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.
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.