Check Valves:There are Many Forms of This Type of Valves

The first category is the most common one. A ball in the shell of the valve fits tightly against the side of the valve where the water comes in. Water pushing through the pipe moves the ball against the spring, allowing water through the valve. When the water is turned off, the ball is pushed into place by the spring and keeps water from flowing backward through the pipe.

The second type is a product with override control to stop flow regardless of flow direction or pressure. It can not only close in response to backflow or insufficient forward pressure, but also can be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure.

The third one is similar to ball check valves, but the plug that seals the valve is shaped like a cone. It also can be called a lift check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. The cone is held on a bar, allowing it to lift out of the way when the water is flowing and drop back into place when the water is off. If water backflows through the pipe, it pushes up against the cone, creating a seal that keeps it from going any further.

The fourth one is the disk valve which is also known as swing check valve. It operates in the same manner as ball and cone valves, but the plug that settles over the opening is a disk. Disk and cone valves tend to wear down more because they have more moving parts and because they get bumped around on top of the flow of water when it is turned on.