The steam locomotive

Among the thousands of mechanical devices which we find about us there is none that is more fascinating than the steam locomotive. Its rugged outlines, its great size, its tremendous power, its aggressive noise—it is the perfect symbol of the machine age in which we live, the embodiment of the power and the speed, which, more than any other qualities, have characterized modern industrial progress. The steam locomotive is a factory in itself, a self-contained industrial plant. It has a furnace and a boiler, which turn water into steam; it has an engine, in which the expansive power of steam is converted into motion; it has the machinery which the motion of the engine serves to operate. In the ordi- nary factory these parts are separate. The furnace and boiler are in one room; in another room you will find the engine, with its glistening, rapidly moving rods and wheels; while in other rooms you will see the machines which are driven by the power of the engine, transmitted through shafting by means of a belt encircling the engine's fly wheel. The steam locomotive is all of this in one. The big driving wheels form the machine to which the engine's power is ap- plied, though it is applied directly by driving rods, and not by means of a belt. The object of the machine, unlike the object of the machinery of a factory, which gives form and shape to various materials, is movement, the transfer of the locomotive and the cars attached to it from one place to another. The product of this machine is not a tangible com- modity, but a service—the service which we call transportation. When water becomes very hot it turns into an invisible gas which we call steam. This gas expands, and if tightly en- closed, it exerts pressure, the amount of pressure depending upon the temperature of the water from which the steam comes. A steam engine is a device for using the pressure of the

steam to do work, to cause movement. It is the device through which the energy of heat is transformed into motion or me- chanical energy. There are not many things in the world much older than work. But the steam engine is not very old. Before the first one was built, all work had to be done by other kinds of power. Long, long ago, the first people who inhabited the earth had no power with which to do their work of hunting, plant- ing, harvesting, weaving and other activities by which they made their living except the power of their own muscles. Man made a great advance on the road toward civilization when he first domesticated animals and taught them to do his harder, heavier work, when he began to use oxen and camels and horses to carry burdens from place to place, to aid him in the

planting and cultivation of his crops. What wonderful inven- tions the first windmill and the first waterwheel must have been, providing the means of using forms of power stronger and more tireless than the muscles of either men or animals. We do not know when these things first came into use. Nor do we know about the origin of the sail boat, by which men could employ the power of the wind to travel on river, lake and ocean. Have you ever read about the galleys which the Romans and other seafaring peoples once used as vessels of commerce and of war? Great ships they were, driven over the water by dozens of long oars, pulled by slaves, chained to their benches and chained to the oars. The sailing vessels were surely a great improvement over the galleys.

The discovery of the way to use the expansive power of steam meant that man had a source of power far greater, and much more dependable, than the power of muscle or the power of rushing winds and running water. So great was the change which the steam engine effected in industry that we say it helped to bring about an "industrial revolution." There were various other changes in productive methods which characterized the industrial revolution, but none of them was so far reaching in effect as the introduction of the steam engine. Some engineers prefer to use the term "power revo- lution" instead of "industrial revolution" because they know that the most important feature of the so-called industrial revolution was the introduction of a new agency of power. It is said that James Watt, who built the first commercially successful steam engine, got the idea of making steam do work from seeing the steam lift the lid from his mother's teakettle boiling over the kitchen fire. "If steam can raise the lid of the kettle," he said to himself, "why can it not be made to do other kinds of work?"

Whether this story is true or not, when James Watt grew to manhood, he spent many years studying the problem of making steam do work, using the ideas of other men who had studied the problem, as well as many fresh ideas of his own. The first use made of the steam engine was to pump water out of coal mines in England. In many English mines water collected more rapidly than it could be pumped out by the muscular power of men or horses, and the mines had to be abandoned long before the coal was exhausted. The steam engine made it possible for these mines to be opened again. There were a few steam engines built before James Watt's time which could be used to pump water. But these early engines could not be used for any other purpose. Watt built engines which not only were better for pumping water than any engines which had been previously built, but could also be used for doing other kinds of work. He built engines which could turn wheels, and operate machines of any kind.

There were not many machines in use, of course, when Watt built his first steam engines, but his engines were eagerly sought to run the machinery that was known. Before long, many new machines were developed to do things which men had before always done by hand. Perhaps the most important of these machines were those employed in the textile industry. With the introduction of these new machines, operated by steam power, a great deal of the spinning and weaving, which previously people had done in their homes, was transferred to factories. The "factory system" of industry is said to have come with the industrial revolution, though as a matter of fact there were many factories where workmen toiled for wages before the steam engine came into common use. Unquestion- ably the steam engine greatly stimulated factory production, and many people believe that it was responsible for the be- ginning of the factory in industry. Not only the manufacture of textiles, but many other home manufacturing industries were established in factories using machines driven by steam engines.

