TM-9-2320-272-10

TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)

TECHNICAL MANUAL; OPERATOR'S MANUAL

SEPTEMBER 2004
CHANGE 2

  TM-9-2320-272-10 - Page 78 of 481

TM 9-2320-272-10
1-61
1-20. COMPRESSED AIR AND BRAKE SYSTEM OPERATION (Contd)
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.
C
PRIMARY FEED CUTOFF
– Manually-operated valve used to isolate
pressure leaks in primary air system from draining wet tank (para. 3-12).
D
PRIMARY AIR RESERVOIR CHECKVALVE
– Presents backflow of air
from primary tank if wet system develops a leak.
F
SECONDARY AIR RESERVOIR CHECKVALVE
– Prevents backflow of
air from secondary tank if wet system develops a leak.
E
SECONDARY FEED CUTOFF
– Manually-operated valve used to isolate
pressure leaks in secondary air system from draining wet tank (para. 3-12).
H
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.
G
REAR EMERGENCY COUPLING
– When towing another vehicle, coupling
allows pressurized air from wet tank to charge towed vehicle’s wet tank.
B
PRIMARY AIR RESERVOIR
– Stores sufficient air pressure to allow operator
to make normal brake applications, should system pressure fail or engine stall.
I
PRESSURE PROTECTION VALVE
– Performs two functions:
• Allows air pressure to build to 60-65 psi (414-448 kPa) before supplying
air to auxiliary air-powered equipment.
• Closes off auxiliary air system from other systems if an accessory fails
and prevents loss of air from secondary reservoir.


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