GILLIG LOW FLOOR, Service Manual

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Air System
AIR GOVERNOR (BENDIx D-2)
The governor, operating in conjunc-
tion with the air compressor unloading
mechanism, automatically controls air
pressure in the air brake or air supply
system between the predetermined
maximum and minimum pressures.
The air compressor runs continu-
ously while the engine runs, but actual
compression of air into the vehicle air
system is controlled by the governor
which stops or starts compression
when the maximum or minimum res-
ervoir pressures are reached. Refer to
Figure 6-13.
Operation
Reservoir air pressure enters the gov-
ernor at one of its reservoir ports and
acts on the piston and inlet/exhaust
valve. As the air pressure builds up,
the piston and valve move together
against the resistance of the pressure
setting spring. When the reservoir air
pressure reaches the cut-out setting of
the governor (130 psi), the exhaust stem seats on the inlet/exhaust valve, closing the exhaust passage,
and then opens the inlet passage. Reservoir air pressure then flows around the inlet valve, through the
passage in the piston and out the unloader port to the compressor unloading mechanism. Air also flows
around the piston, which is slightly larger at the upper end. The added force resulting from this larger
area assures a positive action and fully opens the inlet valve. As the system reservoir air pressure drops
to the cut-in setting of the governor (110 psi), the force exerted by the air pressure on the piston will
be reduced so that the pressure setting spring will move the piston down. The inlet valve will close and
the exhaust will open. With the exhaust open, the air in the unloader line will escape back through the
piston, through the exhaust stem, and out the exhaust port.
Preventive Maintenance
Every 50,000 miles, 6 months, or 1,800 operating hours, perform the following tests:
Figure 6-13, Air Governor
PISTON INLET/EXHAUST
VALVE SPRING
INLET/EXHAUST
VALVE
O-RINGS
LOWER
SPRING SEATS
UPPER
SPRING SEATS
RETAINING
RING
ADJUSTING
SCREW
COVER
ADJUSTING
SCREW LOCKNUT
BODY
PRESSURE SETTING
SPRING
SPRING GUIDE
EXHAUST STEM
SPRING
EXHAUST
STEM
FILTERS