Section 12: BRAKE AND AIR SYSTEM
PA1562
15
21. LOW PRESSURE INDICATOR (LP-3)
Maintenance and repair information on the low
pressure indicators is supplied in the applicable
booklet annexed to this section under reference
number SD-06-1600.
The air system includes two low pressure
switches (Fig. 22), both located on the
pneumatic accessory panel in the front service
compartment. One serves for the parking brake
signal, its pressure setting is 66 ± 6 psi (455 ±
40 kPa). The remaining pressure switch
monitors the parking brake telltale panel
indicator; its pressure setting is 30 psi (205
kPa).
FIGURE 22: LP-3 12214
22. SHUTTLE-TYPE DOUBLE CHECK
VALVE (DC-4)
Maintenance and repair information on the
shuttle-type double check valve is supplied in
the applicable booklet annexed to this section
under reference number SD-03-2202.
The double check valve is located on the
pneumatic accessory panel in the front service
compartment. In the event of a pressure drop in
either the primary or secondary system, this unit
will protect the emergency /parking brake control
valve and the intact portion of the air system
from pressure loss.
FIGURE 23: DC-4 12134
23. EMERGENCY DOOR OPENING VALVES
Two emergency door opening three-way valves
are installed on coaches. One is in the front
service compartment, readily accessible. The
other one is on the R.H. side lateral console,
close to the entrance door. When used, the
valve releases pressure in the door locking
cylinder, thus allowing the door to be manually
opened.
FIGURE 24: THREE-WAY VALVE 12186
24. AIR HORN VALVE
The air horn valve is located in the L.H. front
service compartment. The air horn button is on
the center of the steering wheel. Refer to section
23 “ACCESSORIES” for more information.
25. AIR SYSTEM TROUBLESHOOTING
The following list has been designed to help in
troubleshooting some of the most common
problems in the air system and main causes.
For air brakes troubleshooting, refer to “Air
Brakes Troubleshooting” in this section. For
more troubleshooting information, refer to the
manufacturer's brochures annexed to this
section.
Air pressure doesn't rise to, or doesn't maintain,
a normal setting:
• Defective air gauge (registering incorrectly).
• Excessive leaking in air system.
• Reservoir drain cock open.
• Governor poorly adjusted or defective.
• Defective compressor.
• Worn compressor or excessive wear on
piston and/or ring.
• Air pressure rises to normal setting too
slowly.
Excessive leaking in air system:
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