A hydrodynamic model for an L-valve is proposed based on the theories of multiphase flow and particulate media mechanics. This model can be used to predict the solids flow rate, gas pressure drop, and gas flow rates, according to the properties of gas and solids, L-valve size, and the operational conditions. Predicted results agree well with the experimental data. (C) 2003 Elsevier Science B.V All rights reserved.