The oil to be separated is fed into the separator bowl from the bottom through a hollow spindle, and enters the disc stack. The heavy phase and heavy sludge are forced towards the periphery of the bowl, while the light phase flows towards the centre of the bowl, from where it is pumped out for further processing. The heavy phase is led over a top disc into a chamber where an adjustable paring device pumps it out of the separator. Sludge collects in the sludge space and is discharged intermittently and auto-matically. The discharge is achieved by a hydraulic system, which at preset suitable intervals forces the sliding bowl bottom to drop down, thus opening the sludge ports at the bowl periphery. The sludge is collected in the frame, and leaves the centrifuge via a cyclone.