Abstract: In a separation device for separating particles from a liquid, which is present in a container, a centrifugal rotor is rotatable around a vertical rotational axis. The centrifugal rotor has a tubular inlet member, which extends down into liquid to be treated and which upon rotation of the centrifugal rotor forms a pumping member adapted to pump liquid upwardly and into the centrifugal rotor. The rotatable inlet member is surrounded by a non-rotatable wall, a sealing device being adapted to seal between the rotatable inlet member and the non-rotatable wall. Thereby is avoided that liquid is pumped upwardly on the outside of the inlet member. Furthermore, a smallest possible part of the outside of the inlet member can be in contact with liquid, independent of the level of the liquid surface in the container.