Valve

From Free net encyclopedia

For other uses, see Valve (disambiguation).

A valve is a device that regulates the flow of fluids (either gases, fluidised solids, slurries or liquids) by opening, closing, or partially obstructing various passageways.

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

Some valves are driven by pressure only, they are mainly used for safety purposes in Steam engines and domestic heating or cooking appliances. Others are used in a controlled way in Otto cycle engines driven by a camshaft, and they have a major part in engine cycle control.

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Types of valves

4-stroke cycle engine valves,
Ball cock, often used as a water level controller (cistern);
Ball valve, which is good for on/off control;
Bibcock, provides a connection to a flexible hosepipe
Blast valve, used to prevent rapid overpressures in a fallout shelter or a bunker;
Butterfly valve, particularly in large pipes;
Check valve or Non-return valve, allows the fluid to pass in one direction only;
Cock, colloquial term for a small valve or a stopcock;
Double check valve;
Freeze valve, in which freezing and melting the fluid creates and removes a plug of material acting as the valve;
Gate valve, mainly for on/off control;
Globe valve, which is good for regulating flow;
Hydraulic valve (diaphragm valve);
A leaf valve is a one-way valve consisting of a diagonal obstruction with an opening covered by a hinged flap.
Pilot valves regulate flow or pressure to other valves;
Plug Valve, for on/off control;
Presta and Schrader valves are used to hold the air in bicycle tyres.
Rotary valves and piston valves are parts of brass instruments used to change their pitch.
Schrader valves are used to hold the air inside automobile tyres.
Solenoid valve, an electrically controlled hydraulic or pneumatic valve;
Stopcocks restrict or isolate the flow through a pipe of a liquid or gas.
Tap (British English), faucet (American English) is the common name for a valve used in homes to regulate water flow;

Different valves may be used for a variety of purposes:

A flow control valve maintains a constant flow rate through the valve.
A heart valve regulates blood flow through the heart in many organisms.
A poppet valve is commonly used in piston engines to regulate the fuel mixture intake and exhaust. The sleeve valve is another valve type used for this purpose.
A pressure reducing valve reduces pressure to a preset level downstream of the valve.
A pressure sustaining valve maintains pressure at a preset level upstream of the valve.
A regulator is used in SCUBA diving equipment and in gas cooking equipment to reduce the high pressure gas supply to a lower working pressure
A safety valve or relief valve operates automatically at a set differential pressure to correct a potentially dangerous situation, typically over-pressure.
A three-way valve routes fluid from one direction to another.
Vacuum breaker valves prevent the back-siphonage of contaminated water into pressurized, potable water supplies.