Operation Of Staight Air- Brake Sytem - Continued

Wheeled Vehicle Braking Systems
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closed and prevents any escape of air pressure.

If the driver pushes the foot pedal farther down, more mechanical

force is applied to the top of the diaphragm. When this happens,

more pressure is delivered to the brake chamber and is applied to the

brakes.

If the driver lets the pedal move toward its released position, the

force on top of the diaphragm is reduced. Air pressure below the

diaphragm overcomes the mechanical force on top of it, and the

diaphragm lifts slightly. When this happens, the inlet valve remains

closed and the exhaust valve opens. This exhausts air pressure from

the brake chambers until the air pressure below the diaphragm again

balances the mechanical force on top of it.

If the driver lets the foot pedal return to the fully released

position, the exhaust valve remains open. Thus, all the pressure

from the brake chamber is exhausted, and the brakes are fully

released.

If the driver pushes the pedal down to the fully applied position,

the pressure regulating spring is compressed until the spring guide

strikes the spring slat. This holds the rocker arm down, the inlet

valve is held open, and full reservoir pressure is allowed to pass

through the brake valve to the brake chambers.

The trailer brake control valve is used to apply and release the

trailer brakes without applying the brakes of the towing vehicle.

This type valve is usually mounted on the steering column or on the

instrument panel. The driver may put the handle in any one of

several positions between the released and fully applied position.