Double Check Valves
A double check valve, sometimes called a double check assembly (DCA), is a type of check valve used to protect water supplies from contamination due to backflow. They are also commonly used in air brake systems on heavy trucks. Other places double check valves are found include lawn irrigation, fire sprinkler and combi-boiler systems.
Generally known as a relief valve, double check valves have fairly simple mechanics since their effectiveness is determined by the process flow, which means no other device is needed. They are usually attached to the pump head on the inlet and outlet lines of various types of fluid pipes in pumps and systems. The body of the valve holds in place a ring-like element known as the seat, which extends from the inner walls toward the center-line of the pipe but does not fully close. A plugging mechanism, such as a piston or ball rests in the seat.
Another plugging device is a swinging disk. When pressure is great enough and going in the desired direction, the stopper is lifted away from the seat, opening the gap to allow the process stream to flow freely. The reverse flow then pushes the plug back into the hole, creating an air tight seal that will not be opened again until forward flow pressure is greater than the back pressure. Since check valves allow the stream to flow in only one direction, the system stays clean. Specifically, double check valves consist of two spring check valves assembled in sequence, usually with a ball valve or gate valve at each end.
Double check valves have multiple valves working together for a few reasons. First, one check valve is still able to act even if the other is jammed open. Also, a more reliable seal is possible when one valve is closed, because this reduces the pressure differential across the other and stops leakage of any kind. Size varies among double check valves, as it does among all check valves.
Small valves may be so compact they are not noticeable, particularly when they are integrated into the bodies of existing taps (faucets). Larger check valves may be installed with ball valves at the ends, which are partly there to test the double check valve periodically. This valve system mainly deals with keeping water clean and therefore requires consistent evaluation abilities for proper function. One industry utilizing double check valves is water treatment companies, but others use it often too.
Double Check Valves Informational Video