Safety valve
Safety valve turns up in 2 fields: valves, boilers. Here is what it means to the people in each one.
Safety valve in valves
A spring-loaded pressure relief valve for steam, gas or vapor that opens with a rapid full lift at set pressure.
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."
Safety valve in boilers
The spring-loaded valve on a steam boiler that pops fully open to vent steam before pressure exceeds the boiler's rating.
It is set at or below the boiler's MAWP, 15 psi on a low-pressure steam boiler, and must be able to discharge all the steam the burner can make. No valve may sit between it and the boiler, and its discharge pipe runs full size to a safe point. Operators lift the try lever periodically, with pressure on, to prove the disc is not stuck to the seat.
"Safety valve on number two lifted at 14, that's right where it should be, but the operating control should never let it get there."