Valves are pipeline accessories used to open and close the pipeline, control the flow, regulate and control the parameters of the transported medium (temperature, pressure and flow). According to its function, it can be divided into shut-off valves, check valves, regulating valves, etc.

　　Valves are control parts in fluid transport systems, with functions such as shut-off, regulation, diversion, prevention of backflow, pressure stabilisation, diversion or overflow pressure relief. Valves for fluid control systems, from the most simple shut-off valves to the most complex automatic control systems used in a variety of valves, its variety and specifications are quite large.

　　Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, slurries, oils, liquid metals and radioactive media. Valves are also divided into cast iron valves, cast steel valves, stainless steel valves (201, 304, 316, etc.), chrome molybdenum steel valves, chrome molybdenum vanadium steel valves, duplex steel valves, plastic valves, non-standard custom-made valves, etc. according to the material.

　　Valve is in the fluid system, used to control the direction of the fluid, pressure, flow of the device, is to make the pipeline and equipment within the medium (liquid, gas, powder) flow or stop and can control its flow device.

　　The valve is a control part of the pipeline fluid transport system, used to change the cross section of the pathway and the direction of media flow, with the function of inflow, cut-off, throttling, check, diversion or overflow pressure relief. Valves for fluid control, from the most simple shut-off valve to the most complex automatic control system used in a variety of valves, its variety and specifications, the nominal diameter of the valve from the very small instrumentation valve to the diameter of up to 10m industrial pipeline with valves. The valves can be used to control the flow of various types of fluids such as water, steam, oil, gas, slurry, various corrosive media, liquid metals and radioactive fluids, etc. The working pressure of the valves can range from 0.0013 MPa to 1000 MPa of ultra-high pressure, and the working temperature can be c-270°C of ultra-low temperature to 1430°C of high temperature.

　　The valve can be controlled by a variety of transmission methods, such as manual, electric, hydraulic, pneumatic, turbine, electromagnetic, electro-hydraulic, electro-hydraulic, gas-hydraulic, spur gear, bevel gear drive, etc.; can be under the action of pressure, temperature or other forms of sensing signals, according to the predetermined requirements of action, or do not rely on sensing signals and simple opening or closing, the valve relies on drive or automatic mechanism to make the opening and closing parts for lifting, sliding, swinging or rotary movement. The valve relies on a drive or automatic mechanism to lift, slide, swing or rotate the opening and closing member, thus changing the size of its flow path area to achieve its control function.