Bottom sheet separator-feeder

Claim 1

Sheet handling apparatus including first and second paper trays having a common bottom sheet separator-feeder in which said trays are relatively movable for operatively associating said trays one at a time with the sheet-feeder, said sheet separator-feeder including vacuum feed means extending through at least the front end of each tray when it is associated therewith for acquiring and advancing the bottom sheet in a stack in the tray, air injection means disposed adjacent the front of the tray to inject air into the front end of said stack, and blower means for creating negative pressure at said vacuum feed means and for creating positive pressure at said air injection means, characterised by means for varying the air pressure at the air injection means relative to the sheet acquisition pressure at the vacuum feed means depending upon which tray is associated with said sheet feeder, and wherein said first tray is mounted for movement between a lowered, operative position in which it is seated within the second tray and operatively associated with said sheet separator-feeder and a raised, inoperative position in which it is spaced over said second tray and the latter is operatively associated with the sheet separator-feeder, said air injection pressure being reduced relative to said sheet acquisition pressure when said first tray is in its raised position; and including a common blower for creating negative pressure at the vacuum feed means and for creating positive pressure at the air injection means, duct means extending between said blower and said air injection means, a pressure relief valve in said duct means and means for controlling said pressure relief valve to be open when said first tray is in raised position and closed when said first tray is in lowered position, said first tray being adapted to engage said pressure relief valve to close it when said first tray is in its lowered position.