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Valve definition | Valve functions


A valve is a mechanical device that controls the flow and pressure of working fluid within a system or process.


Valve is a mechanical device specially designed to direct, start, stop, mix, or regulate the flow, pressure, or temperature of the process fluid. Valves are designed to handle any liquid or gas applications. There are many types of valves available in the market for different purposes.

According to the nature of their design, function, and application, the valve comes in a wide variety of styles, sizes, and pressure classes. The small industrial valves can weigh as little as 1lb (0.45Kg) and fit comfortably in the human hand, while the largest can weigh up to 10 tons (9070Kg) and extend in height to over 24ft (6.1m). Valves are using in pressures from vacuum to over 13,000 psi (897bar). Industrial process valves use in pipelines sizes from 0.5 (in nominal diameter DN 15) to beyond 48 (DN 1200). While over 90 percent of the valve uses in process system are install in piping that is 4 (DN 100) and smaller in size.

Today’s spectrum of available valves extends from simple water faucets to control valves equipped with microprocessors. This spectrum provides single loop control of the process.

Valves manufactured from a number of materials, with most valves made from steel, iron, plastic, brass, or a number of special alloys.

Valve functions:

For a given system, may be different modes of operation required at a different time to run the system safe and smoothly. For example, sometimes need to isolate some portion of the system or equipment. Sometimes need to throttle pressure to reduce flow or to relieve excess pressure. One valve cannot handle such types of different functions at the same time. Therefore different valves use for different purposes. A valve controls system or process fluid (liquid/ gas) flow and pressure by carrying out any of the following functions:

  • Starting and Stopping fluid flow (Provide Isolation)
  • Throttling (Regulation or control) the amount of fluid flow
  • Controlling the direction of fluid flow or backflow prevention
  • Regulating the downstream system or process pressure
  • Relieving component or piping overpressure or relief pressure

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