Which valve variant is a check valve that can be manually unlocked to allow operation?

• A. Check valve
• B. Unlockable or De-lockable check valve
• C. Relief valve
• D. Pressure relief valve

Answer: (B)

A check valve normally allows flow in one direction and blocks it in the opposite direction. When a valve variant is described as unlockable or de-lockable, it means there is a manual override that can be released to permit operation, giving you an explicit way to override the one-way action when needed. This makes it the right choice for a valve that is a check valve with a manual unlocking capability.

Relief valves and pressure relief valves, in contrast, are designed to open to relieve excess pressure rather than control the direction of flow, so they aren’t the correct type here.