 valve setting defects determined by 143-144 Watt's, illustration 41 INDIRECT measurement method of ascertaining valve operation 108 slide valve 87 INERTIA, principle of, applied to revolving governing parts. . 231 shaft governor operation 229 temporary control in shaft governor effected by 231 Inside-admission slide valve 87 Instruments, inspection 376 Insulation, thermal losses reduced by 299 Interheater, definition 269 INTERNAL bearings, definition 460 lubrication, see also Lubrication, internal 478-486 slide valve ... ,87 Jarecki Manufacturing Company, throttling governor sizes, table 224 Jig, for boring babbitted bearing boxes 398 Journal and bearing, clearance between 402 Kahl, J. C. oil filter, illustration 474 KNOCK, apparent location deceptive. 410 causes and remedies 410 location ascertained by sounding rod . . 412 LAP angle, definition, illustration 100 steam and exhaust, purposes .... 95 valve, definition 94 Lapping plate 392 LEAD angle, definition, illustration . . . 100 explanation of term 96 measurement, illustration 124 proper for slide valve 115 LEADS, EQUAL, designed-determined definition 114 selected, definition 114 Leads, laps and trial compressions, Corliss- valve engine, table . . 169 Leakage loss, less in compound than in simple engine, explanation 264 Left-hand engine, definition ... 21 PAGE LENTZ ENGINE, high-pressure steam- valve gear, illustration 189 poppet-valve, valve setting direc- tions 188-190 report on record steam rate for uniflow engine 332 single-cylinder, illustration 326 LEVER, governor, method of securing. 201 pencil mechanism, Thompson indicator, illustration 44 Life of engine, effect on selection of engine 437 Lineal clearance, definition 3 LOAD curve, power plant, for engine selection 437 ELECTRICAL, determination with three-phase alternating-cur- rent generator 356 of engine 353-357 factor of power plant, definition. 438 indicator for engine governors, illustration 223 -measuring apparatus, classifica- tion 346 -output determination, direct- current generator, illustra- tion 354 Locomobile steam engine unit 333 Long-stroke engine, definition 32 Losses, steam-engine, classification . . . 293 Loss, mechanical 8 Low-pressure engine, definition 36 -speed engine, definition 36 LUBRICANTS, classification 450 semi-solid, uses 451 solid, use 450 LUBRICATION, automatic, for external bearings, merits 470 chart, steam cylinders and valves 457 DROP-PEED, applications suitable for steam engines 462 of external bearings 461 engine 447-487 EXTERNAL BEARINGS, by hand . . . 460 force-feed circulation system . . 469 gravity-circulation system .... 467 splash system 465 force-feed, compound marine engine with, illustration. . . . 470 iNTERNAL-bearing 478-486 of engines, automizer for, illustration 479 purpose 447 stuffing boxes 480 SYSTEM, choice of oil affected by . 456 for external bearings, classifi- cation 460 steam engines, classification . . . 460 "Lubrication, Practice of," T. C. Thomson, selection of oils for engine lubrication, tables 456-460 LUBRICATOR, FORCE-FEED, illustration 484 installation 485 LUBRICATOR, HYDROSTATIC, care and operation 482 leakages of joints or packing .... 483 prevention of trouble 483 principle 480 water feed valve 483 LUBRICATOR, independent or central, starting 378 mechanical force-feed 483 Meyeringh proportional, illus- tration 486 multiple-feed mechanical 485 proportional, definition 485 506 INDEX PAGE LUNKENHEIMER COMPANY, auxiliary graphite feeder, illustration . 480 drop-feed oil cup, illustration .... 462 Lever-handle oil pump, illustra- tion 480 Me MdNTOSH AND SEYMOUR four-Valve engine 324 governor 253 gridiron valve, illustration 28 engine, valve construction 93 valve-operating mechanism, illustration 92 M MacCord Manufacturing Company, gravity valve, illustration.. 479 MAIN BEARING box, pouring 397 boxes, babbitted while warm. . 397 correct oil grooves 399 heating 403 method of gaging wear 410 normal wear, effect on shaft 409 quartered, dismantling for re- babbitting 396 Main-valve operating mechanism, Mclntosh and Seymour engine, illustration 93 Mandrel, use in babbitting main bearings 397 Marker, stationary, method of plac- ing engine on dead center . . 