ink supplied from an ink source to a filter is guided from a tangential direction with respect to the filter . in addition , a partition wall having a spiral shape reduces the cross - sectional area of an ink passage on the upper surface of the filter and produces a rapid ink flow on the upstream side of the filter . the ink flows from the periphery of the filter to the center of the filter . this ink flow allows air bubbles in the ink to be forced to pass through openings of the filter , thereby being discharged to the exterior of the device . accordingly , faulty ink supply , due to clogging of the filter with air bubbles , is prevented .