A valve in a container in which pressure can build up (as a steam boiler); it opens automatically when the pressure reaches a dangerous level WordNet 3.0 & Open English WordNet

A relief valve or pressure relief valve is a type of safety valve used to control or limit the pressure in a system; excessive pressure might otherwise build up and create a process upset, instrument or equipment failure, explosion, or fire. Wikipedia

A safety valve is a valve that acts as a fail-safe. Wikipedia

A safety valve designed to open in overpressurized system conditions Wikipedia Disambiguation

Mechanism for the release of a substance from a pressurized vessel when the pressure or temperature exceeds preset limits. Wikipedia Disambiguation

Valve that acts as a fail-safe Wikidata

Safety valve used to control or limit the pressure in a system Wikidata

A valve on a boiler to let the steam escape. Wiktionary

A safety valve that relieves pressure when it becomes high but before it becomes dangerous. Wiktionary

Safety valve that relieves pressure. Wiktionary (translation)

A relief valve set to open at a pressure below that at which a container (such as a boiler) would burst. Wiktionary

A relief valve set to open at a pressure below that at which a container would burst. Wiktionary (translation)