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Abstract

Method and apparatus in the headbox of a paper machine and in its approach pipe system. In the headbox, pulp suspension is fed through the approach pipe system and a pressure screen arrangement, if any, to a distributing header part, from which the pulp suspension flow is conducted through a turbulence generator section and further to a lip section. A pulp suspension jet is discharged from a lip aperture of the lip section onto a forming wire or into a throat defined by a pair of forming wires. At least part of the approach pipe system, the distribution header part, and the turbulence generator section are arranged to have two or several substantially parallel pulp suspension flow passages. The different passages operate substantially simultaneously in parallel, when the headbox has been set to operate in a higher flow rate range. One or several of the substantially parallel flow passages are completely closed after the turbulence generator section, when the headbox is being set to operate in a lower flow rate range. With the aid of the substantially parallel flow arrangement, the flow rate of the headbox has been arranged to be adjustable substantially in a range from maximum flow rate to minimum flow rate, in which a ratio of maximum flow rate/minimum flow rate is about 4.

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First Claim