Air Compressor and Tanks
The air compressor is belt driven by the engine. It is
used to supply air pressure for the brakes. The air
compressor governor controls the pressure of operation.
1. Air compressor. 2. Air compressor governor.
If the air pressure in the tanks is low, nothing will
change in the governor and the air compressor will send
air to the tanks. When the tank air pressure goes up to
cutout pressure [125 ± 5 psi (860 ± 35 kPa)], it moves
the governor piston against its spring and lets air go
from the governor to the compressor unloading valves.
Compressed air pushed against the unloading valves
holds them open and stops the delivery of air from the
When the air pressure in the tanks drop to cut-in
pressure [100 to 105 psi (690 to 725 kPa)], the force of
the governor spring will return the governor piston and
stop the flow of air from the air tanks to the compressor
unloading valves. The compressor unloading valves
close and the compressor will send air to the air tanks.
A relief valve is used to prevent damage to the air
system if the compressor governor should have a
failure. The relief valve will open when the air pressure
in the air tanks is approximately 150 psi (1030 kPa).
Each air tank has a drain valve in the front end of it.
of the Control Valve
CONTROL VALVE FOR THE BRAKES
1. Opening to wet tank. 2. Foot pedal. 3. Opening for
reserve tank. 4. Protection unit. 5. Opening for dry
tank. 6. Basic unit. 7. Opening to reserve tank. 8.
Retainer for spring of the emergency piston. 9. Opening
for exhaust to reserve tank. 10. Opening for inlet to
reserve tank. 11. Opening for outlet dry tank. 12.
Opening for Inlet to dry tank. 13. Opening for exhaust to
dry tank. AA. See illustration 54670X1.
The brake is released when the air pressure in the
passages (1), (3) and (5) goes up to 55 ± 5 psi (380 ± 35
kPa) as inlet is sealed and exhaust passage (14) is