A huddling chamber around the disc catches the escaping flow so that once the valve cracks, the extra area snaps it to full lift: the pop. It stays open until pressure falls by the blowdown margin, then reseats. Safety valves protect boilers, steam lines and gas vessels, and each one is stamped with its set pressure and rated capacity. On drawings it carries the PSV tag.
Safety valve on the air receiver popped twice this shift, check the compressor unloader before it does it again.
Also heard as
- PSV
- pop valve
- pop-safety valve
Do not mix it up with
- Relief valve: A relief valve opens gradually in proportion to overpressure and suits liquids; a safety valve pops fully open and suits compressible fluids.
Related terms
Relief valve
A spring-loaded valve for liquid service that opens gradually as pressure rises past its set point.
Pop
For a safety valve to lift suddenly and fully open, discharging with a loud blast at set pressure.
Simmer
For a safety valve to leak with an audible hiss or seep just below its set pressure, before it pops.
Gag
A clamp or screw fitted to a safety valve to hold its disc shut during a system pressure test.
Chatter
Rapid, violent opening and closing of a relief or check valve that hammers the disc against the seat.