Which backflow prevention device uses two check valves separated by a chamber to prevent backflow?

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Backflow prevention devices stop reverse flow into the water supply. The double check valve assembly uses two check valves in series with a small chamber between them. If flow tries to go backward, both valves would have to leak or fail to allow contamination to pass, and the chamber between them provides a place for testing, isolation, and drainage. This configuration gives a reliable barrier for moderate-hazard cross-connections and is specifically designed for that purpose. An air gap prevents backflow by creating a physical separation rather than a valve mechanism. A reduced pressure zone device includes a relief valve and is used for higher hazard situations, not just two checks in a simple chamber. A pressure regulator lowers pressure but does not prevent backflow.