The check valve is normally in the closed position and opens when fluid flows. It also cuts off the flow if the downstream pressure exceeds the upstream pressure. In this respect, it is only used for flow in one direction. Therefore, it prevents backflow through the valve.

The check valve is a two-way valve, one for fluid entry and the other for fluid leaving. Usually, the check valve closes under the elastic force on the left side. When the fluid flows from right to left and the fluid pressure is greater than the peak pressure, the spool moves away from the valve seat and opens the valve.