To load a gathering segment of a gather-stitcher, a printed sheet feeder includes a conveyor drum that draws printed sheets from the bottom of a stack. A stop apparatus halts the printed sheets at the end of their circulating path at the conveyor drum and is disposed downstream of a guide device which, with the conveyor drum, forms a guide gap. An opening apparatus follows the stop apparatus and is disposed upstream of the printed sheets. The guide gap is adjustable by the conveyed printed sheets.

A suction-air control device for a rotatable sheet-transfer drum having suction-type grippers disposed thereon and having a journal with a rotationally symmetrical surface, includes a rotary valve disposed on the journal of the sheet-transfer drum for connecting the suction-type grippers to a stationary suction-air source. A stationary housing is provided for the rotary valve. A device controls a supply of suction air from the suction-air source to the suction-type grippers with a time lead or a time lag as a function of the rotational speed of the sheet-transfer drum. At least one suction-air bore extends from the interior of the journal to the surface thereof. One suction-air bore is connectable to the suction-type grippers. The rotationally symmetrical surface of the journal forms a sealing surface of the rotary valve. At least one closing member formed with at least one air-passage opening disposed over a defined rotational-angle range connects the one suction-air bore formed in the journal with at least one connection hole formed in the housing of the rotary valve.

Method for controlling a valve unit having a rotatable inner part, by which at least one of positive pressure and negative-pressure consumers of a sheet-processing machine is connectible to and disconnectible from a source of positive pressure and negative pressure, respectively, in accordance with an operating cycle of the sheet-processing machine, the operating cycle being repeated at a frequency variable between a minimum cycle frequency and a maximum cycle frequency, includes superimposing an adjusting speed on a rotary speed of the rotatable inner part of the valve unit; and device for performing the method.

Apparatus for opening up folded sheets has a rotary withdrawing conveyor which extracts successive folded sheets from a stack and places successive withdrawn sheets into a path between two rotary spreading elements in such a way that the front edges of the sheet in the path are adjacent to the respective spreading elements and the back of the sheet is located at a level above the front edges. The spreading elements are driven in opposite directions and carry jaws which engage the respective front edges of a sheet therebetween in first angular positions of the spreading elements, whereupon the jaws move the sheet downwardly to move its front edges apart and to separate it from the withdrawing conveyor, and ultimately release the sheet in second angular positions of the spreading elements so that the sheet can descend onto a removing conveyor. The spreading elements are rotated by a crank drive which causes each spreading element to be accelerated during one half and to be decelerated during the other half of each of its revolutions. The spreading elements are in the process of being accelerated when they assume their first angular positions, and the spreading elements are in the process of being decelerated, or their peripheral speeds are relatively low, when they assume their second angular positions.

Signatures for the manufacture of magazines, and the like, are made from preprinted webs of widths smaller than are used conventionally, with no reduction in the size of the pages of the magazine comprising the signature. The reduction in web width is accomplished by eliminating unnecessary laps on certain of the sheets comprising the signature.