CDL Air Brakes TestAir Brake System PartsMedium
A technician is inspecting the air brake system of a commercial truck and observes that the safety valve on the wet air tank repeatedly opens when the air pressure reaches 150 psi. What does this indicate?
- AThe air compressor governor is failing to cut out at the correct pressure.
- BThe air dryer is clogged and causing excessive pressure buildup.
- CThe air compressor is functioning normally, maintaining optimal pressure.
- DThe brake pedal valve is stuck open, leading to pressure loss.
Show answer & explanationAnswer & explanation
Correct answer: A. The air compressor governor is failing to cut out at the correct pressure.
The safety valve is designed to protect the system from over-pressurization. If it's repeatedly opening at 150 psi, it means the air compressor is building pressure beyond the normal cut-out point (typically 125 psi), indicating a failure in the air compressor governor to stop the compressor.
Why the other options are wrong
- B. A clogged air dryer would restrict airflow, potentially causing the compressor to work harder, but wouldn't directly cause over-pressurization to the point of safety valve activation unless the governor failed.
- C. Normal operating pressure is typically 100-125 psi; 150 psi indicates over-pressurization.
- D. A stuck-open brake pedal valve would cause a loss of pressure, not an excessive buildup.
Safety Valve
A pressure relief device on the air tanks designed to open and release air if the system pressure exceeds a safe limit, typically 150 psi.
- Protects against over-pressurization.
- Activates usually around 150 psi.
- Repeated activation indicates a fault, often with the governor.
Memory trick: Safety Valve Saves Systems from Stress.