105 MARKS "MECHANICAL ENGINEERS' HANDBOOK," clearance values, table 297 Rankine cycle rates, table 309 Marine engine, four-cylinder triple- expansion, illustration 280 MEAN EFFECTIVE PRESSURE 12 formula for computing 15 Mean indicator diagram, when neces- sary 274 Measuring rod, head 126 MECHANICAL EFFICIENCY of engine, definition, formula 310 TEST apparatus, for simple engine 360 data sheet 360 purpose 342 "MECHANICAL ENGINEERS' HAND- BOOK," clearance values, table 297 Rankine cycle rates, table 309 "MECHANICAL EQUIPMENT OF BUILD- INGS," HARDING AND WIL- LARD, Corliss engine gover- nor, illustration 192 regulation guarantee tests 204 MECHANICAL LOSSES, definition. . . 8, 294 methods of reducing 300 Mechanical work, small part of total heat converted into by engine. 291 Mechanisms, engine 19-38 MEDiuM-pressure engine, definition. . 36 -speed engine, definition 36 Meyeringh proportional lubricator, illustration 486 Meyer riding-cut-off valve, illustra- tion 28, 134 Model Acme engine, trunk piston mechanism, illustration.... 35 Monel metal, for valves used with superheated steam 421 PAGE MULTI-EXPANSION ENGINE 258-282 advantages and disadvantages. . 260 application 258 best receiver pressure, how found 276 saturated steam operation econo- mics, table 314-315 stopping 387 MULTIPORTED slide valve, advan- tages and disadvantages. ... 90 VALVE, definition 27 setting 131 Multi- valve engine, definition 32 MURRAY IRON WORKS, Burlington Iowa, Corliss-valve dash pot, illustration 159 governor adjusted by weight, illustration 213 gravity trip gear illustration 157 N "National Engineer," T. G. Thurs- ton, gravity-circulation sys- tem, illustration 469 Newton, Sir Isaac, principle of inertia 231 Ninde, W. E., " Design and Construc- tion of Heat Engines," on valve diagrams 84 NON-CONDENSING ENGINE, see also Engine, non-condensing. auxiliary piping and equip- ment, illustration 375 definition 36 Non-condensing operation 283-290 Non-releasing Corliss-valve engine, starting and stopping 380 NORDBERG engine, positively-oper- ated poppet admission valve, illustration 31 engine, variation in steam con- sumption 294 governor, spring-connected dash- pot rod 212 long-range valve gear and gov- ernor 156 standard Corliss valve gear, illustration 159 Nordberg Manufacturing Company, Corliss trip gear, illustration 156 Nugent crank-pin oiler, illustration. . 471 Obliquity, connecting rod, definition and effects 101 OIL barrels, methods of handling 452 chill point, definition 455 choice affected by type of lubri- cating system 456 circulation, table of properties. . . 456 classification 451 collecting devices, illustration. . . 472 compounded, definition 451 CYLINDER, engines using super- heated steam 421 table of grades 458 table of properties 458 deposit-forming 456 filtering outfit, S. F. Bowser and Company, Incorporated. . . . 478 FILTER, see also Filter, oil. filtering materials used 474 fire-point, definition 454 fixed, definition 451 flash-point, definition 454 INDEX 507 PAGE OIL, force-feed circulation systems, table 459 groove, cutting, illustration 400 igh-speed splash-oiled engines, table 460 methods of supplying to moving bearings 471 mineral, definition 451 PURIFIER, operation 474 capacities 476 selection, requirements to be met 455 specific gravity, how found 453 steam-engine lubrication, selec- tion, tables 456 swing joints for supplying crank and crosshead pins, illustra- tion 473 system, filtering and circulation type, illustration 468 tests for properties 452 viscosity, measurement 453 Oil Well Supply Company, Pitts- burgh, Meyeringn propor- tional lubricator, illustra- tion 486 OILER, bottle type 463 crank-pin, illustration 463 crosshead-pin telescopic, illus- tration 472 drop-feed 461 Oiling, hand 461 Operating-condition test, purpose .... 342 Ordinates, method of, for finding mean effective pressure, graph ... 71 Oscillating-cylinder engine, definition 35 Output, electrical, direct-current gen- erator, 354 Outside-admission slide valve 87 Over-all efficiency based on brake horse power, formula 310 PACKING, metallic, used with high- pressure superheated steam . 422 rings 392 sheet, for valve-chest covers and flanged joints 404 soft, replacement 405 steam engine 403 stuffing box, correct and incor- rect arrangement, illustra- tion 405 PANTOGRAPH as an indicator reducing mechanism 46 engine fitted with, illustration. . . 