Patent ID: 7771029

Claim:
An inkjet printer comprising: an ink tank; a printhead integrated circuit (IC) in fluid communication with the ink supply via an upstream ink line, the printhead IC having an array of nozzles each with respective actuators for ejecting drops of ink onto print media; a waste ink outlet in fluid communication with the printhead IC via a downstream ink line; an upstream shut off valve in the upstream ink line, the upstream shut off valve being positioned downstream of the ink tank; a downstream pump mechanism in the downstream ink line; and, a pressure regulator upstream of the printhead IC for maintaining ink in the nozzles at a hydrostatic pressure less than atmospheric pressure; wherein, the pressure regulator is a bubble point regulator which has an air bubble outlet submerged in the ink in the ink tank, and an air inlet vented to atmosphere such that any reduction of hydrostatic pressure in the in the ink tank because of ink consumption draws air through the air inlet to form bubbles at the bubble outlet and keep the pressure in the ink tank substantially constant.