An apparatus for controlling the level and discharge of a suspension or slurry of ground wood in a mechanical wood pulp forming process is described. The apparatus includes, below a wood grinder, a trough in which a slurry of ground wood is formed. The ground wood slurry is passed through a discharge port, which is located near the trough bottom, into a conduit in which a valve is located. The valve is controlled by a slurry level sensor so as to maintain the slurry level at a desired level at least higher than the discharge port. A wood chip cutter is employed at the discharge port and is sized to minimize blockage and facilitate removal of the slurry from the trough. In one form of the invention an apparatus for pressurizing the housing enclosing the wood grinder is described and in another form an open housing structure is shown and described.