Check valve, non-return valve is a mechanical device, which normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, means they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any check valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.

There are types: horizontal lift check valve, wafer lug check valve, swing check valve ,dual plate check valve.