The next step in the use of the steam engine was to have it do the work of transportation, to harness it to a vehicle for moving people and goods from place to place. Robert Fulton proved that the steam engine could be made to turn paddle- wheels to drive a boat over the water, in 1807, when he gave the world its first commercially successful steamboat. We still have steamboats driven by paddle wheels, but many more are driven by screw propellers, which are turned by steam engines in much the same way that paddle wheels are turned. Finally, as you read in a previous chapter, George Stephen son built the "Rocket," a steam locomotive which could pull a train of cars on a railroad.

The steam locomotives of today are much like the loco- motives that Stephenson built. They are larger and heavier, but their essential features are the same, the principle upon which they work is the same, and you can find in the steam locomotive of today the very same important parts that were in Stephenson's first successful locomotive. The biggest parts of the steam locomotive are the boiler and the firebox. They rest on a heavy steel frame, and this frame rests on the axles of the wheels. You have probably noticed that the door of the firebox is near the rear end of the locomotive, while the smokestack, through which the smoke from ihe fire passes to the open air, is at the front end of the

engine. In a large locomotive it is a long distance from the firebox to the smokestack. That part of the boiler just below the smokestack is called the smokebox. In going from the firebox to the smokebox, the smoke, flames, and hot gases of the fire pass through the boiler tubes, or flues. These flues are simply long pipes, and the boiler water is all around them. They are a most important part of the boiler, because they furnish most of its heating surface. If a locomotive boiler had no tubes or flues, it would not be possible for it to make the amount of steam which the engine requires for pulling a heavy load at high speed.

When the water in a locomotive boiler is heated to a point sufficient to create a working steam pressure, ordinarily not less than 200 pounds per square inch, the engine is ready to start. By means of the valve and lever called a throttle, the engineer lets steam from the boiler into a pipe, through which it passes to steam chests. From these steam chests the steam passes through valves to the engine's cylinders. The round cylinders, each with a steam chest just above it, are to be seen, one on each side of the locomotive, near the front end, forward of the driving wheels.

Inside each cylinder is a tight-fitting circular plate, known as a piston. The steam is admitted to a cylinder, first ai one end and then at the other, by the moving valve in the steam chest, and its pressure pushes the piston back and forth in the cylinder. The valve in the steam chest, by which the steam is admitted to the cylinder, works as the piston moves to and fro, letting the steam enter, first on one side of the piston and then on the other. As the valve lets the steam into one end of a cylinder, on one side of the piston, it leaves an opening at the other side through which the steam which has previously spent its force on the piston may pass out of the cylinder into an exhaust pipe. This pipe carries the exhausi steam to the smokebox, and from there it goes up the smoke- stack into the open air. As it rushes out it causes the "choo choo" sound you hear as the locomotive speeds along. The exhaust steam has an important use. It creates a heavy drafi through the smokestack, and this forced draft causes the fire to burn more fiercely in the firebox. The exhaust draft and the multitubular boiler were the two things which made Stephenson's "Rocket" a success. They provided the heating surface and the rapid fuel combustion which were necessary to produce enough steam to keep the locomotive moving at high speed with a heavy load.

Fastened to one side of each piston, at the center, in fact a part of the piston, is a long round piston rod, which sticks out through a central hole in the rear end of the cylinder. The piston rod is made to fit tightly in this opening by means of asbestos or metal packing rings, which prevent steam from leaking out of the cylinders.

The outer end of the piston rod is fastened to a crosshead, a heavy steel block, which moves back and forth in steel guides. Joined to the crosshead by a large steel pin is the connecting rod or main rod of the locomotive. The connect- ing rod extends from the crosshead to a crankpin, a bit off- center, on one of the driving wheels. This driving wheel is connected with the other driving wheels by long side rods, which likewise are fastened to crank pins.

As the steam makes the piston move back and forth in the cylinder, the main rod and side rods also move, the moving rods make the wheels turn, and the turning wheels carry the locomotive along the track. Steam pressure does the work. Such an engine is a reciprocating engine, so named because of the back and forth movement of its piston. In the next chapter we shall have something to say about another kind of steam engine, known as a turbine, in which there is no piston and no back and forth, or reciprocating motion. Nearly all reciprocating engines accomplish their work by transforming the reciprocal motion into rotary motion. In some mechan- ical contrivances, operated both by steam power and by mus- cular power, you may see this reciprocating motion trans- formed into rotary motion, which is then transformed once more into reciprocating motion. An example of such a con- trivance is the old fashioned sewing machine, which is driven by a foot-operated treadle. In the mowing machine, with which a farmer cuts his hay, the rotary motion of the mower's wheels gives a reciprocating motion to the cutter bar.

