A driver is performing a pre-trip inspection on a commercial vehicle with a dual air brake system. They notice that the primary air gauge reads 110 psi, while the secondary air gauge reads 90 psi. What is the most likely cause of this discrepancy?
- AA faulty air compressor.
- BA leaking check valve in the primary system.
- CThe parking brake is partially engaged.
- DA restriction in the air line to the secondary tank.
Show answer & explanationAnswer & explanation
Correct answer: D. A restriction in the air line to the secondary tank.
A significant and consistent pressure difference between the primary and secondary tanks, especially with the compressor running, often indicates a restriction in the air line or a component leading to the lower-pressure tank. A faulty compressor would likely affect both systems more equally or not build pressure at all. Leaking check valves would cause pressure loss, not necessarily a differential when building pressure. The parking brake applies spring brakes, not directly causing a pressure differential between service tanks.
Why the other options are wrong
- A. A faulty air compressor would typically affect both systems or struggle to build any pressure.
- B. A leaking check valve would cause ongoing pressure loss, but not necessarily a differential while building pressure.
- C. The parking brake engagement uses air from the system but doesn't directly cause a sustained pressure differential between the primary and secondary tanks during operation.
Air Pressure Discrepancy
A noticeable and sustained difference in air pressure readings between the primary and secondary air tanks in a dual air brake system, often indicating a problem with air flow.
- Can be caused by restrictions, leaks, or component malfunctions.
- Requires investigation to ensure safe braking.
- Should be addressed before operating the vehicle.
Memory trick: Uneven air means a flow problem, like a kinked hose.