Editing Valve (section)

==Control==
[[File:USN sailor operates fuel valve · 070115-N-9479M-004.JPEG|thumb|300px|A sailor aboard a ship operates the wheel controlling a [[fuel valve]].]]

Many valves are controlled manually with a handle attached to the stem. If the handle is turned ninety degrees between operating positions, the valve is called a quarter-turn valve. Butterfly, ball valves, and plug valves are often quarter-turn valves. If the handle is circular with the stem as the axis of rotation in the center of the circle, then the handle is called a handwheel. Valves can also be controlled by actuators attached to the stem. They can be electromechanical actuators such as an [[electric motor]] or [[solenoid]], pneumatic actuators which are controlled by [[Atmospheric pressure|air pressure]], or [[hydraulics|hydraulic]] actuators which are controlled by the pressure of a liquid such as oil or water. Actuators can be used for the purposes of automatic control such as in washing machine cycles, remote control such as the use of a centralised [[control room]], or because manual control is too difficult such as when the valve is very large. Pneumatic actuators and hydraulic actuators need pressurised air or liquid lines to supply the actuator: an inlet line and an outlet line. [[Pilot valve]]s are valves which are used to control other valves. Pilot valves in the actuator lines control the supply of air or liquid going to the actuators.

The [[fill valve]] in a toilet water tank is a liquid level-actuated valve. When a high water level is reached, a mechanism shuts the valve which fills the tank.

In some valve designs, the pressure of the flow fluid itself or pressure difference of the flow fluid between the ports automatically controls flow through the valve.