User Manual

NOTE
The trailer brake is not to be used as a
substitute for the service brakes. Using
this
brake frequently, instead of using
the foot brake, will cause the trailer
brakes to wear out sooner.
WARNING
Using the trailer hand brake or air
brakes
to hold a parked vehicle is dan-
gerous. Because they work with air
pressure, these brakes could come
loose. Your vehicle could roll, causing
an accident involving death or person-
al injury. Always set the parking
brakes. Never rely on the trailer hand
brake or truck air brakes to hold a
parked vehicle.
Brake Components
The following is a brief description of the
air/brake system.
Compressor: supplies air to the system. System
pressure is controlled by the
governor
.
Governor controls the air pressure in the system
by actuating the compressor
discharge mechanism. Its cut-out
pressure is 1
15 to 125 psi (793 to 862
kPa). Its preset cut-in pressure is set
to between 13 to 25 psi (90 to 172
kPa) below the cut-out pressure
setting (cut-out and cut-in interval is
not adjustable).
Safety Valve installed on the supply air tank outlet.
It should vent off at 150 psi (1034
kPa) permitting air to escape.
Air Dryer collects and removes moisture and
contaminants from the air as it travels
from the compressor to the wet tank.
Compressed
Air Tanks
The wet tank receives air from the air
dryer and cools it somewhat, allowing
moisture to condense for draining.
Relatively dry air is then supplied to
the two service air tanks for
distribution to their respective brake
circuits. The service air tanks are
isolated from each other by check
valves.
Dual Service
Brake Treadle
Valve
delivers air to the two service brake
circuits.
Double
Check Valve
directs the higher air pressure from
either the rear (primary) or front
(secondary) service air tank to the
modulating valve.
• Limits spring brake
hold-off air pressure
delivered to the
spring brake
chambers.
•
Provides a quick
release of air
pressure from the
spring brake
chambers to speed
spring brake
application.
• Modulates spring
brake application in
proportion to front
service application in
the event of a rear
service failure.
• Prevents
compounding of
service and spring
applications.
Modulating
V
alve (SR-1)
used only on full trucks, not tractors,
performs four functions:
Quick-
Release Valve
speeds the release of air from the
brake chambers. When air is
released, the air in the brake
chambers is exhausted at the quick-
release valve, rather than exhausting
back through the treadle valve.
Single Check
Valve
allows air flow in one direction only.
Parking
Brake Valve
Yellow diamond-shaped knob. It
controls the application and release of
DRIVING - Air Brake System (option)
140 Y53-6113-1A1 (11/20)
4