A thermal expansion relief valve is a pressure relief device used on piping systems to prevent overpressurization caused by the thermal expansion of a limited volume of trapped process fluid. A thermal expansion relief valve is normally used on piping systems where cryogenic liquids or cold gases can be trapped between two valves or between two devices. Thermal expansion relief valves are also called line block safeties, pop safeties, or thermal relief valves. This publication addresses requirements for installation and retesting of these valves.
