The purpose of a Reduced Pressure Detector Backflow Prevention Assembly is to keep contaminated water from flowing back into a potable water distribution system when some abnormality in the system causes the pressure to be temporarily higher in the contaminated part of the system than in the potable water supply piping. These assemblies are designed to detect low rates of flow up to 2.0 gpm (0.13 L/s) caused by leakage or unauthorized use.

This standard applies to the two types of assemblies identified as:

a) Reduced Pressure Detector Assembly (RPDA).

b) Reduced Pressure Detector Assembly Type II (RPDA-II).

The RPDA and RPDA-II assemblies consist of 2 independently acting check valves, internally force loaded to a normally closed position, and separated by an intermediate chamber (or zone) in which there is a hydraulically operated relief means for venting to the atmosphere, internally force loaded to a normally open 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 1.3.2.7; and properly located test cocks per Section 1.3.2.5. The assemblies also include a bypass line.