Pressure Relief Valves Information

Pressure relief valvePressure relief valves are designed to provide protection from over-pressure in steam, gas, air, and liquid lines. Relief valves and back pressure regulators are the same device, only differing in application. The pressure relief valve "lets off steam" when safe pressures are exceeded, then closes again when pressure drops to a preset level. A back pressure regulator maintains upstream pressure at the desired setting by opening to allow excess upstream pressure to flow downstream.


Pressure relief valves are self-operating valves that are installed in a process system to protect against over pressurization of the system. Relief valves are designed to continuously regulate fluid flow, and to keep pressure from exceeding a preset value. There are a wide variety of valve designs, but most resemble diaphragm valves, globe valves, or swing check valves. With many of these designs, a helical or hydraulic pressure spring is used to maintain constant force acting on the backside of the valve disk or diaphragm, causing the valve to be normally closed. When the force exerted by the process stream (i.e. fluid pressure) on the valve disk is greater than the constant force exerted by the spring, the valve opens allowing process fluid to exit the valve until the fluid pressure falls below the preset value. These valves can be preset to a specific relief pressure or they may be adjustable.


The flow transfer and control category covers a wide spectrum of products designed to facilitate, control, maintain, meter, or read the flow of material through hoses, pipes, or tubing. The material in question can be liquid, gaseous, or semi-solid (colloids and slurries). The following families fall within this category:

  • valves
  • valve actuators and positioners
  • dispensing valves
  • pumps
  • flow sensing
  • level sensing
  • density and specific gravity sensing
  • viscosity sensing
  • miscellaneous related products


Valves are devices designed to maintain, restrict, or meter the flow of materials through pipes, hoses, tubing, or entire systems. They generally function by allowing flow while in their open position, and restricting flow when closed. The valve family is broken down into product areas based on the mechanism that is used to restrict flow.

The following are the main valve product areas:

  • ball valves
  • butterfly valves
  • check valves
  • diaphragm valves
  • gate or knife valves
  • globe valves
  • needle valves
  • pinch valves (for both industrial and medical applications)
  • plug valves
  • control valves (1/4 turn—isolation and multi-turn, throttling)
  • pressure relief valves
  • AC and DC solenoid valves

Related Information

CR4 Community—Pressure Safety Valves vs. Pressure Relief Valves

CR4 Community—Pressure Relief Valve (PRV) or Pressure Safety Valve (PSV)?

CR4 Community—Pressure Test of Relief Valve Body

Image credit:

SV1XV / CC BY-SA 3.0


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