Method and device for ventilating pocket spaces in a multi-cylinder

Abstract

A method and apparatus for ventilating pocket spaces in a multi-cylinder dryer of a paper machine, in particular a high-speed paper machine whose running speed is higher than about 800 meters per minute, in the area of a so-called twin-wire draw. In the twin-wire draw, the drying cylinders in the drying group are arranged in two rows placed one above the other, in which rows the successive cylinders are placed in the upper row and in the lower row as interlocked. In each cylinder group, there are two drying wires, an upper wire and a lower wire for pressing the paper web against heated faces of the drying cylinder while being guided by guide rolls placed in gaps between the cylinders. The paper web runs as free draws between the rows of cylinders. Pocket spaces are formed in the area between the free draws of the web and the upper wire and its guide roll and the drying cylinder in the lower row and, in a corresponding manner, adjacent pocket spaces are formed in the area between the free draws of the web, the lower wire, its guide roll, and the drying cylinder in the upper row. The pocket spaces are ventilated by pumping air induced by the wire in the multi-cylinder dryer, wherein, at the inlet side of the guide roll, the wire pumps air into the pocket spaces through the wire and wherein the wire pumps air out of the pocket spaces at the outlet side of the guide roll of the wire. Air being pumped out through the wire on its run at the outlet side from the guide roll to the following cylinder is limited as compared with free pumping-in and pumping-out so as to control the pressure level and/or the flow status in the pocket spaces.