CDL Air Brakes TestInspecting Air Brake SystemsEasy
A driver is performing a pre-trip inspection on a vehicle equipped with air brakes. After ensuring the air system is fully charged, the driver applies the service brake and holds it for one minute. The air pressure gauge should not drop more than what amount for a single unit vehicle?
- A3 psi
- B2 psi
- C4 psi
- D1 psi
Show answer & explanationAnswer & explanation
Correct answer: A. 3 psi
For a single unit vehicle, the maximum allowable air pressure drop when applying the service brake for one minute (after full charge) is 3 psi. Exceeding this indicates a leak that needs to be addressed.
Why the other options are wrong
- B. This is incorrect; 2 psi is often the limit for a combination vehicle's applied leak test, or a single unit's static leak test.
- C. This is too high; a 4 psi drop would indicate a significant leak that needs immediate attention.
- D. This is too low; 1 psi drop is generally expected for a combination vehicle's static leak test, not an applied test for a single unit.
Service Brake Applied Leak Test (Single Unit)
This test checks for air leaks in the service brake system when the brakes are applied. The maximum allowable pressure drop for a single unit vehicle is 3 psi in one minute.
- Performed after full air system charge.
- Hold service brake for one minute.
- Maximum 3 psi drop for single unit.
Memory trick: Leaky brakes mean pressure drops, but how much is too much for your rig?