A printing system includes a liquid drop ejector, a fluid flow device, and a fluid flow source. The liquid drop ejector is operable to eject liquid drops having a plurality of volumes along a first path. The fluid flow device includes a first section comprising a plurality of sub-channels created by a partition and a second section comprising a plurality of sub-channels created by a partition. Each partition has a height as viewed from a wall of the fluid flow device. The height of the partition of the second section is less than the height of the partition of the first section. The fluid flow source is operable to produce a fluid flow through the fluid flow device. The fluid flow interacts with the liquid drops to cause liquids drops having one of the plurality of volumes to begin moving along a second path.