Valve is the control of fluid delivery system components, globe, regulation, diversion, preventing upstream, regulator, bypass or overflow the pressure relief function. Valves for fluid control systems, from the most simple valves to complex automatic control system used by the various valves, its variety and size range. Valves are designed to control air, water, steam, corrosive media, mud, oil, liquid metals and radioactive medium, such as various types of fluid flow. Valve according to the material divided into cast iron valves, cast steel valve, stainless steel valve (201, 304, 316), chromium-molybdenum steel valve, chromium-molybdenum-vanadium steel valves, duplex steel valves, plastic valves, non-standard custom valve material. http://www.sellsteels.com/steel-fitting/valve.html