A double check valve or double check assembly (DCA) is a backflow prevention device designed to protect water supplies from contamination. It is also a valve used in air brake systems on heavy trucks.
Usage in Water Supply: In the case of usage in water supply, it consists of two check valves assembled in series. This employs two operating principles: firstly one check valve will still act, even if the other is jammed wide open. Secondly the closure of one valve reduces the pressure differential across the other, allowing a more reliable seal and avoiding even minor leakage.
Small valves may be so compact as to be barely 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, for isolation and testing. Often, test cocks (very small ball valves) are in place to attach test equipment for evaluating whether the double check assembly is still functional.
The double check valve assembly is suitable for prevention of back pressure and back siphonage, but is not suitable for high hazard applications. It is commonly used on lawn irrigation, fire sprinkler and combi-boiler systems. If the hazard is higher, even a relatively low hazard such as using antifreeze in the fire sprinkler system, then a more reliable check valve such as a Reduced pressure zone device may be mandated.
Famous quotes containing the words double and/or check:
“The worst feature of this double consciousness is, that the two lives, of the understanding and of the soul, which we lead, really show very little relation to each other; never meet and measure each other: one prevails now, all buzz and din; and the other prevails then, all infinitude and paradise; and, with the progress of life, the two discover no greater disposition to reconcile themselves.”
—Ralph Waldo Emerson (1803–1882)
“The veto is a President’s Constitutional right, given to him by the drafters of the Constitution because they wanted it as a check against irresponsible Congressional action. The veto forces Congress to take another look at legislation that has been passed. I think this is a responsible tool for a president of the United States, and I have sought to use it responsibly.”
—Gerald R. Ford (b. 1913)