Having explained how the steam is generated, it remains to s_The American Railway: Its Construction, Development, Management, and Appliances

how it propels a locomotive. It does this very much as a person on

a bicycle propels it--that is, by means of two cranks the wheels

are made to revolve, and the latter must then either slip or the

vehicle will move. In a locomotive the driving-wheels are turned

by means of two cylinders and pistons, which are connected by

rods to the cranks attached to the driving-wheels or axles. These

cranks are placed at right angles to each other, so that when one

of them is at the "dead-point" the piston connected with the other

can exert its maximum power to rotate the wheels. This enables the

locomotive to start with the pistons in any position; whereas,

if one cylinder only was used it would be impossible to turn the

wheels if the crank should stop at one of its dead-points.

It will probably interest a good many readers to know how the

steam gets into the cylinders and moves the pistons and then gets

out again, and how a locomotive is made to run either backward or

forward at pleasure.

Figure 20 (p. 118) shows a section of a cylinder, _A A′_, with

the piston _B_ and piston rod _R_. The cylinder has two passages,

_c c_ and _d d_, which connect its ends with a box, _U_, called a

steam-chest, to which steam is admitted from the boiler by a pipe,

_J_. The two passages _c_ and _d_ have another one, _g_, between

them, which is connected with the chimney. These passages are

covered by a slide-valve, _V_, which moves back and forth in the

steam-chest, alternately uncovering the openings _c_ and _d_. When

the valve is in the position shown in Figure 20, obviously steam

can flow into the front end _A_ of the cylinder through the passage

_c_, as indicated by the darts. The valve has a cavity, _H_,

underneath it. When this cavity is over the passage _d_ and _g_,

it is plain that the steam in the back end _A′_ of the cylinder

can flow through _d_ and _g_ and then escape up the chimney. Under

these circumstances the steam in the front end _A_ of the cylinder

will force the piston _B_ to the back end. When it reaches the back

end of the cylinder the valve is moved into the position shown in

Figure 21, and steam can then enter _d_ and will fill the back end

_A′_ while that in the front end escapes through _c_ and _g_. The

piston is then forced to the front end by the pressure of the steam

behind it. It will thus be seen that the steam enters and escapes

to and from the cylinder through the same openings.

[Illustration: Figs. 20 (above) and 21.--Sections of a Locomotive

Cylinder.]

From what has been said it is obvious, too, that every time the

piston moves from one end of the cylinder to the other the valve

must also be moved back and forth in the steam-chest. This is done

by what is called an eccentric.

An "eccentric" is a disk or wheel (Fig. 22) with a hole, _S_,

the size of the axle of the locomotive to which it is attached.

The centre _n_ of the outside periphery of the eccentric is some

distance from _S_, the centre of the shaft. A metal ring, _K K_

(Fig. 23), made in two halves, embraces the eccentric, and the

latter revolves inside of this ring. A rod, _L_, is attached to

the strap, and is connected with the valve so that the motion of

the eccentric is communicated to it. It is obvious that if the

eccentric revolves it will impart a reciprocating motion to the rod

_L_, which is communicated to the valve.

[Illustration: Fig. 22.--Eccentric.

Fig. 23.--Eccentric and Strap.]

If properly adjusted on the axle the eccentric will run the engine

in one direction. To run the opposite way another eccentric must

be provided. Therefore locomotives always have two eccentrics for

each cylinder. These, _J_ and _K_, are shown in Figure 24, which

represents the "valve-gear" of a locomotive. _S_ is a section of

the main driving-axle, to which the eccentrics are attached by

keys or screws. _C_ is the eccentric rod of the forward-motion

eccentric and _D_ that of the one for running backward. As a

locomotive must be run either backward or forward, and, as the

one eccentric moves the valve to run forward and the other to run

backward, we must be able to connect or disconnect the rods to and

from the valve at will. The eccentric rods of the early locomotives

had hooks on the ends by which they were attached to or detached

from suitable pins connected with the valves. But these hooks were

very uncertain in their action and therefore were abandoned, and

now what is known as the "link-motion" is almost universally used

for the valve-gear of locomotives. It consists of a "link" (_a b_,

Fig. 24) which has a curved opening or slot, _k_, in it in which

a block, _B_, fits accurately, so that it can slide from end to

end of the link. This block has a hole bored in the middle which

receives a pin, _c_, which is attached to the end of the arm _N_

of the "rocker" _M O N_. The rocker has a shaft, _O_, which can

turn in a suitable bearing, and two arms, _M_ and _N_; the latter,

as explained, is connected to the link by the pin _c_ and block

_B_. The upper arm _M_ has another pin, _V_, on its end, which

is connected by a rod, _v V_, to the main slide-valve _V_. The

rocker-arms, as will be seen, can vibrate about the shaft _O_.

