A valve is a mechanical 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 myriad of industrial, military, commercial, and residential applications. There are many different types of valves:
- Ball cock, often used as a water level controller (cistern);
- Ball valve, which is good for on/off control;
- Bibcock ;
- Butterfly valve, particularly in large pipes;
- Cock, colloquial term for a small valve;
- Gate valve, mainly for on/off control;
- Globe valve, which is good for regulating flow;
- Hydraulic valve (diaphragm valve);
- check valve or Non-return valve, allows the fluid to pass in one direction only;
- Pilot valves regulate flow or pressure to other valves;
- Plug Valve , for on/off control;
- Solenoid valve, an electrically controlled hydraulic or pneumatic valve;
- Tap (British English), Faucet (American English) is the common name for a valve used in homes to regulate water flow;
- Rotary valves and piston valves are parts of brass instruments used to change their pitch.
Different valves may be used for a variety of purposes:
- A flow control valve maintains a constant flowrate 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.
Other uses of the term
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