The investigation was undertaken as a preliminary study of the 4" Compound Water Cyclone, with regard to its separation efficiency, range of yields obtained and throughput capacity. The main purpose behind this work was to gain some experience with the operation of this type of cyclone and to get an idea of its performance before starting investigations with an 8" Compound Water Cyclone. The cyclone used in those tests is the property of Nortons-Tividale South Africa (Pty)Ltd., Johannesburg. It was borrowed by the Fuel Research Institute and mounted on the existing test rig, consisting of a reservoir tank, feeding pump, recirculating pump and sampling apparatus. A representation of the apparatus and test rig is given in diagrams 1 and 2.