CDL Air Brakes TestInspecting Air Brake SystemsHard
A driver is performing a pre-trip inspection. They notice that the air dryer's purge cycle is excessively frequent (e.g., every 15-20 seconds) even after the system has fully charged. What is the most likely cause of this condition?
- AThe air dryer desiccant cartridge is saturated and needs replacement.
- BThere is a significant air leak downstream of the air dryer.
- CThe air compressor is failing to build sufficient pressure.
- DThe governor cut-out pressure is set too low.
Show answer & explanationAnswer & explanation
Correct answer: B. There is a significant air leak downstream of the air dryer.
An excessively frequent air dryer purge cycle after the system has fully charged typically indicates a significant air leak somewhere in the system downstream of the air dryer. The compressor constantly runs to make up for the lost air, causing the dryer to cycle often.
Why the other options are wrong
- A. A saturated desiccant cartridge would lead to moisture in the air system, but not necessarily an excessively frequent purge cycle after full charge.
- C. If the compressor was failing to build sufficient pressure, the purge cycle might be infrequent or non-existent, and the system wouldn't fully charge.
- D. A low governor cut-out pressure would mean the system charges to a lower pressure, but not necessarily an excessively frequent purge cycle if that lower pressure is maintained.
Frequent Air Dryer Purge Cycle
An indication that the air compressor is cycling too often, often pointing to a problem in the air brake system.
- Commonly caused by a significant air leak in the system.
- Can also indicate a faulty governor or compressor issues.
- Leads to increased wear on compressor and dryer.
- Should be investigated promptly to prevent air loss.
Memory trick: Purge too fast? Air's leaking past!