safety valve

A valve set to open at a pressure below that at which a container holding a gas, vapour, etc. (such as a boiler or pressure cooker), would burst, thus reducing the pressure; a relief valve.

(figurative) Any mechanism offering relief from physical or emotional pressure or tension.

(US, figurative) A United States law, codified at 18 United States Code §3553(f), authorizing a judge to disregard mandatory minimum sentences for some criminals with few or no prior offenses.

A valve set to close a container holding a gas or vapour to prevent excessive loss of pressure.

To use a relief valve on (a container holding a gas or vapour) to relieve excessive pressure which has built up inside.

(figurative) To use some mechanism to relieve (physical or emotional pressure or tension).

To install a relief valve on (such a container) for that purpose.