A novel diagnostic method to characterize the flow patterns in an 80 mm-i.d. L-valve had been developed by using multi-resolution analysis (MRA) of wavelet transformation on the pressure fluctuation signals which were acquired from the standpipe and the horizontal part of L-valve. Parameters including the aeration rate, aeration positions, riser gas velocity and composition of binary particle mixture (194-mu m and 937-mu m sand particles) were used to investigate the relationship of performance of L-valve and its pressure fluctuations. By means of MRA, the original pressure fluctuations were divided into multi-scale signals. They were macro-scale, meso-scale and microscale successfully described the structures of gas-solid flow in the L-valve, such as the gas bubbles/slugs, dune-ripple flow, suspension particle flow, etc. (C) 2008 Elsevier Ltd. All rights reserved.