If an air line ruptures between the compressor and the supply reservoir, what will prevent loss of air pressure in the service brake system?
- Quick release valve
- Foot valve
- Reservoir pressure gauge
- One-way check valves ✓
Answer: D. One-way check valves
One-way check valves prevent air from escaping back out of the supply reservoir when a line between it and the compressor ruptures.
Why this is the answer
The handbook says one-way check valves stop air that has flowed out of the supply tank from returning. The air supply diagram also shows one-way check valves in the supply subsystem around the supply tank and the dry tanks. If the line to the compressor fails, the check valve keeps stored air from flowing back through that failed line, so pressure is held for the service brake system. A pressure gauge only reports what is happening; it does not block airflow.
Why the other answers are wrong
- A. Quick release valve — A quick release valve is not described in the passages as blocking air from returning out of the supply tank.
- B. Foot valve — The foot valve is not described in the passages as the component that prevents backflow from the supply tank.
- C. Reservoir pressure gauge — A reservoir pressure gauge only shows the pressure; it cannot stop air from escaping through a broken line.
Remember it
Picture a one-way door at the supply tank: air can go in, but it cannot come back out through a broken line.
Official handbook: Official MTO Air Brake Handbook, Air Supply Subsystem – One-way check valve