CDL Air Brakes TestDual Air Brake SystemsEasy
A commercial vehicle driver notices that the low air pressure warning light and buzzer activate when the primary air tank pressure drops to 70 psi, but the secondary air tank maintains 100 psi. What does this indicate about the dual air brake system?
- AThe air compressor governor is set too low for proper operation.
- BThe primary system's low air warning is functioning correctly.
- CBoth primary and secondary systems are experiencing a significant leak.
- DThe secondary system is failing to maintain pressure.
Show answer & explanationAnswer & explanation
Correct answer: B. The primary system's low air warning is functioning correctly.
The low air pressure warning systems are designed to activate when pressure drops below 60 psi (or sometimes 55 psi depending on manufacturer, but definitely below 70 psi). If the warning activates at 70 psi, it means the warning for the primary system is working as intended to alert the driver to a potential issue before critical pressure is lost.
Why the other options are wrong
- A. The governor controls compressor cut-in/cut-out, not the activation threshold of the low air warning. The system is still maintaining pressure, just the warning has activated.
- C. Only the primary system shows a pressure drop; the secondary system maintains full pressure, ruling out a leak in both systems.
- D. The secondary system is at 100 psi, indicating it is functioning properly and not failing.
Low Air Warning Function
The low air pressure warning system alerts the driver when air pressure in either the primary or secondary system drops below a safe operating threshold, typically 55-60 psi.
- Activates for individual systems
- Warns of potential brake failure
- Mandatory safety feature
Memory trick: A low pressure warning is like a car's fuel light, telling you to act before you're stranded.