CDL Air Brakes TestAir Brake System PartsMedium
A driver is conducting a pre-trip inspection and notices that the air compressor is cycling on and off much more frequently than usual, even without heavy brake usage. The system pressure still builds to 125 psi and cuts out correctly. What is the most likely cause?
- AA faulty air compressor governor.
- BA clogged air dryer filter.
- CAn over-pressurized air storage tank.
- DA continuous, small air leak in the system.
Show answer & explanationAnswer & explanation
Correct answer: D. A continuous, small air leak in the system.
If the compressor is cycling frequently but still reaches correct pressure, it indicates that air is being lost from the system at a rate higher than normal. A continuous, small air leak would cause the pressure to drop more quickly, forcing the compressor to cycle more often to maintain pressure.
Why the other options are wrong
- A. A faulty governor would typically cause the compressor to not cut out, or cut out at the wrong pressure, not just cycle more frequently while still meeting pressure targets.
- B. A clogged air dryer filter would restrict air flow, potentially causing slower build-up or reducing efficiency, but not necessarily frequent cycling if the pressure targets are still met.
- C. An over-pressurized tank would be a result of a governor failure, and the compressor would likely run continuously or cut out too high, not just cycle more frequently within the normal range.
Continuous Air Leak (Symptom)
A constant loss of air pressure from the air brake system, often indicated by frequent cycling of the air compressor or a noticeable hiss.
- Can be caused by loose fittings, cracked lines, faulty diaphragms, etc.
- Leads to increased compressor wear and reduced system efficiency.
- Must be located and repaired promptly for safety.
Memory trick: Frequent pump means a hidden hump (leak)!