Abstract: A hydrocyclone having a flat lower plate 14 contains a tube or rod 22 placed unconstrained within the body 10. The tube or rod 22 acts as a vortex breaker, reducing the rate at which air is introduced through the center of the vortex at the lower outlet aperture 16 during operation. When the hydrocyclone of the invention is employed for classification of pressurized stabilized gas-liquid emulsions into fractions of greater and lesser bulk density, the greater bulk density fraction is ejected from the lower outlet aperture 16 and the lesser bulk density fraction flows under pressure out the vortex finder tube 20.