TM-9-2320-272-24-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL; VOLUME 1 OF 4
JUNE 1998
TM-9-2320-272-24-1 - Page 69 of 1015
TM 9-2320-272-24-1
1-23. COMPRESSED AIR AND BRAKE SYSTEM OPERATION (Contd)
Key Item and Function
A
FRONT EMERGENCY COUPLING
-When vehicle is being towed, coupling receives compressed
air from towing vehicle’s brake system to charge its own brake system.
PRIMARY AIR RESERVOIR
- Stores sufficient air pressure to allow operator to make normal
brake applications if system pressure fails or engine stalls.
PRIMARY FEED CUTOFF
- Manually-operated valve used to isolate pressure leaks in primary air
system from draining wet tank (TM 9-2320-272-10).
PRIMARY AIR RESERVOIR CHECKVALVE
- Prevents backflow of air from primary tank if wet
system develops a leak.
SECONDARY FEED CUTOFF
- Manually-operated valve used to isolate pressure leaks in
secondary air system from draining wet tank (TM 9-2320-272-10).
SECONDARY AIR RESERVOIR CHECKVALVE
- Prevents backflow of air from secondary tank if
wet system develops a leak.
REAR EMERGENCY COUPLING
- When towing another vehicle, coupling allows pressurized air
from wet tank to charge towed vehicle’s wet tank.
SECONDARY AIR RESERVOIR
- Stores enough air pressure in case constant pressure system
fails or engine stalls. The operator can make normal brake application before running out of air.
PRESSURE PROTECTION VALVE
- Performs two functions:
(1) Allows air pressure to build to 60-65 psi (414-448 kPa) before supplying air to auxiliary air-
B
C
D
E
F
G
H
I
powered equipment.
(2) Closes off auxiliary air system from other systems if an accessory fails and prevents loss of air
from secondary reservoir.
1-59
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