[Illustration: Fig. 24.--Valve Gear.]

The link is hung by a pendulous bar, _g h_, to the end _g_ of

the arm _E_, attached to the shaft _A_. This shaft has another

upright arm, _F_, which is connected by a rod or bar, _G G′_, to

a lever, _H I_, called a reverse lever, whose fulcrum is at _I_.

To save room, in the engraving this lever and the cylinder _G_ are

drawn nearer to the main axle _S_ than they would be on an engine.

The lever is located inside the cab of the locomotive, and is

indicated by the numbers 17 17′ in Figure 36 on p. 133, which is a

view looking from the tender at the back end of a locomotive. The

lever has a trigger (_t_, Fig. 24) which is connected by a rod,

_r_, to a latch, _l_, which engages in the notches of the sector _S

S′_. This latch holds the lever in any desired position and can be

disengaged from the notches by grasping the upper end of the lever

and the trigger.

It is plain that, by moving the upper end of the reverse lever, the

link _a b_ can be raised up or lowered at will. When the link is

down, or in the position represented in the engraving, the forward

eccentric rod imparts its motion to the block _B_, pin _c_, and

thence to the rocker and valve, and the engine will run forward.

If, however, the reverse lever is thrown back into the position

indicated by the dotted line _J I_, the link would then be raised

up so that the end _e_ of the backward-motion rod would be opposite

to the block _B_ and pin _c_ and would communicate its motion to

the rocker and valve, and the wheels would then be turned backward

instead of forward. It will thus be seen how the movement of the

reverse lever effects the reversal of the engine.

A locomotive is started by admitting steam to the cylinders by

means of what is called the "throttle-valve." This is usually

placed in the upper part of the boiler at _T_ (Fig. 16). The valve

is worked by a lever at _l_, which is also shown at 14, 14′ (Fig.

36). The steam is conveyed to the cylinders by a pipe (_s_, Fig.

16, p. 115).

If steam is admitted to the cylinders and the wheels are turned,

one of two results must follow: either the locomotive will move

backward or forward according to the direction of revolution, or

the wheels will slip, as they often do, on the rails. That is, if

the resistance of the cars or train is less than the friction or

"adhesion" of the wheels on the rails, the engine and train will be

moved; if the adhesion is less than the resistance the wheels will

turn without moving the train.

The capacity of a locomotive to draw loads is therefore dependent

on the adhesion, and this is in proportion to the weight or

pressure of the driving-wheels on the rails. The adhesion also

varies somewhat with the weather and the condition of the wheels

and rails. In ordinary weather it is equal to about one-fifth of

the weight which bears on the track; when perfectly dry, if the

rails are clean, it is about one-fourth, and with the rails sanded

about one-third. In damp or frosty weather the adhesion is often

considerably less than a fifth.

[Illustration: Fig. 25.--Turning Locomotive Tires.]

It would, then, seem as though all that is needed to increase the

capacity of a locomotive to draw loads would be to add to the

weight on its driving-wheels, and provide engine-power sufficient

to turn them--which is true. But it has been found that if the

weight on the wheels is excessive both the wheels and rails will be

injured. Even when they are all made of steel, they are crushed out

of shape or are rapidly worn if the loads are too great. The weight

which rails will carry without being injured depends somewhat on

their size or weight, but ordinarily from 12,000 to 16,000 pounds

per wheel is about the greatest load which they should carry.

For these reasons, when the capacity of a locomotive must be

increased beyond a limit indicated by these data, one or more

additional pairs of driving-wheels must be used. Thus, if a more

powerful engine was required than that shown in Figure 14 (p. 113),

another pair of wheels would be added, as shown in Figures 26,

27, and 28. Or, if you wanted a more powerful engine than these,

still another pair of driving-wheels would be provided, as shown

in Figure 30. In this way the Mogul, ten-wheeled and consolidation

engines have been developed from that shown in Figure 14. The Mogul

locomotive (Fig. 27) has three pairs of driving-wheels, but only

one pair of truck-wheels. The engravings shown in Figures 30 and

31 represent consolidation and decapod types of engines which have

four and five pairs of driving-wheels.

[Illustration: Fig. 26.--Six-wheeled Switching Locomotive. By the

Schenectady Locomotive Works.]

