The purpose of a Double Check Detector Fire Protection Backflow Prevention Assembly (herein referred to as the ?assembly?) is to keep polluted water from fire protection systems from flowing into a potable water distribution system when some abnormality in the system causes the pressure to be temporarily higher in the polluted part of the system than in the potable water supply piping. These assemblies are also designed to detect low rates of flow up to 2.00 GPM (0.13 L/s) caused by leakage or unauthorized use.

This standard applies to Double Check Detector Assembly (DCDA) and Double Check Detector Assembly Type II (DCDA-II). The DCDA and DCDA-II 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. The assembly shall include two (2) properly located, tightly closing shut-off valves and properly located test cocks. The assemblies also include a bypass line which provides a visual or audible indication of system leakage or unauthorized use of water. This standard also applies to Manifold Double Check Detector Assemblies consisting of two (2) or more complete DCDA or DCDA-II assemblies in parallel.