CDL Air Brakes TestInspecting Air Brake SystemsMedium
A driver is performing a pre-trip inspection and notices that the spring brakes on the vehicle do not apply when the air pressure drops below 20 psi. What is the most likely cause?
- AThe spring brake control valve is faulty.
- BThe low air warning device is malfunctioning.
- CThe service brake chambers are leaking.
- DThe air compressor is not building enough pressure.
Show answer & explanationAnswer & explanation
Correct answer: A. The spring brake control valve is faulty.
Spring brakes are designed to apply automatically when air pressure drops to a critical level (typically 20-45 psi). If they fail to apply, it indicates a malfunction in the spring brake control valve or the spring brake mechanism itself.
Why the other options are wrong
- B. A malfunctioning low air warning device would not prevent the spring brakes from applying.
- C. Leaking service brake chambers would cause air loss, but the spring brakes should still apply as pressure drops.
- D. Insufficient air pressure build-up would lead to low pressure, but the spring brakes should still apply when the pressure drops low enough.
Spring Brake Automatic Application
Spring brakes are designed to apply automatically when the air pressure in the system drops to a critically low level (usually between 20-45 psi) to ensure safety.
- Activated by a drop in air pressure.
- Prevents vehicle movement if air system fails.
- Failure to apply indicates a problem with the control valve or mechanics.
Memory trick: No air, no play, spring brakes save the day!