A check valve is an automatic valve that allows air or fluid to flow in only one direction while preventing reverse flow. It opens when pressure is applied in the correct direction and closes instantly if the flow tries to reverse, protecting equipment and maintaining proper system operation.

Check valves are widely used in pneumatic and hydraulic systems, pumps, compressors, water lines, and industrial processes. They prevent backflow, pressure loss, contamination, and equipment damage, helping maintain system efficiency, safety, and reliability.