Check valves are used to stop backflow and protect rotating equipment or other mechanical devices from the sudden backflow surges that may occur.

Check valves are normally in the close position and open when the fluid flows through it. It also has the capability of shutting off the flow in the event the pressure downstream exceeds the upstream pressure. In this respect, it is used for flow in one direction only.

Thus it prevents backflow through the valve. Because flow of the fluid through the valve is allowed to be in one direction only, check valves must be installed properly by noting the normal direction of flow.

An arrow stamped on the outside of the valve body indicates the direction of flow. Check valves may be classified as swing check valve and lift check valve.

The check valves are leak-free in one direction and free-flow in the reverse direction. The fluid flow direction can be controlled with a check valve.