Cla-Val Series RF-DBI Rubber-Flex™ Duckbill In-Line Flanged Style Check Valves are for pressurized pipeline applications where it is inserted between pipe flanges. RF-DBI Duckbill In-Line Flanged Style Check Valves have an integral rubber flange for attaching directly between flanged-end pipe connections. A variety of elastomers allow DBI valves to be used with many fluids.