CDL Air Brakes TestAir Brake System PartsHard
A driver is operating a commercial vehicle equipped with an air brake system. They notice that the air compressor is constantly running and the air pressure gauges show that the system cannot build beyond 80 psi, even after several minutes of operation. What is the most probable cause of this issue?
- AA clogged air intake filter for the air compressor.
- BA severe air leak in the brake system.
- CA faulty air compressor governor that is not signaling the compressor to cut in.
- DA stuck-open safety valve on an air tank.
Show answer & explanationAnswer & explanation
Correct answer: B. A severe air leak in the brake system.
If the compressor is constantly running but cannot build pressure beyond a certain point (e.g., 80 psi), it indicates that the compressor's output is being overcome by a significant air leak somewhere in the system. The compressor is working, but the air is escaping faster than it can be generated to reach full pressure.
Why the other options are wrong
- A. A clogged air intake filter would reduce the compressor's efficiency and build-up rate, but typically wouldn't prevent it from reaching full pressure entirely, unless it's extremely clogged. A severe leak is a more direct cause of being unable to build beyond a certain point.
- C. A faulty governor not signaling 'cut-in' would mean the compressor wouldn't run at all when pressure drops, which contradicts the symptom of the compressor constantly running.
- D. A stuck-open safety valve would prevent pressure from building to cut-out, but 80 psi is a specific example, and a severe leak is a more general and common cause of this symptom.
Continuous Compressor Operation (Low Pressure)
A condition where the air compressor runs continuously but fails to build or maintain adequate air pressure (e.g., above 80 psi), typically indicating a severe air leak in the brake system.
- Compressor working hard but losing the battle.
- Indicates a potentially dangerous system integrity failure.
- Requires immediate investigation and repair.
Memory trick: Compressor's Chugging, Pressure's Lagging? A Leak is Bragging!