The valve is a control component in the fluid conveying system, which has the functions of cut-off, regulation, diversion, prevention of backflow, voltage stabilization, diversion or overflow and pressure relief. Valves used in fluid control systems, from simple shut-off valves to various valves used in complex automatic control systems, have a wide variety and specifications. Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. The connection method between the valve and the pipeline is an important parameter. According to this classification, there are:
1. Threaded connection: The valve body has internal thread or external thread and is connected with the pipe thread.​​
2. Flange connection: the valve body has a flange, which is connected with the pipeline flange.​​
3. Welding connection: The valve body has a welding groove, which is welded to the pipeline.​​
4. Clamp connection: The valve body has a clamp, which is connected with the pipe clamp.​​
5, ferrule connection: use ferrule to connect with the pipeline.​​
6. Wafer connection: the connection form in which the valve and the two pipes are directly clipped together with bolts.​​

Valve body material:
1. Metal material: The valve body and other parts are made of metal material. Such as cast iron, carbon steel, alloy steel, copper alloy, aluminum alloy, lead alloy, titanium alloy, Monel alloy, etc.​​
2. Non-metallic materials: The valve body and other parts are made of non-metallic materials. Such as plastics, ceramics, enamel, FRP, etc. 3. Metal lining: The shape of the valve body is metal, and the main surfaces in contact with the medium are lining, such as rubber lining, plastic lining, ceramic lining, etc.