What Is a Pressure Relief Valve?

Pressure relief valves prevent overpressure damage, ruptures and explosions in vessels, pipes, pumps and other pressurized containers that hold liquids or gas. They are designed to be either pre-set or adjustable to a desired relief point at which the completely sealed valve opens to allow the escape of the gas or liquid, reducing or eliminating internal pressure. They are prevalent in every description of industrial, transportation and domestic venue.

Basic Functions

Pressure relief valves can be loosely grouped into two types by function: valves that serve to allow continued system operations and valves that serve to terminate system operations.

Operations Sustaining

Pressure relief valves that sustain operation release pressure to allow a system to continue to operate safely and continuously despite an overpressure condition that could cause damage to the system if it was not abated. An example would be the air braking system in a truck or train. If pressure in the booster tank and air brake lines climbed too high, the pressure relief valve would release some pressure, but not enough to prevent normal braking operations, which could be as dangerous as a bursting tank.

Operations Terminating

Operations terminating pressure relief valves relieve all pressure in a system, usually forcing the termination of the normal operation of the system. Such systems are employed when the only imminent danger is an event caused by the overpressure condition. This type of system is common in many industrial applications such as nuclear power plants, where the overpressure of a reactor cooling system could lead to catastrophic failure. Such situations demand a shutdown.

Operational Modes

A number of pressure-operating modes or algorithms for defining pressure relief valve actuation include an on-off switch, where the valve is either fully shut or fully open. There are also valves that throttle their output over a proportional range, 80 to 100 pounds per square inch, for example. Finally there are valves that come full on at some high set point, and stay full on until they reach a low point or no point again.

Construction

Pressure relief valves are available in many applications, including those used in domestic hot water tanks, workshop air compressors and tanks, and pressure cookers in the kitchen. There are also custom-designed valves for industrial applications.

Common Applications

Pressure relief valves used in safety releases for cryogenic systems, steam boilers, heating systems, compressed air systems and any system where bursting or rupturing would cause damage as a result of overpressure.