A centrifugal separator apparatus for separating components of a fluid stream; the apparatus comprising a support structure and a centrifugal separator unit rotatably mounted on the support structure so as to be rotatable about a rotational axis extending through the centrifugal separator unit; a drive element for driving rotation of the centrifugal separator unit; wherein the centrifugal separator unit comprises a centrifugal separation chamber having an inlet which is connected or connectable to a source of fluid requiring separation, a first outlet for collecting a higher density component of the fluid stream, and a second outlet for collecting a lower density component of the fluid stream; the first outlet being connected or connectable to a first collector for collecting the higher density component and the second outlet being connected or connectable to a second collector for collecting the lower density component; the centrifugal separation chamber comprising a curved or inclined guide surface for guiding flow of the fluid from the inlet in a radially outward direction; wherein the centrifugal separator unit is provided with a wall member which is axially movable to provide a selected degree of occlusion of the first outlet and thereby control flow of the higher density component through the first outlet.