air valve
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GC:n.

CT: High-capacity, single-chamber air valve with triple function for venting and releasing air in pipelines as well as for releasing air during operation. Corrosion-proof due to stainless steel inner parts (in size DN 50, inner parts made of plastic). Safe and reliable operation even at high air-release velocities of up to sonic speed. Suitable for use in water treatment, water distribution, in dams, power plants and in industry.

S: DUOJET – http://www.vag-armaturen.com/en/products/detail-product/product/vag-duojetR-automatic-air-valve.html (last access: 4 November 2014)

N: 1. air (n): c.1300, “invisible gases that make up the atmosphere,” from Old French air “atmosphere, breeze, weather” (12c.), from Latin aerem (nominative aer) “air, lower atmosphere, sky,” from Greek aer (genitive aeros) “air” (related to aenai “to blow, breathe”), of unknown origin, possibly from a base awer- and thus related to aeirein “to raise”. In Homer mostly “thick air, mist;” later “air” as one of the four elements.
valve (n) late 14c., “one of the halves of a folding door,” from Latin valva (plural valvae) “section of a folding or revolving door,” literally “that which turns,” related to volvere “to roll” (see volvox). Sense extended 1610s to “membranous fold regulating flow of bodily fluids;” 1650s to “mechanical device that works like an anatomical valve”.
2. Air valves allow metered flow of fluid in one or both directions. Many of them allow for free flow in one direction and reduced or metered flow in the reverse direction. They are used in pneumatic circuits to regulate the rate of activation or exhaust of cylinders and other pneumatic devices.
3. There are several methods that can be used to classify valves, including the control mechanism and valve function.
===Valve Function===
Valves are a part of many daily- used machines and can perform a variety of functions. The three common valve functions include stopping and starting flow, throttling (control) flow, and acting as a non-return check for flow (check).
Stop/Start valves are used for systems that do not need the flow throttled. The valve opens to allow the flow and closes to stop flow.
Throttle or control valves control the speed and capacity of flow through the system.
Non-return or check valves control the direction of flow. Flow in the desired direction opens the valve, while flow in the opposing direction forces the valve closed. These valves are important for preventing back-flow to systems in applications such as wastewater management.
===Method of control===
The mechanism to control flow can vary based on the application of the valve. In general, there are two means of controlling flow through a valve.
Linear motion valves use a closure member that moves in a straight line to allow, stop or throttle the flow. The closure device could be a disc, slat, or flexible material like a diaphragm. The closure device can be used to:
Move a disc or plug into or against an orifice
Slide a slat, cylindrical, or spherical surface across an orifice
Move a flexible material into the flow passage
Rotary motion valves rotate a disc or ellipse about an angular or circular shaft extending across the diameter of an orifice.
Quarter turn valves will be in their fully open or fully closed state after a 90° turn of the stem.
===Types of Air Valve===
There are many types of air valves.

  • Ball valves provide tight shut-offs, but are not suitable for sanitary applications.
  • Butterfly valves permit flow in only one direction.
  • Check valves are self-actuating and prevent the reversal of process flow.
  • Diaphragm valves separate the flow of water from the closure element.
  • Directional valves steer flow through selected passages.
  • Float valves open or close automatically as the level of a fluid changes.
  • Gate or knife valves are linear motion valves in which a closure element slides into the flow to shut off the stream.
  • Globe and pinch valves are other types of linear motion devices.
  • Needle valves have a slender, tapered point at the end of a valve stem.
  • Poppet valves open and close ports with a sealing device and spring.
  • Plug or stop-cock valves are designed for both on/off and throttling functions.

S: 1. OED – (4 November 2014). 2 & 3. IHS – http://www.globalspec.com/learnmore/flow_control_flow_transfer/valves/air_valves (last access: 4 November 2014)

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CR: electrical energy, energy.