CDL Air Brakes TestDual Air Brake SystemsMedium
A technician is performing a leak test on a dual air brake system. They observe that the primary system loses 2 psi in one minute after the brakes are released, while the secondary system loses 4 psi in one minute. The vehicle is a straight truck. What should the technician conclude?
- ABoth systems are within acceptable leakage limits.
- BThe secondary system is acceptable, but the primary system has excessive leakage.
- CBoth systems have excessive leakage.
- DThe primary system is acceptable, but the secondary system has excessive leakage.
Show answer & explanationAnswer & explanation
Correct answer: D. The primary system is acceptable, but the secondary system has excessive leakage.
For a straight truck with the engine off and brakes released, the maximum allowable air loss rate is 2 psi per minute. The primary system's loss of 2 psi is at the limit, while the secondary system's loss of 4 psi exceeds this limit, indicating excessive leakage in the secondary system.
Why the other options are wrong
- A. The secondary system's loss of 4 psi exceeds the 2 psi limit.
- B. The primary system is exactly at the acceptable limit, not excessive.
- C. The primary system is within the acceptable limit (at the edge), but the secondary is excessive.
Straight Truck Air Loss Rate
The maximum allowable rate of air pressure drop in a straight truck's air brake system (engine off, brakes released) during a leak test, which is 2 psi per minute.
- Tests for air leaks in the system.
- Different limits for combination vehicles.
- Exceeding limits requires repair.
Memory trick: Two PSI is the magic number for straight truck leaks.