NOTE: ALL PIPING DIAGRAMS ARE USED TO ILLUSTRATE BASIC BRAKING PRINCIPLES ONLY AND DO NOT ILLUSTRATE ACTUAL AIR BRAKE SYSTEMS.

BASIC OPERATION PRINCIPLE

Air is pumped by the compressor (1) to the reservoir (2), which is protected from over pressurization by a safety valve (3). The governor (5) controls the pressure in the reservoir by governing the compressor. Air is available from the reservoir to the bottom of the foot valve (6). The driver pushes down the foot valve treadle and air pressure flows to the front and rear brake chambers (7, 8). The brake chamber push rods move the slack adjusters. The slack adjusters rotate the ‘S’ cams, forcing the brake shoes against the drums. This causes friction, which stops the vehicle. The driver releases the foot valve treadle, and the air in the brake chambers is allowed to exhaust through the foot valve, releasing the brakes.

Other valves are necessary to ensure smooth and efficient operation.