Flange Insert (F1, F6, FP) check valves are the ultimate check valve to install in flanged piping systems. Often referred to as wafer check valves, they provide the simplest most economical way to install check valves in a piping system. The valve body helps position itself while bolts are being installed and tightened. Two gaskets are required instead of the one normally used in a flanged joint. See additional installation guidelines or consult the factory for more information.