Valve
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 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. Modern control valves may regulate pressure or flow downstream and operate on sophisticated 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. Even
aerosols have a tiny valve built in. Valves are also used in the military and transport sectors.
