valve and out the upper connection to the unloader
assembly located in the compressor cylinder head.
When the unloader valves open, the compression of air
When reservoir pressure is reduced to the cut-in
setting of the compressor governor (80 to 85 psi), the
governor tube again exerts sufficient spring pressure
on the valve mechanism to depress and close the lower
valve and open the upper valve, thereby shutting off
and exhausting the air from the compressor unloading
mechanism and compression is resumed.
The pressure range and setting should be checked
periodically using an air gauge known to be accurate.
Pressure range may be changed in the type O-1
governor by adding shims beneath the upper valve
guide to decrease the range, or removing shims to
increase the range. Pressure settings may be changed,
if necessary, by turning the adjusting screw to the left
to increase the setting or to the right to decrease the
The strainer should be removed periodically and
cleaned. Check the governor periodically for excessive
leakage in both the cut-in and cutout positions. If the
governor fails to operate properly, it should be repaired
In the type D governor (fig. 7-42) when the
reservoir pressure reaches the cut-out setting (100 to
110 psi), the governor diaphragm is subjected to
sufficient air pressure to overcome the spring loading.
This action allows the valve mechanism to move up,
permitting the exhaust stem to close the exhaust valve
and to open the inlet valve. Reservoir pressure then
passes through the governor to operate the compressor
unloading mechanism. stopping further compression
of the air compressor.
When the reservoir pressure is reduced to the
cut-in setting (80 to 85 psi). the spring loading within
the governor overcomes the air pressure under the
diaphragm. The valve mechanism is actuated, closing
the inlet valve and opening the exhaust valve, thereby
shutting off and exhausting the air from the
compressor unloading mechanism and compression is
Pressure range and setting should be checked
periodically, using an accurate air gauge. The pressure
range (pressure differential) between loading and
unloading of the type D governor is a function of the
design of the unit and should not be changed. The
designed range for this governor is approximately 20
percent of the cutout pressure setting. The pressure
settings of the type D governor may be adjusted by
turning the adjusting nut clockwise to increase or
counterclockwise to decrease the settings.
Both strainers should be removed periodically and
cleaned or replaced. The governor should periodically
be checked for leakage at the exhaust port in both the
cut-in and cutout positions. If the governor fails to
operate properly, it should be repaired or replaced.
Figure 7-42.Type D governor.