Valves are control components in fluid conveying systems that have functions such as cutoff, regulation, diversion, prevention of reverse flow, pressure stabilization, diversion, or overflow pressure relief.

The valves used in fluid control systems range from the simplest globe valves to various valves used in extremely complex automatic control systems, with a wide variety of varieties 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 products, liquid metals, and radioactive media. Valves can also be divided into cast iron valves, cast steel valves, chromium molybdenum steel valves, chromium molybdenum vanadium steel valves, dual phase steel valves, plastic valves, non-standard customized valves, etc.