Patent ID: 8192000

Claim:
A fluid height backpressure system for supplying fluid to a printhead, comprising: a backpressure device disposed in an upright position and including a tower having a plurality of walls spaced apart from one another so as to define first and second chambers, said second chamber containing fluid in a lower portion of said second chamber and air in an upper portion of said second chamber making contact at an air-fluid interface, said first and second chambers connected in flow communication with each other by an outlet of said first chamber that opens into said second chamber above the air-fluid interface of the second chamber such that fluid can drop downward from said outlet through said air of said second chamber to the fluid in said second chamber; a first conduit for interconnecting said first chamber in flow communication with a lower end of a fluid supply tank; a second conduit for interconnecting said second chamber in flow communication with a fluid reservoir of a printhead; and at least one air removal device disposed in communication with said second chamber of said backpressure device near said air-fluid interface in said second chamber and upstream from said second conduit and operable to enable periodically removing some air from said upper portion of said second chamber to maintain backpressure therein for drawing fluid from said first chamber into said second chamber through said air of said second chamber and supplying fluid from said second chamber to the fluid reservoir such that the backpressure is maintained even with an empty fluid supply tank and also so that fluid is supplied to the fluid reservoir substantially without air bubbles being introduced therein.