A method for adjusting an interface formed during operation between a specific light liquid phase and a specific heavier liquid phase to a wanted radial level in a centrifugal separator, in which the separation chamber is emptied of its contents and the inlet opening is brought to a radial inner position in the outlet chamber, after which a pre-determined volume of the specific heavier liquid phase is supplied to the separation chamber and the mixture of the two liquid phases is supplied to the separation chamber via the supply conduit and the inlet chamber whereby the separation chamber is filled up and an interface between the two liquid phases is formed, which is displaced radial outwardly, the displaced specific heavier liquid phase then being pressed radial inwardly in the outlet channel and further into the outlet chamber. A first pressure sensor indicates when the separation chamber has been filled up to a wanted level, after which the position of the inlet opening is moved towards the free liquid surface in the outlet chamber until the inlet opening reaches the liquid surface and the specific heavier liquid phase in the outlet chamber is discharged through the inlet opening and the discharge channel, which is indicated by a second pressure sensor. The inlet opening is prevented from moving at least radially outwardly from its obtain position, which substantially corresponds to a wanted position of the interface. During the following normal operation the liquid phases are separated and discharged through an outlet device each during maintaining the radial level of the free liquid surface in the outlet chamber and consequently also the radial level of the interface.