Method and equipment for controlling the position of an interface between separated liquids in a centrifugal rotor

A method of controlling a separating operation during use of a centrifugal separator for separating a light liquid having a relatively low density and a heavy liquid having a relatively high density from a mixture containing the light and heavy liquids, the centrifugal separator including

• a rotor rotatable around a rotational axis and forming an inlet for said mixture, a separating chamber communicating with said inlet and having a radially inner part and a radially outer part, which parts during a separating operation will contain separated light liquid and separated heavy liquid, respectively, and a space communicating with said radially outer part of the separating chamber such that during a separating operation it will contain separated heavy liquid but not separated light liquid, and
• control equipment including
• a supply device for supply to the rotor of a control liquid having a higher density than said light liquid, said supply device having a pressure source for supplying pressurized control liquid and a supply conduit having one end connected to the pressure source for receiving pressurized control liquid and another end connected to a liquid transferring member for introducing pressurized control liquid into the rotor,
• the method comprising supplying upon need control liquid to the rotor through said supply device only in an amount per unit time required to avoid an interface layer formed in the separating chamber between separated light liquid and separated heavy liquid or control liquid moving radially outwardly from a predetermined radial supply level and, when the rotor is charged with an excess amount of heavy liquid, discharging at least one of said heavy liquid and the said control liquid from said space in the rotor a different way than through said supply device in an amount per unit time required to avoid said interface layer radially moving inwardly from a predetermined radial discharge level.