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.
THE WEINMAN.
The accompanying engraving, [Fig. 289], represents the Weinman pump and the sectional engraving, [Fig. 291], the valve motion.
Fig. 289.
The motion of the main piston is controlled by steam valve, A, which is a hollow cylinder combining a valve piston and slide valve in one and the same casting and sliding horizontally in steam chest, D. This valve is prevented from revolving by a cap screw, B. Small drilled openings, C, C, permit the steam to pass from the steam valve to each end of the steam chest, D. This valve, A, is moved horizontally in either direction by steam pressure, and the movement is controlled by an auxiliary valve, E. The openings, F, F [(Fig. 290)], conduct the steam from the ends of the steam chest to the auxiliary valve, which is connected to the piston rod by a tappet rod and the side arm, X.
Steam being admitted to steam chest, it passes through steam valve, A, to ports, H, H. As the construction permits but one of the ports, H, H, to be in communication at a time with one of the passages, I, I, leading to the opposite ends of the steam cylinder a dead center becomes an impossibility. While one of the ports, H, H, is in communication with one of the passages, I, I, the opposite passage, I, is in communication with the exhaust, J.
