CDL Air Brakes TestDual Air Brake SystemsHard
A driver is inspecting a commercial vehicle and notes that the safety valve on the primary air tank continuously releases air. The air pressure gauges for both primary and secondary systems read 150 psi. What is the most likely issue?
- AA leak in the primary air tank itself.
- BA malfunctioning air compressor governor.
- CA faulty check valve between the compressor and the tanks.
- DA clogged air dryer filter.
Show answer & explanationAnswer & explanation
Correct answer: B. A malfunctioning air compressor governor.
The safety valve is designed to open and release air if the system pressure exceeds a safe limit (typically around 150 psi). If it's continuously releasing air and the gauges read 150 psi, it means the air compressor is not being shut off by the governor, leading to over-pressurization of the system.
Why the other options are wrong
- A. A leak in the tank would cause pressure to drop, not rise to 150 psi and activate the safety valve.
- C. A faulty check valve might cause air to leak back to the compressor or between tanks, but wouldn't directly cause over-pressurization to the point of safety valve activation if the governor was working.
- D. A clogged air dryer filter would restrict air flow, potentially causing slow pressure build-up, not over-pressurization.
Air System Over-Pressurization
Over-pressurization in an air brake system, indicated by the safety valve continuously releasing air and high gauge readings (e.g., 150 psi), is typically caused by a malfunctioning air compressor governor.
- Safety valve opens around 150 psi.
- Governor regulates compressor cut-out/cut-in.
- Failure to cut out leads to over-pressure.
Memory trick: Pressure too high, governor's eye is dry.