The purpose of a Double Check Detector Backflow Prevention Assemblies is to keep polluted water 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 gpm (0.13 L/s) caused by leakage or unauthorized use.

This standard applies to 2 types of assemblies identified as:

a) Double Check Detector Assembly (DCDA).

b) Double Check Detector Assembly Type II (DCDA-II).

The DCDA and DCDA-II assemblies consist of 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 2 properly located, tightly closing shut-off valves per Section 1.3.2.6; and properly located test cocks per Section 1.3.2.4. The assemblies also include a bypass line which provides a visual or audible indication of system leakage or unauthorized use of water.