A separator includes a first piston and a second piston both mounted within a drum assembly volume. The first piston is moveable between a first piston open position and a first piston closed position. In the first piston open position drum ejection passages of the drum assembly are open to the drum assembly volume, while in the first piston closed position the first piston blocks the drum ejection passages so that they are closed to the drum assembly volume. A number of intermediate ejection paths are formed in the separator, each extending from an intermediate ejection path inlet at an intermediate region of the drum assembly volume to an intermediate ejection path outlet. The second piston is moveable to alternately open or close the intermediate ejection paths to the drum assembly volume.