These are products which allow fluid to flow at flow direction and used for preventing flow of fluid at reverse direction. It prevents back flow of fluid when pump is out of service in pump plant. Flap is closed by its own weight or counter force. Check valves should be installed by considering flow direction of fluid. Maintenance of system is made by opening upper cover and easily removing flap with swinging system and replacing with new one. It can used easily in hot and cold water plants, drinking water network and fluids which are free of acid.