FAN 9Z7838 - Caterpillar

Illustration 1 g00278193
Location of secondary brake air control valve
A hand control on the left side of the steering column is for the secondary brake system. The secondary brake air control valve controls air flow to the air circuit for secondary braking. When the secondary brake air control valve is in the OFF position, full system air pressure flows through the secondary brake air control valve to the parking brake air control valve. If the parking brake air control valve is in the OFF position, full system air pressure flows to the parking and secondary brake control valve. This air pressure prevents the application of the parking brakes.When the secondary brake air control valve is in the ON position, the secondary brake air control valve blocks the inlet air. No air will be in the air lines in the rest of the circuit. The parking brakes will be applied.If the secondary air tank loses air pressure, the system will behave as if the secondary brake air control valve is in the ON position.If the engine stops or if the oil pressure decreases, the parking brake will engage slowly as oil pressure decreases.