Mathematical description of separation principle in Floatex Density Separator has been established. Separation performance of the separator is described using a simple slip velocity model. Effects of suspension density and bed voidage are incorporated in this model using an averaging approach. The model is capable of describing the separation performance with reasonable accuracy regardless of the flow regime. The performance of the separator is simulated using the model. It is observed that both bed pressure and teeter water have substantial influence on the separation performance. It is also established that for good concentration effect a threshold bed pressure is required below which the size effects dominate the separation process resulting in classification. Very high bed pressure increases the misplacement of high density particles in the overflow stream. Effect of feed size distribution is also studied and it is observed that a narrow size distribution of the feed gives good concentration performance by reducing the size effect. The predicted results are in good agreement with the experimental observations. (c) 2008 Elsevier B.V. All rights reserved.