A refiner (100) for pulp or like materials, comprising a housing (10) having a chamber (16), a material-admitting inlet (18) and an outlet (20); and spaced apart first (26) and second (30) refining discs mounted in the chamber. The refiner further includes a rotary third refining disc (28) disposed in the chamber between the first and second discs and defining therewith first and second paths for the movement of material from the inlet to the outlet. The third refining disc has a central opening, and the discs are coaxial with each other. The first and second discs respectively also have first and second comminuting projections adjacent to the first and second path and the third disc has third and fourth comminuting projections adjacent to the first and second path and respectively cooperating with the first and second projections to refine the material flowing along the first and second paths. The refiner further includes a mechanism for rotating the third refining disc and comprising a shaft (50) extending through a central opening provided in the first disc, and a hub (102) rigid with the shaft and having a center (112), the hub being received in the third refining disc central opening. The hub has at least one port (136) in the hub from the first path to the second path and between the third refining disc central opening and the center of the hub. IMAGE
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