Watts 9D-M3-1/2 Dual Check Backflow Preventer, 1/2"Intermediate Atmospheric Vent prevent the reverse flow of hot or cold polluted water from entering into the potable water supply. It consists of a brass body with stainless steel internal parts, integral strainer, and two durable, tight sealing, rubber check valves. Designed for continuous pressure, non health hazard applications in smaller supply lines, such as laboratory equipment, processing tanks, sterilizers, dairy equipment, and specifically for