Part 10

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.

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.

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.

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.

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._

+----------+--------+---------+----------+--------+------- Type. |Cylinders.|Diameter|Weight of|Weight of | Approx-| Price | | of |engine in|engine and| imate | per | |driving-| working | tender | price.| pound. | | wheel. | order, | without | | | | |exclusive| water or | | | | |of tender| fuel. | | ---------------+----------+--------+---------+----------+--------+------- |Diam. | Inches.| Pounds.| Pounds. | | Cents. | Stroke. | | | | | "American" | | | | | | Passenger | 8 24 |62 to 68| 92,000 | 110,000 | $8,750 | 7.95 | | | | | | "Mogul" | | | | | | Freight | 19 24 |50 to 56| 96,000 | 116,000 | 9,500 | 8.19 | | | | | | "Ten-wheel" | | | | | | Freight | 19 24 | 0 to 58| 100,000 | 118,000 | 9,750 | 8.26 | | | | | | "Consolidation"| | | | | | Freight | 20 24 | 50 | 120,000 | 132,000 | 10,500 | 7.95 | | | | | | "Decapod" | | | | | | Freight | 22 26 | 46 | 150,000 | 165,000 | 13,250 | 8.03 | | | | | | Four-wheel Tank| | | | | | Switching | 15 24 | 50 | 58,000 | 47,000 | 5,500 | 11.70 | | | | | | Six-wheel | | | | | | Switching, | | | | | | with tender| 18 24 | 50 | 84,000 | 98,000 | 8,500 | 8.89 | | | | | | "Forney" N.Y. | | | | | | 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 | | | | | accord-| | | | | | ing to | | | | | | design.| ---------------+----------+--------+---------+----------+--------+-------

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.

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.

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.

35. Lamp to light the water-gauge, 51, 51.

36. Air-hole for admitting air to fire-box.

37. Tallow-can for oiling cylinders.

38. Oil-can.

39. Shelf for warming oil-cans.

40. Furnace door.

41. Chain for opening and closing the furnace door.

42. Handles for opening dampers on the ash-pan.

43. Lubricator for air-pump.

44. Valve for admitting steam to the chimney to blow the fire when the engine is standing still.

45. Valve for admitting steam to the train-pipes for warming the cars.

46. Valve for reducing the pressure of the steam used for heating cars.

47. Cock which admits steam to the pressure-gauge, 48.

48. Pressure-gauge which indicates the steam-pressure in heater pipes.

49. Pipe for conducting steam to the train to heat the cars.

50. Cock for water-gauge, 51.

51, 51. Glass water-gauge to indicate the height of water in the boiler.

52. Cock for blowing off impurities from the surface of the water in the boiler.

Besides being impressive as a triumph of human ingenuity, there is much about the construction and working of locomotives which is picturesque. A shop where they are constructed or repaired is always of interest. An engine-house (Fig. 35) especially at night, is full of weird suggestions and food for the imagination.

Figure 37 (p. 135) is an illustration from a photograph taken in the erecting shops of the Baldwin Locomotive Works in Philadelphia; and Figure 38 (p. 137) is a view of a similar shop of the Pennsylvania Railroad at Altoona, which suggests at a glance many of the processes of construction which go on in these great works. At Altoona are immense travelling cranes resting on brick arches and spanning the shop from side to side. These are powerful enough to take hold of the largest locomotive and lift it bodily from the rails and transfer it laterally or longitudinally at will. A large consolidation engine is shown in Figure 38, swung clear of the rails, and in the act of being moved laterally. The hooks of the crane are attached to heavy iron beams, from which the locomotive is suspended by strong bars. Figure 39 (p. 138) is a view in the blacksmiths' shop of the Baldwin Works, showing a steam hammer and the operation of forging a locomotive frame.