... 12 years OEM manafacturer experience Rubber Duckbill Valve,flexible check valve,rubber check valve 1: Product ... valve with functions of forward inflow and reverse back stop. 2:Based on analysis and calculation ... the water flow is. 4:During the back stop operation,the valve will vclose naturally,seal ... is sound seal for back stop,no leakage,back flow prevention,the higher the back pressure is ,the better ...