Peterbilt 325 2017, Operator'S Manual

Page: 271 / 392

AIR SYSTEM
Secondary Air Pressure Gauge
Follow the procedure below to
check the compressed air system
for leaks:
1. Periodically, or after maintenance
or replacement of air system
components:
2. Build up air pressure in the system
to the governor cutout point or until
120 psi (827 kPa) is reached.
3. Stop the engine and release the
service brakes.
4. Without applying the brake pedal,
observe the rate of air pressure
drop. This rate should not exceed
2.0 psi (14 kPa) per minute.
5. Start the engine and build up the
air pressure again.
6. Stop the engine, and apply the
brakes fully. Apply the brake pedal
and hold it down for five minutes.
The pressure drop should not
exceed 3.0 psi (21 kPa) per
minute.
7. If you detect excessive leakage
(air pressure loss greater than 3.0
psi (21 kPa) after five minutes of
brake application), a leakage test
should be made at the air line
connections and at all air brake
control units. These tests should
determine where air is escaping.
Air Compressor
Operation
All compressors, regardless of make
or model, run continuously while the
engine is running. System pressure
is controlled by the governor. The
governor acts in conjunction with
the unloading mechanism in the
compressor cylinder block to start
and stop compression of air. The
compressor is unloaded when the
system pressure reaches 120 psi (827
kPa) and compression is reestablished
when system pressure falls to 100 psi
(690 kPa).
(03/17) Y53-6060-1C1
5-61
5