Classifying cyclones are a widely used device for achieving ultrafine particle size separations in industrial applications. However, inherent deficiencies include particle density effects in multicomponent suspensions and ultrafine particle short-circuiting to the underflow stream due to hydraulic entrainment. A detailed in-plant test program has been conducted to evaluate the bene its of tangential water injection into the apex portion of a classification cyclone for the removal or minimization of the ultrafine by-pass. Based on models developed using the test results, ultrafine bypass can be reduced by 50% or more while maintaining the same corrected d(50) value through complex manipulation of operating and geometric parameters. In a subsequent test, the by-pass was reduced from 15% to about 7% while maintaining a d(50(c)) value of 26 microns. However, the magnitude of the benefit in by-pass reduction is subject to the geometric parameters of the conventional classifying cyclone.