CDL Air Brakes TestAir Brake System PartsEasy
A driver observes that when the air compressor builds pressure, it stops pumping air into the tanks once the pressure reaches 125 psi. What component is responsible for this action?
- AThe service brake relay valve.
- BThe air compressor governor.
- CThe air storage tank check valve.
- DThe safety relief valve.
Show answer & explanationAnswer & explanation
Correct answer: B. The air compressor governor.
The air compressor governor is responsible for controlling when the air compressor pumps air into the storage tanks. It has a 'cut-out' setting (typically around 125 psi) at which it stops the compressor from pumping air, and a 'cut-in' setting (typically around 100 psi) at which it allows the compressor to start pumping again.
Why the other options are wrong
- A. Service brake relay valves speed up the application and release of the service brakes, unrelated to compressor control.
- C. Check valves prevent air from flowing back out of the tanks, not controlling compressor operation.
- D. The safety relief valve only activates at much higher pressures (150-175 psi) to prevent over-pressurization.
Air Compressor Governor (Cut-out)
The air compressor governor regulates the air compressor, causing it to stop pumping air into the tanks when pressure reaches the 'cut-out' setting (typically 125 psi).
- Controls compressor on/off cycle.
- Cut-out: Stops compressor (e.g., 125 psi).
- Cut-in: Starts compressor (e.g., 100 psi).
Memory trick: Governor: it's the 'boss' of the compressor.