47 Paper, indicator, requirements and placement on drum 57 Parallel-link pencil mechanism 43 PEENING in main bearing-box 398 snap packing ring 393 PENCIL, indicator, requirements 58 MECHANISM, indicator, advan- tages 42 types 43 PENDULUM, angular speed and ball height 205 LEVER, inverted, with Brumbo pulley, illustration 45 reducing mechanism, construc- tion 44-46 SIMPLE, ball height, formula 206 or Watt's governor, illustra- tion 193 Performance specifications, Corliss- engines 441-442 Peterson oil filter, operation 476 PAGE Pickering and Gardner governor catalogues, selection of throttling governor 224 PICKERING GOVERNOR, methods of adjustment, illustration. ... 216 safety idler feature, illustra- tion 198 Pipe, velocity of fluid in 449 PIPING, engine, inspection 376 indicator, see Indicator piping ... 51 steam, simple engine, illustration 377 PISTON, clearance, definition 3 leakage, rejection losses caused by 296 low-friction, illustration 302 RING, cast-iron snap, replace- ment 389 expanding by peening 393 fitting 390 repairing, illustrations 391 replacement 389 solid, cutting 392 tested for fit 393 worn, expanded by peening. . ; 393 SLIDE VALVE, advantages and disadvantages 88 definition 27 desirable in vertical engines . 27 inside admission type 88 repair 394 setting for selected lead, illustration 121 -rod nuts, methods of locking, illustration . 374 PLANIMETER, Amsler polar, operation 73 averaging, definition 74 Coffin, operation 75 mean effective pressure found by 73 polar, adjustable tracer arm 74 Willis 76 Polar planimeter, adjustable arm, diagram 74 POPPET VALVE 146-191 advantages and disadvantages 159 Ames Unaflow engine, direc- tions for setting 182-186 definition 31 detaching or releasing, defini- tion 31 ENGINE efficiency increased by 146 method of governing 195 starting 385 location in engine cylinder. ... 160 mechanism, typical designs 161 operating mechanism, Vilter engine, illustration ......... 162 positively-operated, definition. . 31 reason for employing 146 repair 395 single- and double-beat, defini- tion 160 Portable slide-valve engine, uses 323 Porter governor, relation between speed, height and weights of balls and counterpoise, formula 208 Porter-Allen engine, variable-cut-off valve-mechanism, illustra- tion 36 POSITIVELY-OPERATED CORLISS and poppet valves, setting 173 valve mechanisms 149 POWER, definition 14 HORSE POWER, see also Horse power. increase due to condensing operation, methods of cal- culating 285 508 INDEX PAGE POWER, output, generator, formula. . 354 PLANT, daily load curve 437 drawing from "Power" iv efficiency based on use of rejected heat 9 inspection 373-377 load factor, definition 438 regular inspection trips advis- able 387 steam engine, formulas for com- puting 14 stroke, heat engine, definition. . . 11 " POWER," energy balance in electric- energy distribution circuits . 300 hydrostatic lubricator, filled by hand oil pump, illustration . . 482 oil filter, illustration 475 power plant drawing from iv savings effected by superheating supply steam, table 423 sight feed for drop-feed oiler, illustration 464 valve leakage test, single-valve engines 389 valve setting without removing chest cover 132 W. H. Wakeman on engine safety devices 200 "Power House," hydrostatic lubrica- tor, illustration 481 PRESSURE and superheats, maximum for engine valves, table 421 and vacuum gages for engine testing 344 approximate mean effective, formula for computing 15 average or mean effective 12 BACK, definition 10 purpose of reducing with condenser 285 boiler, see Boiler pressure. effective, on piston 11 indicator springs, table 53 loss indicated by steam line 62 MEAN EFFECTIVE, found by method of ordinates 70 in cases of over-expansion .... 72 indirect methods of finding ... 77 planimeter for finding 73 net, on piston, definition 10 range of engine, definition 258 receiver, see Receiver pressure. steam, work done by 9 PHONY-BRAKE absorption dynamo- meter, construction 347 cooling 347 illustration 347 lubrication 348 portable, for testing small engines, illustration 348 Providence Engineering Corporation, jacketed engine cylinder, illustration 295 Pulley, governor, method of secur- ing. 201 Pumps, inspection 375 Q QUADRUPLE-EXPANSION ENGINE, com- bined indicator diagrams. . . 281 definition 26 seldom used in stationary power plants 280 Quartered main bearing illustration . . 