The valve for admitting steam to and exhausting it from the cylinder
of this pump is contained within the cylinder and moves simultaneously
with the steam piston, having no outside mechanism. See Fig. 278.
The piston, and also the valve, are of the form of spools, each
representing a hollow sleeve with a ring packed piston head at
either end. The piston is secured to the piston rod and the sleeve
connecting the two heads serves as the valve seat for the cylindrical
valve. The sleeve of the piston contains two longitudinal ports, one
port communicating with one end of the cylinder, and the other port
communicating with the opposite end. Suitable holes drilled through the
walls of the sleeve and communicating with the longitudinal ports, act
as admission and exhaust ports, with which the holes and cavities in
the sleeve coincide at proper positions in the stroke.
Referring to the accompanying engraving, Fig. 279, which represents
the valve and piston in the position occupied when ready to commence a
stroke from left to right, the reader will easily understand the action
of these parts. When the piston reaches the end of the stroke steam
enters through the steam pipe at A, between the pistons, and forces
the valve to the left as shown. This movement opens the port, B, and
also brings the cavity, C, in communication with port, D, steam being
admitted through ports, B and D, into the longitudinal port, F, thence
into the clearance, G, of the cylinder. This causes the piston to move
toward the right. When the piston has moved a short distance to the
right steam is admitted into the space, H, surrounding the valve, and
passing into the cavity, C, and through the port, D, furnishes steam to
complete the stroke.
Should the piston stop at mid-stroke it will start again as soon as
steam is turned on, because the port, D, remains open until the valve
is reversed at the opposite end of the stroke.
When the piston reaches the latter position, Fig. 280, the valve is
reversed, due to steam entering at A, and again forcing the pistons
apart, as shown. The steam, which drove the piston from left to right,
now escapes through the port, I, into the cavity, J, and around the
sleeve to the holes, K, Fig. 279, where it enters the hollow piston,
and finally escapes through the hollow rod, L, and the port, M. The
live steam for the next stroke from right to left, now enters through
ports, N and O, Fig. 280, and flows through the longitudinal port, P,
into the end, Q, of the cylinder.
[Illustration: FIG. 279.]
[Illustration: FIG. 280.]
The exhaust steam may be allowed to flow into the atmosphere or into
the suction chamber as desired. A valve is located in the base of
the pump, which changes the course of the steam from the atmospheric
discharge to the suction chamber. The valve is operated by a lever
shown by dotted lines. When the lever is turned down toward the steam
end, the steam is directed into the atmospheric exhaust, and when
turned in the opposite direction the steam will enter the pump suction
and be condensed.
_There is no valve setting to be done on this pump._ Should the pump
fail to work properly, due to the failure of the steam end, all that is
necessary is to take out the valve and piston and clean them thoroughly
and after replacing them and starting the pump to see that these parts
are properly lubricated. The remainder of the pump requires the same
care and attention that is, or should be, given all pumps.