A. Until the main reservoir pressure falls below ninety pounds, when the
combined spring and air pressure in chamber "f" will force the diaphragm
28 down, seating the pin valve. This shuts off the supply of air from
chamber "d", and the air confined in chamber "b" will escape to the
atmosphere through the vent port "c". The pressure now being removed
from above the governor piston, the spring 9 aided by the steam pressure
under the valve 5, will force the piston upward, unseating the steam
valve 5, allowing steam to pass through the governor to the compressor.
12. Q. When the steam valve is seated, is steam entirely shut off from
the compressor?
A. No; there is a small port drilled through the valve; its purpose is
to maintain a circulation in the steam pipe and keep the compressor
working slowly; thereby preventing condensation when the steam valve is
closed.
13. Q. With the automatic brake valve in release, running, or holding
position, does the maximum pressure head operate?
A. No; as during this time the main reservoir pressure is not
sufficiently high to actuate its diaphragm.
14. Q. Where does the air come from that operates the maximum pressure
head?