396 RACING, causes 222 PAGE RACING, definition 222 engine with shaft governor, causes 243 RANKINE CYCLE ratios, different type engines, table 309 ratio, definition, formula 309 standard of engine perform- ance in steam-engine testing 304 RANKINE ideal cycle 7 water rate, formula 307 Reach-rod, Corliss engine, illustra- tion 383 Re-babbitting, necessary where bear- ings are partially melted out 395 RECEIVER-COMPOUND ENGINE, best receiver pressure, how found 276 definition 267 RECEIVER PRESSURE, best, receiver- er compound or multi-expan- sion engine 276 compound engine, dependent on cylinder ratio 278 correct, necessary for economi- cal operation of compound engines 276 regulation device, illustration. . . 277 variation during stroke 276 Receiver volume 269 Reciprocating engine management, operation and repair.. 373 415 REDUCING MECHANISM, inclined-plane type, illustration 49 test for accuracy of reduction, illustration 50 two indicators operated from, illustration 57 REDUCING MOTION, see also Indicator reducing motion. indicator 43 pendulum-level, illustration 45 REDUCING WHEEL, construction. ..... 48 principle, illustration 48 Regulation guarantee tests for gov- ernor 204 Reheater, definition 269 Rejected heat in steam engine 6 REJECTION LOSSES, cylinder con- densation partly responsible for 297 definition 293 exhaust steam used for heat- ing 297 methods of decreasing 294 Release line, purpose 67 RELEASING CORLISS-VALVE MECHAN- ISM, definition 30 illustration 152 Releasing mechanism, operation 152 Return stroke, definition . H Reversing rocker, reversing rotational direction of engine 140 REVOLUTION COUNTER, continuous. . . 345 definition 344 hand 344 Reynolds trip gear 155 Rheostat, water, generator loading accomplished by 357 Rice and Sargent Corliss engine, jacketed cylinder, illustra- tion 295 Rice-Stix Dry Goods Company plant, engine indicator diagram . . . 329 RICHARDSON-PHENIX COMPANY, crosshead-pin telescopic oiler, illustration 472 oil filter, illustration 476 sight-feed oiler for gravity sys- tem, illustration 468 INDEX 509 PAGE RIDGWAY automatic engine, Rites governor, illustration 247 FOUR-VALVE ENGINE, valve set- ting directions 178 valve-operating mechanism, illustration 148 SIMPLE and cross-compound four- valve engines, results of adjustments, table 179 four-valve engine, table of dimensions for setting 179 tandem compound four-valve engine, results of adjust- ments, table 181 Ridgway Engine Company, recom- mendation for valve setting for unequal leads 130 RIDING-CUT-OFF VALVE, advantages and disadvantages 91 definition 27 engines with, uses. 324 mechanism, setting, explana- tion ... 133 Right-hand engine, definition 21 RiNG-oiled bearing illustration 465 packing, soft, illustration 404 snap, piston, repairing, illustra- tions 391 RITES GOVERNOR, dash-pot or drag springs for limiting rate of movement 246 illustration 232 ridgway automatic engine, illustration 247 special adjustments 248 ROBB-ARMSTRONG SWEET GOVERNOR, adjustment 249 description 248 Robertson, James L. and Sons, Willis planimeter, illustration 75 Rod area, effect in computing work done 13 ROPE BRAKE absorption dynamo- meter 350 illustration 351 ROTARY STEAM ENGINE, construction and disadvantages 319 illustration of principle 320 operation 320 ROTATION, slide-valve engine, rever- sing direction of, 140 method, tare-weight of brake found by 349 St. Louis Iron and Machine Works, piston construction in St. Louis Corliss engine, illustra- tion 374 SAFETY idlers, belt-driven governors. 198 knock-off cams, Corliss gov- ernors 198 stop, engine governor provided with 198 Saturated steam and superheated steam, differences 418 Saybolt viscosimeter, illustration 454 Schaeffer and Budenburg Manufac- turing Company fixed tacho- meter, illustration 346 Schutte and Koerting Company, catalogue, Corliss engine with condenser, illustration, 284 Scotch-yoke mechanism velocity dia- gram 102 PAGE Selected equal leads, definition 114 SETTING, dimensions for, Ridgway simple four- valve engine, table 179 plain slide valves for equal leads, table showing procedure 11&-118 slide valve, first consideration. . . 113 steam-engine valves 107 SHAFT governed engine, eccentric shifting inadvisable 115 governing, forces required 229 GOVERNOR, adjustment 245 balance 235 care of... 245 classification 236 classification table 240 crank pin used in place of eccentric 239 definition . 