CDL Air Brakes TestDual Air Brake SystemsMedium
A driver performs an air loss rate test. With the engine off and brakes released, the pressure drop in the primary system is 2 psi in one minute. In the secondary system, it's 3 psi in one minute. What does this indicate for a straight truck?
- ABoth systems have acceptable air loss.
- BThe secondary system has an excessive leak.
- CBoth systems have excessive air loss.
- DThe primary system has an excessive leak.
Show answer & explanationAnswer & explanation
Correct answer: B. The secondary system has an excessive leak.
For a straight truck (non-combination vehicle), the maximum allowable air loss rate with the engine off and brakes released is 2 psi in one minute. The primary system's loss of 2 psi is at the maximum acceptable limit. However, the secondary system's loss of 3 psi exceeds this limit, indicating an excessive leak in the secondary system.
Why the other options are wrong
- A. This is incorrect. While the primary system is at the acceptable limit, the secondary system has an excessive leak.
- C. Only the secondary system has an excessive leak; the primary is at the maximum acceptable limit.
- D. The primary system's 2 psi loss is at the maximum acceptable limit for a straight truck, not exceeding it.
Air Loss Rate (Straight Truck)
For a straight truck, the maximum allowable air loss rate with the engine off and brakes released is 2 psi in one minute.
- Engine off, brakes released.
- Maximum 2 psi drop per minute.
- Applies to primary and secondary systems individually.
- Higher loss indicates a leak.
Memory trick: Two for straight, three for combo, no more loss, or no go.