The working pressure of the steam in our older locomo- tives is usually about 200 pounds to the square inch. A piston with a diameter of 24 inches presents a surface of more than 450 square inches. With a full pressure against its surface, it is subjected to a force of 90,000 pounds. Many of the Ameri- can locomotives built in recent years have a maximum boiler pressure considerably higher than 200 pounds per square inch, some of them having 300 pounds, or even more. The boiler of a locomotive must be very strong to resist a pressure of 200 pounds per square inch without "blowing up." All locomotive boilers, in fact all steam boilers, even those which provide steam for heating homes, are fitted with safety valves. When the pressure of the steam in a boiler reaches such a point as to make the boiler unsafe, the safety valve

opens, the steam escapes to the open air, and the pressure is relieved. You have all probably had a chance to see a loco- motive with its safety valve open, and hear the loud hiss of the escaping steam. While locomotive firemen try to keep a full head of steam, they try to keep pressure low enough so that the engine will not "pop off," because if there is such an excess of pressure that the safety valve operates, it means that fuel is being wasted.

Even at its best a steam locomotive wastes much of the heat which its burning fuel produces. It must be remembered that while the pressure of steam makes a locomotive go, it is the fuel—the coal or the oil consumed in the firebox—that really furnishes the locomotive's power. Of all the coal or oil which is burned in a steam locomotive, only a small part does any useful work. Scientists tell us that in the very best of our reciprocating steam locomotives only about ten per cent of the heat produced by the burning coal or oil is used in moving the locomotive and in pulling a train of cars. The rest of the heat is wasted. Part of it escapes through the smokestack in smoke and exhaust steam, part is lost by reason of the frictional resistance of the moving parts of the engine. A machine which uses only eight per cent of its source of power and loses the remaining ninety-two per cent is truly a wasteful machine. Many of our locomotives do not use even eight per cent of the energy stored in the fuel which they burn.

During the last forty years there has been a marked im- provement in the efficiency of the steam locomotive. Before 1900, few locomotives employed in useful work as much as five per cent of the fuel they consumed. The improvement in the locomotive's thermal efficiency has been brought about in part by the use of devices which permit a better combustion of fuel and other devices through which some of the heat which once was wasted is now saved and put to work. More- over there has been a great improvement in the design and construction of steam locomotives.

A device which has helped greatly to increase locomotive efficiency has been the brick arch, with which the fireboxes of all locomotives are now equipped. This brick arch is a kind of baffle-plate of firebrick, extending from the lower front end of the firebox, backward and upward toward the firebox door. Of course it does not reach all the way to the rear of the firebox. It is supported by tubes through which water from the boiler circulates. The flames from the burning coal do not go directly forward toward the boiler tubes, but are directed backward till they reach the edge of the brick arch, where they turn upward and forward toward the tubes. The deflection of the flames by the brick arch gives a longer time for combus- tion, and not so much unburned coal and gas are lost through the smokestack.

Nearly all locomotives are equipped with steam superheat- ers and many locomotives also have feedwater heaters. A feedwater heater is a device in which the water for the boiler is heated, almost to the boiling point, before it passes into the boiler. The heat is obtained from exhaust steam. In i he old locomotives, all of this exhaust steam once passed out through the smokestack. Now a part of it is diverted, and heat which once was lost, is made to serve a useful purpose. Locomotive feedwater heaters are found in different places. Many of them are located just in front of the smokestack. They remind one of the knapsack which a soldier carries.

More important than the feedwater heater as a fuel saving device is the steam superheater. It can not be seen on the outside of the locomotive. It consists of a header, placed in the smokebox. and a number of small looped, or U-shaped tubes which extend from the header back into the boiler tubes, some of which are made larger for the express purpose of giving room for the superheater tubes. The superheater gives the steam added heat after it leaves the boiler and before it gets to the cylinders. The steam passes from boiler to super- heater, from superheater to cylinders, and while in the super- heater it gets additional heat from the hot gases which flow through the boiler tubes into the smokebox. Steam, as it comes from the boiler, is said to be saturated, that is, it begins to condense into water as soon as its temperature begins to fall. When saturated steam enters an engine cylinder there is an immediate loss of power because of condensation. Super- heated steam does not begin to condense until its temperature is reduced to that of the saturated steam as it entered the superheater. When the superheated steam enters the cylinders there is no immediate loss of power by condensation. A

smaller amount of steam is required, therefore, for the same amount of work. Since much of the heat which the super- heated steam receives would otherwise be lost through the smokestack, it can readily be seen that the superheater is a most effective device for saving fuel. An engine with a super- heater also consumes less boiler water. Since a superheater has no moving parts to wear out, it is not costly to maintain, and it soon saves its cost of manufacture and installation many times.

There are many parts to the steam locomotive, in addition to the essential parts which we have been discussing. Every locomotive has a tender which carries the fuel and water for firebox and boiler. Some locomotives burn oil for fuel, but most of them burn coal.

The water tank of the tender is fitted with pipes through which the water may pass to the boiler. When a fireman or the engineer thinks the water in the boiler needs replenishing, he turns on an injector, an ingenious contrivance, in which a jet of steam draws water from the tender and blows it into the boiler. Some injectors are operated by exhaust steam, a further saving of fuel for the locomotive. On some locomo- tives and especially upon those which have feedwater heaters, fresh water is forced into the boiler by a pump instead of by an injector.

