Patent ID: 7988265

Claim:
A printing system comprising: a printing fluid reservoir; an inkjet pen having a standpipe plenum in fluid communication with said printing fluid reservoir and a printhead in fluid communication with said standpipe plenum; an air detector having first and second electrodes disposed in said standpipe plenum; and means for removing air from said standpipe plenum, wherein said first and second electrodes are provided adjacent first and second ends, respectively, of said printhead, wherein said standpipe plenum includes an inlet and an outlet, wherein said first and second electrodes extend through said inlet and said outlet, respectively, wherein said printing fluid reservoir provides printing fluid to said standpipe plenum through said inlet in a first direction, wherein said printhead is in fluid communication with said standpipe plenum between said inlet and said outlet, wherein said printhead is adapted to eject drops of said printing fluid in said first direction, and wherein said means for removing air from said standpipe plenum removes air through said outlet to a re-circulation chamber in second direction opposite said first direction when the amount of air reaches a predetermined level.