A valve is a device used to control the direction, pressure, and flow of a fluid in a fluid system. It is a device that allows the medium (liquid, gas, powder) in piping and equipment to flow or stop and can control its flow.

The valve is a control component in the pipeline fluid transportation system, used to change the cross-section of the passage and the direction of the medium flow, and has the functions of diversion, cut-off, throttling, check, shunt or overflow pressure relief. The valves used for fluid control range from the simplest shut-off valves to various valves used in extremely complex automatic control systems. Their varieties and specifications are wide. The nominal diameter of the valve ranges from a very small instrument valve to a diameter of 10m. Valves for industrial piping. It can be used to control the flow of various types of fluids such as water, steam, oil, gas, mud, various corrosive media, liquid metals and radioactive fluids. The working pressure of the valve can be from ultra high pressure of 0.0013MPa to 1000MPa, and the working temperature can be c-270 ℃ ultra-low temperature to 1430 ℃ high temperature.

The valve can be controlled by a variety of transmission methods, such as manual, electric, hydraulic, pneumatic, turbine, electromagnetic, electromagnetic hydraulic, electro-hydraulic, gas-hydraulic, spur gear, bevel gear drive, etc .; Under the action of other types of sensor signals, it acts according to the predetermined requirements, or simply opens or closes without relying on the sensor signals. The valve relies on the drive or automatic mechanism to lift, slide, swing or swing the opening and closing parts Movement, thereby changing the size of its flow channel area to achieve its control function.