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The safety valve

If the governor fails to cut-out the compressor, the safety valve will prevent excessive air pressure to build-up in the system. This valve is located on the supply reservoir and vents air to the atmosphere if the pressure in the reservoir exceeds 1,035 kPa (150 PSI).

Air dryers

Air dryers remove moisture and contamination from the air before the air enters the reservoirs. The contamination gathered by the dryer is expelled into the atmosphere when the governor cuts out the compressor.

Primary brake circuit 


Vehicles that comply with the CMVSS 121 air brake system have two separate service brake circuits, known as primary and secondary. These systems are commonly known as dual braking systems. The primary and secondary service brake circuits are isolated from one another and from the supply circuit by single check valves. These valves prevent air from flowing backward through the system and being lost from a circuit that has failed. Check valves ensure at least one service brake system will remain fully pressurized in the event of an air failure in one of the other circuits. The circuit that remains pressurized will keep the emergency brakes released and allow the driver to bring the vehicle to a controlled stop.

Primary service reservoir

The primary service reservoir stores the air used to control the rear tandem brakes of the vehicle. It receives its air supply from the supply reservoir through a single check valve, which prevents air loss if an air failure occurs in the supply or secondary circuit.

 

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