TM 9-2320-272-24-1
1-23. COMPRESSED AIR AND BRAKE SYSTEM OPERATION (Contd)
Key Item and Function
A SPRING BRAKE WARNING LIGHT SWITCH - Activates warning light when spring brakes are
engaged.
B SPRING BRAKE RELEASE CONTROL VALVE - Pushed in to release spring brakes
independently of mechanical parking brake. Control is also used to release spring brakes in order to
test and adjust mechanical brake.
C DOUBLECHECK VALVE NO. 4 - Allows spring brake air pressure to come from either release
control valve or spring parking brake valve directly to doublecheck valve No. 3.
D INTERMEDIATE FRONT SPRING BRAKE CHAMBER - Contains a large spring which applies
rear brakes when spring brake air pressure is released.
E ONE-WAY CHECKVALVE - Allows air pressure to flow into spring brake reservoir, but prevents it
from coming out if constant pressure system or primary system fails.
F SPRING BRAKE AIR RESERVOIR - Stores enough air pressure to release spring brakes for
emergency operation in event of primary or secondary air system failure.
G QUICK-RELEASE VALVE - Releases spring brake air pressure directly to vent if parking brake
has been set or brake system fails.
H SPRING BRAKE VALVE - Automatically sets spring brakes when parking brake is set. Valve can
be released independently of parking brake when spring brake control valve is pushed in.
SPRING BRAKE RESERVOIR DRAINVALVE - Provides a drain for moisture and air from spring
I
brake reservoir.
J DOUBLECHECK VALVE NO. 3 - Allows spring brake air pressure to come from either release
control valve or spring parking brake valve directly to doublecheck valve No. 4.
K REAR-BEAR SPRING BRAKE CHAMBER - Contains a large spring which applies rear brakes
when spring brake air pressure is released.
e. Primary Service Airbrake System Operation.
(1) The primary service airbrake system is made up of two subsystems:
(a) Primary constant pressure system provides continuous air pressure to:
l Pedal valve
l Rear relay valve
Spring brake air reservoir
l
Spring parking brake valve
l
(b) Primary signal system serves three functions:
Contains pressure only when operator steps on brake pedal.
l
l Is regulated by various valves to give operator control over amount of braking.
l Provides pressure to apply front service brakes and the front two service brakes on
intermediate and rear axles stamped with an A. Service brakes on the intermediate axle
are piggybacked to spring brakes, but operate independently of them.
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