37, 228 full-load running position, illustration 141 hammering, remedy 246 methods of adjustment 229 method of controlling engine speed 233 methods of controlling engine valves 239 more economical than throt- tling governor 228 OPERATION, effects of weight and spring adjustment ... 241 forces of two kinds em- ployed 229 troubles and remedies . . 243-245 permanent control, effected by centrifugal force 230 position fixed 256 principal adjustments, table. . 242 PRINCIPLES and terms same as those for fly-ball governor 229 and adjustments. 228-257 results of combining centri- fugal force and inertia 232 simple weight employed, illus- tration 238 sluggishness, causes 243 speed regulation and govern- ing action 233 temporary control effected by inertia 231 type of engine used on 228 use of both centrifugal force and inertia, explanation 233 variable cut-off governor 228 "Shaft Governors," Hubert E. Col- lins on shaft governor opera- tion 239 Sherwood Manufacturing Company, oil collecting devices, illus- tration 472 Shims, bearings adjusted by means of 400 Short-stroke engine, definition 32 Side-crank engine, definition 20 Sight-feed oiler, four window, gravity oiling system, illustration . . . 468 SIMPLE balanced-slide-valve engine, illustration 321 D-slide valve engine, illustration 23 SiNGLE-acting engine, definition 11 -beat poppet valve, definition. . . 160 -ECCENTRIC DETACHING CORLISS- VALVE engine, valve setting directions 163-169 mechanism, features 154 -VALVE ENGINE, definition 32 simple, construction and opera- : , tion 321-323 510 INDEX PAGE SKINNER engine-governing mechan- ism, illustration 228 tandem-compound engine, gov- erning of high-pressure cylinder, illustration 259 " UNIVERSAL UNAFLOW" ENGINE, steam-consumption curves 331 valve-operating mechanisms, illustration 161 SLIDE VALVE, see also Valve, slide. 84-144 balanced, illustration 89 condensing engine, starting 380 definition 26 displacement, definition 101 engine, direction of rotation 140 function 84 iNsiDE-admission, illustration ... 87 clearance, definition 95 lap, how changed 96 mechanism adjustment Ill method of controlling steam flow 84 motion received from eccentric . . 97 multiported, advantages and disadvantages 90 outside-admission, illustration. . 87 plain, setting for selected lead, illustration 123 proper lead 115 riding-cut-off, advantages and disadvantages 91 SETTING, defects determined by indicator 143-144 effect of governors on 140 first step 113 FOR EQUAL CUfc-offs 129 .leads 115 without removing steam chest cover, explanation 132 three conditions to be set for. . 113 type of engine used in 84 Snap ring, fitting, illustration 390 Sounding rod, knocks located by 412 "Southern Engineer Kink Book," engine alignment 408 "SOUTHERN ENGINEER," oil filter, illustration 474 riding-cut-off valve setting . . 134-140 SPEED, governor adjustments for changing 212 method of control by shaft governor 233 regulation, good shaft governor . . 233 VARIATION, fly-ball governor. . . . 195 governed and ungoverned engines, graph 193 SPLASH oiling systems, advantages . . . 470 -oiled engines, table of oils for . . . 460 system, external bearing lubrica- tion 465 SPRING adjustment, shaft-governor operation, effects. 241 INDICATOR, see Indicator springs. adjustment 56 classification 52 rules for selection 55 safe pressures, table 53 testing apparatus, illustration . 54 -LOADED governor, advantages over simple pendulum gov- ernor 207 governor, comparison with weight-loaded 209 STANDARD CRANK-MECHANISM, defini- tion 34 velocity diagram 102 STARTING block, Corliss engine governor 385 PAGE STARTING block, lever and wrist plate, Corliss engine 384 STEAM and feed-water cycle in power plant, illustration 306 chest diagram, value 64 CONSUMPTION, CALCULATION from indicator diagram. . . 80 on dry-steam basis 304 condensing and non-condens- ing engines, table 286 uniflow engine, variation in. . . 294 dry, weight of 304 ENGINE, see also Engine, steam. approximate attendance costs, graph 439 condensing and non-condens- ing, stopping 382 condensing operation, defini- tion 283 conditions necessary for high- est theoretical efficiency. ... 6 costs of different types, table . . 