Fig. 3328a.
The construction of the steam reversing gear is shown in [Fig. 3328a]. a is a steam cylinder and b a cylinder filled with oil or other liquid. Each of these cylinders has a piston, the two being connected together by their piston-rods c c′. These rods are also connected to a lever d e f, which works on a fulcrum e. The lower end of the lever is connected to the reverse rod f g, the front end of which is attached to the vertical arm of the lifting or reverse shaft. It will readily be seen that if the piston in b is free to move and steam is then admitted to either end of the steam cylinder a, the two pistons will be moved in a corresponding direction, and with them the lever d e f, and the other parts of the reversing gear. A valve, h, is provided, by which communication is opened between the cylinder a and the steam inlet pipe. Another valve, i, is placed between h and the cylinder a, by which the steam may be admitted either into the front or back end of the cylinder. It will be apparent, though, that if the piston in a is thus moved, and the reverse gear placed in any required position, some provision must be made to hold it there securely. This is accomplished by the oil cylinder and piston b. To it a valve, j, is provided, by which communication between the front and back ends of the cylinder may be opened or closed. It is evident that if the piston b is in any given position, and both ends of the cylinder are filled with liquid, the former will be held securely in that position if the liquid in one end cannot flow into the other. If, however, communication is opened between the two ends, then, if a pressure is exerted on the piston b, it will cause the liquid to flow from one end of the cylinder to the other, and thus permit b to move in whichever direction the pressure is exerted.
r is the reverse lever, made in the form of a bell crank, the short end of which works in a slot c, in the upper end of a shaft or spindle d. This shaft is inclosed by a tubular shaft s, to which the fulcrum of r is fastened. The tubular shaft has an arm b. The reverse lever has two movements, the one to raise the end up, and the other to turn on the axis of the tubular shaft. The arm b on the latter is connected by a rod, f, with the valves j and h. The lower end of the shaft d is connected with a bell crank, f′, which, in turn, is connected by a rod, k l, with the valve i. Therefore, by turning the lever r so as to partly revolve the shaft s, the valves j and h may be opened or closed, and by moving the lever r up or down, the valve i is moved to admit steam to the front or back end of a. To reverse the engine, therefore, the lever r is turned so as to open the valves j and h. This opens communication between the opposite ends of b, and h admits steam to i. Now, by reversing the end of the reverse lever r, the valve i is moved so as to admit steam to either end of a, the pressure in which will move the reverse gear to the desired position. When this is done, the valves j and h are closed. This prevents the fluid in b from flowing from one end of the cylinder to the other, and thus securely locks the piston b in the position it may happen to be in, and at the same time the valve h shuts off steam from the cylinder a.
The bar k is graduated, as shown in the plan of r, k, to indicate to the locomotive runner the position of the reversing gear.
This apparatus enables the reversing gear to be handled with the utmost facility, and with almost no exertion on the part of the engineer. The engine can be reversed almost instantly, and it can be graduated with the most minute precision.
THE LINK MOTION AND REVERSING GEAR.
The link motion of an American locomotive is shown in [Figs. 3329] and [3330]. In [Fig. 3329] it is shown in full gear for the forward gear, or in other words, so as to place the engine in full power for going ahead.
The meaning of the term full power is that, with the link motion in full gear, the steam follows the piston throughout very nearly the full stroke.