Overview of how Air Brakes Work

The Governor controls compressor output by cycling and keeping air in a predetermined range. It monitors the supply tank and sends a signal to Air Compressor. This signal tells compressor when to pump and when to rest & keeps the air pressure in range. Cut in pressure is 85psi and cutout is 125psi. The SUPPLY TANK is often called the wet tank.

The Air Dryer helps remove moisture and filter contaminates from the air system. The type of air dryer depends on application and the type of compressor being used. Compressed air enters air dryer thru inlet port and passes thru drying material called desiccant. Desiccant captures moisture as well as oil and other contaminants. When the system cutout pressure is reached, the governor signals to open the Air Dryer purge valve to expel moisture and contaminates.

Dry air flows into the supply tank from the air dryer outlet. Typically there are 3 air tanks or reservoirs.

The air is stored in these reservoirs until brakes air is applied. The supply tank is first tank in system and moisture tends to collect in it more than others. Supply tank has a pressure relief valve if system becomes over pressurized. The Supply tank includes a low pressure indicator which monitors over all system pressure. If pressure falls below 60 PSI – an alarm will sound and light will come on to notify the driver of a low pressure condition.

All the tanks have a manual drain valve at the lowest point that expels water that accumulates over time, these can normally be found by looking in the wheel well areas. Some tanks have an automatic drain valve for convenience.

Starts with a 2 way check valve that directs the higher pressure of the Primary and Secondary tank to the emergency brake. Parking Brakes are controlled by dash Push/Pull valves. When valve is pushed in – air travels to spring brake overcoming spring force and brakes are released.