Pentair Challenger High Head DiffuserReplacement diffuser (Pentair 355148) for 1 2 HP full rated or 3 4 HP up rated Challenger High Pressure High Head pumps, including models CHI NI 1 2F and CHII NI 3 4A. It channels water from the impeller into the volute to maintain head pressure and hydraulic efficiency. This OEM Pentair PacFab part mounts behind the impeller; use it on High Head Challenger versions, not the standard flow model.