A shutdown valve (also referred to as SDV or emergency shutdown valve, ESV, ESD, or ESDV; or safety shutoff valve) is an actuated valve designed to stop the flow of a hazardous fluid upon the detection of a dangerous event. This provides protection against possible harm to people, equipment or the environment. Shutdown valves form part of a safety instrumented system. The process of providing automated safety protection upon the detection of a hazardous event is called functional safety.
Shutdown valves are primarily associated with the petroleum industry although other industries may also require this type of protection system. ESD valves are required by law on any equipment placed on an offshore drilling rig to prevent catastrophic events like the BP Horizon explosion in the Gulf of Mexico in 2010.
A safety shutoff valve should be fail-safe, that is close upon failure of any element of the input control system (such as temperature controllers, steam pressure controllers), air pressure, fuel pressure, current from a flame detector, or current from other safety devices such as low water cutoff, and high pressure cutoff.
A blowdown valve (BDV) is a type of shutdown valve designed to depressurize a pressure vessel by directing vapour to a flare, vent or blowdown stack in an emergency. BDVs fail-safe to the open position upon failure of the control system.[1] The type of valve, type of actuation and performance measurement are similar to an ESD valve.