This This standard applies to the type of backflow prevention assembly identified as Double Check Detector Fire Protection (DCDF). These assemblies consist of two (2) independently-acting check valves, internally force loaded to a normally closed position. These assemblies are designed to operate under continuous pressure conditions. This standard also applies to Manifold DCDF assemblies. They consist of two (2) or more complete DCDF assemblies in parallel. The assemblies do not need to be of the same pipe size. The manifold size shall be identified by the single inlet and outlet of the manifold DCDF assembly. It shall consist of shut-off valves on the inlet and outlet of each of the assemblies in the manifold and the shut-off valves shall be line sized to each DCDF assembly in the manifold.