In centrifuges, counter-flow classification can be performed efficiently with cut-sizes in the micron range. A special centrifuge was developed with rotating joints that the feed slurry, process water and underflow can be controlled by pumps. This allows to adjust the flow rates for an optimal operation. The settled coarse particles are fluidized by the process water and drawn upon with the underflow water. A process equation in a dimensionless format was developed for selecting the proper design and operation parameters especially for highly loaded underflows. Experimental tests have proven this approach.