When hydrocyclones are used in dewatering circuits it is important to know the potential impact of trying to balance the flow of liquid to the overflow and underflow streams and the size distribution, of the solids in these respective streams. The diameters of the vortex finder and spigot play important roles in this balance but neglecting the effect of the feed size distribution could also severely impact the final outcome. This is particularly the case where the transport of coarse particles through the spigot becomes a significant factor. This paper presents a model which accounts for these effects and examines its capability with a data set of over 40 experimental trials with a 225 mm cyclone with a broad range of operating conditions (solids concentration, vortex finder and spigot diameters and flow rates). The model's capability was then subsequently subjected to a further examination by altering the feed size distribution so that it contained a significantly greater amount of material in the size range near the separation size (0.090-0.200 mm). Good results were obtained in both cases. (C) 2002 Elsevier Science Ltd. All rights reserved.