From the illustrations, Figures 28, 30, and 31, it will be seen

that when so many wheels are used, even if they are of small

diameter, the wheel-base must necessarily be long, so that a limit

is very soon reached beyond which the number of driving-wheels

cannot be increased.

Improvements in the processes of manufacturing steel, which

resulted in the general use of that material for rails and tires,

have made it possible to nearly double the weight which was carried

on each wheel when they were made of iron. The weight of rails has

also been very much increased since they were first made of steel.

Twenty or twenty-five years ago iron rails weighing 56 pounds per

yard were about the heaviest that were laid in this country. Now

steel rails weighing 72 pounds are commonly used, and some weighing

85 pounds have been laid on American roads, and others weighing 100

pounds have been laid on the Continent of Europe.

[Illustration: Fig. 27.--Mogul Locomotive. By the Schenectady

Locomotive Works.]

[Illustration: Fig. 28.--Ten-wheeled Passenger Locomotive. By the

Schenectady Locomotive Works.]

[Illustration: Fig. 29.--Consolidation Locomotive (unfinished).]

[Illustration: Fig. 30.--Consolidation Locomotive. By the

Pennsylvania Railroad Company.]

Of late years urban and suburban traffic has created a demand for

a class of locomotives especially adapted to that kind of service.

One of the conditions of that traffic is that trains must stop and

start often, and therefore, to "make fast time," it is essential

to start quickly. Few persons realize the great amount of force

which must be exerted to start any object suddenly. A cannon-ball,

for example, will fall through 16 feet in a second with no other

resistance than the atmosphere. The impelling force in that case

is the weight of the ball. If we want it to fall 32 feet during

the first second, the force exerted on it must be equal to double

its weight, and for higher speeds the increase of force must be in

the same proportion. This law applies to the movement of trains.

To start in half the time, double the force must be exerted. For

this reason, trains which start and stop often require engines

with a great deal of weight on the driving-wheels. In accordance

with these conditions a class of engines has been designed which

carry all, or nearly all, the weight of the boiler and machinery,

and sometimes the water and fuel, on the driving-wheels. For

suburban traffic, the speed between stops must often be quite

rapid, and consequently the engine must have a long wheel-base

for steadiness, as well as considerable weight on the wheels for

adhesion. Four-wheeled engines (Fig. 14) have all their weight on

the driving-wheels, but the wheel-base is short.

[Illustration: Fig. 31.--Decapod Locomotive. By the Baldwin

Locomotive Works, Philadelphia.]

[Illustration: Fig. 32.--"Forney" Tank Locomotive. By the Rogers

Locomotive and Machine Works, Paterson, N. J.]

To combine the two features, engines have been built with the

driving-wheels and axles arranged as in Figure 32. The frames are

then extended backward, and the water-tank and fuel are placed

on top of the frames, and their weight is carried by a truck

underneath. This arrangement leaves the whole weight of the boiler

and machinery on the driving-wheels, and at the same time gives a

long wheel-base for steadiness. This plan of engine was patented

by the author of this article in 1866, and has come into very

general use--since the expiration of the patent. In some cases a

two-wheeled truck is added at the opposite end, as shown in Figure

33. For street railroads, in which the speed is necessarily slow,

engines such as Figure 13 (p. 110) are used. To hide the machine

from view, and also to give sufficient room inside, they are

enclosed in a cab large enough to cover the whole machine.

The size and weight of locomotives have steadily been increased

ever since they were first used, and there is little reason for

thinking that they have yet reached a limit, although it seems

probable that some material change of design is impending which

will permit of better proportions of the parts or organs of the

larger sizes. The decapod engines built at the Baldwin Locomotive

Works, in Philadelphia, for the Northern Pacific Railroad, weigh

in working order 148,000 pounds. This gives a weight of 13,300

pounds on each driving-wheel. Some ten-wheeled passenger engines,

built at the Schenectady Locomotive Works for the Michigan Central

Railroad, weigh 118,000 pounds, and have 15,666 pounds on each

driving-wheel. Some recent eight-wheeled passenger locomotives for

the New York, Lake Erie & Western Railroad weigh 115,000 pounds,

and have 19,500 pounds on each driving-wheel. At the Baldwin Works,

some "consolidation" engines have recently been built which are

still heavier than the decapod engines.

The following table gives dimensions, weight, price, and price

per pound of locomotives at the present time. If we were to quote

them at 8 to 8¼ cents per pound for heavy engines and 9 to 22¼ for

smaller sizes, it would not be much out of the way.

