Valves marked CSO, car-sealed open, or CSC, car-sealed closed, on the P&ID must stay in that position, such as the block valves under relief valves (CSO) or a relief valve bypass (CSC). A wire or plastic seal with a serial number goes through the handwheel and a fixed point, and breaking it requires a permit and an entry in the car seal log. Operators audit them on a set schedule.
Block under PSV-301 is supposed to be CSO and the car seal's gone, write it up and get the shift supervisor out here.
A car seal is administrative control, not a lock; anyone with side cutters can break it, which is why the log matters.
Also heard as
- carseal
Related terms
Safety valve
A spring-loaded pressure relief valve for steam, gas or vapor that opens with a rapid full lift at set pressure.
Relief valve
A spring-loaded valve for liquid service that opens gradually as pressure rises past its set point.
Gag
A clamp or screw fitted to a safety valve to hold its disc shut during a system pressure test.