The Watts 9D-S-M3 1/2" Dual Check Valve Backflow Preventer with Atmospheric Vent protects potable water systems by stopping reverse flow from contaminated hot or cold water sources. Its bronze body, stainless steel internals, rubber check assemblies, and integral strainer deliver reliable performance in continuous-pressure, non–health-hazard applications such as boiler feeds, lab equipment, and processing tanks. Compact and easy to service with union solder connections, it vents safely to atmosphere if the secondary check fouls, ensuring dependable protection and code-compliant operation.