relief valve vs safety valve

relief valve and safety valve both are nouns.

Word	Noun	Adjective	Verb	Adverb
relief valve	Yes	No	No	No
safety valve	Yes	No	No	No

As nouns, relief valve and safety valve are synonyms defined as:

relief valve and safety valve: 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

Other synonyms of relief valve include escape, escape cock, escape valve.

relief valve (noun)	safety valve (noun)
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	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