A centrifugal rotor has (a) an axially movable primary slide (5) for closing or opening peripheral outlets (11) and bordering a closing chamber (14) having inlet (15) and outlet (16) for a closing liquid, and (b) an axially movable secondary slide (20) for allowing or stopping flow through said closing liquid outlet (16), the secondary slide (20) having opposite sides bordering an opening chamber (22) and a closing chamber (21). An axially movable part is located radially outside said closing liquid outlet (16) and forms a partition (12) between the closing chambers (14 and 21) of the primary and secondary slides; the secondary slide's closing chamber (21) is closed radially inwards by an annular seal (24) between the secondary slide (20) and part (12a) of said partition (12); and the secondary slide (20) when opening uncovers an annular opening for passage of a closing liquid from the primary slide's closing chamber (14) to the secondary slide's opening chamber (22).