_Dimensions, Weights, and Approximate Prices of Locomotives._

---------------+----------+--------+---------+----------+--------+-------

---------------+----------+--------+---------+----------+--------+-------

Passenger | 8 24 |62 to 68| 92,000 | 110,000 | $8,750 | 7.95

| | | | | |

Freight | 19 24 |50 to 56| 96,000 | 116,000 | 9,500 | 8.19

| | | | | |

Freight | 19 24 | 0 to 58| 100,000 | 118,000 | 9,750 | 8.26

| | | | | |

Freight | 20 24 | 50 | 120,000 | 132,000 | 10,500 | 7.95

| | | | | |

Freight | 22 26 | 46 | 150,000 | 165,000 | 13,250 | 8.03

| | | | | |

Switching | 15 24 | 50 | 58,000 | 47,000 | 5,500 | 11.70

| | | | | |

with tender| 18 24 | 50 | 84,000 | 98,000 | 8,500 | 8.89

| | | | | |

Elevated | 11 16 | 42 | 42,000 | 34,000 | 4,500 | 13.23

| | | | | |

Street-car | | | | | $3,500 | 19.44

Motor | | | | | to | to

Locomotive | 10 14 | 35 | 22,000 | 18,000 | $4,000 | 22.22

---------------+----------+--------+---------+----------+--------+-------

[Illustration: Fig. 33.--"Hudson" Tank Locomotive. By the Baldwin

Locomotive Works.]

The speed of locomotives, however, has not increased with their

weight and size. There is a natural law which stands in the way

of this. If we double the weight on the driving-wheels, the

adhesion, and consequent capacity for drawing loads, is also

doubled. Reasoning in an analogous way, it might be said that if

we double the circumference of the wheels the distance that they

will travel in one revolution, and consequently the speed of the

engine, will be in like proportion. But, if this be done, it will

require twice as much power to turn the large wheels as was needed

for the small ones; and we then encounter the natural law that

the resistance increases as the square of the speed, and probably

at even a greater ratio at very high velocities. At 60 miles an

hour the resistance of a train is four times as great as it is at

30 miles. That is, the pull on the draw-bar of the engine must be

four times as great in the one case as it is in the other. But at

60 miles an hour this pull must be exerted for a given distance in

half the time that it is at 30 miles, so that the amount of power

exerted and steam generated in a given period of time must be eight

times as great in the one case as in the other. This means that

the capacity of the boiler, cylinders, and the other parts must

be greater, with a corresponding addition to the weight of the

machine. Obviously, if the weight per wheel is limited, we soon

reach a point at which the size of the driving-wheels and other

parts cannot be enlarged; which means that there is a certain

proportion of wheels, cylinders, and boiler which will give a

maximum speed.

The relative speed of trains here and in Europe has been the

subject of a good deal of discussion and controversy. There appears

to be very little difference in the speed of the fastest trains

here and there; but there are more of them there than we have. From

48 to 53 miles an hour, including stops, is about the fastest time

made by our regular trains on the summer time-tables.

When this rate of speed is compared with that of sixty or seventy

miles an hour, which is not infrequent for short distances, there

seems to be a great discrepancy. It must be kept in mind, though,

that these high rates of speed are attained under very favorable

conditions. That is, the track is straight and level, or perhaps

descending, and unobstructed. In ordinary traffic it is never

certain that the line is clear. A locomotive-runner must always

be on the look-out for obstructions. Trains, ordinary vehicles,

a fallen tree or rock, cows, and people may be in the way at

any moment. Let anyone imagine himself in responsible charge

of a locomotive and he will readily understand that, with the

slightest suspicion that the line is not clear, he would slacken

the speed as a precautionary measure. For this reason fast time

on a railroad depends as much on having a good signal system to

assure the locomotive-runners that the line is clear, as it does on

the locomotives. If he is always liable to encounter, and must be

on the look-out for, obstructions at frequent grade-crossings of

common roads, or if he is not certain whether the train in front of

him is out of his way or not, the locomotive-runner will be nervous

and be almost sure to lose time. If the speed is to be increased on

American railroads, the first steps should be to carry all streets

and common roads either over or under the lines, have the lines

well fenced, provide abundant side-tracks for trains, and adopt

efficient systems of signals so that locomotive-runners can know

whether the line is clear or not.