Boiler water often has to be "treated" before it is put in the locomotive tender, to rid it of lime and other mineral sub- stances which the water holds in solution, and which, if not removed would soon form a thick, crusty deposit on the boiler's inner surface and on the boiler tubes, greatly dimin- ishing the boiler's steam producing capacity. Some boiler water is treated in the tender itself. As this treated water boils and evaporates it leaves a soft sludgy deposit in the boiler which may be blown out at frequent intervals in the engine terminal. All locomotive boilers must be cleaned out regularly. An oil burning locomotive makes work fairly easy for the fireman. 1 he liquid fuel is sprayed into the firebox, much as it is done in an oil burning furnace for heating a house, only in much larger quantities. 1 he fireman merely watches his steam pressure gauge and water level and turns a valve to in- crease or reduce the How of oil into the firebox. Anybody who has ridden on an oil-burning locomotive knows how much easier the work of the fireman is than the work of a fireman who works on a coal-burning locomotive and shovels coal into the furnace by hand.

But the work on coal burning locomotives has become much easier in recent years. As manufacturers built larger and larger locomotives, many of them came to have such large fireboxes that it was very difficult to fire them by hand. Mechanical stokers were invented to lire these large locomotives. Now all of our largest coal burning locomotives, and many of our smaller ones too, are stoker-fired, and the firemen are not sub- jected to such backbreaking toil as they once performed. A mechanical stoker is run by a small auxiliary steam engine, which gets its steam from the locomotive boiler. There are several different kinds of locomotive stokers, but they are all much alike in their operation. The coal is carried from the tender to a crusher, which reduces the large lumps of coal into small particles, though it does not pulverize it. The particles are carried by a screw conveyor to a flat iron plate inside the firebox. Small jets of steam, coming from pipes so arranged that they point toward all parts of the firebox, blow the coal from this plate and scatter it over the grate surface. The mechanical stoker not only saves the fireman's back, but it saves coal. It spreads the coal more evenly over the grate surface, and its use makes it unnecessary to open and close the firebox door every time coal is added to the fire. Moreover, the crushed coal burns more completely and cleanly i ban coal in large lumps.

Every locomotive has a cab, in which the fireman and the engineer ride. There is a seat on each side, and windows at the side and front. Through the windows at the front the engineer and fireman can look out along the sides of the boiler to the track ahead, observing whistle posts, crossings, and vari- ous signals, and watching for obstructions. The engineer sits on the right side of the cab, the fireman on the left. On the hand-fired locomotive the fireman does not sit much, however, for he is kept pretty busy shoveling coal from the tender to the firebox, and looking after the fire, so that there will be plenty of steam. On many of the smaller locomotives on English and other European roads there are no seats in the cabs. Both the engineer, or driver, and the fireman must stand during their runs.

A locomotive has a headlight to light the track ahead at night. Large oil lamps were formerly used for headlights, each with a large reflector back of the light, but the head- lights now used are electric. The electricity comes from small dynamos or generators, placed on top of the boiler. They are run by steam from the locomotive boiler. On some of our locomotives the electric headlight is just in front of the smoke- stack, on others it is attached to the circular front of the smokebox, either at the center, or just above. On the top of a locomotive there are ususally two round- topped boxes or domes. From one of these the steam is taken from the boiler; it contains the throttle valve. The other dome is a sandbox. It is filled with clean, dry sand. Small pipes run from the sandbox downward almost to the railroad rail just in front of the driving wheels. When these wheels slip because of cold or rainy weather, or because the train is heavy and difficult for the locomotive to start, the engineer opens a valve which lets tiny streams of sand fall on the rail in front of the

driving wheels. It gives the wheels a better grip on the rails, just as the dust in which a baseball player rubs his hands gives him a better grip on his bat. From the sandboxes on most locomotives the sand is forced out by compressed air instead of being let run out by its own weight.

Every locomotive has a bell and whistle. Passenger train locomotives have two whistles. One is the big whistle on top of the boiler, which is blown by steam or by compressed air and used to let people know the train is coming. The other is a small whistle in the locomotive cab. It does not make a very loud noise, and only the engineer and fireman listen for it. It is a signal whistle by means of which the conductor on the passenger train communicates with the engineer. This whistle is blown by compressed air. In the passenger car of a half century ago there was a long cord above the aisle, reaching from one end of the car to the other, and it was by means of this cord that the whistle in the engine cab was blown. In a modern passenger car there is no signal cord running down the center of the car, but a metal valve mechanism at each end of the car. On some of the older cars, however, the overhead signal cords may still be seen. The cord is not attached to the whistle,—it is used to operate a valve which serves to admit a blast of air into the whistle. Each passenger train has an air signal pipe line, extending throughout the length of the train.

