AIR SYSTEM.

TM 9-2320-279-20-1

Vehicle

Operation

Systems

(Cont)

(fig. 1-14) The air system consists of an engine driven air compressor (1) and four

1-18. AIR SYSTEM.

air reservoirs (2, 3, 4, and 5) (all vehicles except M983 tractor). The M983 tractor vehicle has reservoirs (2,

3, 5, and 6). The system includes the necessary valves and air lines to control the vehicle's air operated

devices. Pressurized air from the air compressor (1) is passed through the air dryer (7) to the quick buildup

reservoir (2). The air dryer (7) removes dirt and moisture from the pressurized air. Air from reservoir (2)

goes to the throttle treadle (8). Depending on how far the throttle treadle (8) is depressed, 0 to 60 psi (0 to

414 kPa) is supplied to the engine air throttle cylinder (9) and to the transmission modulator (10). This air

p r e s s u r e controls vehicle speed.

Once air pressure in reservoir (2) rises above 75 psi (517 kPa), a valve opens and allows reservoirs (3, 4,

or 6, and 5) to be pressurized up to 120 psi (827 kPa). Air from reservoir (4 or 6) goes to the brake treadle

valve (11). This air controls the rear axle service brakes (12). Air pressure in this system is shown by the

red needle on the AIR PRESS gage (13). Air from reservoir (3) goes to the brake treadle valve (11). This air

controls the front axle service brakes (14). Air pressure in this system is shown by the green needle on the

AIR PRESS gage (13). The PARKING BRAKE valve (15) controls air from reservoirs (3 and 5) and applies or

releases the rear axle service (parking) brakes (12). Reservoirs (3, 4, or 6, and 5) are interconnected in such

a way that if one reservoir fails, air would be supplied to release the rear axle service (parking) brakes (12)

from whichever reservoir is functioning. If air pressure falls below 60 to 70 psi (414 to 483 kPa), a buzzer

will sound, the AIR indicator (16) will light, and rear axle brakes will be applied.

On the M984E1 vehicle, the front brake actuator valve (17) is used to apply the front axle service brakes

w h e n using the heavy-duty winch.