In what may be called the period of adolescence of railroads there

was a very decided predilection on the part of locomotive engineers

for large driving-wheels. Figure 34 represents one of the engines

built as early as 1848 for the Camden & Amboy Railroad, with

driving wheels 8 feet in diameter. Other engines with 6 and 7 feet

wheels were not uncommon. In Europe many engines with very large

wheels were made and are still in use. Here, as well as there,

excessively large wheels have, however, been abandoned, and six

feet in diameter is now about the limit of their size in this

country.

[Illustration: Fig. 34.--Camden & Amboy Locomotive, 1848.]

So far as locomotives are concerned, fast time, especially with

heavy trains, is generally dependent more upon the supply of

steam than it is on the size of the wheels. Without steam to turn

them, big wheels are useless; but with an abundant supply there

is no difficulty in turning small wheels at a lively rate. Speed,

therefore, is to a great extent a question of boiler capacity, and

the general maxim has been formulated that "within the limits of

weight and space to which a locomotive boiler must be confined,

it cannot be made too big." But the maximum speed at which a

locomotive can run when an adequate supply of steam is provided

also depends on the perfection of the machinery. At 60 miles an

hour a driving-wheel 5½ feet in diameter revolves five times every

second. The reciprocating parts of each cylinder of a Pennsylvania

Railroad passenger engine, including one piston, piston-rod,

cross-head, and connecting rod, weigh about 650 pounds. These

parts must move back and forth a distance equal to the stroke,

usually two feet, every time the wheel revolves, or in a fifth of

a second. It starts from a state of rest at each end of the stroke

of the piston and must acquire a velocity of 32 feet per second,

in one-twentieth of a second, and must be brought to a state of

rest in the same period of time. A piston 18 inches in diameter

has an area of 254½ square inches. Steam of 150 pounds pressure

per square inch would therefore exert a force on the piston

equal to 38,175 pounds. This force is applied alternately on each

side of the piston, ten times in a second. The control of such

forces requires mechanism which works with the utmost precision

and with absolute certainty, and it is for this reason that the

speed and the economical working of a locomotive depend so much on

the proportions of the valves and the "valve-gear" by which the

"distribution" of steam in the cylinders is controlled.

[Illustration: Fig. 35.--Interior of a Round-house.]

The engraving (Fig. 36) on p. 133 represents the cab end of a

locomotive of the New York Central & Hudson River Railroad, looking

forward from the tender, and shows the attachments by which the

engineer works the engine.[12] This gives an idea of the number of

keys on which he has to play in running such a machine. There is

room here for little more than an enumeration of the parts which

are numbered:

1. Engine-bell rope.

2. Train-bell rope.

3. Train-bell or gong.

4. Lever for blowing whistle.

5. Steam-gauge to indicate pressure in boiler.

6. Steam-gauge lamp to illuminate face of gauge.

7. Pressure-gauge for air-brake; to show pressure in

air-reservoirs.

8. Valve to admit steam to air-brake pump.

9. Automatic lubricator for oiling main valves.

10. Cock for admitting steam to lubricator.

11. Handle for opening valves in sand-box to sand the rails.

12. Handle for opening the cocks which drain the water from the

cylinders.

13. Valve for admitting steam to the jets which force air into

the fire-box.

14, 14′. Throttle-valve lever. This is for opening the valve

which admits steam to the cylinders.

15. Sector by which the throttle-lever is held in any desired

position.

16. "Lazy-cock" handle. A "lazy-cock" is a valve which regulates

the water-supply to the pumps and is worked by this handle.

17, 17′. Reverse lever.

18. Reverse-lever sector.

19, 19′, 19″. Gauge-cocks for showing the height of the water

in the boiler; 19′ is a pipe for carrying away the water which

escapes when the gauge-cocks are opened.

20, 20. Oil-cups for oiling the cylinders.[13]

21. Handle for working steam-valve of injector.

22. Handle for controlling water-jet of the injector.

23. Handle for working water-valve of injector.

24. Oil-can shelf.

25. Handle for air-brake valve.

26. Valve for controlling air-brake.

27. Pipe for conducting air to brakes under the cars.

28. Pipe connected with air-reservoir.

29. Pipe-connection to air-pump.

30. Handle for working a valve which admits or shuts off the air

for driving-wheel brakes.

31. Valve for driving-wheel brakes.

32, 32′. Lever for moving a diaphragm in smoke-box, by which the

draught is regulated.

33. Handle for raising or lowering snow-scrapers in front of

truck-wheels.

34. Handle for opening cock on pump to show whether it is forcing

water into the boiler.

The American Railway: Its Construction, Development, Management, and Appliances · 第 8 / 33 段

Having explained how the steam is generated, it remains to show