These are products which allow liquid to flow at flow direction and used for preventing flow at reverse direction. It prevents fluid back flow when pump is out of service in pump plants. Ball is closed by its own weight or counter force. Check valves are mounted considering the fluid flow direction. Ball system deforms late with respect to flap system. In the event that it is deformed , upper cover is opened and ball is removed and new one is installed and maintenance of checkvalve is made easily. It can be used easily in drinking water plants and fluids which are free of acid.