It is with great pleasure and satisfaction that we introduce this volume which comprises the papers accepted for the 4th International Conference on Hydrocyclones held in Southampton from 23rd to 25th September 1992. As the name implies, this is the fourth Conference in the series, with the previous ones held in Cambridge in 1980, Bath in 1984 and Oxford in 1987. The papers cover a wide span of activities, from fundamental research to advances in industrial practice and, as in the earlier volumes, make a significant contribution of lasting value to the technical literature on hydrocyclones....