nip rollers 36 38 which are arranged to grip the sheets as they are fed through the gap 33 and to deliver them onwards for further processing as indicated by arrow 39 means are provided to direct jets of air from each side of the feed mechanism towards the bottom sheet of the stack 11 of sheets to assist in its separation from the bottom of the stack these air jets are indicated schematically at 40 in fig3 in operation a stack 11 of sheets is laid on the feed mechanism with the front edges of the sheets in contact with the restraining plate 32 the position of the plate 32 is adjusted to set an appropriate gap 33 and the position of the roller 30 is then adjusted in relation to the housing in order to produce an amount of protrusion of the belt 26 which is appropriate for the particular type e g thickness density material of sheets which are to be fed by the mechanism then air is blown towards the sides of the bottom sheet of the stack through jets 40 and the belt 26 is driven intermittently from drive shafts 22 24 with the synchronised intermittent generation of suction within the chamber 14 the bottom sheet of the stack 11 is attracted towards and is held down against the belt 26 by the suction is separated from the remainder of the stack is corrugated at its centre by the distortion.