CDL Air Brakes TestInspecting Air Brake SystemsHard
A driver is performing a pre-trip inspection on a tractor-trailer. After ensuring the air system is fully charged (125 psi), they shut off the engine, release the parking brake, and chock the wheels. They then allow the air pressure to stabilize. After one minute, the air pressure has dropped to 121 psi. What does this indicate?
- AAn excessive static air leak requiring immediate repair.
- BA normal and acceptable air loss for a combination vehicle.
- CInsufficient time allowed for pressure stabilization.
- DA faulty air pressure gauge, given the low pressure drop.
Show answer & explanationAnswer & explanation
Correct answer: A. An excessive static air leak requiring immediate repair.
For a combination vehicle during a static air leak test (engine off, parking brake applied/released with chocks), the air pressure should not drop more than 3 psi in one minute. A 4 psi drop (125 - 121 = 4) is excessive and indicates a leak that must be repaired before operation.
Why the other options are wrong
- B. Normal static air loss for a combination vehicle is no more than 3 psi in one minute.
- C. One minute is the standard time for monitoring the drop after stabilization.
- D. The gauge reading is consistent with a leak, not necessarily a faulty gauge.
Static Air Leak Test (Combination Vehicle)
This test checks for air leaks in the air brake system of a combination vehicle with the engine off and parking brake applied (or released with chocks), without operating the service brakes.
- Engine off, parking brake applied (or released with chocks).
- Fully charge air system.
- After initial stabilization, monitor pressure for one minute.
- Pressure drop should not exceed 3 psi for a combination vehicle.
Memory trick: Combined and static, a 3 psi drop is not erratic; more, and it's problematic.