Sheet stacker

In a stacker for sheets such as paper, comprising a transfer table, means for conveying such sheets in overlapping manner to said transfer table, a stacking table to receive said sheets, means for raising and lowering said stacking table, means for conveying sheets from said transfer table to said stacking table along a conveying direction, a bar screen including a plurality of bars, and means for introducing the bar screen above the stacking table in the conveying direction between sheets which have already been stacked and sheets being conveyed to said stacking table, the improvement which comprises free spacers positioned below said transfer table, the free spacers receiving the bars of the bar screen at a level above the top of the stack on the stacking table, a first nozzle for blowing gas in the conveying direction of said sheets, said first nozzle being positioned adjacent the forward end of the transfer table below the level of supply, and a second nozzle for blowing gas, said second nozzle being positioned adjacent the forward end of the transfer table below the level of supply to blow gas downwardly toward the top of the stacked sheets, whereby the bar screen can be advanced to receive the new sheets for stacking while the stack therebelow is removed without reducing the conveying speeds.