CDL Air Brakes TestDual Air Brake SystemsHard
A technician is diagnosing a commercial vehicle's dual air brake system for a slow air pressure build-up. The air compressor is functioning, but it takes an unusually long time to reach cut-out pressure. All visible lines and connections appear intact. What component is most likely causing this issue?
- AA stuck open safety valve on an air tank.
- BA faulty air dryer desiccant cartridge.
- CA leaking check valve between the primary and secondary tanks.
- DA restricted air intake filter on the compressor.
Show answer & explanationAnswer & explanation
Correct answer: D. A restricted air intake filter on the compressor.
A restricted air intake filter on the compressor would limit the amount of air the compressor can draw in, thus significantly slowing down the rate at which it can build pressure in the entire system, even if the compressor itself is mechanically sound.
Why the other options are wrong
- A. A stuck open safety valve would cause a rapid loss of air, preventing pressure build-up entirely, not just slowing it down.
- B. A faulty air dryer desiccant cartridge would affect air quality (moisture), not typically the rate of pressure build-up, unless it caused a severe restriction.
- C. A leaking check valve between tanks would cause one tank to lose pressure to the other or back to the compressor, but wouldn't typically cause a slow build-up for the entire system from scratch.
Slow Air Build-up Cause
A common cause for slow air pressure build-up in a dual air brake system, when the compressor is otherwise functional, is a restricted air intake filter on the compressor.
- Limits air intake
- Reduces compressor efficiency
- Prevents proper pressure build-up rate
Memory trick: If the air's slow to fill, check the compressor's 'breathing' filter still.