IRLF B 3 RAILWAY SIGNALING A COMPREHENSIVE TREATISE ON MODERN METHODS OF RAILWAY SIGNALING, COV- ERING PRINCIPLES OF OPERATION AND TYPES OF APPARATUS Written by a Staff of Expert Signal Engineers Published by THE ELECTRIC JOURNAL 42 #4 Sixth Avenue Pittsburg, Pa. 1908 Copyright, 1908, by THE ELECTRIC JOURNAL Preface The lack of any adequate literature on the subject of Railway Signaling was called to the attention of the editors of THE ELECTRIC JOURNAL about two years ago, when an attempt .was made to secure some information on the subject. On looking over such material as was available it was found that there were no publications giving a logical treatment of the subject in the present state of the art. It was, therefore, thought quite worth while to undertake the publication of a comprehensive series of articles along this line. An outline, cover- ing the subject, was prepared and permission was finally obtained from the management of The Union Switch & Signal Company to have a number of their engineers prepare a series of articles for the JOURNAL. In this way it has been possible to obtain at first hand the latest and most authoritative information from men who are making a life study of the subjects which they treat and who are closely in touch with the latest developments in signaling. In describing the various principles of operation and types of apparatus, many of which appear very complicated, especially in installations of large size, the effort has been to make the reading pages and illustrations easily understood by the average reader. In many cases special il- lustrations have been prepared to show the operation of apparatus in principal rather than in detail. It is believed that the following pages will prove of much value to all who are interested in railway work. The following men, engineers of The Union Switch & Signal Company, are entitled to much credit for the painstaking manner in which they have handled their particular subjects: T. George Will- son, Interlocking Engineer; W. H. Cadwallader, Signal Engineer; John D. Taylor, Assistant Electrical Engineer; T. H. Patenall, Sig- nal Engineer; W. E. Foster, Engineering Assistant to the General Manager; J. B. Struble, Assistant Electrical Engineer. Pittsburg, Pa., June, 1908. 256806 Reprinted from a series of articles on RAILWAY SIGNALING Published during the year 1907 in I|p Elertrtr Journal A monthly magazine dealing with subjects of interest to the engineering fraternity in gen- eral, and to those in the elec- trical field in particular. Its staff of contributors consists almost entirely of engineers engaged in active engineering work :: :: :: :: :: :: :: TABLE OF CONTENTS CHAPTER I MECHANICAL INTERLOCKING 7-18 Types of Machines Method of Signaling a Plan of Tracks Form of Signals Details of Construction. CHAPTER II. .ELECTRO- PNEUMATIC INTERLOCKING. . 19-37 General Principles Principal Items The Power Plant The Interlocking Machine The Operating Tower Pneumatic and Electric Connections Switches, Locks, Signals Auxiliary Appliances. CHAPTER III ELECTRIC INTERLOCKING 38-52 Development of Electric Interlocking Switch and Lock Mechanism Safety Controller for Switches. CHAPTER IV. THE ELECTRIC TRAIN STAFF SYSTEM. 53-71 Development Application of Train Staff System Principal Advantages of the Electric Train Staff System Absolute Staffs and Staff Instruments Per- missive Feature Control of Signals Switch Locking Siding and Junction Instruments Pusher Engine Attachments. CHAPTER V AUTOMATIC BLOCK SIGNALING. . . . 72-80 Definitions and Classifications Early Block Systems Automatic Block Signals Length of Blocks Sema- phores on Separate Posts Semaphores on Same Posts -Three Position Signals Overlap Systems Construction. CHAPTER VI. .AUTOMATIC BLOCK SIGNALING DIRECT CURRENT 81-87 Systems of Circuits Relays Operating Mechanism Cost. CHAPTER VII . .AUTOMATIC BLOCK SIGNALING- ALTERNATING CURRENT 88-95 General Signal-Rail System Application of the Single-Rail System Signaling on Steam Roads. CHAPTER VIII. .AUTOMATIC BLOCK SIGNALING- ALTERNATING CURRENT 96-100 Double-Rail Return System Direct-Current Train Propulsion Alternating-Current Train Propulsion. CHAPTER IX. THE LANGUAGE OF FIXED SIGNALS.. 101-108 CHAPTER I MECHANICAL INTERLOCKING AN interlocking plant consists of a group of levers concen- trated at a central point for operating certain switches and signals, and so arranged as to interlock such levers and make it impossible to give clear signals for conflicting routes. The advantages derived therefrom are safety, facility of operation and saving in cost of manual labor employed. It is the purpose of this article to give, as briefly as possible, a general outline of what is accomplished by interlocking, the manner in which the work is done, and the -construction of a particular type of machine. TYPES OF MACHINES As has been intimated, various types are in use, and they may be divided into classes as follows: Mechanical, hydro-pneumatic, electro-pneumatic, pneumatic, and electric. Each style of machine is known by the kind of power utilized to perform the various functions for which it was designed, and as all were designed for the purpose of doing a certain kin'd of work, a description of the original (mechanical) machine, will give not only the method of operation peculiar to itself, but also a general idea of the principle of interlocking as used in all machines. An interlocking machine may be small in size, that is, may have but few levers, sufficient to properly protect a single track grade crossing ; or it may be to take care of a crossover between the tracks of a double track road; or to protect a junction point where two single track roads converge. Or, on the other hand, the machine may be a large one, with many levers, sufficient to properly handle a grade crossing where several roads cross other roads, and per- haps having interchange tracks; or, it may be for handling a large classification yard, a large passenger terminal, or a combination of any of the above. Therefore, the size of machine depends entirely upon the arrangement of tracks at the point to be protected. METHOD OF SIGNALING A PLAN OF TRACKS When it is desired to install an interlocking plant, the first thing is to have a plan of tracks, which is then signalled up, that is, all 8 ^RAILWAY SIGNALING the switches to be operated are noted ; the derails, signals, tower, and run of connections are located; the size of machine and func- tions of each lever are determined; and a diagram of the leadout made, as illustrated by Fig. i. From the signalled plan, a locking RAILWAY SIGNALING 9 sheet is then made, that is, the proper interlocking to be done be- tween levers is determined, as illustrated by the locking sheet in Fig. 5. From the locking sheet, a dog sheet is made, this being a diagram which shows the arrangement of the interlocking parts as they are to be placed in the machine. This is illustrated by the dog sheet in Fig. 5. The plan, as shown on Fig. I, is a typical layout of tracks, showing a, grade crossing protected by derails, and a siding connect- ed with one of the main tracks by a crossover. At each switch or derail a signal is located to govern movements over the point where the tracks intersect. The numbers shown at each switch, derail, sig- nal, etc., mean that that particular switch, derail, signal, etc., is to be operated by a lever in the machine having the same number. That is, lever I will control signal i, lever p derail p, etc. By referring to the scheme, it will be found that eighteen levers will be required to operate this plant, but as mechanical machines are built up of four lever sections, a machine will be used having eighteen working levers and two spare spaces, the latter being available for levers in case it be necessary to make an addition to the plant at some future time. When no movements are being made over the crossing, all de- rails are open, the switch on the siding set for the stub end, and all signals are in the horizontal (danger; stop) position, and when in such position, they are known as being normal and the levers in the machine are normal also. When a derail is closed, a switch thrown, or a signal cleared, they are then known as being in the reverse posi- tion, and the lever by which the operation is performed is then also known as being in the reverse position. When a movement is desired over any one of the tracks, it is necessary to set all switches and derails in the right position for such movement, then lock them in such position, after which the signal governing traffic over that particular track may be cleared. Under the head of "Manipulation" in Fig. I, is a table showing just what levers are to be reversed to allow movements over the various routes. For example, in order to allow a train to go from A to D, levers 13-11-9-8-2 and i must be reversed in the order named, and the last lever reversed locks all of the preceding ones. The closing of either derail in the route will lock the derails of conflicting routes normal, they in turn will hold the signals normal. Therefore it will be seen that where two or more routes conflict, the signals of but one can be cleared. io RAILWAY SIGNALING SWITCHES AND DERAILS A switch is used to deflect traffic from one track to another. A derail is in reality a switch, and is also used for deflecting traffic, but not from one track to another, for as its name implies, its purpose is to derail, or deflect from the rails onto the ties, or ground, or into some short track or obstruction, in order to stop traffic if the signal be disregarded. Nos. 9-12-13-14 in Fig. I represent derails. They operate in such a way that if, for any reason, an engineer attempts to take his train over a crossing when the signal governing the movement is normal (stop) his train will be derailed, and as the derails are located 300 feet from the crossing, the train would not reach the tracks of the other road, (which may be occupied by an- other train), even though it may have been moving at high speed before leaving the rails. Although derails will accomplish this, it is not expected or desired that this should occur, and it very rarely happens for the reason that, if an engineer knows his train will be derailed if he attempts to pass a signal at danger, he will be very careful to stop at the signal. THE DETECTOR BAR At each switch is a bar which lies against the outside of the rail, and is so adjusted that the top of the bar, when in the normal posi- tion, is three-eights of an inch below the top of the rail. This is what is known as a detector bar, and works in conjunction with the lock on a switch, so that when a movement is being made over a switch, the wheels will prevent the bar from being raised, thus pre- venting the leverman from unlocking the switch when a train is passing over it. Before a train movement can be made, all switches, after having been set in the proper position, must be locked. This is done by a bolt or dog being thrust through a notch or hole in a bar connected to the points of the switch. If for any reason the switch points do not go to the proper place when the lever by which the switch is operated is thrown, it is obvious that the bolt or dog cannot be thrust through the bar and the switch cannot be locked, thus indicating to the leverman that the switch is not in proper posi- tion. METHOD OF LOCKING SWITCHES AND DERAILS A switch may be moved and also locked by a single lever. When this is done, a mechanism called a switch and lock movement RAILWAY SIGNALING II 12 RAILWAY SIGNALING is used, it being located opposite the switch. When actuated by a lever in the machine, the first part of the stroke unlocks the switch, the mid-stroke throws it, and the last part of the stroke locks it. Thus the switch is locked either normal or reversed, depending upon the position of the lever. When such a device is used, on main tracks, the signals governing movements over such tracks are also made to lock the switch by means of what is called a bolt lock, which makes it impossible for a signal to be cleared if for any reason the switch is not in the proper position. Fig. 2 illustrates a switch and lock movement with bolt lock applied to a derail. While some roads use switch and lock movements on main tracks, most roads use them only for the siding end of cross-overs, or for derails on unimportant sidings, preferring the use of a sepa- rate lever to operate the locks on main line switches. When a sepa- rate lever is used, the lock is called a lacing point lock, getting its name from the fact that originally a switch was locked only when traffic was to be given the right of way in the direction facing the switch point, but present practice is to lock all switches whether traffic be facing the points or trailing. Some roads also use a bolt lock, operated by the signal, as an additional precaution, even when a switch is locked by a facing point lock. Fig. 3 shows a facing point lock with bolt lock applied to a switch. FORM OF SIGNALS Referring again to Fig. i, it will be noticed that all signals lo- cated on main tracks are shown high and the two located on siding are low, it being the general practice to use high signals for main tracks, in the direction of ordinary traffic, and low or dwarf signals for movements on or out of sidings or against traffic on main tracks. A high signal with square end blade is called a home signal ; with the end of blade notched, it is known as a distant signal. A distant bla'de horizontal means caution, that the home signal in advance of it may be at danger. When a distant blade is inclined, it means clear, and indicates that the home signal is clear also. Therefore, if an engineer approaches a distant signal and finds it at clear, he may proceed at high speed, knowing that the main line route has been set up and ready for him to proceed without a stop ; but if he finds the distant at caution, he must approach the home signal ex- pecting to find it at danger. A dwarf signal with the blade horizontal indicates danger, stop ; with the blade inclined, indicates clear, proceed slowly, as move- RAILWAY SIGNALING 14 ; RAILWAY SIGNALING ments on or out of a siding or against traffic on main tracks neces- sarily should be made cautiously. DETAILS OF CONSTRUCTION The dotted lines in Fig. I leading from the tower along the tracks, indicate the location of the pipe and wire connections from the machine to the various switches, signals, etc., these connections being shown in detail under the heading Leadout. In the leadout each full line represents a single line of pipe, and each dotted line represents two wires, each line having a number corresponding to its operating lever. Pipe lines are supported by roller carriers on wood, iron or concrete foundations, placed every seven feet, and when such lines are over fifty feet long, a compensator (to take care of expansion and contraction due to changes in temperature) is used. Wire lines are supported in the same manner as pipe, except- that the carriers are placed every twenty-one feet, and compensation is usually taken care of by adjusting screws located in the tower. The letters ZZ on the leadout shown in Fig. i represent the point on Fig. 4, where the vertical cranks and wheels are located, and through which connection is made to the machine. In the ma- jority of cases machines are located so as to be operated from the second floor of a tower, because it is desirable that a lever man shall have a good view of the tracks and signals. Some machines are built, however, to be operated from the ground floor. All machines have the levers numbered consecutively, begin- ning with the left-hand end facing the levers. Mechanical machines may be 'divided into two classes, those having lever locking and those having latch (or preliminary) locking. The levers of all ma- chines are provided with latches, the purpose of which is to keep the levers in the normal or reverse position. In a machine having lever locking, the latch is used for no other purpose than that stated above, the interlocking parts being actuated only by changing the position of the lever itself, which necessarily brings great strain on the lock- ing parts, when an attempt be made to throw a lever when it is locked. Therefore, for such a machine, the locking parts must be made large and strong. In a machine having latch locking, the latch is used not only for holding the lever in the normal or reverse posi- tion, but also for actuating the locking parts. That is, these parts are connected to and operated by the latch, instead of the lever, thus permitting lighter construction. As the raising of the latch is a preliminary step to the throwing of a lever, the locking will there- RAILWAY SIGNALING 15 fore be accomplished before the lever moves from its position. This will be more readily understood by referring to Fig. 4, which shows a machine with the levers in the normal position. The machine il- lustrated is known as the Saxby & Farmer, a type generally used, not only because of the preliminary locking feature, but also because of the design of the locking parts. The parts of this machine by FIG. 4 END VIEW OF SAXBY AND FARMER INTERLOCKING MACHINE WITH CONNECTIONS AS LOCATED IN TOWER which the interlocking between levers is accomplished, are known as the latch, rocking link, shaft, driver, bar, dogs and cross locks. See Fig. 4. When a latch is raised, a bar is moved a certain dis- tance ; to this bar dogs are riveted, which in turn drive the cross locks against other dogs which are riveted to bars operated by other 1 6 RAILWAY SIGNALING latches. With a lever in its normal position, the raising of the latch gives half of the necessary stroke to the bar, the remainder of which is given by dropping the latch after the lever has been reversed. As the same is true when throwing a lever from the reverse to the nor- mal position, therefore, no matter in which position a lever stands, when the operation of moving it takes place, the first thing to happen is the raising of the latch, which accomplishes all of the locking, then occurs the movement of the lever, during which time no change in the locking takes place, last, the dropping of the latch which re- leases those levers which are to be thrown next. Fig. 5 shows a locking and dog sheet, the former showing just what locking is desired, the latter showing the arrangement o F A i -| f ~ I 2 rr* n ^ \- | r 1 1 1 r J | L 1 p 00 => S JO 1 1 I J Dl Z] c ^ Dl 1 J- I \ \ I - U B. R FIG. IO PLAN AND ELEVATION OF SIMPLE SWITCH up" the plant. The branch connections are also provided with stop cocks so that the air can be shut off at any particular switch or sig- nal at any time without interfering with any of the others. The pipes are usually