COMPRESSED AIR AND BRAKE SYSTEM OPERATION (Contd)
INTERMEDIATE FRONT SPRING BRAKE CHAMBER - Contains a large spring which applies rear brakes when
spring brake air pressure is released.
ONE-WAY CHECK VALVE - Allows air pressure to flow into spring brake reservoir but prevents it from coming out
if constant pressure system or primary system fails.
SPRING BRAKE AIR RESERVOIR - Stores enough air pressure to release spring brakes for emergency
operation in event of primary or secondary air system failure.
QUICK-RELEASE VALVE - Releases spring brake air pressure directly to vent if parking brake has been set or
brake system fails.
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 brake reservoir.
DOUBLECHECK VALVE #3 - Allows spring brake air pressure to come from either release control valve or spring
parking brake valve directly to doublecheck valve #4.
REAR-REAR SPRING BRAKE CHAMBER - Contains a large spring which applies rear brakes when spring brake
air pressure is released.
Primary Service Airbrake System Operation.
The primary service airbrake system is made up of two subsystems: (a) Primary constant pressure
system provides continuous air pressure to:
Rear relay valve.
Spring brake air reservoir.
Spring parking brake valve.
Primary signal system serves three functions:
Contains pressure only when operator steps on brake pedal.
Is regulated by various valves to give operator control over amount of braking.
Provides pressure to apply front service brakes and the front two service brakes on the intermediate
and rear axles stamped with an A Service brakes on the intermediate axle are piggybacked to
spring brakes but operate independently of them.