Printer utilizing pressure control of air in sump

1. An inkjet printer, comprising:

a printhead for printing onto a media substrate, the printhead defining a plurality of nozzles from which ink is expelled;

an ink tank provided upstream of the printhead;

a sump provided downstream of the printhead for collecting unused ink from the printhead, the sump having a lower portion for holding the unused ink and an upper portion defining a headspace of air above the unused ink;

a first fluid conduit extending between the printhead and the sump for communicating the unused ink from the printhead to the sump, the first fluid conduit connecting the sump to a position in the printhead upstream of the plurality of nozzles; and

a pump connected to the sump, the pump for drawing air from the headspace of the sump into atmosphere and effecting a negative pressure in the printhead upstream of the nozzles, wherein

communication of ink from the ink tank to the printhead is effected by the negative pressure generated by the drawing of air from the headspace of the sump.

2. An inkjet printer according to claim 1 , wherein the sump has a vent for allowing a throttled flow of air into the headspace as the pump is drawing air out of the headspace.

3. An inkjet printer according to claim 2 , wherein the vent has a filter for removing particulate contaminants from the throttled air flow into the headspace.

4. An inkjet printer according to claim 1 , further comprising a maintenance assembly provided downstream of the plurality of nozzles, the maintenance assembly for receiving ink drained from the nozzles.

5. An inkjet printer according to claim 4 , further comprising a second fluid conduit extending between the maintenance assembly and the sump, the second fluid conduit for communicating ink from the maintenance assembly to the sump.

6. An inkjet printer according to claim 5 , wherein the pump is provided along the second fluid conduit, in between the maintenance assembly and the sump.

7. An inkjet printer according to claim 6 , wherein the pump operates in a first direction to draw air from the headspace of the sump into atmosphere, and operates in a second direction opposite to the first direction to communicate ink from the maintenance assembly to the sump.

8. An inkjet printer according to claim 1 , further comprising an ink supply reservoir provided upstream of the printhead, the ink supply reservoir for storing a volume of ink for use by the printhead.

9. An inkjet printer according to claim 8 , wherein the printhead includes an ink distribution manifold, the ink distribution manifold being connected to the ink supply reservoir at a first end of the ink distribution manifold via a third fluid conduit.

10. An inkjet printer according to claim 9 , wherein the first fluid conduit connects the sump to the ink distribution manifold at a second end of the ink distribution manifold opposite the first end.