This 6" lead free stainless steel double check detector backflow preventer assembly with grooved butterfly valves, post indicator valve and a cubic feet per minute meter measures water flow to detect ground leaks and unauthorized taps. Primarily used on fire line sprinkler systems at referenced cross-connections identified as non-health hazard continuous pressure applications, it prevents the backflow of fire protection substances into the potable water supply and protects against backsiphonage and backpressure. The easy maintenance assembly consists of positive seated thermoplastic independently operating torsion spring check modules, UL/FM grooved gear operated butterfly gate valves with tamper switch and top mounted test cocks. The temperature range is 33 to 140 degrees F (0.5 to 60 degrees C). The maximum working pressure is 175 psi (12.1 bar).