Components and functions of an air brake system

Compressor

Build air pressure.

The air compressor operates entire time vehicle is running. The function of the air compressor is to build up and maintain air pressure required to operate air brakes. Air compressors are either gear driven directly from the engine or belt driven. As engine speed is increased, the pulley or gear attached to the air compressor will spin quicker, and more air will be produced. Compressors run continuously while the engine is running, but air compression is controlled and limited by a governor which loads or unloads the compressor.

Governor

Maintain air pressure

When the system reaches maximum pressure of approximately 120 psi, the governor directs the compressor to take the compressor out of its pumping stage and discharge air into the atmosphere. Conversely, when the air brake system reaches its minimum operating pressure at a minimum of 100 psi, the governor directs the compressor to pump air into the system’s reservoirs.

Working together

One way to think of the relationship between the governor and the compressor is that the governor is the wife and the compressor is the husband. When the system reaches minimum pressure the wife tells the husband to go to work and put air in the system. When air builds back to maximum pressure, the wife (governor) tells the husband (compressor) to stop.

Air Tanks / Reservoirs:

Steel pressure-rated tank holds a supply of compressed air until required for braking or operating auxiliary air systems.

The number and size of air tanks varies among vehicles. If the compressor would stop working, reservoirs hold enough air to allow the brakes to be used several times. The maximum air pressure available for brake applications depends on how much air is in the reservoir.

Each reservoir is equipped with a drain valve called a drain cock. Opening the drain cock allows reservoirs to be drained of moisture and other contaminants that build up in the system.

Driveshaft with clamp next to air tank

Brake Chambers:

Convert compressed air pressure energy into mechanical force and movement, which apply the vehicle’s brakes. When you press down on the foot valve, air pressure enters the pressure side of the brake chamber through the inlet port and forces against the diaphragm, which moves the push rod assembly forward. When air pressure is released from the service-brake chamber, the return spring returns the diaphragm and push rod to their released positions.

Brake Drum and Shoes:

Located rear end of the vehicle axles. The wheels are bolted to the drums. The braking mechanism is inside the drum. To stop, the brake shoes and linings are pushed against the inside of the drum. This causes friction, which slows the vehicle.