Double check valves back flow prevention assembly is used to protect water supplies from contamination or pollution due to back flow. Three top mounted test cocks ensure easy access during repair and maintenance. Consists of two spring-loaded poppet type check valves and a mechanically independent, hydraulically dependent pressure differential relief valve. Designed to give maximum protection against back flow caused by back-pressure or back-siphonage from a cross-connection wherein a contaminant hazard exists.