Patent ID: 7981248

Claim:
A method of treating pulp including the formation of a pulp web on a porous surface of a rotating drum cylinder having a lower drum portion in a vat of pulp slurry and a radial array of filtrate conduits draining filtrate passing through the porous surface to an axial filtrate chamber, the method comprising: rotating the drum about an axis of the drum; as the porous surface of the drum rotates through the vat, drawing filtrate from the slurry through the porous surface by a suction applied to the filtrate conduits; draining the filtrate from the filtrate conduits to the axial filtrate chamber and to a filtrate suction conduit extending to an elevation below the vat; forming a pulp mat on the porous surface which passes filtrate and substantially blocks fibers; removing the pulp mat on the porous surface from the vat as the drum rotates; continuing the draining of filtrate from the filtrate suction conduit as the filtrate conduits are rotated through angular positions during which liquid filtrate applied to the surface of the pulp fills the conduits, and after liquid filtrate is no longer applied to the pulp mat and before excessive gases passing through the porous surface enter the filtrate conduits, switching a fluid flow downstream of the filtrate conduits from a path directed through the filtrate suction conduit and to a gas vent passage, wherein the gas vent passage is offset and below the axis of the drum.