Abstract: Centrifugal separating apparatus comprises a rotatable drum formed from at least two axially-spaced parts. The adjacent portions of adjacent parts have frusto-conical walls which co-operate to define a chamber which receives a component separated in the drum. The adjacent edges of the parts comprise lips which bound an outlet opening from the chamber and are operable for selectively closing the opening, for example by moving the lips together. A fluid lock chamber is formed in the lip structure between radially inner and outer lips for allowing discharge of a heavier product from the lock chamber while the lock chamber is itself isolated from the lighter liquid in the centrifuge drum. The lips are actuated by electro-magnets and are connected to the rods which drive the lips. At least one of the lips is integral with a ring which is connected by tie-rods to a second ring of soft iron which forms an armature of the driving electro-magnet.