A dual check valve is similar to a double check valve in that it is a mechanical backflow preventer consisting of two independently acting, spring-loaded check valves. However, it usually does not include shutoff valves, may or may not be equipped with test cocks or ports, and is generally less reliable than a DC.
A dual check valve is effective against back-pressure backflow and back-siphonage but should be used to isolate only non-health hazards and is used primarily at water service connections to single-family homes.
A picture of a Dual Check Valve is provided below:
