Abstract: An apparatus and method for centrifugally separating a continuous flow of substances having differing densities along a constrained helical course. The assembly (10) comprises a helical conduit for constraining the flow having a velocity established along a closed helical tubular course (25), including an inlet (26) and an outlet (28) respectively situated at opposite terminal ends of the conduit. The invention is characterized by a peripheral outlet duct (42) disposed in either of an inner or preferably an outer periphery of the conduit between the inlet (26) and outlet (28) terminals for removing a peripheral fraction concentrated by centrifugal forces in either of the inner or outer periphery, respectively, of the conduit. An unremoved fraction of the flow is allowed to continue along the helical course to and through the terminal outlet.