The Apollo DUC-4N Series Dual Check Valve Backflow Preventer is designed to prevent cross connections of non potable water (non-hazardous) into safe drinking water systems. It is a compact and economical device that consists of two independently-acting, spring-loaded check valves in a corrosion-resistant material. Each of the two spring-loaded check valves is designed to open at 1 psi differential in the direction of flow. The check valves will remain tightly closed until there is a demand for water downstream. If the downstream pressure of the device increases above the supply pressure or there is a reverse direction of flow, the check valves will close to prevent backflow. If the second check valve is prevented from closing tightly, the first check will close to provide protection from a backflow condition. Replaceable check modules. Industry lay lengths. Maximum Working pressure 175 psi. 33/180 degrees F Operating temperature range. ASSE1024 and CSA approved. Cast Bronze C84400 body. Brass union tailpiece and union nut. Glass-Filled PPO/Acetal check modules. Stainless steel spring. Buna-N Seat Discs.