The engineer knows what message the conductor is giving him by the number of times the whistle blows. The whistle code employed on our passenger trains is uniform on American railroads. If a train is moving and the whistle blows three times, it means, "Stop at the next station." If it blows twice when the train is moving, it means, "Stop at once." If it blows three times when the train is standing still it means for the engineer to back the train. There are other signals for other messages.

    The standard code of operating rules, in force throughout the United States, prescribes many engine whistle signals, of which the following are extensively used:
  • Approaching public grade crossing—Two long, two short.
  • Approaching station, junction or railroad crossing—One long.
  • Alarm for persons or animals on track—Succession of short toots.
  • Apply brakes, stop—One short whistle.
  • Release brakes, proceed—Two long whistles.
  • Flagman protect rear of train—One long, three short.
  • Flagman return from west or south—Four long.
  • Flagman return from east or north—Five long.
  • Call for signals—Four short.
  • Back up (when standing) —Three short.
  • Stop at next station (when running) —Three short.

Some day when you are on a train you will hear a long
"Too-o-o-o-oot!"from the locomotive whistle. The engineer
is saying, "We are getting close to a station." The conductor
reaches up to the cord and pulls it once, twice, three times.
Then the locomotive whistle goes, "Toot, toot, toot." The
engineer is saying to the conductor, "I heard your signal and
will stop at the station." Pretty soon you will feel the brakes,
the train slows down, and comes to a stop at the station
platform.

    The bell cord communicating signals from train to engine cab are:
  • Two short: When standing, start.
  • Two short: When running, stop at once.
  • Three short: When standing, back up.
  • Three short: When running, stop at next passenger station.
  • Four short. When standing, apply or release air brakes.
  • Four short: When running, reduce speed.
  • Five short: When standing, recall flagman.
  • Five short: When running, increase speed.
  • Six short: When running, increase train heat.
  • One short, one long, one short: Shut off train heat.
  • One long: When running, brakes sticking; look back for hand signals.

In 1944 a few American railroads began to use a new system of train communication, a system which could be installed on both freight and passenger trains, a system which not only enabled the engineer in his cab to communicate with the con- ductor in the caboose, but made it possible for the crew of a moving train to communicate in a new manner with operating forces in railroad stations, yards and oflices and even on other trains. This new means of communication was not by a code, nor by any kind of visual signal. It was vocal; the communica- tion was by actual speech. The new science of electronics about which we have heard so much, in connection with radio, and radar, and all kinds of automatic devices for controlling the operation of machines, made it possible to develop this new method of train communication.

Some railroads are making use of radio. A two-way tele- phone, like that found in patrolling police cars, or like the "walkie-talkie" of the army, provides the means of communi- cation, and government authority has already assigned certain wave bands for railroad use. Other roads use an "induction" system, in which the electrical impulse is transmitted first to the railroad rail, picked up "inductively" by wires on the train or along a station, and amplified in cab, caboose or sta- tion. Another method employs radio transmission between the train or station and the telegraph or telephone wires along the railroad's right of way, and the wires carry the impulses to the amplifying mechanisms.

This new method of communication is proving to be very useful, especially on long freight trains, where heretofore it has been difficult for the conductor in the caboose to give messages and instructions to the engineer. Hand signals are often impossible to discern because of weather conditions, and freight trains have never had the "bell cord" and loco- motive signal whistle. On a train with telephone communi- cation, a trainman who detects a smoking hotbox on a freight car can tell the engineer and have the train stopped in the proper manner, before an accident occurs. Formerly, if the trainman could not have his hand signal perceived, he either had to endeavor to make his way forward to the locomotive, or set the air brakes himself, running the risk of having the train break in two.

The new means of communication enables the conductor and the engineer to co-operate in getting the train ready for its departure, and to exchange information at any time with regard to the movement of the train and the state of its equip- ment. Exchange of information between moving trains, and between a moving train and operating offices, often permits train movements to be speeded up. It can readily be seen that the new means of communication may be a safety device of high importance, just as is the radio on a ship at sea. Many of our railroads are installing one or another of the different kinds of telephonic train communication, and there is no doubt that its use will soon be general.

At the front end of a locomotive is a pilot or cowcatcher. If the locomotive should strike an object on the track the pilot may throw it to one side and keep it from getting under the wheels and into the moving parts of the locomotive. On the steam locomotives of today there are a great many things which we often call "gadgets"—ingenious contrivances or devices, which were unknown to the engineers and firemen of a generation ago. There are machines to shake the grates ai the bottom of the firebox, work that was once a part of the fireman's job; machines to ring the locomotive bell. The en- gineer operates the reversing gear of his locomotive by a mechanical device now, instead of by a heavy reverse lever, which all locomotives had not so many years ago. All these gadgets make the labor of the engineers and firemen much easier than it used to be. Some of the devices are operated directly by steam, others by compressed air. But in either case it is steam which really does the work.

