Three classes of automatic feeders are in general use: 1) the pile feeder, which operates by means of a jet of air which raises the sheet and brings it into contact with a suction wheel which moves it forward into the feed table. As the sheets feed off the top of the pile, the entire pile is raised to keep the top sheet always at the same level. Some pile feeders separate the sheets by means of push fingers that buckle up the corners of the paper and move it forward one sheet at a time; 2) the continuous feeder, which uses bands of webbing to carry the sheets which are previously fanned out and placed on the feeder. The bands carry the sheets around a roller and up to the feed wheels where a combing wheel advances the top sheet to a guide. At the correct moment, the guide drops and another wheel drops on the edge of the paper and carries it forward. Some continuous feeders use an air jet and suction wheel to advance the sheets; 3) the friction feeder, which operates in a manner similar to the continuous, expect that the sheets are not carried around a roller; in this case each new lift of paper must be slipped under the edge of the previous lift. (278 , 320 , 339 )
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