At the contrary, the valve is closed while the medium flows back.  swing test valves have a disc this is tilted and rotates on its axis and paintings in a similar way to lift test valves.  check valves are often used as bottom valves in pumping units to save you the backflow of water.  check valves

Check valve is to rely on the flow of the medium itself and automatically open and close valve disc, used to prevent the media flow back valve, also known as check valve, one-way valve, countercurrent valve, and back pressure valve.  Check valve is a kind of automatic valve, its main function is to