encased in wooden conduits and placed under RAILWAY SIGNALING 29 ground, those crossing tracks being placed deep enough to prevent any disturbance by section men when raising or lowering tracks or tamping ties. The wires from the machine for controlling the various func- tions are usually carried in yellow pine conduit or "trunking" to protect them from mechanical injury. This conduit is usually sup- ported on oak stakes or foundations about six inches above the ground, although it is sometimes buried so as to come level with the top of the ground. The former method is preferable to the latter MAGNETS FIG. II SECTIONAL VIEW OF CYLINDER AND VALVE being much easier of access and more apt to be free from moisture. The insulated wires between the machine and the various functions are usually made up in five conductor cables, as five wires are re- quired for the control of each switch or crossover and the signals are usually so located that a cable can be used to advantage for two of them. The conductors of these cables are made of different col- ors so that the five conductors can be easily distinguished. A per- centage of spare wires is usually provided for use in case of breaks or grounds. Terminal boxes are installed at frequent intervals 30 RAILWAY SIGNALING which form convenient places for conducting tests and for making joints, as no splices are allowed in the conduits. SWITCHES LOCKS SIGNALS The switches are operated by switch and lock movements act- uated from air cylinders of suitable size. Both the cylinders and movements are rigidly attached to iron plates which in turn are bolted to the switch ties of the switch to be operated. Working in conjunction with each switch is a "detector" bar, the operation and function of which was described in the chapter on mechanical interlocking. P'ig. 10 shows such a movement and detector ap- plied to a single switch. The switch and lock movement has a total stroke of eight inches. The first two inches of its movement unlocks the switch and throws the detector bar, the next four inches Indication Ma Switch Valve Magnets Indication Box Indication Circuit Contacts conn oil in j_ switch valve Switch lever Normal Indicatioji t Reverse Indicatiori Common Return FIG. 12 CONNECTIONS FOR A SINGLE SWITCH CIRCUIT shifts the switch from one position to the other and the last two inches locks it in its new position. An electric switch valve which controls the admission of air to, or the discharge of air from, the cylinder is attached to each switch cylinder. In one of the chambers of the switch valve, and con- stantly under pressure is a slide valve mounted in a manner similar to that of a steam engine. The valve lies between the ends of two small plungers extending from the pistons of two single acting cyl- inders which are each provided with a separate magnet and pin valve to control their movement. The air for these pin valves is forced through a port drilled from their chamber to that of the slide valve. In practice one or the other of the pin valve magnets is energized by current from the tower at all times. Consequently the pressure is always against one or the other of the pistons used RAILWAY SIGNALING 31 for shifting the slide valve. A pneumatic bolt lock is applied to the slide valve and it is absolutely necessary that this be withdrawn be- fore the valve can be operated. This bolt lock consists of a bal- anced piston the plunger of which is normally forced into a recess in the slide valve by the action of a coil spring. The air pressure is normally confined to the cylinder both above and below the piston, the former by a pin valve controlled by an electro-magnet. When the magnet is energized, the air is exhausted from above the piston and the pressure below it raises it, compresses the coil spring and lifts the bolt lock from the slide valve. When the magnet is again de-energized further escape of air from above the piston is prevent- ed and the coil spring again forces the bolt lock into the slide valve. A sectional view of a cylinder and valve is shown in Fig. n. Cylin- FIG. 13 CONNECTIONS FOR CROSS-OVER CIRCUIT ders for the operation of single switches are usually five or six inches in diameter, and for the operation of slip switches and mov- able point frogs, seven and one-half inches. One end of a double slip and the movable frog are generally operated from the same cyl- inder, the cylinder being placed at the frog points, working them through two switch and lock movements coupled in tandem, and by mechanical connections working the slip points through a single switch and lock movement at the slip end. When hooked up in this manner, the switch indication box is placed on the movement far- thest away from the cylinder. In addition to the five wires mentioned previously as being re- quired for the control of a switch, there is a common return wire for the entire interlocking. The wires are known by the function they control, viz. a normal, a reverse and a lock control ; a normal and a reverse indication. The circuits for a single switch are shown in Fig. 12. By referring to this diagram it may be seen that the first RAILWAY SIGNALING movement of the lever in the machine energizes the centre or "lock" magnet on the switch valve before the circuit is broken on the re- verse magnet, and by so doing withdraws the bolt lock from the slide valve. Continuing this movement energizes the reverse shifting magnet, and by unseating a pin valve admits the air to the reverse auxiliary cylinder, at the same time de-energizing the normal mag- net and releasing the aiir in the normal auxiliary cylinder, thereby moving the slide valve to the opposite side by means of the piston Roller Connectors or Terminal B|>ard in Interlocking MachineAj! ng Arranged on Combination to Open Normal at vetr stirt of lever stroke and close ^ re rersed at very end of stroke FIG. 14 CONNECTIONS FOR A SINGLE SWITCH, USING TRACK CIR- CUIT IN LIEU OF DETECTOR BAR and piston rod. The shifting of the slide valve in turn transfers the air pressure from one end of the cylinder to the other and throws the switch, through the medium of the switch and lock movement. When a switch is normal, as shown at Fig. 12, the first move- ment of the lever to the reverse position breaks the normal indication magnet control on the machine and drops the armature and latch. The last movement of the switch closes the reverse indication con- trol circuit through the indication box contact springs, showing that RAILWAY SIGNALING 33 the switch has been shifted and locked in its new position, lifts the armature and latch, and releases the segment which allows the lever to be placed in the extreme reverse position and the latch dropped. The placing of the lever in the extreme reverse position also releases any mechanical locking that may depend on that particular lever. The moving of a switch in the opposite direction reverses the order of these operations. When two or more switches are operated from one lever by two independent cylinders as for example a crossover the indication circuit is carried through indication boxes on each movement in series as shown in Fig. 13. From the above description, it is apparent that the objections offered to the use of switch and lock movements in mechanical work, viz: the small stroke available for locking the switch, the danger of forcing the lever completely over through lost motion in the connections, and that a switch may not correspond to the posi- tion of its lever due to broken connections, do not hold good in the electro-pneumatic in- terlocking system, as a positive indication must be received in the tower that the switch has make its complete stroke and has been locked, before its lever can be put to the full normal or reverse position. In many cases "electric detector" circuits are installed in lieu of the mechanical de- tector bars, in which case, a short section of track is insulated ahead of the switch, and the indication wire passed through a relay contact, the relay being actuated by a battery connected to the rails of the track. Where "detector circuits" are used the switch lever is equipped with a latch circuit controller similar to the one applied to signal levers, which closes a circuit on the indication magnet through the relay contact. This is illustrated in Fig. 14. From a reference to this figure it is ob- vious that both the normal and reverse indication magnets are nor- mally on open circuit, and either one is energized by the first move- ment of the lever latch providing the "track section" is unoccupied. High signals are of iron pipe construction. The spectacle cast- ing carrying the semaphore arm and the colored glass for night indi- cation are so counterweighed as to always gravitate to the "danger" or "stop" position. Hence it is only necessary to use a single stroke FIG. 15 SIGNAL MOVE- MENT AND CIRCUIT BREAKER 34 RAILWAY SIGNALING cylinder to work against gravity for the operation of signals, and in- dicate to the operator in the tower, that the signal is in the "stop" position. Signal cylinders are ordinarily three inches in diameter, and are fitted with an electro-magnet and valve for the controlling of the admission and discharge of air. At the side of each cylinder is clamped a circuit breaker so arranged that the circuit is made only when the signal is at "danger." A signal movement and circuit breaker are shown in Fig. 15. As previously stated, each signal lever in the machine is equip- ped with a latch circuit controller, the object of which is to close a contact as soon as the latch is raised, thereby completing a circuit Circuit Closer FIG. l6 DIAGRAM OF SIGNAL CIRCUITS through the circuit controller on the signal cylinder and the lock magnet on the machine, and by so doing lift the armature and latch, release the segment and allow the lever to be moved to the right or left, depending on the mechanical locking and signal to be operated. The movement of the lever closes the circuit controlling the magnet on the signal cylinder through one of the bronze bands on the roller. The magnet in turn opens the valve and allows the air to enter the cylinder and clear the signal. A diagram of signal circuits is shown in Fig. 1 6. This diagram shows that when more than one signal is controlled from the same lever the lock wire is carried through cir- cuit breakers on each of the signals so that it is absolutely necessary for all of them to be at "danger" before the lock magnet can be energized and the lever restored to its normal position. Low or dwarf signals used between tracks are operated by means of direct acting cylinders, which act against strong coil springs so arranged as to be compressed when air is applied to the cylinders, in clearing the signals and to force the signals back to RAILWAY SIGNALING 35 ''danger" when the air pressure is removed. Dwarf cylinders differ from those of high signals in that they are movable and their pistons are stationary. Their piston rods are hollow and serve as ports for the admission and discharge of air to and from the cylinder. The cylinder is directly connected to the semaphore shaft by means of a rod enclosed in the post. Fig. 17 shows a sectional view of a dwarf signal. At the side of each dwarf signal cylinder but insulated therefrom is a brass plate which closes a circuit when the signal is in the stop position by resting against contact springs fastened to AIR DUCT ELEVATION SECTIONAL VIEW FIG. 17 DWARF SEMAPHORE SIGNAL the base of the signal. This circuit controller performs the same functions as the one previously described in connection with the high signal. In mechanical work, it is not considered good or safe practice to operate more than one signal from one lever although two or more can be so operated through what is known as a "selector." It is sufficient here to say that selectors in mechanical work are very unsatisfactory and unreliable. In electro-pneumatic interlocking RAILWAY SIGNALING this selection is done electrically in the tower through the "combination" on the hard rubber roller of the machine levers. Opposing signals for the same track, or signals that govern traffic up to the same track from converging tracks, may be worked with perfect safety from the same lever in the electro-pneumatic interlocking sys- tem. As a means of illustrating how this select- ing is accomplished, the layout shown in Fig. 18 is assumed. Previous mention was made that the normal position of signal levers is in the cen- tral position and that they are capable of being- moved to the right or left. By reference to Fig. 1 6 it may be seen how opposing signals for the same track are operated from a right or left hand movement of the lever. By referring to Fig. 1 8 it may be seen that but one train can move out of the yard to the main track at any one time and the signals governing movements to the main track are all operated from the same lever, shown as No. 4. Here is where the "com- bination" on the electro-pneumatic machine is used to advantage for, by it, current is supplied to the desired signal. The "combination" for the above layout is shown in Fig. 19. If, for ex- ample, it is desired to clear the signal on track 5, it is first necessary to reverse switches 5 and ii, so that the track will be in shape for the train to proceed over it. Signal lever 4 is then moved to the left, which will energize magnet on signal 4Le, through closed circuit breakers on levers 5, /, p, and 11. A study of the layout and combina- tion will show that any one of the signals can be given through the contacts on the rollers of the switch levers. AUXILIARY APPLIANCES The control of annunciators is accomplished by means of a section of bonded and insulated track at the distance from the tower at which it is desired to announce an approaching train. At one RAILWAY SIGNALING 37 end of this insulated section is located the battery and at the other a relay. The annunciator magnet control is carried through a con- tact on this relay. As soon as a train strikes this bonded section the relay is shunted. This in turn opens the annunciator control and causes the miniature signal to assume the "danger position" and the J3 tn 4L l 14 f 1.1 *% 4L 1L: rt *i 2L Battery FIG. 19 "COMBINATION" FOR TRACK LAYOUT SHOWN IN FIG. 13 annunciator in so moving closes a circuit on a single stroke bell, thus indicating to the towerman that a train is approaching. Track sections are also installed for automatically setting sig- nals to the "danger" or "stop" position, after a train has passed them and preventing them from again being cleared as long as the train is on the track section, but this feature will be dealt with in a later article. CHAPTER III ELECTRIC INTERLOCKING A VERY long stride in the direction of improved interlocking apparatus was made when electricity came into use as the motive power for operating the switches and signals. That the use of electricity for the purpose supplied a want, is proved by the rapidity with which electric interlocking has assumed a place second to none in the estimation of the railroad world. Electric interlocking was first introduced commercially in 1900. Since that time growth in the number of installations has been very rapid ; the number increasing in a ratio such that the number of installations in any year exceeds that of tjie two preceding years combined. The superiority of electricity as a motive power in interlocking work, as well as for a great many other purposes, is due to the facility with which it can be stored and retained for indefinite pe- riods of time with very small loss from leakage, and to the small loss incurred in transporting it from the point where it is generated or stored, to the point where it is to be used. The conversion of electrical into mechanical energy can be effected with a high degree of efficiency the question of efficiency of conversion, being, how- ever, of less importance in interlocking work than the high degree of insulation that is possible to attain. The circuits of an inter- locking plant can easily be so well insulated that the loss on account of leakage is practically nothing, and faults in insulation can very easily be detected and removed; in fact, immediate attention is called to faults of a serious nature in electric circuits, by their in- terference with the proper operation of the plant. When a switch lever in a mechanical interlocking plant is moved from normal to reverse and latched, the locking between it and the signal lever, controlling the signal governing movements over the switch reversed, is immediately released. When the lever is reversed and latched, it is assumed that the switch has followed the movement of the lever and is also reversed and locked. The possibility of the pipe line breaking, or buckling enough to allow the lever to be put into full reversed position with the switch only partly reversed, is not considered. But when electric power is used RAILWAY SIGNALING 39 for operating the switches (and the same may be said of other forms of power), the movement of the lever merely turns on the power and it is not safe to assume that the switch necessarily fol- lows the movement of the lever and takes up a position correspond- ing. The circuit may be open at any one of a number of places so that current will not reach the motor at all; or the movement of the switch may be obstructed so that the motor is unable to move it. In order that a failure of the switch to respond to the movement of its controlling lever, may not result in dangerous consequences, the lever movement is divided into two parts : the preliminary movement for closing the operating circuit of the motor and the final movement for releasing the locking of other levers. The lever is stopped at the end of the preliminary move- ment by a latch known as the indication latch, because its disen- gagement from the lever serves as an indication that the switch R P ' n P BI = FIG. 20 has been moved home and locked. The latch is lifted and the lever freed to make its final movement at the proper time by an electro- magnet or motor known as the indication magnet or the indication motor. The necessity for an indication or automatic release of the locking when power of any kind is used for operating switches, was recognized from the first, but the problem still confronting the signal engineer was to find a suitable source of current for energiz- ing the indication magnet. The first thought that would occur to one trying to solve the problem, would be to employ the main source of current used in operating the plant, for energizing the indication magnet, and have the switch mechanism operate a cir- cuit controller to close the indication circuit at the proper time. Such a method is shown