Ames Deringer™ 20 and 20G Double Check Valve Assemblies are designed to prevent non-health hazard pollutants from entering the potable water supply system caused by backpressure and/or backsiphonage conditions. Deringer 20 features integral Eccentric-seal™ butterfly shutoff valves for a short lay length, and Dual-action™ checks for high performance at low- and high-flow rates. Deringer 20G also features Dual-action checks, but with OS&Y shutoff valves.