Loop-seals are commonly used in circulating fluidized bed systems to convey particles from a low pressure region to a high pressure region. One of the principal functions of loop-seal is to avoid the undesirable inverse gas flow and to provide gas tightness. Formation of a moving solid bed in the supply chamber of the loop-seal provides the primary functions of the loop-seal in terms of pressure drop balance and gas leakage minimization. Loop-seal operation in an interconnected fluidized bed system is presented in this work. Ilmenite and two sand particles are used with corresponding density of 4750 kg/m(3) and 2650 kg/m(3) and average diameters ranging from 128 to 368 pm. The pressure drop variations in different elements of the loop-seal are analyzed as function of gas and solid flow rate and pressure balance across the solid circulation loop. Moreover, minimization of gas leakage and formation of the moving solid column in the supply chamber is investigated in terms of gas flow rate, solid flow rate, external aerations, and pressure drop downstream of the loop-seal. The horizontal solid and gas flows in the loop-seal are finally investigated. Results are then compared with some of the existing flow correlations for non-mechanical valves available in the literature. (C) 2012 Elsevier B.V. All rights reserved.