The printer has a print head unit 204 with a reservoir 200 that is coupled to a supply line 98. A second line 220 is provided as an air ventilation line that is activated for ink filling of the chamber. The unit has a built in filter plate 244. Ink is drawn in under positive pressure from the ink reserve to the ink supply line and reservoir to clear air from the supply line and reservoir before the start of printing. Back pressure is maintained in the ink reserve to the reservoir with a relative negative pressure at the ink reserve to prevent leakage of ink from the ink head opening.
