Pocket ventilator

A method for controlling the injection of air into a drying pocket in a paper web drying apparatus, the web drying apparatus comprising at least three substantially axially parallel rotatable drying cylinders, a first cylinder and a third cylinder being vertically offset from a second cylinder and the web being consecutively trained thereover defining the pocket therebetween, the method comprising the steps of:

• A) providing an elongated structure mountable adjacent the first cylinder and between the first and second cylinders;
• B) mounting said structure such that a longitudinal axis thereof is substantially parallel to that of the first cylinder and such that a first lateral edge of said structure is proximal to a peripheral surface of the first cylinder thereby defining a gap therewith through which the web trained on the first cylinder may travel toward the second cylinder;
• and
• C) reducing an inflow of air dragged into the pocket by a motion of the web from the first cylinder to the second cylinder using said structure as an air block to the pocket.

An apparatus for drying a paper web, the apparatus comprising an upper row of rotatable drying cylinders, a lower row of rotatable drying cylinders, the web being trained through said rows forming at least one pocket, a porous dryer felt urging the web against the drying cylinders of said upper row while the web is trained thereover, a felt roller mounted between two successive drying cylinders of said upper row, referred as first upper and second upper drying cylinders, said felt roller guiding said felt away from said first upper cylinder and toward said second upper cylinder, a pocket ventilation system comprising means for establishing a positive pressure zone of air between said first upper cylinder and said felt roller outside said pocket causing air to penetrate in said pocket through said felt and means for producing an air jet between a cleft defined between said felt roller and said felt and a cleft defined between said second upper cylinder and said felt outside said pocket and directed away therefrom causing a negative pressure zone and consituting means for extracting moisture laden air from said pocket through said felt and, an elongated structure longitudinally mounted to said ventilation system adjacent and substantially parallel to said first upper cylinder, a first lateral edge of said structure proximal to a peripheral surface of said first upper cylinder defining a gap therewith such that the web trained thereon may travel through said gap while said structure reduces an inflow of air dragged into said pocket by a motion of the web from said first upper cylinder to said second row.