A centrifuge rotor for a centrifugal separator for separation of a relatively heavy phase of a fluid from a relatively light phase of the fluid is disclosed. The centrifuge rotor includes a stack of conical disks, and has a central axis of rotation. Each conical disk has an outward surface and an inward surface. The stack of conical disks includes a plurality of interspaces between adjacent conical disks. The interspaces include first interspaces for separation of the relatively heavy phase from the relatively light phase, and second interspaces. A check valve device is provided in each second interspace for closing the second interspace in an inward direction towards the central axis, and permitting opening of the second interspace in an outward direction. Also a centrifugal separator, a method for separation and a conical disk are disclosed.