diagrammatically in Fig. 20, divested of most of the apparatus and circuit controllers not directly concerned in the formation of the indication circuits. An indication circuit is 40 RAILWAY SIGNALING closed in either extreme position of the track switch, by the circuit closer C actuated by the rod H which is connected to some point of the switch movement, preferably to the lock bar. . It can easily be seen by a mere inspection of the diagram, that an accidental contact of the wire Q with the common return wire, such as could easily happen through faulty insulation, and as indicated by the dotted line X, would cause an indication to be given irrespective of the position of the controller C and, therefore, irrespective of the posi- tion of the track switch. An actual contact of the two wires is not required to produce this result. If both are grounded the effect is the same. No matter how good the insulation may be or how care- fully the work of construction and installation may be done, there is always the possibility that the insulation may break down. An indication given by a current drawn from the main source of supply FIG. 21 which operates the plant, is, therefore, little better than no indica- tion at all. It will be noticed that this method of operation and indication requires four wires, two operating and two indication, extending between the lever and the switch, in addition to a wire which is common to all switches lying in the same general direction from the cabin. DEVELOPMENT OF ELECTRIC INTERLOCKING The first real step towards developing a practical system of electric interlocking, was made when a means was discovered for utilizing a current generated by the switch operating motor itself, for actuating the indication magnet. This method is illustrated by Fig. 21 in which the parts are shown in the proper connection for generating the indication current. During the switch movement supposed to be just completed, the controller CC' was in the upper position when current flowed through the armature and fields in the direction of the arrow j, and the counter electro-motive force had RAILWAY SIGNALING 41 the direction indicated by the arrow 2. At the instant the switch movement is completed, the controller CC is shifted to the position shown, which puts the motor and indication magnet on a circuit independent of the battery. The electro-motive force induced in the armature, which is still rotating due to the momentum previously acquired, drives a current, through the indication magnet in the di- rection of arrows 2. It is obvious that the only effect that a con- nection between the wire R and the common wire could have, would be to prevent current reaching the indication magnet ; thus the error, if any, would be on the side of safety. If the wire R should by accident become connected to N, current would flow through the indication magnet, but harm from this is prevented by putting an- other magnet with its coils in circuit with the wire N, directly un- der the indication magnet, so that the indication armature rests nor- mally on its poles. So long then as current is flowing in the wire N, the indication magnet will be unable to lift the armature, no matter how strongly it may be energized. If the wire N should be broken and another live wire should at the same time become connected with the wire R, a false indication might result ; but this requires the simultaneous happening of two things, either of which alone would be immediately discovered and removed. Interlocking ap- paratus is considered safe when its wrong operation requires such a coincidence. The apparatus shown at 5 is employed for removing the only remaining chance for false indication, not taken care of by the means previously mentioned. It comprises two magnets, one in each ope- rating circuit, acting on a contact lever capable of bearing on a fixed contact on either side. The lever and contacts form a circuit switch, the function of which is to close the proper indication cir- cuit. If the operating circuit is good so that current flows in it, the corresponding indication circuit will be closed, but then current will flow in the safety magnet under the indication magnet and will prevent a premature indication. If the operating circuit happens to be open, the corresponding indication circuit will not be closed, so that it will be impossible for a stray current to reach the indica- tion magnet. It will be noticed that in Fig. 21 only two wires, besides the common wire, are required for the operation and indication of the switch : the operating wire for one movement becomes the indica- tion wire for the next movement. This system, therefore, is not only much safer than that using the main battery for indications, but requires only a little more than half as much wire. 4 2 RAILWAY SIGNALING Fig. 22 shows an entirely different method of obtaining a safe and reliable indication of the movements of the switch. In this the indication current is drawn directly from the main battery, but it is transformed into an alternating current, and an alternating- current induction motor is employed for actuating the indication latch. The transformation of the battery current into an alternating current is effected by means of a transformer and an apparatus for varying the strength of the current in its primary coil. The transformer is located in the cabin and its primary coil is included in the operating circuit. The secondary coil is connected directly to a small induction motor provided with suitable gearing to cause the rotation of the armature to lift the indication latch. The appa- ratus for producing the variations in the current should be located at the switch, so that the circuit closer actuated by the switch mech- anism for closing the indication circuit may be between this appa- FIG. 22 ratus and the transformer. A convenient means for producing the variations in the current is afforded by a collector ring on the arma- ture shaft of the switch operating motor, connected to one segment of the commutator. At the end of the switch movement, after it has been locked, and after the motor has been disengaged from the mechanism by the clutch interposed between the motor and the mechanism for the purpose, the operating wire is switched from the operating brush to the brush bearing on the collector ring. The motor armature will continue to rotate, driven by the current enter- ing by way of the collector ring and passing out by way of the brush connected to the common wire, and as the segment to which the ring is connected alternately approaches and then recedes from the common brush, the current in the circuit including the primary coil of the transformer will rise and fall alternately. The undulatory current thus produced, induces magnetism of a like character in the iron core, which in turn generates an alternating current in the sec- ondary coil. The current from the secondary flows through the RAILWAY SIGNALING 43 coils of the induction motor causing a rapid rotation of the armature which results in lifting the indication latch. It can easily be seen that a connection either accidental or in- tentional of the wire N with any other wire, would cause only a direct current to flow through the primary coil of the transformer, which would have no effect on the secondary except to produce a single impulse at starting of the current and again at stopping. Such impulses have only a barely perceptible effect on the armature of the induction motor, and no effect, whatever, on the "centrifuge" by means of which the rotation of the armature is converted into a di- rect axial thrust. As the induction motor is built to require approxi- mately one hundred alternations per second to make it operative, it is quite apparent that it could not be affected by any succession of impulses that could be produced by accident. The accidental con- tact of the wire N with the wire to another switch which is in the act of indicating, could not result in a false indication, because it is in connection with the operating brush of the motor until the movement is completed, which would hold it at a uniform potential either high or low and would prevent fluctuation. It will be noticed that this system, also, requires only two wires between the operating lever and the switch ; the operating wire for any movement becoming the indication wire for the same movement. During the entire movement in either direction except a small part at the end of the movement, the two wires lead to the operating brush of the motor. Two field coils F and F' are provided, one in each operating wire, for the purpose of reversing the direction of the movement at any point. The field coils are so connected that cur- rents through them from the battery produce opposite magnetizing effects, while the current always flows in the same direction through the armature. A simple means is thus afforded for reversing the direction of rotation of the motor armature, which is effected by merely changing the position of the operating lever and thus con- necting one or the other operating wire to battery. The quality of reversibilty is of considerable importance, for it sometimes happens that the movement of the switch points is obstructed by something that prevents the point coming up solidly against the stock rail. If, in such an event, the switch can be put back to its original position, other routes will be freed that would be locked up if the lever had to remain in its intermediate position until the obstruction is removed. Again, the obstruction may be of such a nature that it may be crushed and might fall out of the way if the pressure of 44 RAILWAY SIGNALING the point were removed. A second attempt would then secure the desired movement. Two field coils cannot be used for reversing the motor with the system shown in Fig. 21, because, as will be seen later, such means for reversal would interfere with the proper performance of the functions of another essential piece of apparatus. Reversibil- ity is secured by attaching the cores of two solenoids to the rod connecting the blades of the controller CC'. By means of these solenoids, one of which is in each operating circuit, the controller CC may be manipulated from the cabin. SWITCH OPERATION BY STRAY CURRENTS There is one other consideration quite as important as the in- dication, which must receive due consideration in the design of an electric interlocking system, and that is, the provision of means for preventing a stray current reaching a switch or signal motor, and M FIG. 23 causing an improper movement of the switch, or a clear indication by the signal when the track ahead may not be in proper condition for a train to pass. An improper movement of a switch, due to a stray current reaching it through faulty insulation, would have practically the same result as a false indication, as it would put the switch in a position not corresponding with the position of the lever; but, if there is any difference, the condition would be more dangerous, as there would not be as much likelihood of its being discovered by the operator. Fig. 23 shows a very effective means for guarding against im- proper movements of switches and signals by stray current, as ap- plied to the system illustrated in Fig. 21. This means comprises a circuit breaker held normally closed by current in the coils of an electro-magnet. The electro-magnet has two coils, one a high resist- ance coil Q continuously in circuit with the main battery, and the other a low resistance coil in the common lead of the indication circuits. If current flows in the coil P in a direction to make its RAILWAY SIGNALING 45 influence additive to that of Q, no effect is produced ; but if it flows in the opposite direction, the magnet will be neutralized and the circuit breaker T, released, thus opening the main lead from the battery and cutting off current from the entire plant. Each indi- cation current passes through the coil P, but in the direction of the arrow 2, in which direction it aids the coil Q in holding the circuit breaker T; but a current from a live wire in contact with the wire R or any of its connections would flow back through the coil P in the direction of the arrow I and would cause the circuit breaker T to open the circuit. It can now be seen why two field coils can- not be used for reversing the switch operating motor, for the use of such coils for the purpose would cause the indication current to flow in the direction of the arrow /, and would open the circuit breaker T at each movement of a switch. It can easily be seen N FIG 24 that the effectiveness of the device as a protection depends on the wire R being unbroken from the point of improper contact, back through the coil P, to common. But this wire was used as indi- cation wire in making the last movement and if it had been broken then the break would have been discovered and repaired. A failure, therefore, requires, practically, the simultaneous happening of two things either of which alone would be discovered and repaired on the first attempt to operate the switch. All apparatus used in con- nection with the operation and indication of the switch and not directly concerned in the operation of the safety device, has been omitted from the diagram. Another form of safety device adapted especially to the system shown in Fig. 22, is illustrated in Fig. 24. This apparatus is located near the switch motor and comprises two solenoids for operating circuit controllers. Only enough of the circuits are shown to illus- trace the principles of its action in preventing improper movements. 46 RAILWAY SIGNALING The ii.-strument also serves to open the circuit and stop the current when the lever movement is completed, and to switch the indication wire from the brush bearing on the collector ring, to the operating brush preparatory to the next movement. The wire R is the one that will be used to lead current to the motor for effecting the next movement of the switch. The preliminary circuit includes the field F', magnet M', lever L ' , and resistance G' . Current in this circuit will energize the magnet A/', causing it to attract the lever L which it will pull up against the contact K. If the current is properly started by a movement of the controlling lever in the cabin, the lever L' will also be drawn back against the contact J ' , thus cutting the resistance G' out of the motor circuit ; but if the current enters the wire R through faulty insulation the lever in the cabin not hav- ing been moved, a current will flow in the circuit including the field F, magnet M, lever L, and the armature, and will result in holding the lever L' away from the contact /. The latter circuit has no extra resistance in it, while the former includes the resistance G. The current through the field F will, therefore, be very much stronger than that through F', and it will determine the polarity of the field magnet, which will be the same as it was in making the last movement. The motor armature will, therefore, rotate idly in the direction it did in making the last movement, and without any effect on the switch mechanism. It may be well to mention here that the motor armature is connected to the mechanism by means of a clutch which permits the motor to be disengaged at the end of each movement, and to run without load while transforming the current for indication. It also runs without load when the safety device becomes operative to prevent an improper movement. The counter electro-motive force of the motor acts as a resistance to limit the current required to operate the safety device to three or four amperes. The circuits, both that improperly charged and the safe- ty circuit, lead to the same brush of the motor. The former in- cludes the resistance G' which, with the maximum resistance in the lines, reduces the current in the field F' to one-fifth that in the field F. It will be noticed that, in this method as in that previously described, the action of the safety device depends on the continuity of a wire. In this case it is the wire which was last used in operat- ing the switch and which must have been good when the last move- ment was made. The two methods are, therefore, equal in the de- gree of jsafety afforded. There is one point of difference that may RAILWAY SIGNALING 47 be worth mentioning. The safety device shown in Fig. 24, when it becomes operative, affects only the switch to which it is connected, while that shown in Fig. 23 throws the whole plant out of service, or as much of it as is connected to one common return. If the cir- cuit breaker T is cut into the common instead of the main positive lead, and one cut-out is provided for each common return, then when one of them is opened by an improper connection, only that part of the plant served by that common return is put out of ser- vice. Obviously, this principle could be extended, so as to cut out only one switch, by using a separate return for each switch instead of a common wire, and by putting a cut-out in each return. FIG. 25 VIEWS OF ELECTRIC INTERLOCKING MACHINE SHOWING END AND FRONT ELEVATION After what has been written in preceding articles descriptive of interlocking apparatus, an extended description of the apparatus used in connection with the all-electric system is unnecessary. A brief description of the more important parts peculiar to the electric system may, however, be of interest. An interlocking machine now in quite extensive use, is shown in Fig. 25. This resembles, in general appearance, the electro-pneu- matic machine already described. The only difference is in the indi- cation apparatus which, for the electric machine, is adapted to the alternating current described in connection with Fig. 22. The indica- tion motor has its armature shaft in a vertical position, to which is 4 8 RAILWAY SIGNALING attached a piece of centrifugal apparatus very similar in construction to the well known form of governor used on the steam engine. The rapid rotation of the armature causes the weights to separate, and through a system of levers, to lift the indication latch and release the lever. This mode of construction makes it necessary to have a very rapid rotation of the indication motor armature to produce the desired effect, and this rotation can be secured only by a rapid succession of alternating impulses in the coils of the motor. A di- ne. 26 AND 27 PLAN AND ELEVATION SHOWING ELECTRIC SWITCH AND LOCK MOVEMENT rect current through these coils has no effect other than to lock the armature against rotation. SWITCH AND LOCK MECHANISM Fig. 26 is a plan and Fig. 27 a side elevation, showing a switch and its operating mechanism. The switch and lock movement is driven by a direct-current motor of about 1.5 