Which valves fail in the closed position?

• A. Engine PRSOV
• B. APU LCV
• C. Engine HP valves
• D. All of the above

Answer: (D)

In aviation systems, valves that control critical flows are designed to fail safe by default to the closed position. When their actuators lose power or fail, springs or other bias mechanisms pull the valve to shut, preventing unwanted fuel, air, or bleed flow.

The engine PRSOV operates in a way that, if its control power or signal is lost, the valve closes to isolate the system and prevent unintended flow. High-pressure engine fuel valves follow the same pattern: without actuation, they return to closed, stopping high‑pressure fuel from reaching the engine. The APU LCV likewise uses a fail‑closed setup so that loss of control power prevents unwanted APU operation or fuel flow.

So, all of these valve types can end up closed if their actuation fails, which is why “all of the above” is the best answer.