Check valves are also commonly known as the non return type valve as it allows the flow of liquid to be in only one direction. It is a two port valve having one for the liquid to enter and other one for it to leave the valve. These types of valves are frequently used in the household items and find its application in a number of application areas. The construction of these valves is relatively simple and has a smaller size. The main thing in the Check Valve is the operating pressure at which the valve opens and closes. There is a minimum pressure at which the valve operates it is known as the cracking pressure. The check valve is used in the mixing loops in the systems that mix the heating and cooling operation for ensure that it is executed properly and also prevents reverse flow of the fluid.