a high speed machine that inserts about twelve thousand sheets or stacks of sheets of paper per hour into the same number of envelopes . a first table delivers an elongate horizontal queue of thousands of envelopes to an envelope hopper . a second table , parallel to the first table , includes a plurality of independently - controllable sheet feeders and delivers individual groups of stacked sheets to an envelope insertion station that is transversely spaced apart from the envelope hopper . a third table is disposed transversely to the first two tables and includes the envelope insertion station . clamps carried by an elongate sprocket chain mounted in the third table sequentially remove envelopes from the bottom of the envelope hopper and pull them past an envelope flap - opening structure to the envelope insertion station where the envelopes are opened by a puff of air . the envelopes are then pulled past a moistening device , an envelope flap - closing device , and a roller that seals the envelopes and ejects them from the third table to a collection station . pusher members that push the sheets into the envelopes at the envelope insertion station are mounted on a high speed rotary assembly that eliminates the back - and - forth motion of earlier pusher members .