Valves

A valve is a device that regulates the flow of substances (either gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but usually are discussed separately. more...

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Valves are used in a variety of applications including industrial, military, commercial, residential, and transportation.

Oil & Gas, Power Generation, Mining, Water Reticulation, Sewerage & Chemical Manufacturing would constitute the majority of valves used by industry.

Plumbing valves are the most obvious in everyday life, taps for hot and cold water, gas control valves on cookers and barbecues, small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems are all simple valves.

Most valves are operated manually, either by a hand wheel or lever. Some valves are 'self operating' driven by changes in pressure, temperature or flow. These changes in pressure or temperature often act against springs or capsules filled with expanding substances. Examples of this type of valve found commonly are safety valves fitted to hot water systems or steam boilers.

Valves are also found in the Otto cycle (internal combustion) engines driven by a camshaft, lifters and or push rods where they play a major role in engine cycle control.

Applications

A huge variety of valves are available and have infinite applications with sizes ranging from 1/4" (6mm) to 24" (600mm) Special valves can be manufactured to be in excess of 200" (5000mm) diameter.

Valves range from inexpensive, simple, disposable valves to items in exotic materials that in some instances cost thousands of dollars (US$) per inch (25mm) of diameter. These items would only be used on specialized extreme applications.

Disposable valves are inside some common household items including liquid or gel mini-pump dispensers, aerosol spray devices, some rubber bulbs for pumping air etc.

Types/Designations

Valves can be categorized into the following design types and although there are hundreds of variations they all fit into these basic types:

Gate, Plug, Globe, Check, Butterfly, Diaphragm & Ball.

Valve parts

Body & Bonnet

The main part of the valve consists of the valve body and bonnet. These two parts form the vessel or casing that holds the fluid going through the valve. Valve bodies are usually metallic. Brass, bronze, cast or ductile iron, steel, alloy steels and stainless steels are very common. Plastic bodies are used for relatively low pressures and temperatures. PVC, PP, PVDF, Glass Reinforced Nylon are common plastics used for valve bodies.

Read more at Wikipedia.org