The accompanying engraving, Fig. 289, represents the Weinman pump and
the sectional engraving, Fig. 291, the valve motion.
[Illustration: 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.
[Illustration: FIG. 290.]
Suppose that the steam piston has moved to the end of its stroke, the
auxiliary valve, which, as stated above, is connected to the piston
rod, is shifted. This releases the steam from one end of the steam
chest, D, through port, K, to exhaust, L. The steam pressure at the
opposite end of the steam chest causes the steam valve to slide to
opposite end of the steam chest, thus reversing the motion of the main
steam piston.
To set the auxiliary valve, remove the pendulum or tappet lever, X,
and the cap or bonnet, O, and take out the auxiliary valve, E. With a
straight edge and scriber indicate the working edges on the end of the
valve, and mark the edge of the port on the valve seat so that it can
be seen when the auxiliary valve is in its proper place. Replace the
valve, and the pendulum lever, omitting the bonnet.
[Illustration: FIG. 291.]
Push the steam piston to one end of the stroke, then swing the pendulum
lever toward the end of the cylinder corresponding to the piston, and
until the auxiliary valve uncovers the port leading to the end of the
valve chest farthest from the piston. Connect the horizontal rod to the
bottom of the pendulum lever. Then remove the lever from the auxiliary
valve stem and replace the bonnet and pendulum lever, shown by dotted
lines. The length of the stroke may be regulated by raising or lowering
the end of the horizontal rod in the slotted lower end of the pendulum
lever. Lowering the rod produces a longer stroke, and raising it
shortens the stroke.