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CDL · General

What is the purpose of the air compressor in an air brake system?

Correct answer

To pump air and build up pressure in the air storage tanks (reservoirs) that operate the brakes

  1. A To cool the brakes
  2. B To pump air and build up pressure in the air storage tanks (reservoirs) that operate the brakes
  3. C To apply the brakes directly
  4. D To steer the vehicle

Why this is the answer

The AIR COMPRESSOR pumps air to build up and maintain pressure in the air storage tanks (reservoirs). ASVAB/CDL air brake systems use compressed air to apply the brakes. The compressor is driven by the engine; the GOVERNOR controls when the compressor pumps air (cutting in/out to maintain pressure, typically around 100-125 psi). The compressed air stored in the reservoirs is what operates the brakes when the driver presses the pedal. Knowing the compressor builds air pressure (and the governor controls it) is fundamental air brake knowledge.
Source: FMCSA CDL Manual — Air Brakes, Compressor

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