Dual Air Brake System
A dual air brake system consists of two independent air brake systems that use a single set of brake controls. Each system has its own reservoir, plumbing, and brake chambers. The primary air system operates the service brakes on the rear axle; the secondary air system operates the service brakes on the front axle.
Primary Air Brake System
Loss of air pressure in the primary air system causes the rear service brakes to become inoperative. The front brakes will continue to be operated by the secondary air system.
Secondary Air Brake System
Loss of air pressure in the secondary air system causes the front axle brakes to become inoperative. The rear service brakes will continue to be operated by the primary air system.
Emergency Braking System
When air pressure is lost in one air system, the air compressor will operate, but the air supply in the leaking system will not be replenished. There will be enough air in the working system to stop the vehicle safely. The dual air brake system thus provides emergency braking capability. When the low air pressure warning light and emergency buzzer first come on, stop the vehicle immediately. Do not drive the vehicle until the cause of the problem is corrected.
Parking Brakes
Pulling out the yellow diamond-shaped knob (parking brake control valve) on the auxiliary dash panel applies the parking brakes (spring brakes). See Fig. for the standard parking brake control valve and Fig. for the Intellipark™ parking brake control valve.
Note: If either control valve does not apply the parking brakes, the driver can manually set the parking brakes one of two ways:
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With the ignition in the OFF position, pump the brakes to lower the air pressure in the system.
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If the vehicle is equipped with a dump switch, turn the ignition to the ON position and press the dump switch to lower the air pressure in the system.
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Parking Brake Control Valve
Fig. 1, Parking Brake Control Valve
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Light Emitting Diode