Lock-up valve test

A lock-up valve test verifies that the lock-up (shut-off) valve on a pressure-control or actuator line holds the last commanded position when supply pressure or signal is lost, a safety function on pneumatic and hydraulic control loops such as cargo valves and turbine governors. The test drops the control signal or air supply and confirms the valve freezes the actuator rather than drifting open or closed, then checks reseating and leak tightness on restoration. It is part of commissioning and periodic function testing of the control and safety systems. A lock-up that fails to hold defeats the fail-safe logic the system depends on, so it is condemned until repaired.