hp, designed to be operated at no volts. The shaft of this motor is connected by means of a magnetic clutch to a shaft extension in the same line, working a cam drum, which operates the switch and lock. Intermediate between the magnetic clutch and drum, there is a reduction gearing RAILWAY SIGNALING 49 with a speed ratio of twenty-five to one. It will be noticed that there are two cams on the drum, one of these working the lock rod and detector bar, and the other the switch, connection being made to the detector bar and switch through cranks. The lock is worked direct by a straight bar which slides longitudinally underneath the car.., motion being imparted by means of a lug fitting the cam slot. It will be noticed that in each case the cam slot, for a portion of its travel, moves in a plane at right angles to the shaft, so that while that portion is passing the hub on the driving bar or crank, no movement of the latter takes place; it is only while the hub is en- gaged by the diagonal portion of this slot, that movement is im- parted to the switch or lock mechanisms. The operation is there- fore on the principle of the switch and lock movement, with which signal engineers are quite familiar, and briefly is as follows : When the drum is revolved by the motor, the lock rod and detector bar immediately begin to move, and as soon as these have completed their stroke, the motions of these mechanisms cease and the move- ment of the switch begins. After the switch has been moved over against the stock rail, further motion of the lock bar locks the switch and at the same time operates a knife switch which opens the control circuits and closes the indication circuit. A noticeable feature of this switch and lock movement is the arrangement of the parts in one long and narrow mechanism which occupies but little space between the tracks. For this reason it can be used in many places between tracks that come too close together to admit movements of other design, which in some places must be placed outside the tracks with long rod connections, passing under intermediate tracks to the switch. Another feature of this design worth noticing, is the fact that the cam drum is reversible, so that the movement can be operated either right or left, merely by changing the drum end for end, the position of the motor and clutch remaining the same. The motor, clutch, and drum are all attached to a steel base plate. Returning now to the motor part of the movement; the direc- tion of rotation for reversing the switch is controlled by means of a double field winding, one part of which is cut out while the other is in circuit. When the switch is to be thrown in the reverse direc- tion, the lever on the interlocking machine merely changes the con- nection of the operating circuit to the other field winding. The use of the magnetic clutch is an advantage in several ways. It permits the breaking of the motor connection with the throwing 50 RAILWAY SIGNALING mechanism instantly and at the proper time, and the absence of a rigid connection prevents breaking or straining of the parts if the movement of the switch should become blocked, as by the dropping of a lump of coal or other obstruction. The blocking of the switch FIG. 28 SIDE ELEVATION OF SOLENOID SAFETY CIRCUIT CONTROLLER FOR SWITCH MOVEMENT merely causes the clutch to slip until a fuse is blown on the inter- locking machine. It should here be noted that the motion of the switch follows the lever. If the switch is found to be blocked, it can be thrown back by simply reversing the lever. SAFETY CONTROLLER FOR SWITCHES The safety controller used with the system shown in Fig. 24, and which automatically cuts out a switch motor if the lines be- FIG. 29 PLAN VIEW OF CIRCUIT CONTROLLER come improperly connected, combines in one, the functions ot two electro-magnetic circuit controllers. The function of one is to open the motor circuit when the lever movement is completed, and of the other to open the next operating circuit when it is energized by con- RAILWAY SIGNALING FIG. 3O END ELEVATION OF CIRCUIT CONTROLLER nected wires, and thus to prevent a wrong movement. The instru- ment which is illustrated in Figs. 28, 29, 30 and 31 comprises two solenoids A and A, fixed to a cast iron base V. Each solenoid has a moveable core D, connected by means of a jaw E to a lever F. The lever F is pivoted at its middle to a fixed support G and is connected at its up- per end to a rod H, free to move longitudinally. The rod H carries a contact bridge I, which will connect the contact points / and K when the core D is drawn into the sole- noid, and will connect the contact points L and M when the core D is drawn out- ward. The levers F and F' are connected near the lower ends by a spring Z, which causes the bridge /' to connect L' and M', when the core D is drawn into its solenoid A to nearly the full ex- tent. Similarly the contact bridge / is made to connect L and M when the core D' is drawn into the solenoid A'. The contacts / and K are carried by the slate block N, with springs interposed so that they may be pushed in about three-sixteenths of an inch. The contacts L and M are fixed to the slate block O. The relation of the parts is such, that the bridge / touches the contacts / and K, while the core D is still three-six- X X teenths of an inch from its complete forward stroke, and the bridge /' touches L' and M' with the core D about one-sixteenth of an inch from its full inward stroke. These clearances are allowed for making good contact. Each solenoid has two coils of wire. The coil C has 100 turns of No. 13 B. & S. gauge and the coil B, I 100 turns of No. 15 B. & S. gauge. The resistance coils U and C/', each of twenty ohms, are in series with the coils B and B' at the starting of a movement, and the circuits in- cluding them may be called the starting circuits. The coil B is con- nected to terminals P and Q, and the coil C is connected to term- inals R and S. FIG. 31 WIRING DIAGRAM 52 RAILWAY SIGNALING At the beginning of a movement, current flows through coils C, B, and U in series, and draws in the core D, causing the bridge /' to connect L' and M', which shunts the coils B and U, so that the operating and indicating currents flow only through the coil C, of a very low resistance, but having sufficient turns to hold the core D in place. The bridge / will touch / and K before I' touches L' and M r , so that if the current happened to come from a foreign source without the lever having been moved, current would also flow from the last operating wire, which is still in connection with battery, through coils C , B', bridge I, and the motor, and would hold /' away from L' and M', by drawing in the core D'. This cur- rent will run the motor light in the direction it ran in making the last movement, and without energizing the clutch. The contact K is provided with a head on its inner end, which makes connection with a contact X, when K is pushed outward by the spring, but when K is pushed in by the bridge /, it is separated from X. The object of this is to cause the cut-off current to flow only through the safety contacts / and K, and thus afford a -test of their condi- tion at each movement of the switch. When the core D is drawn completely into the solenoid A, the latch T drops into the path of a projection on the lever F r , so that if the magnet A' is energized while A is still holding its core, the core D' will be stopped by the latch T before it puts the bridge /' against /' and K'. A similar latch, T, stops the core'D under sim- ilar conditions. These latches come into play in the action of the cut-off current. If in that case the bridge /' were allowed to move far enough to touch /' and K', the safety circuit would be tem- porarily closed and cause sparking at the contacts. CHAPTER IV THE ELECTRIC TRAIN STAFF SYSTEM DEVELOPMENT THE electric train staff system of to-day is a gradual develop- ment from a simple principle for the operation of railroads which was recognized in England as early as 1840 ; namely, that to safely pass over a given section of single track, every train should have in its possession a tangible right to do so in the form of some specific article of which there is only one obtainable. The first train staff was a metal bar about two feet long, which had cast or engraved on it the name of the two stations between which it alone gave authority for any train to proceed. Unless trains moved alter- nately in opposite directions the staff had to be returned over the sec- tion by a special engine or in some cases by road. To partially overcome this difficulty the staff and ticket system was devised, in which device the original staff became a key that would unlock a box at either end of the section and permit tickets to be taken therefrom. If it was desired to forward, say three trains from one station to another before one should proceed in the opposite direction, the ticket box was unlocked by the staff and a ticket given to the first and second trains, the third train receiving the staff. Since an engineer or guard of any train when receiving a ticket was required to see the staff as well, this system, while making head- on collisions impossible, did not permit trains to enter a section from the end at which the staff did not happen to be. To accomplish this result, Mr. Edward Tyer, in 1878, introduced his electric tablet ap- paratus, which consisted of two instruments, one at either end of a section, each instrument containing a certain number of tablets any one of which constituted the right of a train to pass over that section. The two instruments were electrically connected and synchronized so that the removal of a tablet from either instrument absolutely pre- vented any other being taken out. In 1889 Mr. Webb, the chief mechanical engineer, and Mr. Thompson, the signal superintendent of the London & Northwestern Railway, invented the Webb & Thompson electric train staff, in which staffs were substituted for the tablets in the Tyer system and a permissive feature added whereby several trains could follow each 54. RAILWAY SIGNALING other into a block section if desired, in a manner similar to that em- ployed in the non-electric staff and ticket system. The first installation of the Webb & Thompson system was made with eminently satisfactory results in May, 1894, on the Chicago, Milwaukee and St. Paul Railway between Savanna, 111., and Sabula, Iowa, and is described herewith : APPLICATION OF TRAIN STAFF SYSTEM * "The lines of the Southern district of the Chicago, Milwaukee & St. Paul Railway cross the Mississippi river between Savanna, Illi- nois, and Sabula, Iowa. The distance between these two stations is three miles, and there is one grade crossing, one draw bridge, and one local station in the block. Over this track, which is single, the traffic of about three thousand miles of the St. Paul company's lines passes. These lines extend directly to Kansas City, Omaha, Sioux City and Chamberlain on the west, and to Chicago, Milwaukee and Racine on the east. During the larger part of the year the traffic is heavy (the bridge block being the neck of the bottle, so to speak) and rarely falls below fifty trains per day at any time. The division yard is located at Savanna, on the east side of the Mississippi river, making it necessary for the trains of both divisions west of the river to use the bridge block, and, moving the traffic from so large a territory, it is to be expected that they will be irregular in number, and that they will bunch during certain hours. The use of a time table showing the trains over the river block was abandoned, because it was found impossible to arrange it so that it was a reason- ably correct exhibit of the traffic. Nor was it possible to move the trains through the dispatchers of either division, as the work on their respective divisions would not permit the close attention to the bridge block which the nature of the service demanded. For a time in the early history of the bridge this was done, but the work was finally put in the hands of the operators at each end of the block. It was found to be necessary to use some other than the ordinary dispatching systems. That was found to be too slow and cumbersome to meet the requirements of the quick work necessary under the conditions constantly arising incident to unexpected delays, and to increase or decrease of traffic. To meet the conditions described a train order by card system was adopted, which was in successful use for *From a paper read before the Western Railway Club by Mr. C. A. Goodwin, at that time superintendent of the Chicago, Milwaukee & St. Paul Railway. RAILWAY SIGNALING 55 many years. It was virtually a staff system the card representing the staff but it lacked one element: it was impossible to interlock the cards. As traffic increased, and increased acceleration of trains became necessary, it was apparent that the company would be com- pelled to either double-track the bridge block or find some unobjec- tionable way of handling the trains. Owing to the character of the country the construction of a second track would have been very ex- pensive, and the selection of a satisfactory system for handling the traffic became the subject of much thought and investigation. After a thorough examination and inquiry the Webb-Thompson electric staff system, largely in use on the London & North- Western Railway and in Australia, was adopted and placed in service in May, 1894. This was the first installation of the staff system in the United States, and probably in either of the Americas. "From the preceding brief description it is clear that with this system the bridge dispatcher has no responsibility except to give the proper trains the preference. He may delay traffic, but he cannot create a condition of danger. It is not necessary for him to provide for a proposed or supposed movement of trains by sending numerous orders, only to find it necessary to cancel them because the train can- not move as expected. He is in touch with the yardmaster at Sa- vanna and with the dispatcher at both divisions, and through these sources is fully informed in regard to the probable movement of trains in both directions. He may have expected to hold a freight train for a passenger train, which is reported on time at some distant station, only to find that the passenger train has lost time and that he can just squeeze the freight train into the terminus. There is no ne- cessity for sending hurried orders with attendant possibility of errors. He simply signals for a staff, and in five seconds or less the engineer has his authority to go forward. Or supposing the situation revers- ed. A passenger reported late has made up so much time that an- other train which is approaching, and for which a staff has been withdrawn, cannot go forward. Transportation men know the delay which results when it is necessary to change or make void telegraphic orders. No such delays occur with the staff system. It is only necessary to leave the signal at danger, replace his staff in the in- strument (enabling one to be withdrawn at the other end of the block,) and the passenger train goes forward with no loss of time. In case of there being so great a delay to a train, to which a staff has been delivered, that it is desired to recall its permission to move, the staff is brought back to the office and replaced in the instrument, 56 RAILWAY SIGNALING thereby cancelling its authority to proceed and in a manner which cannot be misunderstood. "When a work train is to occupy the block the delivery of a staff means that it is to be protected in both directions, and that no flag- man need be sent out, delaying fifty or a hundred men while he comes in. "These few examples of the many complications that must necessarily arise in the handling of traffic on a single track are cited to illustrate the facility with which the staff system does its train dis- patching ; its possibilities in connection with the movement of trains on single track, and its especial adaptability to short stretches of track used by the trains of several divisions or different railways, as com- pared with the telegraphic movement ; the advantage both as regards safety and facility of handling being distinctly with the staff system. "It is not the intention to decry our system of train dispatching. There can be no question but what it is a most economical and satis- factory method of handling traffic under ordinary conditions with not too heavy a train movement ; but we are obliged to admit that the system is open to objections which particularly relate to safety as well as facility, "t he staff system is capable of extended application. It is at once a block signal, a train dispatcher and a time table. It is to the movement of trains between stations what the interlocking of switches and signals is at stations and grade crossings." The main objection to the extended adoption of the Webb & Thompson apparatus was the size of the staff, which made it difficult to catch at high speed. To overcome this objection, a new design was introduced in 1900, -known as the high speed train staff system, which was based on the same general principles and method of operation as the Webb & Thompson, but possessed the essential ad- vantage of employing staffs only six inches in length, weighing six and one-half ounces ; as against staffs twenty-two inches long, weigh- ing four pounds, of the Webb & Thompson system, thus greatly simplifying the problem of taking the staff at high speeds. On the Atchison, Topeka & Santa Fe Railway, among other places, it was applied to a section extending from Trinidad, Colo- rado, to Raton, New Mexico, a distance of 25 miles, which was di- vided into seven block sections. This portion of the Atchison com- prises mountain grades averaging three and one-half percent for a greater part of the distance, over which a traffic of approximately 60 trains a day is operated. On account of the number of trains, and also from the fact that each train required two and sometimes RAILWAY SIGNALING 57 three engines on the up-grade, an average of one hundred and fifty train orders was issued in each twenty-four hours, most of which were sent to not less than two stations, so that the total delay to trains awaiting these orders can easily be imagined. With the introduc- tion of the staff system as many, or more, trains have since been handled over this section with no collision and a minimum of delays. At the intermediate stations on this section, staff cranes are provided from which the enginemen can take the staffs at a speed up to 25 miles an hour without the use of any special attachments on the en- gine. The latest type of staff instrument, known as the electric