This standard applies only to two types of backflow prevention assemblies identified as (RP) "Reduced Pressure Principle Backflow Preventers" and (RPF) "Reduced Pressure Principle Fire Protection Backflow Preventers. "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 an 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. The assembly shall include two (2) tightly closing shut-off valves, and contain properly located test cocks. This standard also applies to Manifold Reduced Pressure Principle Backflow Assemblies. They consist of two or more complete Reduced Pressure Principle Backflow Preventers in parallel. The assemblies do not need to be of the same pipe size. The manifold size shall be identified by the single inlet and outlet of the manifold reduced pressure principal backflow assembly. It shall consist of shut-off valves on the inlet and outlet of each of the assemblies in the manifold and the shut-off valves shall be line sized to each backflow assembly in the manifold.