A driver is performing a pre-trip inspection. They notice that the air dryer continuously purges (releases air) at short, irregular intervals, even when the air system is fully charged. What is the most likely cause of this behavior?
- AA normal operation indicating the air dryer is efficiently removing moisture.
- BAn air leak in the air dryer's purge valve or a stuck open check valve.
- CInsufficient air pressure in the primary and secondary air tanks.
- DA faulty air compressor governor, failing to cut out at the set pressure.
Show answer & explanationAnswer & explanation
Correct answer: B. An air leak in the air dryer's purge valve or a stuck open check valve.
If the air dryer continuously purges at short intervals when the system is supposedly fully charged, it indicates that the system is losing pressure, causing the compressor to cycle on and off frequently. This is often due to an air leak within the air dryer itself, such as a faulty purge valve or a check valve that isn't sealing properly, allowing air to escape.
Why the other options are wrong
- A. Continuous, irregular purging when fully charged is not normal; normal purge cycles are typically less frequent and occur when the compressor cuts out.
- C. Insufficient air pressure would prevent the dryer from purging effectively or would cause the low air warning to activate, but not necessarily continuous short purges at full charge.
- D. A faulty governor would cause the compressor to run continuously (not cut out) or not cut in, leading to over-pressurization or under-pressurization, but not necessarily continuous short purges if the system is holding air.
Air Dryer Continuous Purging
When an air dryer purges frequently or continuously at short, irregular intervals, especially when the system should be fully charged, it indicates an air leak in the dryer itself or elsewhere causing the compressor to overcycle.
- Normal purge occurs when the compressor unloads (cuts out).
- Continuous short purges suggest a constant air loss.
- Common causes include faulty purge valve, check valve, or internal leaks in the dryer.
- Leads to excessive compressor wear and reduced air system efficiency.
Memory trick: Dryer's constant sneeze means a leak, a system weak.