A horizontal rapid gas-particle separator dedicated to the fluid catalytic cracking (FCC) process was tested on a small scale cold circulating fluidized bed. Air and typical FCC particles (density 1400 kg m(-3), mean diameter 70 mu m) are used. The inlet gas velocity is kept constant at 7.3 m s(-1) while the inlet solid loading and the separator dipleg back pressure range from 0 to 16 kg kg(-1) and 100-500 Pa, respectively. The solid collection efficiency increases with the inlet solid loading and reaches an asymptotic value close to 95% when the inlet loading is above 5 kg kg(-1). Two flow regimes are observed in the separator dipleg through the range of inlet solid loadings, related to the available flow section modification and the interstitial gas entrainment. At constant gas collection efficiency, the separator pressure drop is maximum under single-phase flow conditions and reaches a minimum when the inlet solid loading is close to 2.5. The pressure drop increases again for higher inlet solid loading. A modified cyclone model is proposed to predict the separator operation for all inlet solid loading conditions when the gas collection efficiency is at 100%.