The invention relates to a centrifugal separator comprising a casing which delimits and seals off a space in which a rotor is arranged. The rotor forms a separation space which is sealed or isolated from the space, and in which separation space centrifugal separation of a higher density and a lower density component from a fluid takes place. An inlet extends into the rotor for introducing fluid to the separation space, and a first outlet extends from the rotor for discharge of a component separated from the fluid. The space is connected to a pump device which is arranged to remove gas, thereby maintaining negative pressure in said space. The rotor comprises at least one second outlet extending from the separation space to the space for discharge of at least one higher density component separated from the fluid. The invention also relates to a method in such a centrifugal separator.