Patent ID: 7585269

Claim:
A centrifugal concentrator for separating particulate material of higher specific gravity from particulate material of lower specific gravity comprising: a) a hollow drum having an open end and interior surface; b) means for rotatably supporting the drum on an axis; c) drive means for rotating the drum about the axis; and d) material supply means to deliver the particulate material into the end of the drum spaced from the open end; wherein the interior surface of the drum comprises a migration zone, a retention zone above the migration zone for retaining said particulate material of higher specific gravity and a lip zone above the retention zone, and where the respective lengths of said migration, retention and lip zones and the relative degrees of inclination of the migration and lip zones are selected to provide a sufficient component of force on the particulate material to expel the lighter particulate material from the drum and to permit the heavier particulate material to be retained in the retention zone, and wherein the lip zone has a variable diameter provided by a flexible cylindrical member having an inner diameter which is selectively and uniformly decreased or increased by variation of the pressure applied to the member, wherein pressure is variably applied to the outer surface of said flexible cylindrical member by a flexible annular member whereby by decreasing the inner diameter of the lip zone the volume of material able to be retained in said retention zone is increased.