CDL Air Brakes TestDual Air Brake SystemsHard
A driver is inspecting a dual air brake system and notices that the low air pressure warning light and buzzer activate only when the primary air tank pressure drops to 50 psi, while the secondary tank pressure is still at 70 psi. What is the most accurate conclusion?
- ABoth warning systems are faulty as they should activate simultaneously.
- BThe warning system for the primary tank is functioning correctly.
- CThe warning system for the secondary tank is faulty or has a delayed response.
- DThe low air pressure warning should activate at or above 60 psi for both tanks.
Show answer & explanationAnswer & explanation
Correct answer: D. The low air pressure warning should activate at or above 60 psi for both tanks.
Federal regulations (FMCSA) require the low air pressure warning device to activate at or above 60 psi in either the primary or secondary system. If it activates at 50 psi for the primary tank, it's activating too late. The secondary tank being at 70 psi means its warning hasn't activated, which is correct if the threshold is 60 psi. The issue is with the primary system's warning activating below the required threshold.
Why the other options are wrong
- A. They should activate independently based on their respective tank pressures, not simultaneously. The primary's warning is faulty (too low).
- B. The warning activated at 50 psi, which is below the required 60 psi threshold, so it's not functioning correctly.
- C. The secondary tank is at 70 psi, so its warning should not be active if the threshold is 60 psi, indicating it's likely functioning correctly.
Low Air Warning Threshold
The minimum air pressure level (60 psi) at which the low air pressure warning device must activate in a commercial vehicle's air brake system.
- Mandated by federal regulations (FMCSA).
- Applies to both primary and secondary systems.
- Crucial for driver safety awareness.
Memory trick: Sixty PSI is the 'danger zone' for air brakes.