One of the most useful parts of the steam locomotive, which should be described with some detail, is the air brake mechanism, consisting, on the locomotive, of an air pump, a main air reservoir, an engineer's brake valve, and the devices by which brakes are applied to the locomotive's own wheels. The air pump, which is run by steam from the locomotive boiler, compresses air in the main air reservoir, and the pres- sure of the air is used to force the brake shoes against the wheels of the cars and the locomotive and bring the train to a stop. The air pressure works just like steam pressure, but compressed air does not have to be hot, like steam. The com- pressed air is taken from the main air reservoir on the loco- motive to auxiliary reservoirs beneath the cars, through an air pipe. The air pipes of the cars are connected with one another by rubber air hose, which couple together between the cars. You can see the air hose and coupling at the end of any car or locomotive. On passenger cars you see three sets of hose couplings. One is for the air for the air brake; one is for the air which blows the signal whistle in the locomotive cab; the third is for the steam which comes from the locomotive boiler to heat the passenger cars in cold weather. On some trains the air connections, and other pipe connections between cars, are made of metal.

Before the air brake was invented trains were brought to a stop with hand brakes. Cars still have hand brakes but they are used now only when the cars arc disconnected from the engine. It used to be hard, dangerous work for brakemen to run over the cars in all kinds of weather, turning on brakes, one after another, as fast as they could. Now the brakemen can stay inside their "caboose," and let the engineer work the brakes from the locomotive cab, just by turning a little brass valve that stands in front of his seat.

George Westinghouse was the inventor of the air brake. It was one of the most useful inventions we have had on the steam railroad. It made it possible to have long heavy trains, which could be slowed down or stopped more easily than a very small train could be controlled by hand brakes.

The first air brake invented by Westinghouse was called a straight air brake. It had only one air reservoir, that be- neath the engine, and this reservoir was connected by pipe and hose to the brake cylinders beneath the cars. To set the brakes the engineer opened a valve in the engine and let the compressed air of the reservoir flow swiftly through the train pipe to the brake cylinders. Here it pressed against a

piston connected by levers to the brake rods, and the levers and rods pressed the brake shoes against the turning wheels of the cars. To release the brakes the engineer closed the valve

in the engine, shutting off connection between the reservoir and the train pipe, and at the same time permitting the air in the train pipe and brake cylinders to escape to the atmosphere, While this type of brake worked very well, it had one great defect. It was not automatic in its action. That is, if a train broke in two, or if the train pipe or an air hose broke, the straight air brake would not bring the train to a stop. In fact it became entirely useless, for if the engineer opened his brake valve all the compressed air in the reservoir would merely escape to the outside air, without affecting the brakes at all.

Seeing that a straight air brake would not be satisfactory on trains of cars, Westinghouse set to work to make an auto- matic air brake, such as we now have on all our trains. The most essential part of the automatic air brake is a de- vice known as a triple valve. Beneath each car is an auxiliary reservoir and a brake cylinder. They are connected with each other and also with the train pipe through the triple valve. The auxiliary reservoir holds enough air to operate the brakes on its car.

When the train is moving with brakes released, the adjust- ment of the triple valve is such that a passage is open between the train pipe and the auxiliary reservoir, and another passage is open between the brake cylinder and the outside air. The air pressure in the main reservoir on the engine, in the train pipe and in the auxiliary reservoir is the same. To apply the brakes on the train the engineer opens the brake valve in the cab of his engine. This valve shuts off the connection between the main reservoir and the train pipe, and at the same time permits the air in the train pipe to escape. The reduction of the air pressure in the train pipe causes the triple valve beneath each car to operate in such a way that it closes the opening from the brake cylinder to the outside air, closes the passage between the auxiliary reser- voir and the train pipe, and opens the passage between the auxiliary reservoir and the brake cylinder. The compressed air rushes from the auxiliary reservoir to the brake cylinder and causes an immediate application of the brakes.

To release the brakes the engineer closes the brake valve in his cab. The air from the main reservoir flows into the train pipe. The rise of pressure in the train pipe causes the triple valve to operate so as to open the passage between the train pipe and the auxiliary reservoir, close the passage be- tween the auxiliary reservoir and the brake cylinder, and open the passage between the brake cylinder and the outside air. The compressed air in the brake cylinder escapes and the brakes are released, and the air pressure in the train pipe, the auxiliary reservoir and the main reservoir again becomes the same.

Since the brakes are made to work by a reduction of the air pressure in the train pipe, it can be seen that if a train should break in two or if the train pipe or an air hose should become broken, all the brakes on the train would at once be applied and the train brought to a stop.

The first triple valve invented by Westinghouse was some- what slow in its action, and could be used successfully only in short trains. When it was tried on long trains the brakes in the cars near the engine set so much more quickly than the brakes in the cars farther back in the train that the cars would come together in a series of violent and destructive shocks. When the brakes were released, the action was so slow that often a train would pull in two because of the tardy response of the valves near the rear end of the train. In 1887 Westinghouse developed a much better triple valve, the action of which was much more rapid. This new kind of valve, known as Type H, could be used quite well in trains having as many as fifty cars.

