A. When steam is turned on at the boiler it flows through the steam pipe
and governor, entering the compressor at the steam enlet, then through
the steam passage "a" to the reversing valve chamber "C" also to the
main valve chamber "A" between the differential pistons 77 and 79. The
area of the piston at the right being greater than the one at the left,
the main valve is moved to the right, (See Fig. 2) admitting steam to
port "b" which leads to the lower end of the steam cylinder; steam is
now free to flow under the main piston, forcing it upward. When the
piston has almost completed its upward stroke, the reversing plate 69 on
top of the piston 65 engages a shoulder on the reversing rod 71, moving
the rod and reversing valve 72 upward (See Fig. 3). The upward movement
of the reversing valve closes the ports "f" and "h" and opens port "g";
thus permitting steam to enter the chamber at the right of the large
piston 77, balancing the pressure on this piston, and the pressure
acting on the right side of the small piston 79--the chamber at the left
being open to the exhaust--will force the main valve to the left.
[Illustration: Diagrammatic View, Up Stroke Fig. 2.]
When the main valve moves to the left, steam is admitted through port
"c" to the upper end of the cylinder on top of the piston 65, forcing it
downward. At the same time the lower end of the cylinder is connected
through exhaust cavity "b" of the main valve to the exhaust port "d",
allowing the steam below the piston to escape to the atmosphere.
44. Q. When the piston has about completed its downward stroke, what
takes place?
A. The reversing plate 69 engages the button "k" on the end of the
reversing rod 71 pulling the rod and the reversing valve down. This
movement of the reversing valve closes port "g" and the cavity in the
face of the valve connects ports "f" and "h", which allows the steam in
chamber "D" at the right of the large differential piston to escape to
the exhaust, thus allowing the main valve to move to the right,
exhausting the steam from the top end of the cylinder, and at the same
time admitting steam to the lower end, causing an upward stroke of the
piston.