TM-9-2320-272-23-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; FIELD MAINTENANCE MANUAL; VOLUME 1 OF 5
SEPTEMBER 2012
TM-9-2320-272-23-1 - Page 253 of 1313
AIR VENTING SYSTEM OPERATION
The air venting system vents air from brake system and powertrain and fuel vapors from fuel system into air intake
stack where it is released into the atmosphere. The components of the air venting system are:
A. SPRING BRAKE RELEASE CONTROL VALVE
- This valve functions as an override when a failure in
the air supply system (causing spring brakes to engage) occurs. When valve is manually pushed in,
emergency air is supplied to the spring brake chambers. This releases the spring brakes, allowing
vehicle
movement.
B. PEDAL VALVE
- Vents primary or secondary signal air pressure when pedal is released.
C. FRONT BRAKE CHAMBER VENT
- Vents air pressure inside chambers when pedal valve is released.
D. LIMITING VALVE
- Vents signal air pressure going to front brake chambers so rear brakes apply first.
E. STEP BOX QUICK-RELEASE VALVE
- Vents air pressure from spring brake chambers when parking
brake valve has been actuated.
F. REAR BRAKE CHAMBERS
- Vents ports on chambers to prevent air pressure buildup.
G. RELAY VALVES
- Vents air pressure in rear brake chambers directly to intake tube when brake pedal
is released. Vents signal air pressure through upper port in valve.
H. AIR INTAKE STACK
- Venting point for the vent system.
I. TRANSMISSION VENT
- Vents internal air pressure buildup due to internal heat.
J. SPRING PARKING BRAKE VALVE
- Vents air pressure from air and double check valves No. 3
and
No.
4.
K. TRANSFER CASE VENT
- Vents internal air pressure buildup due to internal heat.
L. FUEL TANK VENTS
- Vent fuel vapors to prevent partial vacuum from stopping fuel flow.
TM 9-2320-272-23-1
0003
0003-48
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