high- speed train staff, Model No. 2, has been developed during the past four years, and employs practically the same size and weight of staff as the Model No. I machine, over which it possesses the following advantages: By having separate drums for putting in and taking out the staffs, equal wear on all staffs is secured; whereas, in the earlier instrument some of the staffs would be practically worn out from constant use, while others were hardly ever used at all. The second advantage lies in the special type of indicator employed in this machine, which plainly shows the operator by the display of a white or red disc whether or not his instrument is in condition for him to remove a staff, and thus leaves him no excuse for unduly forcing the mechanism. Numerous other improvements exist in this type of machine, but they consist principally in minor details of construction. ' , An installation of this type has been in operation over fifteen months on a section of the Southern Pacific Railway between Truckee, California, and Colfax, California, a distance of 98 miles, divided into 37 blocks. This portion of the Southern Pacific is in the Sierra Nevada mountains and 14 of the staff stations are located in the snow sheds, of which there are nearly 40 miles. PRINCIPAL ADVANTAGES OF THE ELECTRIC TRAIN STAFF SYSTEM While in the foregoing the general principles on which the elec- tric train staff is operated have been described, yet particular atten- tion is called to the following points : First The electric train staff system may be considered as a mechanical assistant, which issues metal train orders under the gen- eral direction of the train despatcher, giving trains the right to pro- ceed over certain sections of track, and will only issue one such order at one time for any section, except in the case of following 58 RAILWAY SIGNALING trains where the permissive feature is used, thus obviating all dan- ger of "lap orders." Second In place of eliminating the train despatcher, as has at times been erroneously supposed, the train staff, by removing all dangers of collision and doing away with all train orders, relieves his mind from the constant strain imposed upon it under the present system and thus gives him ample time to issue orders to operators on his division for the proper movements of the trains under his control. Third It avoids all the delay now experienced in waiting for train orders. If conditions are right for a train to proceed the staff can be obtained immediately and when the permissive system is em- ployed trains can follow each other as closely as the rules of the road permit. Fourth It alone of all block systems provides a tangible piece of evidence in the shape of the staff to the engineer or conductor of his right to the particular block section he may occupy. Fifth It can be surrounded with all such additional safeguards as conditions and locations may warrant, including semaphore sig- nals and continuous track circuit, electric locks, etc. Sixth It can be safely operated by any railroad employee of average intelligence. A knowledge of telegraphy is not necessary for its operation. Seventh At stations where telegraph operators are employed who have other duties, it is found that the operation of the staff takes up considerably less of their time than is now expended on tele- graphic train orders. Eighth In most installations, the absolute staff system is em- ployed which permits but one staff to be out of any pair of machines at one time and consequently allows but one train in a block. In a number of cases, however, where the blocks are of neces- sity long and traffic is heavy through certain portions of the day, the permissive feature is introduced which, while it makes it impossible for two trains proceeding in opposite directions to be in any given block at one time, permits as high as twelve trains to follow each other in the same block at close intervals. RAILWAY SIGNALING 59 ABSOLUTE STAFFS AND STAFF INSTRUMENTS In the operation of the electric train staff the track to be pro- tected is divided into blocks or sections of such length as to best accommodate local and traffic conditions. These blocks usually ter- minate at existing stations or telegraph offices, though occasionally, as in the telegraph block system, additional block stations have to be installed when the distance betwen any two existing stations is too great for the expeditious handling of traffic. Each section is controlled by two instruments of the type shown in Fig. 32, one at each end of the section, which for convenience in this description are referred to as "X" and "Y." Each instrument is equipped with a sufficient number of staffs (varying from 10 to 35 per section) to take care of the traffic conditions. No train is permited to proceed between X and Y in either direction unless the conductor or engineer has in his possession one of these staffs which is in effect a metal train order. The instruments at X and Y are electrically connected and synchronized so that the withdrawal of a staff from either can only be effected by the joint action of the opera- tors at X and Y, and but one staff can be out of both instruments at any one time. To move a train from X to Y the manipulation of the instru- ments is as follows : The operator at X presses bell key A, Figs. 32 and 34 the number of times prescribed in the bell code, which rings bell L, Figs. 33-4 at Y through circuit I, 2, 3, 4, 5, 6, 7, 8, 9, 10, u, 12, 13, 14, 15, 16, 17, 18. The operator at Y first acknowledges receipt on his bell key by ringing bell L (Figs. 33-4) at X (through circuit 10, 20, 21, 8, 7, 6, 5, 4, 22, 23, 24, 25, 17, 16, 15, 14, 13, 26,) and then holds it closed, thereby deflecting the "current in- dicating needle" F at X (Figs. 32-34) to the right. This in- forms X that Y has furnished X current and he proceeds to remove the staff by turning the preliminary handle B Fig. 32 to the right as far as it will go, which raises the armature J Fig. 33 up to the magnets K (Fig. 33) transferring the cur- rent from the bell L to the coil K88 (Fig. 34) through the circuit 10, 20, 21, 8, 7, 6, 5, 4, 22, 23, 27, 28, 25, 17, 16, 15, 14, 13, 26, and at the same time closing the circuit on coil K 360 (Fig. 34) 6o RAILWAY SIGNALING through the circuit I, 2, 29, 50, 28, 25, 18, after which the pre- liminary spindle handle B ( Fig. 32) is permitted to automatical- ly return to its normal position. This unlocks the revolving drum C (Figs- 33 and 35) and indi- cates the fact by displaying a white instead of a red disc in the indicator at F (Fig. 32). The operator now moves the end staff E (Fig. 32) up the vertical slot into engagement with the drum C, (Figs. 33 and 35) the outer guard TV (Fig. 32) having first been turned to the right position; revolves the latter through half a turn, using the staff as a handle, and finally withdraws the staff through the opening at M (Fig. 32). In making the half turn, the drum C has reversed the polarity of the operating current, thereby throwing the instruments at X and Y out of synchronism with each other, and moving the "staff indicating needle" G at X (Fig. 35) from "Staff In" to "Staff Out." Immediately on withdrawing the staff the op- erator at X once more presses his bell key A, which indicates to the operator at Y by moving his needle from "Staff In" to "Staff Out" that the operation is completed. A side view of a staff instrument with the outer case removed is shown in FIG. 32 STAFF INSTRUMENT SHOWING => TRAIN STAFFS, REVOLVING PLATE, IN- The staff withdrawn is now DICATING DIAL, SIGNALING BUTTON, ddivered tQ thfi tra j n by hand j f ETC. RAILWAY SIGNALING 61 FIG. 33 BACK VIEW OF STAFF INSTRUMENT SHOWING MECHANISM 62 RAILWAY SIGNALING the train is at rest or passing at a speed less than 25 miles per hour. For higher speeds the staff is placed in a special holder and delivered by methods similar to those followed in the railway mail service, the engine being fitted with a catcher and deliverer. A glance at the ac- companying cuts (Figs. 37 and 38) will make this clear. As men- tioned before, in taking out a staff, the polarity of the operating cur- rent is reversed. This prevents a second staff from being taken out of either instrument, as may be noted from the following. The polarity of the local current flowing through magnet K jdo (Fig. 34) is never changed, the polarity of the current flowing Polarized Indicator FIG. 34 DIAGRAM OF CONNECTIONS FOR SIGNALING, INDICATING AND OPERATING CIRCUITS FOR ONE BLOCK SECTION through K 88 (Fig. 34) is changed each time a staff is put in or taken out of either instrument. This puts the instruments either in or out of synchrony. The magnet K (Fig. 34) is formed of two separate coils, one energized by the local and one by the line battery. The construction of this magnet is such that when the currents in both coils run in the same direction, the lines of force flow around the cores and connecting straps, thus forming no point of attraction for the armature. When the current is reversed in one coil, however, RAILWAY SIGNALING the lines of force oppose each other and the armature being brought to the point of attraction is held there. With the staff out, the cir- cuits are as follows : starting from the -)- side of battery at Y, (Fig. 34), through ip, 20, 21, Bell Key A closed, 8. 7, 6, 5, 17, 25, 24, 23, 22, 4,16, 15, 14, 13, 26, to side of battery at Y. If an attempt be made to release a staff by turning the pre- liminary handle, the operating current would be transferred from the bell L to coil K88 (Fig. 34) through /o, 20, 21, bell key A (at Y) closed, 8, 7, 6, 5, 17, 25, 28, 27, 23, 22, 4, 16, 15, 14, 13, 26 to side of battery at Y. By comparing this circuit with the one described for releas- ing a staff, it will be seen that in the for- mer the currents flow- ing through coils K 360 and 88 (Fig. 34) oppose each other and in the latter they do not, which pre- vents the releasing of a staff. On arrival of the train at Y the staff is delivered either by FIG. 35 FRONT VIEW OF STAFF INSTRUMENT WITH hand or deliverer to STAFF INSERTED IN DRUM AND OUTER GUARD , By rotating to position shown in Fig. 32 the the operator, W h O staff may be released. having seen that the train is complete by observing the rear end markers, places the staff in the opening M (Fig. 32) of his instrument having first turned the outer guard N (Fig. 32) to place, moves the staff into engagement .with the drum, D, (Fig. 33), revolves it through one-half turn, using 6 4 RAILWAY SIGNALING FIG. 36 SIDE VIEW OF STAFF INSTRUMENT SHOWING MECHANISM the staff as a handle and al- lows it to roll down the spi- ral. He then presses his bell key the prescribed number of times, thus noti- fying X that the train is out of the section, which operation also moves the "staff indicating needle" at X from "Staff Out" to "Staff In." The operator at X presses his bell key in acknowledgment and by so doing moves the "staff indi- cating needle" at Y from "Staff Out" to "Staff In" (Fig. 39). The machines are now synchronized and another staff can be obtain- ed from either in the man- ner above outlined. The staff being put in the instrument at Y, the circuits are as follows : From + side of battery at Y through ip, 20, 21, Bell key A closed at Y through 8, 14, 15, 16, 4, 22, 23, 24, 25, 17, 5, 6, 7, 13, 26, to- side of battery at Y. Should a release be required, the preliminary spindle at X would be turned and cur- rent transferred from the bell to magnet K 88 (Fig. 34) through the following circuit; from-]- side of bat- tery at Y through ip, 20, 21, Bell key closed at Y, through 8, 14, 15, 16, 4, 22, 23, 27, 28, 25, 17, 5, 6, /, RAILWAY SIGNALING 13, 26, to side of battery at Y. It will be seen that the current flowing through magnets K 360 and 88 are again opposing each oth- er, consequently, a staff can be released. While it takes some little time to describe the method of operat- ing the staff instruments, yet as a matter of fact, the removal of a staff actually takes less than five seconds and the operation of putting one in an instrument less than two seconds under ordinary condi- tions. The same methods are followed at each succeeding staff station, FIG. 37 APPARATUS FOR AUTOMATICALLY CATCHING AND DELIVERING TRAIN STAFFS SIMULTANEOUSLY AT HIGH SPEED but no two adjacent sections use the same design of staff; that is to say, the staffs used between X and Y will not fit the instruments con- trolling the section between Y and Z. Usually four different de- signs of staffs are employed in actual practice to avoid any possibil- ity of their being improperly used. PERMISSIVE FEATURE While the absolute system, where but one train is allowed in any section, is the ideal arrangement, yet cases occur where it is desir- 66 RAILWAY SIGNALING able to allow several trains to follow each other into the block at short intervals. This is known as the permissive system, and con- sists of an attachment (Fig. 40) to the absolute machine at each end of the section with one permissive staff. An absolute staff is al- ways locked in a permissive attachment when it does not contain the permissive staff. To operate this feature an absolute staff is withdrawn from the instrument at X in the usual manner and ifsed as a key to unlock the attachment or base (Fig. 40) containing the permissive staff (Figs. FIG. 38 TRAIN STAFF CATCHER MOUNTED ON LOCOMOTIVE TENDER As used on the Cincinnati, New Orleans & Texas Railway on their fast express trains where the staff has to be caught at speeds frequently exceeding sixty miles an hour. 41 and 42) which is then taken out. The opening of the base and the removal of the permissive staff locks the absolute staff in the permissive attachment, there to remain until the permis- sive staff is replaced at either X or Y. The permissive attachment with outer case removed is shown in Fig. 44. The permissive staff consists of a steel rod and n removable rings RAILWAY SIGNALING (Fig. 43) any one of which authorizes a train to pass through the section to Y. If less than 12 trains are to follow each other, the last one takes all the remaining rings and the steel rod. When all the rings and the rod are received at Y , the operator reassembles them into the complete permissive staff (Fig. 42) which he then places in the, permissive attachment or base (Fig. 41) and locks it therein by the absolute staff already in the lock of this attachment. By so do- ing he releases the absolute staff which he restores to the absolute instrument in the regular manner. The machines are now synchronized and a movement can be made with the absolute staff in either direction and from Y to X with the permissive. If it is again found nec- essary to move several trains from X to Y under the per- missive system, the permis- sive staff must be obtained by Y as before described and forwarded to X as a whole by the first train mov- ing in that direction. When a train receives the entire permissive staff it confers the same rights as does an absolute staff. CONTROL OF SIGNALS In its capacity as a key the absolute staff has a num- ber of uses in addition to that already described. Where signals are used to indicate to an approaching train whether or not it will receive a staff, an instrument known as the staff lever lock (Fig. 45) is attached to each lever operating such signals. To clear a signal the staff after being withdrawn is first used to unlock the lever lock (Fig. 45). The signal is then cleared and the staff removed from the lock and delivered to the train. FIG. 39 FRONT VIEW OF STAFF INSTRU- MENT WITH STAFF READY TO ROLL DOWN THE SPIRAL 68 RAILWAY SIGNALING To insure the signal being placed at danger behind a train the act of unlocking the signal lever opens the staff circuit, and no com- munication can be made between the two staff stations until the sig- nal is at danger, and the lever locked in that position. This does not indicate, however, that the operator will have the staff ready for de- livery by hand, or in the mechanical deliverer. To cover this point an electric slot is attached to the signal governing train movements into the staff section, which slot is controlled by the staff and lever lock and the mechani- cal deliverer, so that before the signal can be cleared the staff must be released, used .to unlock the signal lever and put in the staff deliverer, which closes the circuit on the electric slot. The signal can then be cleared. With this ar- rangement, therefore, a clear signal can not be given until the staff is actually in the deliv- erer. When the train picks up the staff, the circuit on the slot is opened, automatically setting the signal to danger, which can not again be cleared until the op- eration described above is repeated. SWITCH LOCKING The staff is also used as a key to unlock siding switches which may occur between staff stations, the switch locks being so designed that the staff cannot be removed from the lock until the switch is set and locked for the main line, thus providing absolute protection against misplaced switches. FIG. 4O FRONT VIEW OF STAFF INSTRUMENT WITH PERMISSIVE AND PUSHER ATTACHMENTS RAILWAY SIGNALING 69 SIDING AND JUNCTION INSTRUMENTS In some sections there is a siding of sufficient length to hold a train, but traffic would not warrant placing a staff at this point. That the usefulness of this long siding may not be lost, a special in- strument is placed at the siding which enables it to be used FIG. 41 PERMISSIVE for meeting or pass- FIG. 42 PERMISSIVE STAFF ing trains. ASSEMBLED The operation is as follows : A train ar- riving at the staff station X has not time to proceed to Y, but can proceed as far as the siding. The operator at X gives the train a staff with instructions to proceed to the siding. Unlocking the switch with the staff, the train sS^KSsjJ^D takeS thC Sidin ' ClOS6S and 10CkS thC Switdl > DOOR OPEN places the staff in the siding instrument, and turns the drum to the right. The staff is now locked in the instru- ._ ment, and the staff in- struments at X and Y FIG. 43 PARTS OF PERMISSIVE STAFF are synchronized, and the fact indicated to both operators so that trains may be sent through the section in either direction. FIG. 44 BACK VIEW When all trains having precedence over the one in the siding have passed through the sec- ING MECHANISM tion, and the staffs have been replaced in the instruments ; X and Y ;o RAILWAY SIGNALING acting in conjunction can release the staff at the siding, which on being removed changes the circuits so that no staff can be released either at X or F. The train on the siding then unlocks the switch with the staff and proceeds to F or back to X. A junction or diverging line may be situated between two points most suitable for staff stations ; but on