A valve is a device that regulates, directs, or controls the flow of a fluid (gas, liquid, fluidized fluid, or slurry) by opening, closing, or partially blocking various passages. Valves are technically connected, but are usually discussed as separate categories. In an open valve, fluid flows from a higher pressure to a lower pressure. The word comes from the Latin valva, which is the moving part of a door, so e goes to the rotation.

^Simple, ancient valve is a free-hinge flap that can drop in one direction to block the flow of liquid (gas or liquid), but is pushed away by the flow in the opposite direction. This is called a check valve because it blocks or "checks" the flow in one direction. Modern control valves regulate pressure or flow downstream and operate complex automation systems.

Valves have many uses, including water for irrigation, industrial applications for control processes, residential uses such as home use/shutdown and pressure control, and the use of washing machines and faucets at home. Even aerosols have a small valve. Valves are also used in the military and transportation sectors. Valves have been found in almost every industrial process, including water and wastewater treatment, mining, power generation, oil, gas and petroleum, food manufacturing, chemical and plastics manufacturing, and many others.

Even in developed countries, people use valves in their daily lives, including plumb bobs, tap water, gas control valves on cookers, small valves, safety devices installed on hot water systems, and safety on hot water systems. The device, as well as the valve on the car engine.