Editing Valve (section)

{{Short description|Flow control device}}
{{About|the flow control device|the electronic component|Vacuum tube|the video game company|Valve Corporation|other uses|Valve (disambiguation)}}
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[[File:Water valves with spigots.jpg|thumb|300px|These water valves are operated by [[handle#Twist handles|rotary handle]]s.]]
A '''valve''' is a device or natural object that regulates, directs or controls the flow of a [[fluid]] (gases, liquids, fluidized solids, or [[Slurry|slurries]]) by opening, closing, or partially obstructing various passageways. Valves are technically [[Piping and plumbing fitting|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 swings down to obstruct fluid (gas or liquid) flow in one direction, but is pushed up by the flow itself when the flow is moving in the opposite direction. This is called a [[check valve]], as it prevents or "checks" the flow in one direction. Modern [[control valve]]s may regulate [[pressure]] or [[Fluid dynamics|flow]] downstream and operate on sophisticated [[Automation#Industrial automation|automation]] systems.

Valves have many uses, including controlling water for [[irrigation]], industrial uses for controlling processes, residential uses such as on/off and pressure control to dish and clothes washers and taps in the home. Valves are also used in the military and transport sectors. In [[Heating, ventilation, and air conditioning|HVAC]] [[Duct (flow)|ductwork]] and other near-atmospheric air flows, valves are instead called [[Damper (flow)|dampers]]. In compressed air systems, however, valves are used with the most common type being ball valves.