The engravings, Figs. 287, 288, show the valve gear, also section of steam cylinder and steam chest. The piston and valves are in their central position, which condition never occurs in the operation of this pump; if it did the pump would stop. The valves and pistons being at one end or the other of the stroke uncovers the ports, and the moment steam is admitted the pump will start. Referring to the engravings, A, is the main steam pipe, and B, the auxiliary steam pipe. These pipes are one, inside the casting, so that one pipe supplies both. Assume the valve, C, moved to the left so that the port, D, is uncovered. [Illustration: FIG. 287.] [Illustration: FIG. 288.] Live steam then flows through the port, D, and pushes the balanced piston valve, E, to the left, carrying the slide valve, F, with it to the left, so that the port, G, is opened to the steam cylinder. The steam enters through the port, G, pushes the main piston, H, to the left, completing one stroke of the piston. As the piston travels to the left the lever, J, pushes the crosshead, I, to the right, which opens corresponding ports in the left-hand end of the cylinder, and the piston valve, E, is pushed to the right, which admits steam on the left-hand side of the main piston through the port, K, pushing the piston to the right, completing the second stroke of the piston. The auxiliary slide valve, C, is operated by the crosshead, I, coming in contact with the tappets, L L. The auxiliary tappets and stem, M M, theoretically could be dispensed with, but they are put in place for the reason that occasionally the valve, E, might stick, due to the pump standing for some time unused or from some other cause. In such a contingency the crosshead, I, is pushed to the right by the action of the main piston and comes in contact with the tappets, M M, which causes the piston valve to start, after which steam will complete the work. When the pump is running, the crosshead, I, never quite touches the tappets, M M, because it engages the tappets, L L, admitting steam to the piston valve and shifts it before the tappets, M M, are touched. The reason of the double ports in the auxiliary steam chest is to have one port, D, for steam, and one port, N, for the exhaust. Steam being imprisoned between these two ports forms a cushion, preventing the piston valve from striking the heads of the chest. The tappets, L L, set closer together or farther apart control the stroke of the main piston, H. When the pump is running very fast the momentum of the moving parts increases and the tappets will have to be set closer together for high speed than for slow. The tappets, M M, are adjustable to their right relation with the tappets, L L. The general design and easy means of adjustment make a reliable single cylinder valve motion. _To set the valves._ There are no complicated internal parts requiring adjustment, and almost all parts requiring manipulation can be handled while the pump is running.