The phase split that occurs naturally at T-junctions has been further enhanced to provide a viable partial gas-liquid separator. Previous experimental investigations have mainly considered only single junctions but here the performance of a separator system consisting of two T-junctions in series is reported. The addition of control valves on the exit pipes extends previous fundamental studies and incorporates the concept of control and flexibility. A simple active control strategy is proposed on the basis of two control valves, one associated with an automatic level control, the other optimizing liquid residence time, leading to the development of a conceptual T-separator. Experiments were performed in the stratified and slug flow patterns using air and kerosene at ambient temperatures. (c) 2007 American Institute of Chemical Engineers.