This Standard applies to Reduced Pressure Principle Backflow Preventers (RP) and Reduced Pressure Principle Fire Protection Backflow Preventers (RPF). These assemblies consist of two (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 atmosphere, internally force loaded to a normally open position. These assemblies are designed to operate under continuous pressure conditions. This standard also applies to Manifold Reduced Pressure Principle Backflow Assemblies consisting of two (2) or more complete Reduced Pressure Principle Backflow Preventers in parallel.