Sheet brake for printing press delivery

Abstract

A delivery arrangement for a printing press having a conveyor releasing sheets one by one and which includes a jet type vacuum pump facing and closely spaced to the path of a released sheet for slowing the forward movement thereof. The vacuum pump includes a venturi nozzle having a throat at its inlet end and over which is superimposed an injector. The injector has a central opening which is in register with the throat and which is in slightly overhanging relation so that the lip of the opening forms an annular orifice adjacent the throat, the orifice being supplied with air from a pressure chamber which surrounds the nozzle. When the pressurized air flows through the orifice in the form of an annular jet, it is deflected along the wall of the throat by the so-called 'Coanda effect' and subsequently expanded, with the resulting venturi action, creating suction at the opening. The suction causes a drag on each passing sheet. A series of such vacuum pumps are spaced across the width dimension of the sheet, separately supplied by high pressure lines of small diameter but with a common exhaust at a remote point. In the preferred embodiment each pump is provided with a disc which defines a small vacuum plenum and which includes elongated transverse slits for applying suction to the sheet.