Valve

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

There are a number of names for particular types of valve:

• Ball cock, often used as a water level controller (cistern)
• Ball valve
• Bibcock
• Butterfly valve
• Cock, colloquial term for a small valve
• Gate valve
• Globe valve
• Hydraulic valve (diaphragm valve)
• Non-return valve or check valve, allows the fluid to pass in one direction only
• Pilot valves regulate flow or pressure to other valves.
• Solenoid valve, an electrically controlled hydraulic or pneumatic valve
• Tap (British english), Faucet (US english)

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 operates automatically to correct a potentially dangerous situation.
• A thermionic valve, also known as a vacuum tube, is used in electronic valve amplifiers to amplify sound signals.
• A three way valve routes fluid from one direction to another.