Pressure Relief Valves

Pressure 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 valve that is 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 a 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, and miscellaneous related products.

Valves are apparatus 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 area: 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, and AC and DC solenoid valves. 

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• Niobium Solves a Rupture Disk Corrosion Problem (.pdf)
  Rupture disks have been used for many years to protect pressure vessels from being over pressured. In addition to being used alone, the ASME Code also allows them to be used at the inlets of pressure...
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• Flare Gas Monitoring Systems (.pdf)
  Flare stacks are used in many industries to burn off unwanted waste gas byproducts, or flammable gases released by pressure relief valves during unplanned over-pressuring of plant equipment....
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Part Numbers for Pressure Relief Valves