TM 9-2320-272-24-l
1-23. COMPRESSED AIR AND BRAKE SYSTEM OPERATION (Contd)
Key Item and Function
A PRIMARY AIR PRESSURE GAUGE - Indicates amount of air pressure in primary system.
B LIMITING VALVE - Serves three functions:
Regulates signal air pressure going to front brake chambers so rear brakes are applied first.
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Regulates signal air pressure to front brake chambers so operator has control over amount of
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braking.
Releases air pressure in front brake chambers directly to vent in the valve when brake pedal is
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released.
C FRONT BRAKE CHAMBERS - Convert air pressure to mechanical force which applies front
service brakes.
D PRIMARY RESERVOIR LOW AIR PRESSURE SWITCH - Activates warning buzzer and
warning light when air pressure goes below 60 psi (414 kPa).
E PEDAL INTO VALVE - Allows air pressure from primary constant pressure system to flow into
primary signal system when operator depresses brake pedal.
F DOUBLECHECK VALVE NO. 1 - Serves two functions:
Allows system to receive signal pressure from either pedal valve or, when towed, from brake
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system of towing vehicle.
Serves as a tee between front and rear primary signal lines.
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G FRONT SERVICE COUPLING - When vehicle is being towed, coupling is connected to towing
vehicle so the brake systems of the two vehicles work together.
H ONE-WAY CHECKVALVE - Allows air pressure to flow into primary reservoir, but prevents it from
coming out if constant pressure system fails or engine stalls.
PRIMARY AIR RESERVOIR - Stores enough air pressure so the operator can make five normal
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brake applications before running out of air if constant pressure fails or engine stalls.
J DOUBLECHECK VALVE NO. 2 - Allows either primary or secondary signal air pressure to
activate stoplight switch while keeping the two systems separate.
K STOPLIGHT SWITCH -As brake pedal is depressed, switch receives an air pressure signal which
closes electric contacts turning on stoplight.
L REAR SERVICE COUPLING - When towing another vehicle, coupling is connected to towed
vehicle so the brake systems of the two vehicles work together.
M INTERMEDIATE FRONT BRAKE CHAMBERS - Converts air pressure to mechanical force
which applies intermediate rear service brake.
N PRIMARY RESERVOIR DRAINVALVE - Provides a drain for moisture and air from primary air
reservoir.
Boosts signal air pressure to rear brake chambers. Air signal from brake pedal opens valve to
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route constant air pressure to rear brake chambers.
Regulates signal air pressure from brake pedal to rear brake chambers so operator has control
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over amount of braking. Regulates amount of constant air pressure going to brake chambers as
the operator depresses the brake pedal.
Releases air pressure in rear brake chamber directly to vent system when brake pedal is
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released.
P REAR FRONT BRAKE CHAMBERS - Converts air pressure to mechanical force which applies
rear service brakes.
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