CDL Air Brakes TestAir Brake System PartsHard
A driver is inspecting the air tanks on a commercial vehicle. They notice that the check valve between the primary and secondary air tanks is stuck open. What consequence would this have on a dual air brake system?
- AThe parking brake would automatically apply when the service brakes are used.
- BThe air compressor would constantly run without building pressure.
- CThe low air pressure warning system would fail to activate.
- DA loss of air pressure in one tank would quickly lead to a loss of pressure in both.
Show answer & explanationAnswer & explanation
Correct answer: D. A loss of air pressure in one tank would quickly lead to a loss of pressure in both.
In a dual air brake system, check valves prevent air from flowing from one tank to the other. If a check valve is stuck open, a leak or failure in one tank (or its associated system) would rapidly deplete air pressure from both the primary and secondary tanks, compromising the entire braking system.
Why the other options are wrong
- A. The parking brake is controlled by its own valve; a check valve issue wouldn't directly cause this specific interaction.
- B. This describes a problem with the unloader valves or governor, not a check valve.
- C. The low air pressure warning system monitors tank pressure independently; a stuck check valve would still allow the warning to activate once pressure drops in both tanks.
Dual Air System Check Valve
A one-way valve that prevents air from flowing from one air tank to another in a dual air brake system, ensuring that pressure loss in one system does not affect the other.
- Maintains separation between primary and secondary air systems.
- Crucial for safety in case of single system failure.
- A stuck-open valve compromises dual system redundancy.
- A stuck-closed valve prevents one tank from receiving air.
Memory trick: Check valve is a wall, if it falls, both tanks will stall.