The 8'''' 350ASTDAOSYPI Double Check Detector Aseembly with OS&Y gate valve tamper switch and Post Indicator gate valves protects against both backsiphonage and backpressure in low health hazard, fire protection applications. Its stainless steel body, access covers, internals, fasteners, and springs are corrosion-resistant for reduced maintenance costs. Featuring a metered bypass system, the 350ASTDAOSYPI efficiently detects leaks and any unauthorized water use. Its single access cover reduces downtime and added costs associated with maintenance and repairs. The 350ASTDAOSYPI features a short lay-length for compact, versatile installation in horizontal or vertical positions.