A valve is a device that regulates, directs, or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways.

Valves are technically valve fittings but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door from volvere to turn, roll. The most straightforward and old valve is simply a freely hinged flap that drops to obstruct fluid (gas or liquid) flow in one direction but is pushed open by flow in the opposite direction.

This is called a check valve, as it prevents or “checks” the flow in one direction. Valves have many uses, including controlling water for Irrigation, industrial benefits for managing processes, and residential services such as on / off & pressure control to dish and clothes washers & taps in the home.

Even aerosols have a tiny valve built in. Valves are also used in the military & transport sectors. Valves are found in virtually every industrial process, including water & sewage processing, mining, power generation, processing of oil, gas & petroleum, food manufacturing, chemical & plastic manufacturing, and many other fields.

People in developed nations use valves in their daily lives, including plumbing valves, such as taps for tap water, gas control valves on cookers, small valves fitted to washing machines and dishwashers, safety devices provided to hot water systems, and poppet valves in car engines. In nature, there are valves, for example, one-way valves in veins controlling blood circulation, & heart valves controlling the flow of blood in the heart chambers and maintaining the correct pumping action. Valves may be operated manually by a handle, lever, pedal, or wheel. Valves may also be automatic, driven by changes in pressure, temperature, or flow.

These changes may act upon a diaphragm, or a piston, which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.

More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator. An actuator will stroke the valve depending on its information and set-up, allowing the valve to be positioned accurately and controlling various requirements.

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