Provided is a cartridge unit for a printer. The cartridge unit has upper and lower plate members having an ink bag located between the plate members to define an ink volume. The plate members can be displaced towards and away from each other by an external force. A bag constrictor assembly engages the plate members and is configured to act on the bag when the plate members are displaced towards each other to reduce the ink volume. A valve insert has an inlet valve to facilitate refilling of the bag with ink and an outlet valve to facilitate ink delivery to a printhead. A filter cover is positioned between the valve insert and the ink bag to filter contaminants and air bubbles passing between the ink bag and said valve insert.