An apparatus for dissolving pulp and producing a paper pulp suspension for use in papermaking. The apparatus comprises a container having a stirring rotor therein and, in the area of the lower wall of the container, an outlet chamber to which is connected a dilution water inlet pipe and an outlet pipe. A plate connected to the stirring elements defines the upper extremity of an outlet space and has a plurality of radial ribs connected thereto and extending downwardly into the outlet chamber. As the plate is rotated, the ribs cause mixing of the suspension which flows downwardly into the outlet chamber together with the dilution water to thereby produce a suspension having a lower consistency than the suspension within the container itself. In order to prevent dilution of the suspension within the main area of the container, a retaining wall is provided on the lower surface of the plate at a position radially outward of the axis of rotation. This wall substantially impedes the flow of the more dilute solution and water between the plate and wall of the container into the main portion of the container itself.