A check valve allows flow in one direction and automatically prevents backflow (reverse flow) when fluid in the line reverses direction. They are one of the few self-automated valves that do not require assistance to open and close. Unlike other valves, they continue to work even if the plant facility loses air, electricity, or the human being that might manually cycle them. Check valves are found everywhere, including the home. If you have a sump pump in the basement, a check valve is probably in the discharge line of the pump. Outside the home, they are found in virtually every industry where a pump is located.
A dual plate check valve is also known as a butterfly check valve, folding disk check valves, double-disc or split disc check valve. As the name suggests, two halves of the disk move towards centreline with the forward flow and reverse flow two halves open and rest on the seat to close the flow. Use of Dual Plate Check Valve is popular in low-pressure liquid and gaseous services, its lightweight and compact construction make it a preferable choice when space and convenience are important. It is 80 to 90% lighter than conventional full body check valve. Frequently used in systems that used butterfly valves. The cost of installation & maintenance is very low compared to other types.
Some styles of check valves are specifically designed to allow their disc, or flapper, to slam shut in certain conditions, such as the reversal of fluid flow. This sudden shutting, or slamming, creates a wave of pressure in the liquid that reverberates throughout the system and, depending on the precise application, can ultimately lead to reduced process efficiency, valve damage, gasketed joint leaks, and other issues. This inevitable — but controllable — phenomenon is commonly referred to as water hammer. Non-slam check valves are designed specifically for use in these situations. As their name implies these valves close without slamming, meaning no excess pressure spikes are created. The disc of a non-slam check valve has an internal spring opposing the opening fluid flow pressure. When the flow of a media is strong enough, the spring compresses and the valve opens; the disc is smoothly pushed back toward the seating surface in the valve by the spring as the flow decreases and stops, but before flow direction reverses. Non-slam check valves are ideal for vertical runs of piping, or complex applications that require constant and controllable pressure levels.