A check valve, also called a one-way valve, return valve, or isolation valve, is an automatic valve that uses its own weight and pressure of the medium to prevent backflow of the fluid. The valve disc can move in two ways: lift type and swing type. The lift check valve operates similarly to a globe valve but without a valve stem. This type of valve allows fluid to flow in at the inlet end and out at the outlet end. When the inlet pressure exceeds the combined weight of the disc and its flow resistance, the valve will open. On the other hand, when the medium flows back, the valve will close automatically. The swing check valve, which has a disc that can rotate around an axis at an angle, works in the same way as the lift check valve.
Check valves are commonly used in pumping devices as bottom valves to prevent water backflow. They can also be used in combination with globe valves to provide extra safety and isolation. However, check valves have some disadvantages, such as high resistance and poor sealing performance when closed.