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CDL · Air Brake Parts

What does the air brake governor control?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

When the air compressor pumps air into the reservoirs (cut-in and cut-out pressures)

  1. A The engine speed
  2. B The steering
  3. C The headlights
  4. D When the air compressor pumps air into the reservoirs (cut-in and cut-out pressures)

Why this is the answer

The GOVERNOR controls when the air compressor PUMPS air into the reservoirs — it stops the compressor from pumping (CUT-OUT) when pressure reaches the maximum (around 125 psi) and starts it again (CUT-IN) when pressure drops to the minimum (around 100 psi). ASVAB/CDL air brakes. This maintains air pressure within the proper operating range automatically. The governor prevents over-pressurization and ensures enough air is always available. Knowing the governor controls the compressor's cut-in and cut-out (maintaining the air pressure range) is commonly tested.
Source: FMCSA CDL Manual — Air Brakes, Governor

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About this topic: Air Brake Parts

Knowing the parts of the air brake system — compressor, governor, supply tank, dryer, slack adjusters, spring brakes — is required so you can recognize defects during inspection. This is one of 22 Air Brakes questions on air brake parts, each with a full explanation on a single study page.

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

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