US Patent 7104637 Ink supply system and method of supplying ink

A closed ink supply system wherein air is sealed outside the system and not allowed to flow into components of the system may include an ink source. A first ink sub-reservoir may also be included that comprises a first top fluid surface at a first sub-reservoir fluid height, a first sub-reservoir ink inlet fluidly connected to the ink source, and a first sub-reservoir outlet and a second sub-reservoir outlet that is above the first sub-reservoir outlet. A print head may also be included that comprises a first print head portion fluidly connected to the first sub-reservoir outlet, and a second print head portion fluidly connected to the second sub-reservoir outlet. The second print head portion may be above the first print head portion, whereby a first pressure at the first print head portion is substantially equal to a second pressure at the second print head portion.