A check valve, also known as a non-return valve or one-way valve, is a mechanical device designed to allow fluid or gas to flow through it in only one direction. It consists of a movable disc or a flap that opens and closes automatically based on the pressure of the fluid. When the pressure is higher on the inlet side, the valve opens, allowing the fluid to pass through. Conversely, when the pressure on the outlet side is higher, the valve closes, preventing backflow. Check valves are essential components in systems where preventing reverse flow or maintaining the direction of flow is crucial, such as in plumbing systems, pumps, compressors, and various industrial applications.