The valve is a control component in the fluid delivery system, which has functions such as cut-off, adjustment, flow diversion, reverse flow prevention, pressure stabilization, flow diversion or overflow pressure relief. Valves can be used to control air, water, steam, various corrosive media, mud, oil, liquid metal, etc.

It is a general term for components that play the roles of connection, control, direction change, diversion, sealing, support, etc. in the pipeline system. According to different processing techniques, it is divided into four categories, namely, butt-welding fittings (with and without welds), socket welding and threaded fittings, and flanged fittings.