Abstract: A decanter centrifuge has a screw conveyor within an imperforate bowl defining a helical chamber. The conveyor is provided with a baffle extending in generally axial direction between the screw flights, thereby dividing the helical chamber within the bowl into a separating zone and a heavy phase discharging zone. The outer portion of the baffle defines with the bowl a restricted passageway which permits the underflow of separated heavy phase material from the separating zone to the heavy phase discharging zone. Pressurizing means, preferably means for maintaining the inner surface of the separated light phase layer inwardly of the weir surface of the heavy phase discharge port, helps advance the separated heavy phase material through the restricted passageway and toward the port through which heavy phase material is discharged.