Rotor unit for a centrifuge for purifying flowing fluids, which rotor unit (12) comprises a plurality of disk elements (14) which are stacked concentrically one on another and provided with at least one centrally located fluid flow-through hole, where the disk elements (14) have lead-through openings by means of which the disk elements (14) are pushed onto a number of essentially axially elongate guide elements (16) distributed in the circumferential direction for guiding the disk elements in the circumferential direction and radially. The disk elements (14) are held together by a first and a second end element (18, 20) at the ends of the stack of disk elements. A central portion of at least some of the guide elements (16) are interconnected by means of a cross-stay construction (36) in order to prevent deflection of the rods owing to the centrifugal force during rotation of the rotor unit (12).