340 depreciation rates 431 EFFICIENCIES and perform- ance, tables 311-317 how increased 291-317 mathematical methods of computing 302-317 ways of expressing 303 efficient, definition 9 ELEMENTARY, construction. ... 2 operation 3 energy abstracted from steam . 7 expansion line in 65 first cost, factors influencing. . 335 fly-ball governors, principles and adjustment 192-227 function and principle 1-18 GOVERNOR, see also Governor, steam-engine. functions 37 heat converted into mechan- ical work 291 horizontal, definition 20 inclined, definition 20 ideal, illustration 7 indicators 40-83 LOSSES, classification 293 large part unavoidable 292 LUBRICATION 447-487 selection of oils for, tables. . . 456-460 systems, classification 460 mechanisms and nomencla- ture 19-38 MODERN, classification as to type, table 336-339 types 319-340 packings for 403 performance guarantees 440 plant, heat-flow, explanation. . 1 power, formulas for computing 14 purposes of testing 342 rejection losses, methods of decreasing 294 rotary, construction and dis- advantages 319 specifications for quotations.. 444 suitable applications for drop- feed lubrication 462 TESTING, see also Engine test- ing 342-372 data and results 369-371 ideal Rankine cycle stand- ard of engine performance 304 TYPE using slide valves 84 classification table 19 VALVES, repair 393 INDEX 511 PAGE STEAM ENGINE VALVE, setting 107 vertical, definition 20 warmed and drained before starting 377 water rate taken as measure of economy 308 " Steam Engine Test Code," American Society of Mechanical Engi- neers, Outline 369-371 "STEAM ENGINE TROUBLES," H HAMKEN , enclosed-spring governor, illustration 202 governors 193 governor with horizontal ten- sion spring, illustration 194 STEAM expansion line, form of curve . . 16 EXPANSIVE USE, economy 12 when not desirable 13 FLOW, controlled by slide valve 84-87 DIRECTION, INTO COUnterfloW- engine cylinder, illustra- tion 33 uniflow-engine cylinder, illustration 33 jacketing, method of decreasing rejection losses 296 LINE, ideal 63 pressure losses indicated by. . . 62 variations, illustration 63 methods for controlling used, with fly-ball governors 195 port locations, marking for valve setting 127 "Steam Power," Hirshfeld and Ulbricht, engine classifica- tion 19 "STEAM POWER PLANT ENGINEER- ING," frictional losses of engines 301 Gebhardt, steam engine efficien- cies and performance, tables 311-317 STEAM quality determination 362 rate, four-valve engines 327-329 saturated and superheated, dif- ferences 418 SUPERHEATED, see also Super- heated steam. use in engines 417-426 TOTAL, used per hour by engine . . 81 work g WEIGHT USED by engine with no clearance, formula 79 computation 78-81 WORK DONE BY direct pressure '. 9 expansion 12 work necessary to expell from cylinder 4 IQ Stone, A. O., hydrostatic lubricator, illustration 481 STROKE, definition 11 working, heat engine, defini- tion 11 Stuffing boxes, inspection 375 SUPERHEAT, effect of, B u c k e y e engines, graph 423 influence on water-rate, graph . . . 423 and pressure, maximum for engine valves, table 421 SUPERHEATED STEAM, advantages and disadvantages, table 425 and saturated steam, differ- .. ences 418 cylinder oil for engines using. . . . 421 desirability of compounding partially obviated by 422 economical in uniflow engines. .. 424 PAGE SUPERHEATED STEAM, effect in de- creasing cylinder condensa- tion and leakage, graph.. 425 gain resulting from use in engines 417 generation 418 metals for valves and seats used with 421 USE IN compound or triple- expansion engines 424 engines 417-426 valves for engines using 419 Superheater installation, typical, illus- tration 418 SUPERHEATING, effect on efficiency of simple engine, graph. '. 295 supply steam, saving effected by, table 423 Supplies, engine, inspection 377 SWEET governor, operating gridiron valve, illustration 244 valve, Erie Ball Engine Com- pany, illustration 90 Symbols list xii Tabor indicator, curved-slot parallel motion, illustration 44 TACHOMETER, definition 345 fixed 346 hand 346 TANDEM-COMPOUND ENGINE com- bined diagrams 272 definition 23 governing of high pressure cylinder, illustration 259 starting 387 surface condenser connected with, illustrati9n 284 typical high-speed, illustration. . 323 water rate determination, illus- tration 366 Tare-weight of brake, definition 348 Telescopic tubes, eccentrics and crosshead pins oiled by 473 Temperature range of engine, defini- tion 258 TEMPLET, application in finding dead centers of eccentric 106 arrangement on valve chest for valve setting, illustration. .. 