Patent ID: 7104637

Claim:
A closed ink supply system wherein air is sealed outside the system and not allowed to flow into components of the system, the system comprising: (1) an ink source; (2) a first ink sub-reservoir comprising: (a) a first top fluid surface at a first sub-reservoir fluid height; (b) a first sub-reservoir ink inlet fluidly connected to the ink source; and (c) a first sub-reservoir outlet and a second sub-reservoir outlet that is above the first sub-reservoir outlet; (3) a print head comprising: (a) a first print head portion fluidly connected to the first sub-reservoir outlet and having a first pressure at the first print head portion; and (b) a second print head portion fluidly connected to the second sub-reservoir outlet and having a second pressure at the second print head portion substantially equal to the first pressure, the second print head portion being above the first print head portion by a difference proportional to a difference between the second and first sub-reservoir outlets; (c) wherein the first and second pressures are primarily caused by capillary forces.