In flexible or split wedge gate valves, liquid trapped in the cavity between the two seating faces can be heated or left at high pressure while the line depressurizes. That pressure pushes each half of the wedge against its seat, adding far more friction than the actuator was sized for. A related problem, thermal binding, happens when a valve closed hot cools and the body shrinks onto the wedge. Fixes include a cavity relief hole or bypass.
MOV wouldn't open after heat-up, classic pressure locking, they're drilling a relief hole in the upstream disc at the outage.
Also heard as
- pressure lock
Related terms
Wedge
The tapered closure member of a gate valve that is driven down between two inclined seats to seal.
Gate valve
A multi-turn isolation valve that lifts a flat or wedge-shaped gate clear of the flow path to open.
Trunnion-mounted ball valve
A ball valve whose ball is anchored top and bottom on trunnions while spring-loaded seats press against it.
MOV
Motor-operated valve: a valve driven by an electric actuator with a motor, gearbox, torque switch and limit switches.