Abstract: In a continuous ink jet printing apparatus, an ink circulating system allows maintenance of the ink supply reservoir at approximately atmospheric pressure while providing for positive withdrawal of ink from the catcher and/or print head outlet of the apparatus. The system is operable with a single pump. To achieve such positive withdrawal of ink, elements are provided in a bypass line extending from the supply pump outlet to the atmospheric region of the ink reservoir or in the passage from that region of the ink reservoir to the pump intake line, for generating a region(s) of sub-atmospheric pressure, and such region(s) are coupled to the catcher and/or print head outlet.

Abstract: A continuous multi-jet ink jet printer produces a pattern of guard drops such that each drop in a jet is separated by one or more guard drops, drops from jet-to-jet in a row are separated by one or more guard drops, and the pattern includes one or more rows of all guard drops to thereby reduce the raggedness of edges in characters produced by the ink jet printer.

Abstract: To protect critical operative portions (e.g. the orifice plate) of ink jet printing apparatus from airborne debris particles (e.g. paper dust), a wall is provided to substantially enclose a region around those critical operative portions and filtered air is induced to flow through the enclosed region from a location proximate the operative portions to a droplet outlet. In one mode the energy of printing droplet streams induces the air flow. In another embodiment the energy of printing substrate movement induces the air flow.