An experimental apparatus including a dipleg and a trickle valve was established to simulate the operation of a suspended dipleg-trickle valve system of cyclone used in fluid catalytic cracking (FCC) unit.The flow regimes in the dipleg and the discharge modes in the trickle valve were studied by combining the observation of experimental phenomena with the analysis of transient pressure fluctuation.The results show that the flow regimes in the dipleg have two types—the dilute-dense phase coexisting falling flow and the dilute falling flow.Correspondingly,the trickle valve also has two discharge modes—the intermittent periodic dumping discharge and the continuous trickling discharge.The power spectrum density of pressure fluctuation displays that the gas-solids flow in the dipleg-trickle valve system is characterized by a low-frequency pulsation.The coherence coefficient explains the origin and propagation of pressure fluctuation in the system.Eventually,a map describing the flow regimes and discharge modes related to the operation parameters was proposed,which can provide a helpful guidance for the operation of cyclone dipleg-trickle valve system in FCC unit.