Where is a pressure relief valve required?

• A. Open tank with no cover
• B. Non-pressurized vessel
• C. Any piping with no valve
• D. Any closed vessel containing refrigerant under pressure

Answer: (D)

Relief devices exist to protect a container from overpressure. A pressure relief valve is required on any closed vessel that contains a refrigerant under pressure because, if heat is added or equipment fails, the pressure inside could rise above what the vessel can safely contain. The valve opens at a set pressure below the vessel’s maximum allowable working pressure and vents the fluid to a safe location, preventing rupture or explosion.

An open tank with no cover cannot develop a significant internal pressure because it is open to the atmosphere. A non-pressurized vessel has no internal pressure to relieve. Piping with no valve may carry pressure, but it isn’t a closed vessel containing refrigerant under pressure, so the demand for a relief valve doesn’t apply in the same way. Thus, the scenario that requires a pressure relief valve is any closed vessel containing refrigerant under pressure.