This standard applies to two types of backflow prevention assemblies identified as a (Double Check Backflow Prevention Assembly (DC) and a Double Check Fire Protection Backflow Prevention Assembly (DCF). These assemblies consist of two (2) independently acting check valves, internally force loaded to a normally closed position, two (2) tightly closing shut-off (isolation) valves, and properly located test cocks. These assemblies are designed and constructed to operate under intermittent or continuous pressure conditions. This standard also applies to Manifold Double Check Backflow Prevention Assemblies. These consist of two or more complete Double Check Backflow Prevention Assemblies in parallel.