Abstract: A centrifuge comprising an elongated rotary drum and a rotor journalled coaxially within the drum for rotation at a slightly different speed. Means are provided for supplying a raw material containing a solid and a liquid phase to the separating space defined by the drum and the rotor. The rotor carries at least two continuous screw helices for transporting solid matter axially towards one end of the separating space. An aperture is provided in each helix whereby the axial movement of at least some of the transported solid matter is temporarily stopped when that matter passes through the aperture. A washing liquid is supplied through openings in the rotor shortly upstream of each aperture for acting upon the solid matter during the period in which its axial movement is interrupted. The apertures in the helices are off-set relative to one another along the circumference of the rotor.