TRUCK SERVICE MANUAL
BRAKES-AIR
CHAPTER I
GOVERNOR
BENDIX-WESTINGHOUSE D-2 TYPE
DESCRIPTION
The air compressor governor along with the
compressor unloader mechanism automatically limits
system pressure to a predetermined range by opening
unloading valves and stopping compression when
system pressure has been built up to maximum pressure
limit and by closing unloading valves and starting
compression when system pressure has dropped to
minimum pressure limit.
The D2 governor has a piston upon which air
pressure acts to overcome the pressure setting spring
and control the inlet and exhaust valve to either admit or
Fig . 2 Sectional View of type d-2 Governor
exhaust air to or from the compressor unloading
mechanism.
piston moves against the resistance of the pressure
setting spring. The piston and inlet and exhaust valve
Type D2 governors can be attached hed to the
move up when the reservoir air pressure valve move
compressor or mounted remotely. They are adaptable to
cutout setting the governor. aivernor.
either mounting. Connections in this system are to the
reservoir and compressor unloading ports. They also
The exhaust stem seats on the inlet and exhaust
have an exhaust port.
valve and then the inlet passage opens.
Reservoir air pressure then flows by the open inlet valve,
through the passage in the piston and out the unloader
port to the compressor unloading mechanism. The air,
besides flowing to the compressor unloading
mechanism, also flows around the piston and acts on the
additional area of the piston, assuring positive action and
fully opening the inlet valve.
As the system reservoir air pressure drops to the
cut-in setting of the governor, 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.
SERVICE CHECKS
Operating Tests
Fig .
1
Type D2 Governor
Start the vehicle engine and build up air pressure
in the air brake system and check the pressure
OPERATION (Fig. 2)
registered by a dash or test gauge at the time the
governor cuts out, stopping the compression of air by the
Reservoir air pressure enters the governor at ,one
compressor.
The cutout pressure should be in
of its reservoir ports and acts on the area of the piston
accordance with the piece number of the governor. The
and beneath the inlet and exhaust valve. As the air
more common cutout pressures vary between 105125
pressure builds up, the
psi.
139