But as time went on it became desirable for railroads to have larger and heavier trains. This meant that better brakes were needed, valves that would respond more quickly than the Type H valve. In 1905 the Type K triple valve was introduced. It was much more rapid in its action, and with it trains of a hundred cars could be easily controlled. But locomotives grew larger and more powerful, and trains longer and heavier. It became apparent that the Type K triple valve would not meet the needs of the railroads. Engi- neers must find something better, a valve which would make it possible to control trains having a hundred and fifty cars or more. After several years of research and experimentation in laboratories and in actual train service, a new valve known as the AB valve, was developed, and first put into actual use in 1933. The AB valve is not exactly a triple valve, though it performs the same duties, in a better fashion.

The AB valve works more rapidly and more smoothly than the triple valve, when the brakes are applied to bring a train to a stop. An even more important feature is its greater speed and certainty of action in the releasing of the brakes. With the K triple valve, the increase of pressure in the train pipe necessary to bring about the release of the brakes was supplied entirely from the air from the main air reservoir on ihe locomotive. On a long train it took too much time to restore this train pipe pressure. With the AB equipment, in addition to the ordinary auxiliary air reservoir beneath each car, there is a second supplemental reservoir. When it is desired to release the brakes, the AB valve permits the air in this supplemental reservoir to flow into the train pipe. The release of the brakes therefore comes more quickly, and there is no danger either that any brake will stick. The air in the supplemental reservoir can be used in applying the brakes too, when a sudden or "emergency" application is desired.

One problem the engineers had to solve in designing the AB valve was to make possible its use in trains of cars, pan of which were equipped with K triple valves. It would not be possible to change the valve on all cars at once. Many new cars now being built are fitted with the AB brake equip- ment, and as the old Type K equipment wears out on other cars it will be replaced with AB brakes. In a few years most of our railroad cars will have the new type of valve. The AB valve is one of the most recent of a long list oi important inventions that have done so much to increase the efficiency and the safety of railroad operation. Perhaps

it can hardly be called an invention. It is not the work of one man, but represents the combined efforts of many men, who for several years devoted much of their time and energy to patient study and research, trying to solve a problem which it was necessary to solve if the development of the steam rail- road was to continue.
Nearly all steam locomotives have some wheels which are smaller than the driving wheels. These smaller wheels are

called truck wheels. Those in front of the driving wheels carry the weight of the front end of the locomotive. When two are used, they are called pony truck wheels. On many locomotives there are truck wheels back of the driving wheels, supporting the weight of the firebox. These are called trail- ing truck wheels.

Some locomotives have "boosters" attached to their trailing truck wheels, or to the wheels of their tenders. The booster is a small two-cylinder steam engine, geared to the axle of the truck wheels. It operates when the locomotive starts or is climbing a steep hill at low speed. By its use the truck wheels can be made to help the driving wheels in moving the engine forward. When there is no booster, the truck wheels have nothing to do with propelling the locomotive.

Truck wheels were an American invention, introduced very soon after the beginning of steam railroad transportation in this country. The wheels on the first locomotives were either all driving wheels, four in number, or perhaps two driving wheels and two carrying wheels, which could not turn inde- pendently of the driving wheels. Our early railroads were

built with many curves, because of the expense of making cuts and fills, and it was found that the first locomotives were likely to "jump the track" when going around sharp curves. Truck wheels placed under the front end of the locomotive helped overcome its tendency to keep going ahead in a straight line when it came to a curve in the track.

Trailing truck wheels were added many years after the in- traduction of leading truck wheels. As locomotives became larger and more powerful, fireboxes also had to be larger. Fireboxes directly over driving wheels were somewhat shal- low; those placed between driving wheels were somewhat narrow. With trailing truck wheels a locomotive could have a firebox both wide and deep. For nearly a half century no American locomotive had more than a single pair of trailing truck wheels. But on many of the heavy passenger and freight locomotives now in use there are four-wheeled trailing trucks. Such a truck makes possible the construction of a very wide and deep firebox, in which there can be a thorough combus- tion of coal in large quantities.

There are many kinds or types of steam locomotives. Some are built chiefly for speed, some are built not so much for speed as to draw heavy loads. The different types of locomo- tives are classified according to the number and arrangement of their driving wheels and truck wheels. This classification is known as Whyte's classification, after the man who first used it. Railroads have a more elaborate method of classifying their locomotives, using a combination of figures and letters which tell much more about the design of the locomotives than the number and arrangement of wheels.

Under Whyte's classification, a series of figures indicates the number of leading truck wheels, the number of driving wheels, and the number of trailing truck wheels. For example, a 4-6-2 locomotive has four leading truck wheels, six driving wheels, and two trailing truck wheels; a 4-6-0 locomotive has the same number of leading truck wheels and driving wheels but no trailing truck wheels.

