ain valve connects port "g"
with the exhaust port "X", thus allowing steam above the piston "H" to
escape to the exhaust, at the same time steam is admitted through port
"s" to the under side of piston "H", forcing it upward. As this piston
very nearly completes its stroke, the tappet plate "L" (see Fig. 20)
engages the button on the tappet rod "P", moving the main valve "A" to
its upper position. Exhaust cavity "r" now connects port "o", which
leads to the lower end of the cylinder at the right, with the exhaust
port "X", thus allowing the steam under piston "T" to escape to the
exhaust, at the same time steam is admitted through port "V" to the
upper end of the cylinder at the right, on top of piston "T", forcing it
downward; as it very nearly completes its stroke, the tappet plate "Q"
engages the shoulder on the tappet rod "P", moving the main valve "C" to
its lower position. The exhaust cavity "r" in the valve now connects
port "s" with the exhaust port "X", allowing steam below piston "H" to
escape to the exhaust, and at the same time steam is admitted to the top
of this piston, forcing it down, thus completing a cycle of the
compressor.

165. Q. Explain the operation of the air end of the compressor.

A. As the piston in the low pressure cylinder "D" moves up (see Fig.
19), a partial vacuum is formed below it, and air flowing through the
strainer passes downward through the air passage, then past the lower
receiving valve "W" into the lower end of the cylinder, filling it with
air at about atmospheric pressure. In the meantime the air that is being
compressed above the piston holds the receiving valve "U" to its seat,
and lifts the upper intermediate discharge valve "K" from its seat,
allowing the air to pass from the low to the high pressure cylinder "F".
The high pressure piston now moving up causes a partial vacuum to be
formed below it, and air from the atmosphere flows past the lower
receiving valve "N", filling this end of the cylinder with air at about
atmospheric pressure. The air above the piston being compressed, holds
the upper intermediate valve "K" and receiving valve "J" to their seats
and lifts the upper final discharge valve "M", allowing the air to pass
to the main reservoir. The action is the same on the down stroke, only
air is compressed in the opposite end of the cylinders and the opposite
air valves are used.

166. Q. What should be the lift of the different air valves?

A. In the No. 1 a