An empirical study was performed on a gravitational air classifier that is used in a Swedish quarry. The classifier works in two steps and is used to classify a VSI-crushed 0-2 mm fraction into three different products for use in the concrete and asphalt industry. The study was performed using the statistical method of design of experiments (DOE), with which the influence of three different variable control parameters was investigated. The influence of these parameters on the separation cut size and air flow into the machine has thus been obtained. The results show that different parameters as well as control strategies should be applied depending on the quality and capacity requirements of the final products. (C) 2012 Elsevier Ltd. All rights reserved.