PREVOST X3-45 2016, Maintenance Manual

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Section 12: BRAKE AND AIR SYSTEM
12
X3-45 Commuter PA1593 DOB 2400-2489 Section 12 Updated Sept. 2015
FIGURE 15: BENDIX SWITCH
12140
17. PARKING BRAKE ALARM SWITCH
Refer to the appropriate annexed booklet
(Bendix, SL-5 Stop Light Switch; reference no.
SD-06-2501).
The parking brake alarm uses the same switch
as the stoplights. It is mounted on the spring
brake valve and operates in conjunction with a
NC relay to sound a warning alarm by
completing the electrical circuit when the ignition
switch is turned OFF with parking brake
released.
18. BRAKE RELAY VALVE (R-12 & R-14)
The primary air system includes three brake
relay valves being supplied by the dual brake
valve, and which function is to speed up the
application and release of the service brakes.
One Wabco R-14 valve located in the rear
underframe supplies the drive axle service brake
air line, while the other two R-12 valves supply
independently both the tag axle right and left
service brake air line and act as interlock valves.
These valves are accessible from under the
vehicle at the level of the tag axle. Maintenance
and repair information on these valves is
supplied in the applicable booklet annexed to
this section under reference number
SD-03-1064.
FIGURE 16: R-12
12074
FIGURE 17: R-14
12207
19. 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 18: 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.
20. 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.