CDL Air Brakes TestDual Air Brake SystemsMedium
During a pre-trip inspection of a vehicle with a dual air brake system, the driver notes that the air compressor governor cuts out at 130 psi. When the service brakes are applied, the governor cuts in at 100 psi. What do these readings indicate?
- AThe air tanks are undersized for the vehicle's braking demands.
- BThere is a significant air leak that requires attention.
- CThe system's governor is operating within normal parameters.
- DThe air compressor is faulty and needs immediate repair.
Show answer & explanationAnswer & explanation
Correct answer: C. The system's governor is operating within normal parameters.
A normal air compressor governor should cut out between 120-140 psi and cut in between 100-115 psi (or approximately 20-25 psi below the cut-out pressure). 130 psi cut-out and 100 psi cut-in are well within these acceptable ranges.
Why the other options are wrong
- A. Tank size is not directly indicated by governor cut-in/cut-out pressures, which relate to compressor operation.
- B. A leak would cause the compressor to cycle more frequently or fail to reach cut-out, which is not indicated here.
- D. The compressor is functioning correctly, as indicated by the normal cut-in/cut-out pressures.
Air Compressor Governor Operation
The air compressor governor controls when the air compressor pumps air into the storage tanks, ensuring pressure stays within a safe operating range.
- Cut-out: 120-140 psi (compressor stops).
- Cut-in: 100-115 psi (compressor starts).
- Maintains system pressure for reliable braking.
Memory trick: Cut-out high, cut-in low, all in the zone, good to go.