A centrifugal separator for separating two liquid components from each other has normally continuously open outlets for both liquid components, an interface layer formed in the separating chamber between the separated liquid components being maintained at a predetermined radial level. The present invention concerns a special arrangement for continuous discharge of the light liquid component but intermittent discharge of the heavy liquid component. For this purpose a first outlet channel (20) in the centrifuge rotor for the heavy liquid component communicates through a calibrated opening (24) with a stationary second channel (23) outside the rotor, said second channel comprising a shut off valve (31). Sensing equipment (28) is arranged to sense when an interface layer formed in the separating chamber (8) of the rotor between the separated liquid components has moved radially inwards to a certain level (29), and provides a signal to a control unit (34) which opens the valve (31) for a time to allow the desired amount of heavy liquid component to be discharged from the separating chamber (8).