Sheet feeding apparatus and image forming system

An image forming system comprising:

• a sheet supporting portion configured to support a plurality of sheets;
• a sheet feeding portion configured to feed a sheet supported on the sheet supporting portion to a sheet feeding direction;
• an air blow unit comprising an air blower configured to blow air, an opening portion through which air blown from the air blower is blown out, a duct configured to form a flow path through which air flows between the air blower and the opening portion, an adjustment portion arranged to oppose to an upper surface of the duct and the opening portion and configured to vary an opening dimension in a height direction between the upper surface and the adjustment portion, the air blow unit being configured to separate a plurality of sheets, including an uppermost sheet, among the sheets supported on the sheet supporting portion by air blowing out from the opening portion;
• a drive source configured to drive the adjustment portion;
• a control unit configured to execute, in a state where a length of the sheet supported on the sheet supporting portion in the sheet feeding direction is a first length, a first mode in which the drive source is controlled such that the opening dimension is set to a first dimension, and to execute, in a state where the length of the sheet supported on the sheet supporting portion in the sheet feeding direction is a second length that is longer than the first length, a second mode in which the drive source is controlled such that the opening dimension is set to a second dimension that is smaller than the first dimension;
• and
• an image forming unit configured to form an image on a sheet fed from the sheet feeding portion.