Ink jet printing apparatus with air purge function

An ink jet printing system with a pen body having a first chamber and a second chamber. A print head on the pen body is connected to the second chamber, and an ink-transmissive barrier separates the second chamber from the first chamber. A pump is connected to the pen body in communication with the first chamber, and operates to generate a positive pressure in the first chamber to motivate ink from the first chamber, through the barrier, and into the second chamber. An ink supply cartridge may be provided that removably connects to the pen body, and which has openings in registration with corresponding openings in the pen body into the first and second chambers, respectively. A sliding shutter or other valve may be provided on each of the pen body and the cartridge to close the openings when the cartridge is removed from the pen body. An actuator portion of the cartridge may operate to engage the pump upon installation of the cartridge, and to displace any gas bubble from the second chamber to the supply cartridge; upon disengagement of the cartridge, the actuator may release the pump, drawing ink from the cartridge into the first chamber.