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Air Compressor


Compresses air for the air brake system and other air operated accessories.

The compressed air is stored in air tanks (reservoirs), for future use.

Compressors on an air brake system are almost identical to a garage compressor. The compressor pressurizes air and fills a storage tank. Both garage and air brake compressors are fitted with a governor. The garage compressor’s governor turns off the electric motor when the system reaches maximum pressure. When the system lowers to minimum pressure, the governor turns on the electric motor.

The governor on an air brake system is also a switch, but instead of turning the compressor off and on, the governor puts the compressor into the load (cut-in) and unload (cut-out) phase.

In other words, the compressor pumps the entire time the engine is running. The governor on the air brake system changes the compressor to load or unload. When the governor puts the compressor into the load phase, it pumps compressed air into the system. When the governor puts the compressor into the unload phase, it pumps air into the atmosphere.

At the same time the compressor is in the unload (cut-out) phase, it cools owing to the fact that it is just spinning over – similar to a small engine with the spark plug removed.


During the compressor build-up test, most modern compressors will pass the minimum standard with “flying colours.” In Manitoba and many other provinces, for example, the compressor must build air between 50 and 90psi (345-620kPa) within 3 minutes at a high idle. Most modern air brake compressors will build this amount of air pressure well under 2 minutes.

Build-Up Test


Modern compressors are a true parasite. These use the engine’s lubricating system. Compressors are bolted onto the side of the engine block and powered by gears. The air compressor pulls air from the atmosphere through the engine’s main air intake.

The compressor builds ample air for the air brakes, air ride suspension and other air accessories on the vehicle. Fortunately not air windshield wipers – those were tossed out with the Chia pet.

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