PSV vs. PRV: the difference and why it matters for compliance
PSV and PRV are used interchangeably in casual talk, but they refer to slightly different things. The distinction matters for inspection and for understanding what the valve is actually supposed to do.
PRV — Pressure Relief Valve
A general term for any valve designed to relieve excess pressure. Includes both PSVs (which open suddenly at a set pressure to vent gas) and pressure relief valves used in liquid service (which open proportionally as pressure rises).
PSV — Pressure Safety Valve
A specific subset of PRVs used in gas/vapor service. Designed to "pop" — open fully and rapidly — at the set pressure, then reseat once pressure drops below a blowdown threshold. PSVs are the dominant type in fired-equipment and pressure-vessel service.
What it means for service
- Set pressure: the pressure at which the valve opens.
- Blowdown: how far pressure must drop below set before the valve reseats.
- Reseat pressure: the pressure at which the valve closes again after relieving.
- We bench-test all three and certify in writing. That paperwork goes into your inspection records.
Testing cadence
Most operators align PSV testing with their API 510 inspection cycle. We work alongside your inspection firm — we're the valve specialists, they own the vessel scope. Tell us when your next inspection is and we'll schedule testing to align.
Related guides.
Thief hatches: what they do, why they fail, when to replace
Thief hatches sound boring. They are — until one fails and you get a six-figure call from the environmental team.
What's in a BMS audit (and why pre-inspection audits matter)
Most BMS inspection failures aren't catastrophic — they're documentation gaps and one or two sensors that drifted out of spec. A proper pre-inspection audit catches them before the inspector does.