Valves are control components in fluid‑transport systems, performing functions such as shut‑off, regulation, flow diversion, backflow prevention, pressure stabilization,分流 (diversion), or overflow and pressure relief.

　　Valves used in fluid control systems range from the simplest shut-off valves to highly complex types employed in automated control systems, with an extensive variety of models and specifications. They can regulate the flow of diverse fluids, including air, water, steam, various corrosive media, slurry, petroleum products, liquid metals, and radioactive substances. Based on material, valves are further classified into cast‑iron valves, cast‑steel valves, stainless‑steel valves (such as 201, 304, and 316), chromium‑molybdenum steel valves, chromium‑molybdenum‑vanadium steel valves, duplex steel valves, plastic valves, and custom‑made non‑standard valves, among others.