Hydraulic Relief Valve

relief valve
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
Used at the discharge of a positive displacement pump. An adjustable, spring-loaded valve opens when a preset pressure is reached. Used to prevent excessive pressure buildup that could damage the pump or motor.
The relief valve (RV) is a type of valve used to control or limit the pressure in a system or vessel which can build up by a process upset, instrument or equipment failure, or fire.

hydraulic
(of cement) Hardening under water
(hydraulically) in a hydraulic manner; "the block is then tested hydraulically to its full design test pressure on each stream separately"
Denoting, relating to, or operated by a liquid moving in a confined space under pressure
Of or relating to the science of hydraulics
moved or operated or effected by liquid (water or oil); "hydraulic erosion"; "hydraulic brakes"
of or relating to the study of hydraulics; "hydraulic engineer"