Abstract: A horizontally journalled centrifugal rotor has support bearings at its opposite end portions resting on the bottoms of notches in respective end wall elements of a frame which also includes longitudinal elements extending on each side of the rotor and fixing the end wall elements relative to each other along their entire side edges, the support bearings having flanges parallel with the end wall elements and coacting therewith to fix the support bearings against endwise movement relative to the frame. The upper edges of the end wall elements, the longitudinal elements and the bearing flanges form together an endless contact surface disposed in a single plane and in sealing engagement with a similar contact surface of a top cover for the frame.