128 method of ascertaining valve operation 109-111 valve setting, for indirect-valve engine 126 Terminal drop, compound engine, definition 271 "Test Code," American Society of Mechanical Engineers, water-rate test specifications 365 Testing, engine, see also Engine testing 342-372 Test results facilitated by calculation of engine and brake con- stants 368 Theoretical water rate computation, based on ideal Rankine cycle formula 307 THERMAL EFFICIENCY based on brake horse power, formula 310 computation on basis of indicated horse power, formula 307 definition 303 computation 364 formula 305 test, purpose 342 512 INDEX PAGE THERMAL LOSS cylinder condensation partly responsible for 297 definition 8, 293 method of reducing 299 Thompson indicator, illustration.. 40, 42 THOMSEN, T. C., lubrication chart for steam cylinders and valves 457 "Practice of Lubrication," selec- tion of oils for engine lubri- cation, tables 456-460 Throttling governor, selec^n 224 Thurston, T. G., Gravity-circulation system, illustration 469 Tolle governor, general arrangement, illustration 209 Tools, engine, inspection 377 TORQUE, definition of term 260 regularity increased in compound engines explanation 265 variation graphs, tandem-com- pound engine 266 Tram, illustration 104 TRAMMEL, application in finding dead centers of eccentric 107 gage, valve setting with 125 method of placing engine on dead center 104 Travel, valve, definition 98 Trinks, W., "Governors and the Governing of Prime Movers" on racing 222 TRIP GEAR, function 157 operation 152 Reynolds, for Corliss engines, illustration 152 TRiPLE-compound engine, definition. 25 EXPANSION ENGINE, definition. . . 25 seldom used in stationary power plants 280 use of superheated steam 424 pumping, receiver and drain arrangement, illustration. . . 270 TROT AUTOMATIC ENGINE directions for reversing 235 method of balancing governor flywheel, illustration 236 Troy Engine Company method for setting vertical engine on dead center 105 Trunk-piston mechanism, definition. 35 Twin-cylinder engine, definition 23 U UNIFLOW ENGINE, construction and operation 33J CYLINDER, connection to sur- *** face condenser, illustration 283 direction of steam flow from, illustration ' 34 lubrication 424 definition 33 four-valve, for non-condensing service 329 manufacturer's guarantees 443 most profitable degree of vacuum 289 NON-CONDENSING, construction and operation 332 economy 333 starting 385 superheated steam economical 424 "Universal una-flow" engine, valve- operating mechanism, illus- tration 161 PAGE VACUUM, actual and theoretical dif- ference 382 most profitable degree in uniflow engine 289 Oil Company, cylinder oil for use with superheated steam . 422 VALVE adjustments, importance of dead centers 103 arms, steam and exhaust, Harris- burg four-valve engine, table showing advance 178 automatic by-pass, Ames una- flow engine, illustration 185 balanced slide, advantages and disadvantages 89 CHEST, templets arranged on. ... 129 vertical-engine, measurement for valve setting 127 Corliss, see also Corliss valves 146-191 D-SLIDE, advantages and dis- advantages 87 illustration 26 detaching-poppet admission, "Hamilton" engine, illus- tration 32 diagrams, definition 84 double-ported Corliss, illustra- tion 29 ellipse, definition 84 ENGINE, repair 393 using highly superheated steam 419 friction in engines 301 GEAR ADJUSTMENTS, Ames una- flow engines, table showing effects 187 effects on detaching Corliss- valve engines, table 170-171 Allis-Chalme.rs heavy duty Corliss engine, illustration. . 158 Ames four-valve non-releasing Corliss engine, illustration. . 150 "Valve Gears," C. H. Tessenden, on valve diagrams 84 VALVE, governor-operated cut-off. ... 28 gridiron, illustration 28 HAND-adjustable cut-off 28 -operated, engine with, illus- tration 4 inspection 374 LAP, definition 94 effects of changing, table 96 LEAKAGE, rejection losses caused by 296 revealed by expansion line. ... 66 single valve engine, test for . . . 389 maximum pressures and super- heats for different types, table 421 MECHANISM, releasing or detach- ing, definition 30 variable-cut-off, engine equip- ped with, illustration 36 Meyer riding-cut-off, illustra- tion 28 multiported slide, illustration. . . 