Valves are found in virtually every industrial process, including water and sewage processing, mining, power generation, processing of oil, gas and petroleum, food manufacturing, chemical and plastic manufacturing and many other fields.
People in developed nations use
valves in their daily lives, including
plumbing valves, such as taps for tap water,
gas control valves on cookers,
small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems, and poppet valves in car engines.
In nature there are
valves, for example
one-way valves in veins controlling the blood circulation, and
heart valves controlling the flow of blood in the chambers of the heart and maintaining the correct pumping action.
Valves may be operated manually, either by a handle, lever, pedal or wheel.
Valves may also be automatic, driven by changes in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the
valve, examples of this type of valve found commonly are
safety valves fitted to hot water systems or boilers.
More complex control systems using
valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator. An actuator will stroke the
valve depending on its input and set-up, allowing the
valve to be positioned accurately, and allowing control over a variety of requirements.