account of the small amount of traffic over the diverging line it would not be desirable to FIG. 45 VIEW OF STAFF LEVER LOCK WITH CASE REMOVED make it a staff station. Such a point can be controlled in a similar manner. PUSHER ENGINE ATTACHMENT Another adjunct to the staff system is known as the pusher en- gine attachment and staff (Fig. 40) which is used on heavy grades where pusher engines are required, and is intended to both obviate the necessity of the pusher engine proceeding through the entire staff section, and to better equalize the traffic. It can readily be seen from the foregoing description of the staff system that under ordi- nary rules every train having a pusher engine attached would receive RAILWAY SIGNALING one staff to proceed up grade as from X to F. On arrival at F the pusher engine would necessarily have to receive a staff to return to X. Supposing the traffic up and down grade to be equal and that each train going up grade requires a pusher, it is apparent that twice as many staffs would go down hill as came up, resulting eventually in all the staffs arriving at the foot of the grade, X, from which they could only be returned to F by some special person authorized to unlock the instruments and remove the staffs by hand. Furthermore, the summit of the grade may be FIG. 4 6-pusHER STAFF half-way between X and Y, but un- der the rules a pusher could not cut off at the summit and return to F, but must continue on to X and receive a staff to return. To overcome these two objections the pusher attachment is em- ployed. It consists (like the permissive attachment) of a separate device which may be attached to any absolute instrument (Fig. 40) and contains a staff of special design (Fig. 46) which can only be released by a regular staff, though, unlike the permissive staff, it can be out of its receptacle at the same time as the regular staff, but when so removed it opens the controlling circuits of the system, preventing any other movement be- ing made until it has been returned and locked in the pusher attachment. Fig. 47 is a rear view of a pusher atachment showing the mechanism. The operation is as follows : A train with a pusher wishes to proceed from X to Y. Y re- leases a staff at X, and X uses this staff to re- lease the pusher staff. X then hands the regu- lar staff to the train and the pusher staff to the pusher engineer. The train passes through the section and delivers the regular staff at Y. This is placed in the instrument there, the pusher engine retaining the pusher staff and returning to X. Until this latter staff is put into the pusher attachment at X and locked, the staff circuits are not re-established and no other staff can be re- leased. FIG. 47 BACK VIEW OF PUSHER ATTACH- MENT SHOWING MECHANISM CHAPTER V AUTOMATIC BLOCK SIGNALING GENERAL GIVEN a section of railroad from which large earnings are to be derived and assuming that there is plenty of business to handle, the problem is to move the maximum number of trains over it with economy and safety. If every train had a track of its own, no block system would be necessary, but on the leading railroad systems the traffic has increased much faster than the trackage. One of the most helpful and efficient means for safely handling a large number of trains over the same track is a good block system. DEFINITIONS AND CLASSIFICATIONS Before enlarging upon this subject, a few definitions may be of value to the reader. A block is a length of track of defined limits, the use of which by trains is controlled by fixed signals. A block signal is a fixed signal controlling the use of a block. The word "fixed" refers to location only since block signals are movable signals in fixed locations. Block signals may be classified in three ways : ist As to the manner in which their day indications are dis- played. 2d As to the manner in which they are controlled and op- erated. 3d As to what they control. Under the first classification there are : (a) Banner signals, the indications being displayed by a re- volving banner. (b) Disc signals, the indications being displayed by a movable disc in front of a fixed background; and (c) Semaphore signals, the indications being displayed by the position of an arm moving in a plane at right angles to the track. In all types under class one the night indications are displayed by tolored lights. Under the second classification there are : (a) Manual, the signal being controlled and operated by man RAILWAY SIGNALING 73 power, (b) Controlled manual, the signal being operated manually and constructed so as to require the co-operation of the signalmen at both ends of the block, (c) Automatic, the signal being operated by power which is controlled entirely by the presence or absence of a train in the block, or the condition of the track. Under the third classification there are : (a) Home block signal, a fixed signal at the entrance of a block to control trains in entering and using said block. The indica- tions displayed by a home signal are "stop" and "proceed", or in some cases "stop", "caution" and "proceed". (b) Distant block signal, a fixed signal used in connection with a home block signal to regulate the approach thereto. An absolute block system is one which never allows more than one train in the same block at the same time. A permissive block system is one which may allow more than one train in the same block at the same time, provided the trains are going the same direction and the second train has been warned by signal that another train is in the block. EARLY BLOCK SYSTEMS The older block systems in this country were all manual or manually controlled, following the practice in England and Germany. The enormous increases in the amount of traffic to be handled with only slight increases in trackage, together with the fallibility of the signalmen operating the signals, led to the development and use of automatic block signals. Briefly, both economy and safety led to this development. In the days when the station agent was ticket agent, baggage man, freight agent, freight handler, telegraph opera- tor, etc., it was thought that to let him also handle the manual block signals would be good for him while he was resting. As traffic in- creased, these various duties became more and more onerous, the stations were not close enough together to be serviceable as block stations, and the men became too busy to handle the signals reliably. The next move was to install block stations in the outlying dis- tricts. This meant a first cost of about $i ooo for the station and signals, and a yearly wage cost of not less than $i ooo to $i 500 for each block station. Furthermore, the men still made mistakes and gave wrong signals. AUTOMATIC BLOCK SIGNALS The automatic block signal must be a permissive signal in order that, if a signal is out of order and assumes the stop position, traffic 74 RAILWAY SIGNALING may not be entirely suspended for several hours. On double track lines this is not serious, as a train, after stopping at a signal out of order, may. proceed with caution through the block expecting thai another train is already ahead of it in the block, that a switch is misplaced or that a rail is broken. On single track lines it was thought that the delays might become serious, since when a train re- ceives a stop signal it is necessary to protect it by sending a flagman ahead through the block. For this reason automatic blocking on single track has not met with* general favor. The only two single track lines using this system extensively are the C. N. O. & T. P. Ry. and the Harriman Lines, the latter having installed several thousand automatic signals on single track. The Harriman Lines already claim to have shown that the expense of the system was warranted on account of the numerous cases of broken rails which have been reported by the automatic signals. It is the purpose of this article to describe only the arrange- ments of signals in common use on double track lines and the auto- matic electric semaphore signal which is in most general use. LENGTH OF BLOCKS The ideal arrangement of automatic signals to secure the max- imum capacity for train movements over a given piece of track would be to first decide upon the maximum distance required for stopping any train on the road. This can be decided from the air brake tests, and this distance would have to be the minimum length of the block. Since it is more difficult to stop on a descending grade and less difficult to stop on an ascending grade, the blocks would gradually be lengthened out on the descending grade and gradually shortened on ascending grades. As large terminals are approached the blocks would gradually be shortened on account of the limited speed of trains and congestion of traffic at such places. Having fixed the locations, the control of the signals should be such as not only to warn an engineman when he reaches a block which is oc- cupied, but also to warn him in time to permit him to stop his train before reaching the entrance of the occupied block. With this ar- rangement and control of signals it would be possible to start two trains from one end of the line two blocks apart, run them the length of the road at the same speed and have them arrive at the other end still just two blocks apart. The second train would receive clear signals all the way; or if the first train should stop at any point, the second would receive due warning and would have plenty of space RAILWAY SIGNALING 75 to stop in before reaching the block which was occupied by the first train. In ordinary practice to-day the minimum length of block is seldom used, and the length commonly varies from 4 ooo feet to 12 ooo feet. Frequently so little heed is paid to the principles men- tioned above that the ideal arrangement is far from being reached. One of the principal reasons for improper spacing is that if a signal is located in its proper place for uniform spacing of trains, it cannot be readily seen on account of the curvature of the line or obstruc- tions to the view, such as bridges. All of the diagrams of signal arrangement in Figs. 48 to 52 show the home signals as arms with square ends and the distant signals as arms with forked ends. In every case the block is the space between home signals, the distant signals being nothing more than repeaters for the home signals. SEMAPHORES ON SEPARATE POSTS Fig. 48 illustrates the arrangement of signals in an automatic block system using semaphore home and distant signals mounted on FIG. 48 separate posts. This arrangement is used very little excepting where traffic is light and the home block signals are considerably more than one mile apart. The distant signals would probably be located not more than 4 ooo feet from their respective home signals. A home signal is shown at a in the stop position with a train just past it in the block. The arm is horizontal and a red light would be displayed at night. It means "stop and wait the prescribed time (usually I minute) then proceed under control expecting to find a train in the block, a misplaced switch or a broken rail." The distant signal for a is shown at a t and is in the "caution" position. Some roads use a green light for the night indication ; others use a yellow light instead. It means "expect to find next home signal in the stop position." & is a home signal in the proceed position. The arm is inclined at an angle of 60 or 75 degrees from the hori- zontal. On roads using green for "caution" a white light would bt, displayed at night. On roads using yellow for "caution" a green light would be displayed at night. It means "proceed, the block is unoccupied, all switches are set right and rails are unbroken." & t 76 RAILWAY SIGNALING is the distant signal for b and is in the proceed position. On roads- using green for "caution" a white light would be displayed at night. On roads using yellow for "caution" a green light would be display- ed at night. It means "proceed, expect to find the next home signal in the proceed position." Using this arrangement, trains can run at speed if spaced a dis- tance equal to one block (a to b) plus the distance between a home <*- It !.. it =g=pr : asjiowfi. a sectional^ie^ cHr a Central type^of relay. RAILWAY SIGNALING Fig. ^ show^-a sectional view of ^a cofnbine^i-rieutral^atitf pol^br- ized type of relay,, If it is assumed that there is a train in the section in advance of H' the home arm at H ' would be in the "stop" position and the bat- tery would be reversed on the track section HH! At H the contact K would be closed and the contact K ' would be open so that the home arm would be in the "proceed" posi- FIG. 54 tion and the distant arm would be in the "caution" position. When the train passes out of the section and the home arm at H ' goes to the proceed position, thus reversing the polarity of the battery on the track section HH', it may be noted that while the pole changer is shifting, i. e., for a fraction of a second, the relay at H would be de- energized arid the contact K would open and then close. This open- ing of contact K would tend to release the home arm at H and re- turn it to the "stop" position if provisions were not made to prevent FIG. 55 it. This is prevented by applying a closed circuit inductive coil to the relay R or to the holding magnet of the signal, either of which will hold the signal arm clear momentarily by induction. If this slow releasing feature is applied to the relay, the contact K will re- main closed long enough for the pole changer to shift. If it is ap- RAILWAY SIGNALING 83 plied to the holding magnet of the signal it will hold the arm long enough for the pole changer to shift in spite of the fact that K may open for an instant. The latter scheme is usually employed.] ^X) * Another automatic block signal system which is if anything bet- ter suited to meet all around conditions than the polarized system provides for the control of distant signals by line wires as shown in Fig. @. The home ;irms are controlled directly from the. track re- lays as previously described but the distant arm a 1 is controlled through an additional relay R 2 which in turn is controlled through line wires and a circuit controller (c) operated from the home arm a in advance. The distant arm is also controlled by a circuit con- troller operated by the home arm b on the same post. The line FIG. 56 SECTIONAL VIEW OF NEUTRAL TYPE RELAY FIG. 57 SECTIONAL VIEW OF COMBINED NEUTRAL AND POLARIZED TYPE RELAY wires have to be protected with lightning arresters but even then the distant arms are frequently out of service on account of lightning. For this reason other schemes which provide for the control of the home arms through line wires are objectionable and cause unneces- sary delays to traffic. Fig. sl-also shows what is done when the track section between signals is too long to operate as one section. It may be noted that the track circuit is relayed at the cut sections by a method somewhat similar to that employed in telegraph lines. Usually^from 3 ooo ^W 5 ooo feet of track can be operated without a cut. ^ThTsignal oper> ating batteries B and B ' each consist of 16 cells of caustic potash 8 4 RAILWAY SIGNALING primary battery, connected in series and housed in a receptacle placed sufficiently deep to prevent freezing ; or they might each con- sist of five cells of storage battery in an iron cas'e beneath the signal operating mechanism. The track batteries B 2 -B & consist of two or three cells of gravity battery connected in multiple and placed in an iron chute below the frost level. One cell of storage battery with from one to two ohms resistance in series with it may be used in- stead. Fig. 59 shows a cut section of a typical battery and relay shelter. Storage batteries give the best results on both track and signal operating circuits, but their first cost is usually greater. Fig. 60 shews the signal operating mechanism now almost ex- clusively used on the leading railroads. About 25 ooo are in use. It consists primarily of a motor and an electric clutch or holding HM B i Line wires FIG. 58 DIAGRAM OF CONNECTIONS WHEN TRACK CIRCUIT RELAY IS USED magnet, the latter being mounted on a compound lever to which the operating rod of the signal arm is attached near the center. This compound lever is pivoted near one end and the motor, through a train of gears, drives a chain carrying a trunion which engages with the free end of the lever and raises it when the operating current is applied to the motor and magnet. After the arm is raised the motor is automatically cut out and stopped by a friction brake. The end of the lever then drops back a little and rests on a catch where it is held, free from the motor gearing and chain, until the magnet is de- energized by the opening of the control relay. When the magnet is de-energized the lever arm drops down by gravity because the arma- ture of the magnet releases the train of levers in the arm and thus releases the end of the arm from the catch. The fall of the lever arm is eased by means of the dash-pot connected outside the pivot end. Fig. 60 shows a two arm movement, the lever arm at the front RAILWAY SIGNALING being lifted to operate the home signal arm and the lever arm at the back being down with the distant signal arm in the "caution" posi- tion. '-Beneath the clutch, or slot magnet, as it is called, is the pole changer operated by the home signal lever arm. ^ The leverage is such that the armature of the slot magnet has to hold up only from one to three pounds, although the combined load of operating rod, signal arm and slot lever arm is over 100 pounds. The slot magnets are compound wound, a low resist- ance winding being in series with the motor and cut out with it, and a high resistance winding (500 to 2 ooo ohms) being in multiple with the motor to hold the arm after the motor cuts out. The operating voltage is usual- ly about ten volts, the time re- quired for operating one arm about six seconds, and the motor current about two amperes. This mechanism is exception- ally free from friction, the arma- ture of the slot magnet is far enough from the core so that it cannot be held by residual mag- netism and the weight of all moving parts tends to restore the signal to the stop position as soon as the track relay cuts off the battery current. The protection of switches in block signal territory has been left to the last in order that the main scheme might not be confus- ing. Each switch is insulated so that the track circuit passes through it unbroken. A circuit controller such as shown in Figs. 61 and 62 is FIG. 59 SECTIONAL VIEW OF BATTERY AND RELAY SHELTER 86 RAILWAY SIGNALING attached to the point of the switch and adjusted so that if the switch is open one-fourth of an inch