27 operating mechanism, Mclntosh and Seymour engine, illus- tration 92 OPERATION, indirect-measure- ment method of ascertain- ing 108 Ridgway four-valve engine, illustration 148 PISTON SLIDE, advantages and disadvantages 88 INDEX 513 PAGE VALVE, PISTON SLIDE comparison to D-valve 27 POPPET, see also Poppet valves 146-191 single-seated admission, illus- tration 31 positively-operated poppet ad- mission, illustration 31 SETTING, Ball Corliss engines . . . . 173 Chuse condensing uniflow engine 188 compound engine 280 Corliss and Poppet valves. 146-191 defects, remedies 143-144 double-eccentric detaching Corliss- valve engines 172 " Fleming-Harrisburg " four- valve engine 175-178 Lentz poppet-valve engines 188190 measuring rod for 126 methods of 107 new engine 112 old engine 113 operations, indicator used 142 Ridgway four-valve engine... 178 selected equal leads, example, illustrations 119 shaft-governed engine 114 single-eccentric detaching- Corliss-valve engine 163-169 templets used for 129 unequal leads 130 Vilter poppet-valve engine. . . . 190 with trammel gage 125 without removing chest covers, example 125 simple automatic, engine with, illustration 4 single-ported Corliss, illustration 28 SLIDE, see also Slide valve 84-144 flat type 26 piston type 26 stem adjustment, illustration 111 TEMPLET, laying off 127 length 128 TRAVEL with eccentric motion, illustration 98 relation to eccentricity 99 VARiABLE-cut-pff engine, definition. . 37 speed engine, definition 216 Velocity diagram, standard crank and scotch-yoke mechanisms... 102 Vertical steam engine, definition 20 VILTER MANUFACTURING COMPANY, Corliss-valve trip gear, illus- tration 156 poppet-valve engine, illustra- tion 160 Tolle governor, illustration 209 Watt governor number two, illustration 214 Vilter poppet-valve engine, valve setting directions 190 Viscosimeter, illustration 454 VISCOSITY OF liquid, definition . . 450 oil, variation with temperature change 450 Voltmeter, use in determining output of generator 354 W WAKEMAN, W. H., in "Power" on engine safety devices .... 200 PAGE WATER BRAKE, horse power absorbed by. 352 definition and operation 352 principle, illustration 352 WATER in cylinder, knocks caused by 410 RATE, approximate calculation by means of indicator cards . 364 calculation on basis of indi- cated horse power, formula . 363 determination by boiler-feed method 361 STEAM ENGINE, determination by steam condenser. . . . 357 measure of economy 308 tandem-compound engine, equipment for determining. 366 TEST, apparatus, illustration.. 358 data sheet 362 purpose 342 simple engine 360 wet steam weight expressed in terms of dry steam weight 336 American Society of Mechanical Engineers' specifications 365 theoretical, computation based on ideal Rankine cycle, for- mula 307 rheostat, explanation, illustra- tion 357 Watt, James, inventor of governor. . . 193 Wattmeter, direct-current, load-put- put of generator determined with 355 WATT'S governor, illustration 193 high-speed loaded governor, gen- eral arrangement, illustra- tion 214 indicator, operation 41 Wear, definition 447 WEIGHT adjustment, shaft-governor operation, effects 241 -LOADED GOVERNOR, advantages over simple pendulum gov- ernor 207 comparison with sp r i n g - loaded 209 Weiss, W. R., hydrostatic lubricator filled by hand oil pump, illustration 482 Wheel, reducing, use of 48 Wiley, John and Sons, engine per- formance tables 311-317 Willis planimeter, illustration. '. 75 WIPER CUP, eccentrics and crosshead pins oiled by 473 method of using in oiling cross- head pin, illustration 472 WoOLF-compound engine, definition, illustration 267 -tandem compound engine, tem- peratures in various parts, illustration 263 WORK, net, steam upon piston 11 per double stroke by any engine, formula 13 total, done by steam 8 Wrist-pin bearing, heating 403 UNIVERSITY OF CALIFORNIA LIBRARY This book is DUE on the last date stamped below. Fine schedule: 25 cents on first day overdue 50 cents on fourth day overdue day overdue. 1 6 1948 ' MAY 349 *' NOV 4 - 1349 W/\R 15195 APR V 1B50 MAY 2 5 1950' "' M95^ GCT28 1950 _ OCT QCT * 1950 LD 21-100m-12,'46(A2012si6)4120 DEC 1 1 1S5C I 1 1 19F1 /DEC 29 1951 /i N 191952 NOV 7 1952 27 1953 N; 195 YC 33283 Engineering Library UNIVERSITY OF CALIFORNIA LIBRARY