A hermetic centrifugal separator for centrifuging components, contained in a liquid mixture and having different density, comprises a rotating centrifuge rotor, which is arranged to rotate around a centre axis and comprises a casing which defines an inner separation space, a set of separation discs which are provided in the inner separation space of the centrifuge rotor, at least two channels, which connect to the separation space and comprise at least one inlet channel for supply of the liquid mixture of components to be separated to the separation space and at least one outlet channel for discharge of a component separated during operation from the separation space, a torque transmitting part around the centre axis and fixedly connected to the centrifuge rotor adapted to be driven in such a way that the centrifuge rotor is brought to rotate, outlet sealing means arranged to seal between the outlet channel and the rotating centrifuge rotor preventing entrainment of unwanted substances. To come to terms with the pressure drop in the separator, and especially in the area of the outlet sealing the invention is characterized in that between the separation space and said outlet sealing means is a pumping means arranged to provide pressure to feed the separated liquid through said outlet channel.