A rotor of a centrifugal separator, wherein the rotor comprises a central shaft on which an axially movable plate stack, formed by multiple plates, is arranged. A stack base is arranged on the shaft under the plate stack. A stack cap is arranged in an axially moveable manner on the shaft above the plate stack. The rotor includes a compression spring surrounding the shaft, with a first end supported on the shaft and a second end supported on the stack cap, pressing the plate stack together. The rotor includes a sleeve-like extension arranged on the stack cap, projecting into the plate stack and surrounding the shaft with a separation. The compression spring is located inside the extension, at least over a majority of the axial length thereof. A support surface for the second end of the compression spring, is arranged on a base of the extension.