The various classes or types of locomotives in use on Ameri- can railroads are also named. The American type (4-4-0) has four driving wheels, and four truck wheels in front. The At- lantic type (4-4-2) has four driving wheels, four truck wheels in front and two truck wheels behind. Both these types have been used chiefly for passenger trains. The Atlantic type is more powerful than the American, because it is heavier and because the pair of trailing truck wheels permits it to have a larger firebox.

The Mogul locomotive has six driving wheels and two truck wheels in front, while the Consolidation type has a pair of truck wheels in front and eight driving wheels. These two types are used for freight trains.

The ten-wheel locomotive has four front truck wheels and six driving wheels. The Pacific locomotive is just the same except that it has a pair of truck wheels back of the driving wheels. These two types are used for heavy passenger trains and for light, fast freight trains.
The Mikado type has two truck wheels in front and two behind, and eight driving wheels; the Santa Fe type has the same number and kind of truck wheels, and ten driving wheels. These two types are used to draw heavy freight.

Switching locomotives have no truck wheels. The whole weight of these locomotives rests on the driving wheels, and they can stop and start more quickly than other locomotives. Some of them have four, some six, some eight, and a few have ten driving wheels. The most powerful steam locomotives are really two loco-

from the Smokestack motives joined into one. They are articulated or jointed loco- motives but are usually called Mallet locomotives, after the French engineer who built the first one. An articulated loco- motive has but one firebox and one boiler, but it has two sets of driving wheels and cylinders. The articulated locomotives also have truck wheels in front and behind, sometimes four, and sometimes two. They are very heavy and strong, and are often used as "pushers" to help heavy freight trains over steep hills. They are also used on high speed, heavy freight trains.

On American roads each locomotive is numbered, and has its number painted in large figures on the tender, or on the cab, and often on a plate at the front end of the boiler, or at some other place. The name of the railroad which owns the locomotive is also painted on the cab or on the tender, and sometimes on both.

When steam railroads were new, most of the locomotives were not numbered, but had names. Some were named after famous men, such as Washington, Hamilton, Jefferson, Frank- lin; some were named after old Greek and Roman gods and heroes, such as Jupiter, Vulcan, Mars, Hercules, Mercury, Jason; some were named after animals, such as Lion, Tiger,

Antelope, Elk; some were named after towns and cities, count- ies and states, and some had beautiful Indian names. The famous "John Bull" locomotive was brought from England and placed on the Camden and Amboy Railroad in 1831. Robert L. Stevens bought this locomotive. Do you remember what important thing he did on the ship while on his way to Eng- land to buy it? The "John Bull" was the first locomotive used in New Jersey. Some day, when you go to Washington, go to the Smithsonian Institution, and there you will see this famous locomotive. It does not look exactly as it did in 1831, for after it had been here a few years a headlight, a cowcatcher, a bell, a whistle, and a shelter for the engineer and fireman were added to it. Some of our railroad companies have re- cently begun to name their locomotives again, though they still keep their numbers too.

Many new ideas in the design of steam locomotives have been brought forward both in this country and in Europe in recent years. Nearly all of the locomotives now built in America have a working steam pressure of at least 250 pounds, and experiments are being conducted with much higher pressures. In Germany, before the war began, a locomotive was constructed to operate with a steam pressure of 1700 pounds. Some American locomotives have three cylinders instead of two, the third cylinder being placed midway be- tween the other two, and the driving wheels with which its piston is connected being fitted with a crank axle. In 1939, the Pennsylvania Railroad built in its own shops a locomotive with four cylinders, eight driving-wheels, six leading and six trailing truck-wheels. It was exhibited at the New York World's Fair and was said to be the largest high speed locomo- tive ever built. New types of boilers have been designed in which the amount of heating surface has been greatly increased over the amount found in older types. Locomotives are now built with roller bearings, which, it is claimed, reduce the frictional resistance of wheel and axle, and result in a saving of fuel. Some of these new locomotives are veritable giants of the rail. It is interesting to note some of their specifications.

These are some typical locomotives built in recent years by American locomotive builders for use on American railroads, in freight and passenger service. Many other locomotives have been built, some larger, others smaller. They represent a great change in American locomotives since the beginning

of steam railroad transportation, particularly with respect to size. A hundred years ago a steam locomotive of 25 tons was considered to be gigantic. Now locomotives with a total weight, engine and tender combined, of 500 tons, are common sights on American railroads. While the efforts to improve the steam locomotive have led to important results, the attempts to find a substitute for it have been extremely interesting, and perhaps even more im- portant in their results. Other kinds of motive power have been introduced on many steam railroads, both in the United States and in other countries, with such marked success in many instances that many persons profess to believe the old style steam locomotive is doomed to pass entirely out of use on our railroads. In the next chapter we shall tell about some of the engines which have been developed to take the place of the reciprocating steam locomotive.