The purpose of Reduced Pressure Principle Backflow Prevention Assemblies (RP) 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 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.