CDL Air Brakes TestAir Brake System PartsEasy
During a pre-trip inspection, a driver notices that the air pressure in the system consistently builds from 85 psi to 100 psi in less than 45 seconds while the engine is at operating RPM. What does this indicate about the air compressor?
- AThe air compressor is faulty and needs immediate replacement.
- BThe air compressor is over-pressurizing the system, which is dangerous.
- CThe air compressor's governor is set too low, requiring adjustment.
- DThe air compressor is functioning correctly and meets minimum performance standards.
Show answer & explanationAnswer & explanation
Correct answer: D. The air compressor is functioning correctly and meets minimum performance standards.
Federal regulations and CDL air brake tests require the air compressor to build air pressure from 85 psi to 100 psi within 45 seconds at operating RPM. Meeting this standard indicates proper function.
Why the other options are wrong
- A. A build-up rate within the specified time indicates proper function, not a fault.
- B. The system is building to 100 psi, which is within the normal operating range, not over-pressurizing.
- C. The governor's setting is related to the cut-out pressure (typically 120-140 psi), not the build-up rate between 85-100 psi.
Air Compressor Build-Up Rate
The air compressor must be able to build air pressure from 85 psi to 100 psi within 45 seconds for a properly functioning air brake system.
- Standard applies at engine's operating RPM.
- Ensures adequate air supply for safe braking.
- Failure to meet rate indicates potential compressor or system issues.
Memory trick: Fast air build-up keeps you on the road, slow build-up means trouble could explode.