CDL Air Brakes TestInspecting Air Brake SystemsEasy
During a pre-trip inspection, a driver observes that the air pressure gauge shows 100 psi. When the brake pedal is fully depressed and held for one minute, the pressure drops to 95 psi. The vehicle is a single unit truck. What does this indicate?
- AA normal and acceptable air loss.
- BAn excessive air leak in the service brake system.
- CInsufficient air pressure for safe operation.
- DA faulty air pressure gauge requiring immediate repair.
Show answer & explanationAnswer & explanation
Correct answer: B. An excessive air leak in the service brake system.
For a single unit truck, an air loss of more than 3 psi in one minute with the service brakes applied is considered excessive. A 5 psi drop from 100 psi to 95 psi indicates a significant leak that needs to be addressed before operation.
Why the other options are wrong
- A. Normal air loss for a single unit truck with applied brakes is no more than 3 psi in one minute.
- C. While the leak is a problem, 95 psi is still within the operating range, but the leak itself is the critical issue.
- D. The gauge reading itself isn't necessarily faulty; the drop indicates a system leak.
Applied Air Leak Test (Single Unit)
This test checks for air leaks in the service brake system by applying the brakes and monitoring pressure loss.
- Engine off, parking brake off, wheels chocked.
- Fully charge air system.
- Apply service brake fully and hold for one minute.
- Pressure drop should not exceed 3 psi for a single unit truck.
Memory trick: Applied pressure leaks reveal system's integrity.