In a method of treating wood-fibre pulp, particularly pulp which contains recycled paper, the pulp is dewatered and then heated by means of superheated steam under pressure prior to being passed to a disperser (10), in which the pulp is finely divided. The pulp is passed from the disperser to a plug-outfeed screw (20) withouth separate departure of steam from the system. One end of the screw is closed by means of a valve device (21), so that the pulp carried by the screw will be compacted to form a plug which seals the system. The valve device (21) located at one end of the screw (20) is constructed to open when the pressure exerted thereon by the plug exceeds a pre-determined value. The invention also relates to a disperser (10) having a substantially rectangular outlet which is connected to a plug-screw (20) of the above kind.
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