the track circuit will be short-circuited as if by the presence of a train. For the guidance of trains com- ing out of a siding onto the signaled track, a switch indicator mounted on an iron post near the switch is employed. The switch indicator is usually so controlled that when a train is approaching FIG. 60 ELECTRIC SIGNAL OPERATING MECHANISM The right hand rod at the top connects with the home signal arm and the left hand rod connects with the distant signal arm. There is a second chain back of the one shown for operating the distant lever arm. on the main track two blocks away the miniature semaphore is set to the "stop" position to warn the train in the siding not to open the switch. All sidings are made a part of the track circuit up to the RAILWAY SIGNALING 87 fouling point to protect trains on the main track from cars which may not clear it. The average cost for an automatic block system using home and distant signals on the same post is from $750 to $1100 per block section, depending on the length of block, number of switches FIGS. 6l AND 62 VIEW OF CIRCUIT CONTROLLER APPLIED TO SWITCH AND ALSO IN DETAIL and method of signal control. The average cost of maintenance and operation of such a system is from $75 to $100 per two-arm signal per year. CHAPTER VII AUTOMATIC BLOCK SIGNALING ALTERNATING-CURRENT GENERAL THE proper operation of a direct-current track circuit may be interfered with when the track rails have the additional duty of conducting current for other purposes, such as the propul- sion of trains. It has, therefore, become necessary to use a kind of signaling current in the rails which, while performing the functions previously described, will in addition be able to operate a track relay selectively; i.e., which will respond to the signaling current Trolley or Third Rail Car Propulsion ^XT D.C Generator () Return Rail Block Rail Signal // Signal Light 4*0 Rail Insuktion 1 n r i A. 4 Reactance Coil AAAAA! N/WWI Track Transformer Signal A. C. Generator A. C. Signal Mains FIG. 63 TYPICAL ALTERNATING-CURRENT TRACK CIRCUIT USING THE SINGLE- RAIL SCHEME and to no other. Thus alternating current, because of its inductive properties, has been substituted for direct current. Two schemes of alternating current are in use, the single-rail return system and the double-rail return system. In the former, one rail of each track is insulated into block sections for signaling RAILWA Y SIGNALING 89. purposes, the other rail serving as a continuous return for the power current and as one side of the alternating-current track cir- cuit. In the latter, both are insulated into block sections and both are used for the power current. This is accomplished by the use of balanced inductive bonds and is used in preference tx> the single-rail system , un- der certain conditions. The single-rail scheme and some features of interest in its application will be considered in this article. FIG. 64 FORM OF GRID USED FO^NON-INDUCTIVE RESIST- SINGIE-RAIL SYSTEM ' i ; ig. 63 shows a typical alternating- current traek circuit using the single-rail scheme, and its relation to the propulsion system. As practically all of the propul- rail within the distance, D, the length of the block, and relatively little through the block rail, there will be. a drop in voltage in the former and not in the latter. This drop ap- pears at A and at B, the sum, of which will equal D. Thus a small amount of propulsion current will flow through a track relay at one end of the section and through the secondary of the track transformer at the other, the effect of which is to magnetize the iron of each to a certain extent and, if excessive, to diminish the influence of the alternating signal current. In or- der to limit this effect of the propul- sion current on the relay, a non-in- ductive resistance, Pjgp6<$ is connected in series with the relay and a react- ance, KilfZdS 1 , of low ohmic resistance in multiple with the relay. In like manner the track transformer, Fig. 66, FIG - 6 5~Low RESISTANCE IMPED- is protected by a non-inductive resist- ance in series with it. As a further precaution against the magnet- izing effect of the propulsion current, the iron of both transformer and reactance coil is provided with an air gap. In case of a short- RAILWAY SIGNALING circuit between the power and block rails, fuses protect the appara- tus from injury. The resistance in circuit with the transformer secondary serves the further purpose of limiting the flow of alter- nating current when the rails are short-circuited by a train. The type of alternating-current relay used with the single-rail scheme *& -shown in Figs. 67 and 68 and consists of a movable alumi- num disc or section of a disc passing between the poles of a magnet. A part of the pole faces are enclosed by a closed conductor thus causing a distorted field which by the repulsion between it and the field set up by the eddy currents induced in the disc causes the nec- essary mechanical movement of the disc. The shaft upon which this disc is mounted carries contact parts (at a short radius) which operate to con- trol other circuits which operate the sig- nals. When a block is not occupied by a train, the drop in propulsion voltage D (see Fig. 63) is divided between A and B in proportion to the ohmic resistance of the apparatus connected across the rails at those points, the drop in the block rail being relatively negligible. This is the case also when a train is in the middle of the block. When, however, a train is at A, both the block and return rail are at the same potential at that point because connected by the wheels and axles, which also shunt the relay. Drop D now appears at B, thus creating perhaps the most unfavorable condition for the transformer, for it now receives the maximum direct current from the track while delivering an increased amount of alternating-current. When a train is at B the transformer re- ceives no direct current and delivers the maximum alternating cur- rent. Simultaneously the relay receives direct current due to the total drop D, and ?t would not matter if its iron were saturated, for alternating current is not present because a train occupies the block, hence the relay is properly inoperative and the signal indicates dan- ger. The means provided to protect the track transformer and relay from the effect of the propulsion direct-current drop, limits to some extent the useful effect of the alternating-current in the track cir- FIG. 66 TRACK TRANSFORM- ER WITHOUT CASE RAILWAY SIGNALING 91 cuit. Clearly then there is a limit to the amount of direct-current drop under which an alternating-current track circuit of given length will be operative with the single-rail scheme. Fortunately this point has not been reached in practice, for a loss of energy in a rail return system sufficient to disable the alternating-currfht track circuit could not ordinarily be tolerated. In the single-rail scheme the amount of alternating signal cus- rent in the track rails is relatively small so that its drop in voltage between the transformer and relay is not serious. The insulation resistance between the block rail and return rail is another factor FIG. 67 ALTERNATING-CURRENT RELAY FIG. 68 RELAY WITH BASE REMOVED, WITH GLASS COVER REMOVED SHOWING MOVABLE VANE greatly affecting the operation of the track circuit. Not only does this decrease as the length increases, but it varies greatly with weather and other conditions. The expedient of increasing the transformer capacity to overcome leakage difficulties (occasionally as low as two ohms per thousand feet of track) is not wholly ad- vantageous because increasing the alternating-current track voltage at the transformer increases in like proportion the leakage current from block to the return rail, and it increases the alternating-cur- rent drop in the rail because of this increased current, so that the relay is not greatly benefited. It is better to reduce the length of the track circuit where necessary, as that is more beneficial in every way. This does not necessarily mean that the block must be short- ened for the track between the signals may be subdivided into a number of track circuits, each one of which controls the signal. It may be seen that the signaling equipment is in a sense a compromise 92 RAILWAY SIGNALING with respect to a number of conditions which are conflicting and which to some extent cannot be known in advance. Experience thus far has not presented track conditions requiring more than one track circuit between signals. A number have been in service more than three years which are about one mile in length and give no trouble. APPLICATION OF THE SINGLE-RAIL, SYSTEM The most notable installation in which the single-rail alternat- ing-current track circuit is used is that of the New York Subway. In this the automatic block signals, Figs. 69 and 70, automatic train stops, Fig. 71, and interlocking switch and signal plants, (the latter FIG. 69 FRONT VIEW OF A TYPICAL BLOCK SIGNAL IN THE NEW YORK SUBWAY signals being semi-automatic) are of the electro-pneumatic type. The track relay control circuits which in turn, control magnetically operated pin valves governing the admission of air to the cylinders which actuate the signals and train stops. In this installation the two alternating-current signal mains carry current at 500 volts and 60 cycles. To these mains are connected the primary leads of the track circuit transformers which step down by one secondary wind- ing to ten volts for supplying the track circuit, and by another sec- ondary winding to 55 volts for the signal lights. The non-inductive resistance of one ohm between the track rails and the ten-volt sec- RAILWAY SIGNALING 93 ondary causes a drop of about two and one-half volts, so that the alternating-current potential across the rails opposite the trans- former is seven and one-half volts. A similar resistance in series with the alternating-current track relay at the opposite end of the block causes an additional drop of two volts, reducing the voltage of the relay to about five volts which allows one-half a volt for drop in the rails. These values are only approximate. The alternating-current energy required per block may be summed up as follows : That for the signal lights, the one ohm re- sistances and the leakage (from rail to rail), non-inductive, and that for the track transformer, the impedance of the rails, the track relay and the impedance coil con- nected across the relay terminals, partially inductive. The power- factor of the whole is about 80 percent and the load per average block with average traffic, 80 watts. In order to secure the greatest safety as well as density of traf- fic on the express tracks .and at curves on the local tracks, the signals were placed at intervals as close as the braking distance of a train plus a reasonable mar- gin of safety would permit. The element of personal error on the part of the motorman was elimi- nated by the automatic stops, Fig. 10, which apply the brakes when he fails to observe a dan- ger indication of the signal. It has been found, however, that the moral effect of this train stop is very great, for no motorman will carelessly invite the censure of his employers and the public FIG. 7O SIGNAL APPARATUS REAR VIEW* *This figure shows the details of the alternating-current signals as ap- plied to the Subway in New York. The track transformer is at the top. Beneath it is the instrument case containing the grid resistances, track re- lay and reactance coil. Below the case is the electro-pneumatic valve for controlling the automatic train stop. 94 RAILWAY SIGNALING by a non-observance of the signal thus made conspicuous by the noise of escaping air and the sudden stoppage of the train. In such a case, the only question of veracity at issue is whether the stop was in the danger position while the signal indicated safety, a situation which exists when some part of the stop mechanism or its controlling circuits are deranged. To avoid serious delay to traffic when the stop apparatus is out of order, means are provided whereby a guard may hold the stop in the clear position while his train pulls over it, but as soon as this act of the guard ceases the stop returns to the danger position. The remarkable record of performance of the signal system in the New York Subway is worth noting. The failures due to all causes, many of which are not directly chargeable to the sig- nal apparatus, are about one to every 400000 signal opera- tions. Some months it is not so good while in others it is even better. ALTERNATING - CUR- RENT SIGNALING ON STEAM ROADS Recent develop- ments indicate that al- ternating-current sig- naling will have a large field on steam roads. This is primarily due to the trouble ex- perienced with foreign direct currents, chiefly from trolley cars, which interfere with the battery current commonly used in the track circuit. For this purpose alternating current at a frequency of 25 cycles is most desirable because of the relatively low impedance in the line wires and track rails due to reactance. No inductive bonds at the ends of the track circuits are required; hence the necessary alternating current in the rails is limited to the needs of the track relay and leakage from rail to rail. By the use of a relay of special design requiring a very small amount of current to operate, the total current in the rails is so small as to cause but little drop, which per- mits of the use of a long track circuit. FIG. 71 DWARF SIGNAL AND AUTOMATIC TRAIN STOP RAILWAY SIGNALING 95 Alternating-current signaling on steam mads lends itself read- ily to the wireless control of distant signals, without the use of per- manent magnets and the danger of residual magnetism. In this connection, it should be noted that with the alternating- current relay the shunting voltage is practically the same as the pick-up voltage. Incidental but important advantages of the use of the alternating-current for signaling steam roads are that the signals may be operated and lighted by alternating-current taken from the mains which supply the track circuit. Thus all batteries are elimi- nated as well as oil for the lights and the services of lampmen. One two candle-power, four and one-half watt lamp per sig- nal blade gives better illumination than the average oil light and it does not smoke the lenses nor blow out. The lights may be al- lowed to burn continuously night and clay, as it ordinarily would not pay to turn them off because of the small energy required and P""*^} the long life of such lamps. The signals may be operated by in- duction motors (having neither FIG. 72 DETAILS OF AUTOMATIC TRAIN brushes nor commutators) and the slot magnets likewise may be operated with alternating current. The foregoing considerations, in addition to the chief advantage of non-interference of foreign current in the track circuit, are all in favor of alternating instead of direct-current operation. The weak- ness of the alternating-current system, however, lies in the possi- bility of disabling a number of signals due to breakage or crosses of the two wires constituting the signal supply mains. High voltage wires are not desirable on telegraph pole lines, but if conditions permit the use of low voltage, say 500 volts, they may be placed on poles with other wires, but should be on the top cross-arm, so that other wires, which break more readily, may not fall upon and cross them. A good arrangement is to have an inde- pendent pole line for the signal mains if a high-tension pole line is not available, and make the construction so substantial that it will not break down. The stations supplying current to the mains should be equipped with apparatus in duplicate. By thus treating the equipment which is common to a number of signals with the same care that is bestowed upon electric power and lighting sys- tems, this part of the signal system could be made reasonably reliable. CHAPTER VIII AUTOMATIC BLOCK SIGNALING ALTERNATING CURRENT DOUBLE-RAIL RETURN SYSTEM DIRECT-CURRENT TRAIN PROPULSION SIGNALING by the double-rail return system, in which both rails are used as return conductors for the train propulsion current simultaneously with the alternating-current block sig- naling current, is accomplished by the use of balanced inductive bonds connected across the rail insulations at the ends of the blocks. These bonds offer impedance to the passage of the signaling current, but not to an appreciable extent to the passage of the return train propulsion current. 