Pressure safety valve, relief
An angle-pattern body with a coiled spring bonnet on top. The spring sets the cracking pressure. Once relieved, the disc reseats. PSVs are mechanical safety devices with no PLC channel.
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How it’s drawn.
An angle-pattern body with a spring on top. The spring sets the pressure at which the valve lifts. Once the overpressure is relieved the disc reseats. It is a mechanical safety device with no signal and no remote actuator. It appears on vessels, on lines, and on positive-displacement pump discharges.
Typical usage.
Vessel overpressure protection, line relief on positive-displacement pump discharges, thermal relief on isolated piping. Sized per API 520, 521. Documented in the relief load study.
Telling it apart.
- The spring on top is the safety marker, setting the lift pressure. There is no controller and no signal behind it.
- A relief valve and a control valve are different roles. The relief valve protects against overpressure. It is not a modulating element.
- The set pressure and relief sizing live in the relief study and the datasheet, not in the symbol.