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 valves 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, in turn from volvere, to turn, roll.
The simplest, and very ancient, valve is simply a freely hinged flap which 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 uses for controlling processes, residential uses 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 fitted to hot water systems, and poppet valves in car engines.
In nature there are valves, for example one-way valves in veins controlling the blood circulation, & heart valves controlling the flow of blood in the chambers of the heart and maintaining the correct pumping action.
Valves may be operated manually, either 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.
Type of Valves
Globe valve, A valve controlled by a wheel, Large butterfly valve, Cast iron butterfly valve, Cast iron butterfly valve, Hastelloy ball valve, Stainless steel gate valve,Stainless steel gate valve, Hastelloy check valves, Duplex ball valve, Inconel gate valve, Stainless steel wafer check valve, Inconel check valve, Stainless steel ball valve, Cryogenic 254 SMO gate valve, Inside view of a tilting disc inconel check valve, Duplex ball valves, Cryogenic super duplex gate valve frozen up during operation, Super duplex ball valves, Flanged nozzle inconel check valve or axial check valve, Inside hastelloy check valve, wafer configuration, Large carbon steel swing check valve, Disc for an alloy check valve also known as axial check valve, Balls for alloy ball valves, Wafer check valve, Nuts and bolts for incoloy valves, Inconel check valve springs, Ball for a titanium ball valve