Editing Double check valve (section)

{{Short description|Backflow prevention device to protect water supply from contaminants}}
{{about|a specialized valve for plumbing|a component of a truck brake system|Air brake (road vehicle)}}
{{More citations needed|date=May 2014}}
[[Image:Dcvnormal.png|right|Double check valve during normal operation]]
[[Image:Dcvreverse.png|right|Double check valve during reverse flow]]
A '''double check valve''' or double check assembly (DCA) is a [[backflow prevention device]] designed to protect water supplies from [[backflow (plumbing)|contamination]].<ref name="Findeisen">Dietmar Findeisen (2005) ''Ölhydraulik: Handbuch für die hydrostatische Leistungsübertragung in der Fluidtechnik''; 5. Auflage; Springer Verlag; {{ISBN|978-3-540-23880-5}}; Seite 637; [https://books.google.com/books?id=QIAoLWPYYDIC&dq=zwillingsr%C3%BCckschlagventil&pg=PA637 Online]</ref> It is different from the two-way check valves (sometimes erroneously referred to as double check valves) used in [[Air brake (road vehicle)|air brake]] systems on heavy trucks which select from the highest pressure source.

It consists of two [[check valve]]s assembled in series.<ref name="oregon">{{cite web|url=https://www.portlandoregon.gov/water/article/28163|website=portlandoregon.gov|title=Double Check Detector Assembly article, portlandoregon.gov|access-date=2024-03-26}}</ref> 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 valve]]s 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]]<ref name="oregon"/> and [[combi-boiler]] systems.<ref>{{Cite web |title=ASHRAE Terminology |url=https://xp20.ashrae.org/terminology/index.php?term=backflow%20preventer |access-date=2022-07-27 |website=xp20.ashrae.org |publisher=ASHRAE Technical Committee}}</ref> 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.