1 A good form of reactance bond is that shown roDcy or i nird Rail A.C. Signal Generator FIG. 73 TRACK AND SIGNAL CIRCUITS The dotted and full line arrows show the direction of the alter- nating and direct currents respectively. in Fig. 73, in which the propulsion current passes from the rails into the ends of the coil at A and B and out at C, the middle of the coil of the bond, or in at the middle at D and out at the ends E and F. With equal amounts of return current in each rail the magnetizing effect on the iron is nil, but the signaling current, which flows from end to end of the bond (A to B), sets up a reactance, which main- tains a difference of potential between the rails sufficient to operate the inductive track relay. The propulsion current is shown fey full arrows and the signaling current by dotted arrows. Unlike the sin- gle-rail return system, the drop of voltage in each rail due to the RAILWAY SIGNALING 97 propulsion return current is, under favorable conditions, nearly equal, so that little or no propulsion current flows through the track transformer at one end or the track relay at the other end of the block. For this reason it is not necessary to interpose resistances between the track and this apparatus, nor to connect an inductive shunt across the relay coils. The iron of the track transformer has a closed magnetic circuit, that is, it is without an air gap. Adjustable magnetic leakage filler blocks are inserted between the primary and secondary coils, causing a drop of voltage and FIG. 74 INDUCTIVE BONDS The wooden covers are removed to show details of bonds. limiting the current when the transformer is short-circuited by a train in the block. It is probably never true in practice that equal amounts of pro- pulsion current are carried by each rail of a block owing to unequal resistance due to defective bonding and the like. The difference in the amount of current in the two rails is called unbalancing cur- rent because its effect on the iron of the bond is not neutralized by an equal amount of current through the opposite half of the bond. It should be noted here that a bond as a unit consists of the coil and iron within a cast iron case included between A and B, and an- 9 8 RAILWAY SIGNALING other like bond between E and F. The middle points of their coils are connected by a conductor C D. Properly the inductive bond around each rail insulation consists of one-half of each bond as A C D E and B C D E. In order to reduce the magnetizing effect of the unbalanced propulsion current on the bond A B or E F so that its reactance to the alternating signaling current will undergo but little change, an air gap is introduced into the iron of the bond. Obviously, the re- luctance of this air gap considerably reduces the reactance to the alternating signaling current, thus requiring additional signaling cur- rent through the bond to maintain the necessary difference of alter- nating-current potential between the rails. TTThe increased current required by the bond E F at. the relay end of the block causes additional alternating-current drop in the rails, which in turn necessitates a higher voltage and more current from the track transformer. Thus the bond A B at the transformer A. C. Mains J VVW Track C ^Inductive Bonds (^Transformer _^*fcB T7? ! ' Track j 9~p9 wv Relay Exciting P Transformer Relay H Q 1 FIG. 75 receives more current than it otherwise requires in order that the bond E F at the relay receive enough to maintain sufficient voltage to operate the track relay. Hence the signal mains must have suffi- cient copper and the generating plants be of sufficient capacity to maintain these conditions. For the above reasons it is occasionally desirable to locate the track transformer in the middle and use a track relay at each end of the block, or an equivalent, and in some respects better arrangement is to use but one track relay having wire-wound field and armature and energize the field from one end of the track circuit and the ar- mature from the other through a small step-up transformer and line wires. (See Fig. 75.) It will be seen that the design of, and power required for, a signal system depends upon the kind of maintenance which a railroad company gives the return conductors, the rails, in the way of bonding; for if the bonding is good, with a resulting equal amount of current in each rail, the air gap in the bonds may be made RAILWAY SIGNALING 99 very small. Such desirable conditions mean a saving in line copper, capacity of generating plant and operating expenses, or if conditions warrant it, a considerable increase in the workable length of track circuit. Ordinarily railroad companies are not willing that even very defective bonding should result in a danger signal with the block unoccupied, so that alternating-current signal plants are now, and more will be, in service in which the inductive bonds have unbalanc- ing capacities equal to perhaps one-half or more of the total propul- sion load. The importance of this feature is perhaps more clearly seen when compared with the simplicity and economy of the single- rail system of alternating-current signaling on direct-current roads, \l\JWVVfVV FIG. 76 SIGNALS ON ELECTRIFIED RAILROAD Inductive bonds are shown on each track between the rails. and especially on steam roads. In this connection it will be noted that in a general way, the double-rail return system is preferable to the single-rail system in cases where the blocks are long, hence re- quiring relatively few inductive bonds, and where the running rails are the sole conductors for the return of the propulsion current, whereas the single-rail scheme is to be preferred for the opposite conditions, a notable illustration of which is the Interbo rough Rapid Transit System in New York City. The current taken by the track relays and the inductive bonds, has considerable lag owing to the highly inductive nature of the ap- paratus, while that which leaks from rail to rail, due to the compara- tively low resistance of the ballast and ties, has a power- factor of unity. 100 RAILWAY SIGNALING The frequency ordinarily used is 25 cycles. The track relay is of the induction type and does not respond to direct current. ALTERNATING-CURRENT V->- PROPULSION I The double-rail return system of alternating-cur- rent roads is very similar to that for direct-current roads, except that the in- ductive bonds have no air gaps and are of smaller capacity, and the track re- lays are of a somewhat dif- ferent type. As the propulsion cur- rent has a frequency of 25 cycles or less, the sig- naling current is given a frequency of 60 cycles in order that a track relay may be used which re- sponds to a current of the latter frequency and not to the former. In other words, the relay operates selectively on fre- quency and, of course, does not respond to any foreign direct current which may be present, jf This system is now in service on the New York, New Haven and Hartford railroad, and gives satisfactory results. FIG. 77 TRANSFORMERS Used to step down voltage from high tension signal mains to low voltage signal circuits. CHAPTER IX GREEN ffi YELLOW BLACK THE LANGUAGE OF FIXED SIGNALS THE previous chapters have dealt with the principle^ and with the actual details of the apparatus used in operating the vari- ous forms of signal apparatus. To the railway employes, to the passengers and to the casual observer the signal indications them- selves are the important features of a signal system. The actual mech- anisms used to accomplish the desired results are not of especial in- terest so long as they give the positive indications de- sired relative to the condi- tion of the tracks and posi- tions of trains. Two kinds of indications are used, one for day and one for night service. The semaphore arm, in various positions, is used in the daytime. A light, mounted behind a spectacle attached to the STOP PROCEED CAUTION PROCEED HOME SIGNAL DISTANT SIGNAL FIG. 78 ONE-ARM, HIGH, TWO-POSITION IN- TERLOCKED TRACK SIGNALS MEANINGS Home Signal. Stop Remain stopped ; route is not ready for train to proceed. Proceed Route is ready for train to pro- ceed. Distant Signal Caution Prepare to stop at next home signal. Proceed Expect to find next home sig- nal in proceed position. semaphore and holding col- ored roundels is used at night. The semaphore sig- nal is primarily a position signal, yet in many sys- tems the shape and color of the signal blade must also be considered in order to properly interpret the vari- ous indications displayed. The oldest and most common types of inter- locked track signals are shown in Fig. 78. The two semaphore arms on the left have square ends and are painted red with a white band near the end. The night indications show a red light when the the blade is horizontal and a white light when the blade is inclined. The semaphore arms on the right are called distant signals and have notched ends. They are painted green with a white V-shaped band near the end. At night, with the blade horizontal, a green light would appear and with the blade inclined a white light. SIGNALING For many years red and green have been used on railroads to in- dicate danger and caution, yet on most roads they still paint their signal blades these colors and then educate their trainmen so that they un- derstand that it is the po- sition of the blade and not its color which really counts. If only two positions are used, it is evident that in the case of the distant sig- nal, the blade must be painted a different color or have a different shape, or both, in order that its day B STOP PROCEED A PROCEED FIG. 79 TWO-ARM, HIGH, TWO-POSITION IN- TERLOCKED HOME TRACK SIGNALS MEANINGS Stop Remain stopped; no routes ready for train to proceed. Proceed "A" Superior route is ready for train to proceed. Proceed "" One inferior route is ready for train to proceed. indications may be distin- guished from those of the home signal. The home signal shown in Fig. 78 would be used only to govern movements over a track hav- ing no facing point switches for diverging routes, but this I ^j track may have one or more derails or trailing switches, which must be properly set and locked before the. signal can be cleared. In Fig. 79 are shown two- arm, high, two-position inter- locked home track signals. The blades are all painted red with a white band, and the night indications are either red or white, depending on whether the blades are hori- STOP PROCEED "A" PROCEED PROCEED V "c" FIG. 8O THREE-ARM, HIGH, TWO-POSITION INTERLOCKED HOME TRACK SIGNALS MEANINGS Stop Remain stopped; no routes is ready for train to proceed. Proceed "B" Second main route is ready for train to proceed. Proceed "C" One inferior route is ready for train to proceed. zontal or inclined. These sig- nals are used where there is one superior or main route and two or more inferior or branch routes. The lower arms gov- ern movements to any of the inferior routes. Many roads never RAILWAY SIGNALING 103 use more than two arms on any post, although there may be more than one superior route. Some roads always place two arms on one post although there may be no diverging routes. This is done for uniformity and in this case the lower arm would be immovable. In Fig. 80 are shown the in- dications obtainable by the use of three-arm two-position interlocked home track sig- nals. The blades are all painted red with white bands, either red or white. This arrangement of signals and one or more inferior routes. The use of this type STOP PROCEED STOP PROCEED PROCEED "A" "A" "B" "B" "c" FIG. 8 1 ONE- AND TWO- ARM, TWO-POSITION DWARF INTERLOCKED HOME TRACK SIG- NALS MEANINGS ' Stop Remain stopped; route is not and the night indications are ready for train to proceed. Proceed "A" Route is ready for train to proceed. Stop "B" Remain stopped; no routes should be employed only at are ready for tram to proceed. .-.* Proceed "B" Superior route is ready the junctions of two main for train to proceed. Proceed "C" One inferior route is ready for train to proceed. of signal is constantly be- coming less frequent, and ( the necessity for its use is met by another develop- ment to be described later. Dwarf track signals are .used on main tracks to govern movements against .the regular direction of traffic and on other tracks STOP PROCEED to govern all movements. HOME SIGNAL The different indications of one and two-arm two- position dwarf signals are CAUTION PROCEED DISTANT SIGNALS TWO-POSITION INTERLOCKED TRACK SIGNALS MEANINGS Home Signal ,_. Stop Remain stopped; route is not shown in Fig. 8l. Ihe ready for train to proceed, blades are red with a Proceed Route is ready for train to pro- white band and the night Distant signals indications either red or . Caution Prepare to stop at next home white. Since all dwarf Proceed Expect to find next home sig- signals govern movements nal in proceed position, which should be made at low speed, the two-arm type is very seldom used. However, track conditions sometimes require their use in IO4 RAILWAY SIGNALING order that one arm may be used to govern one particularly im- portant route only. The signals shown in Fig. 82 are the equivalent of those shown in Fig. 78, the only difference being that the sweep of the arm is 90 degrees instead of 60 degrees, and the blades are painted a neutral color, such as yellow. Two types of distant signals have been used as shown. The distant blade with the square end was the first consistent de- velopment of the practice of giving both home and distant signal indications distinctly without any regard to color or shape of blade. The types of signals shown in Fig. 83 are the equivalent of those shown in Fig. 79, the only difference being in the sweep of the arms and the color of the blades. All of the signals just described indicate only the condition of the tracks as far as the position of interlocked switches and derails is concerned. They do not indicate the presence of trains or whether the interlocked cross-overs and turn-outs are so constructed that the movements over them can be safely made at a moderately high speed. STOP PROCEED A" PROCEED B FIG. 83 TWO-ARM, HIGH, OX) DEGREE TRAVEL, TWO-POSITION INTERLOCKED HOME TRACK SIGNALS MEANINGS Stop Remain stopped; no routes are ready for train to proceed. Proceed "A" Superior route is ready for train to proceed. Proceed "B" One inferior route is ready for train to proceed. RAILWAY SIGNALING 105 Block signals are used to indicate the presence or absence of trains between definite points. Automatic block signals usually indi- cate more than this because, in addition to the other meanings, they indicate the condition of the track as far as broken rails or mis- placed switches are concerned. d_.^ MIIINII I During the past few years when the railroads have been having so much trouble on account of broken rails, auto- matic block signals have been a great protection. On one road as many as a dozen cases of broken rails in one month were indicated by their automatic block signals and serious wrecks were doubtless PROCEED STOP PROCEED CAUTION HOME SIGNAL DISTANT SIGNAL FIG g^ ONE-ARM, HIGH, TWO-POSITION prevented. AUTOMATIC HOME AND DISTANT BLOCK SIGNALS MEANINGS Home Signals Proceed Block is in condition for train to proceed. _ Stop Stop and wait prescribed time, then proceed with caution, expecting to find train in block, misplaced switch or broken rail. Distant Signal Proceed Expect to find next home signal in proceed posititon. Caution Prepare . to stop at next home signal. block signals of the one-arm type shown by Fig. 84 cannot be distinguished from the in- terlocked signals such as those shown in Fig. 78, al- though their meaning is dif- ferent. This similarity has caused some roads to place a marker, such as an illumi- In appearance automatic PROCEED STOP PROCEED STOP "A" "B" "A" "B" FIG. 85 TWO - ARM, HIGH, TWO-POSITION AND ONE-ARM, HIGH, THREE-POSITION AUTOMATIC HOME AND DISTANT BLOCK SIGNALS MEANINGS Proceed "A" Block is in condition for train to proceed. Expect to find next home signal in proceed position. Proceed "B" Block is in condition for train to proceed. Prepare to stop, at next home signal. Stop Stop and wait prescribed time,, then proceed with caution expecting to* find train in block, misplaced switch or broken rail. io6 RAILWAY SIGNALING iiated letter A, on each of their automatic block signal masts, so that when an engineer comes to a stop signal, he can, after making the stop, readily distinguish between the interlocking and block signals. Later developments in the art have led to further refinements in i ^ i ' this particular. The home and distant signals on separate posts are used in overlap block systems, in single track block systems and in double track block sys- tems where the blocks are unusually long. Automatic signals are more commonly used on double track roads with heavy traffic and the blocks are short, so that the home and frequently ^ JES STOP PROCEED PROCEED PROCEED "A" "B" "C" FIG. 86 THREE- ARM, TWO-POSITION INTER- , . . LOCKED HOME TRACK AND SPEED SIGNALS MEANINGS Stop Remain stopped. No routes are ready for train to pro- ceed. Proceed "A"K high speed route is ready for train to pro- ceed. Proceed "B" A moderate speed route is ready for train to pro- ceed. Proceed "C" A low speed route is ready for train to proceed. mounted on the same post or the equivalent three position CAUTION signal shown in Fig. 85, is used. All of the signals pre- viously described are types in common use. They have not, however, been found adequate for the conditions which have recently been arising. It has been found necessary to increase the capacity of roads by getting the trains over them faster. High speed turnouts and crossovers have been put in, so that this can be accomplished. On one road it is quite common practice to put in a crossover on each side of a sub- PROCEED PROCEED "A" "B" FIG. 87 TWO-ARM, HIGH, TWO-POSITION INTERLOCKED DISTANT TRACK AND SPEED SIGNALS MEANINGS Caution Prepare to stop at next home signal. Proceed "A" Expect to find next high speed home signal in proceed position. Proceed "B" Expect to find next moderate speed home signal in proceed position. RAILWAY SIGNALING 107 urban passenger station, so that while a local train is making the sta- tion stop, an express can come up behind and run around it at a speed of forty miles per hour. Since many turnouts cannot be taken at even moderately high speeds, a new requirement is that interlocked signals shall also indi- cate speed as well as tracks and hence the de- velopment shown in Fig. 86. These signals require the corresponding distant signals shown in Fig. 87. A further require- ment is that interlocked signals shall also indicate the condition of the block i i as well as the tracks and Stop Prot-eed Proceed Proceed Proceed Proceed Proceed "A" "B- "C" "D" "E" "F" speed. This led to the de- FIG. 88 - THREE-ARM, HIGH, QO DEGREE UPWARD TRAVEL, THREE-POSITION INTERLOCKED TRACK, SPEED AND BLOCK SIGNALS . VClOpment ShOWn in b Ig. 88. At prCSCllt this IS MEANINGS Stop Remain stopped. Route or block not ready for train to proceed. Proceed "A" Proceed on high speed track. Prepare to stop at next home signal. Proceed "B" Proceed on high speed track. Expect to find next home signal in proceed position. Proceed "C" Proceed on moder- ate speed, track. Prepare to stop at next home signal. Proceed "D" Proceed on moder- ate speed track. Expect to find next home signal in proceed position. Proceed "E" Proceed with ex- treme caution on low speed track. Proceed "F" Proceed on low speed track. being used on only one road, but is being seriously con- sidered for general adoption by other leading roads. This scheme also provides for a distinguishing feature between automatic block and interlocked signals. PROCEED PROCEED PROCEED STOP "A" "B" "C" FIG. 89 TWO-ARM, HIGH, QO DEGREE UPWARD TRAVEL, THREE-POSITION AUTOMATIC BLOCK AND INTERLOCK- ING DISTANT SIGNALS MEANINGS Proceed "A" Proceed. Expect to find next high-speed home signal in caution or proceed position. Proceed "B" Proceed. Prepare to stop at next home signal. Proceed "C" Proceed. Expect to find next moderate-speed home sig- nal in caution or proceed position. Stop Stop and wait the prescribed time, then proceed with caution ex- pecting to find train in block, mis- placed switch or broken rail. io8 RAILWAY SIGNALING All interlocked signals have the arms and lights, one ver- tically below another, while the automatic block signals have the arms and lights staggered as shown in Fig. 89. On approaching an interlocking, the block signals are also used as distant signals for the interlocking home signals. Where the block indication only is given, the lower arm is fixed in the horizontal position and is really only a marker. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO 5O CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. APR 15 1939 181942 U CO DECS 1960 REC'D jut 5 1963 DVD 01365 5 2. REC'D HOV17'65-3PM LOAN DEPT. LD 21- UNIVERSITY OF CALIFORNIA LIBRARY