Hydraulic tests conducted to improve the design of a centrifugal air stripper, (used in this instance to remove volatile organic compounds of a jet fuel from contaminated groundwater) are described. The stripper comprised a torus filled with packing materials, rotating within a fixed housing, the water admitted at the inner circumference of the torus being driven by centrifugal force through the packing and contacting air admitted under pressure between the outer circumference of the packing and the housing. Alternative packing materials of similar surface area per m3 were used, one a spongy metallic material of nickel and chromium, the other a wire gauze. The rotation speed and the rates of water and air injection were adjusted until the on-line hydrocarbon analyser gave a constant reading for 30 minutes. The hydraulic capacity of the unit, determined by the depth of the packing, was varied in 3 steps and the rotational speed varied until flooding of the packing, arising when the gravitational force on the water exceeded the centrifugal, occurred. The data collected suggested that the Sherwood flooding formula, previously used to determine this limit, had over-estimated the rotational speed at which it occurred and should be modified to take account of the specific surface area of the packing. Some fouling of the packing, identified as iron, was experienced and water treatment for iron removal is recommended as a pre-treatment.