The performance of hydrocyclone with a truncated cone and water injection facility at its apex has been studied. It was found that the flow rate of water in the overflow of the cyclone is higher when smaller cone is used. However on injecting water at the apex, the overflow water rate is minimum when smallest cone is used implying localised effect of injection of water in the displacement of fines. Experiments using silica as feed, along with water injection showed that the weight percent of particles less than a particular size in the under flow is reduced this size being a function of inlet pressure and truncated cone diameter.