CDL Air Brakes TestDual Air Brake SystemsMedium
A driver observes that the air pressure in the primary system of their dual air brake vehicle drops significantly faster than the secondary system during a leak test, even though both initially held pressure. This indicates a potential issue with the separate controls or lines of which system?
- AThe primary system, as it is losing pressure more rapidly.
- BThe air compressor, as it is not equalizing pressure.
- CThe secondary system, as it is maintaining pressure better.
- DThe parking brake system, as it is linked to the primary system.
Show answer & explanationAnswer & explanation
Correct answer: A. The primary system, as it is losing pressure more rapidly.
If the primary system is losing pressure significantly faster, it indicates a leak or fault within that specific system's lines or controls. The fact that the secondary system is holding pressure confirms the issue is isolated to the primary system.
Why the other options are wrong
- B. The compressor is not actively involved in holding pressure during a leak test with the engine off; it builds pressure.
- C. The secondary system is performing correctly by holding pressure, so it's not the source of the problem.
- D. While the parking brake is linked to the primary system, the issue is identified as a general pressure drop in the primary system, not necessarily just the parking brake components.
Dual System Differential Leakage
Observing a faster pressure drop in one air system (primary or secondary) during a leak test indicates a fault or leak specific to that compromised system.
- Helps isolate the location of a leak.
- Highlights the value of separate systems.
- Requires investigation of the faster-dropping system.
Memory trick: One tank drops fast, that's where the leak is cast.