Section 12: BRAKE AND AIR SYSTEM
PA1562
14
FIGURE 18: R-14 12207
18. QUICK RELEASE VALVES (QR-1)
The quick release valve is located on the front
axle service brakes air line and permit rapid
exhaust of air pressure from brakes, thus
decreasing the brake release time.
FIGURE 19: QR-1 12075
Maintenance and repair information on this valve
is supplied in the applicable booklet annexed to
this section under reference number SD-03-901.
19. SPRING BRAKE VALVE (SR-7)
The spring brake valve is located in the rear
underframe. The SR-7 Modulating Valve is used
in conjunction with a dual air brake system and
spring brake actuator and performs the following
functions:
• Provides a rapid application of the spring
brake actuator when parking.
• Modulates the spring brake actuator
application using the dual brake valve
should a primary failure occur in the service
brake system.
• Prevents compounding of service and spring
forces.
Maintenance and repair information on the
spring brake valve is supplied in the applicable
booklet annexed to this section under reference
number SD-03-9043.
FIGURE 20: SR-7 12206
20. PRESSURE PROTECTION VALVE (PR-4)
Maintenance and repair information on the
pressure protection valve is supplied in the
applicable booklet annexed to this section under
reference number SD-03-2010.
The air system includes two pressure protection
valves (Fig. 21). One valve is installed on the
manifold block, and insures at all times a
minimum pressure of 70 psi (482 kPa) in the
suspension air system in the event that a
pressure drop occurs in either the suspension
air system or accessory air system. This valve is
located in the front service compartment beside
the air filter.
FIGURE 21: PR-4 12174
The other valve is installed on the accessory air
tank, and insures a minimum pressure of 70 psi
(482 kPa) in the accessory air system in the
event that a pressure drop occurs in either the
suspension air system or braking air system
(refer to Fig. 1 & 2 for accessory air tank
location).
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