The development of the concept and theory of pulsed-flow air classification are summarized. Methodology and equipment for testig various air classifiers are described. Laboratory experimentation shows that pulsed-flow air classification is capable of superior separations by density than conventional classifiers. Comparisons with other types of air classifiers, including passive pulsing classifiers, show the active pulsed-flow air classifier to be superior. Continuous-feed comparison testing with a conventional zigzag classifier shows the superiority of the active pulsed-flow system both in terms of separation efficiency and operational considerations, which are extensively discussed.