The American Railway: Its Construction, Development, Management, and Appliances

by Thomas Curtis Clarke

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.

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.