CDL Air Brakes TestInspecting Air Brake SystemsMedium
A driver is performing a pre-trip inspection on a vehicle with air brakes. They notice that the air compressor's discharge line, connecting the compressor to the first air tank, is coated in oil. What is the most likely cause of this observation?
- AA normal condition indicating proper lubrication of the compressor.
- BA leak in the discharge line and/or worn compressor piston rings.
- COver-pressurization of the air brake system.
- DInsufficient air dryer function, causing moisture buildup.
Show answer & explanationAnswer & explanation
Correct answer: B. A leak in the discharge line and/or worn compressor piston rings.
Oil in the discharge line indicates that the air compressor is passing oil, usually due to worn piston rings or seals. This oil can then leak out of the line connections or build up internally, causing system contamination.
Why the other options are wrong
- A. Oil coating on the exterior of air lines is never normal and indicates a leak or internal issue.
- C. Over-pressurization would likely result in safety valve activation, not necessarily oil on the discharge line.
- D. Moisture buildup is related to water, not oil, and would typically be handled by the air dryer, not cause oil on the line.
Air Compressor Oil Contamination
Oil found in the air lines or tanks, particularly the discharge line, indicates the air compressor is allowing engine oil into the air system.
- Usually caused by worn piston rings, cylinders, or seals in the air compressor.
- Can lead to contamination of air dryer, valves, and other components.
- Reduces braking efficiency and can cause component failure.
- Requires repair or replacement of the air compressor.
Memory trick: Compressor's oily sweat means internal wear, a system threat.