1,200,818. Tube mills; wet grinding. ASHMORE, BENSON, PEASE & CO. Ltd. 2 May, 1968 [2 May, 1967], No. 20914/68. Heading B2A. A wet grinding mill has a.discharge compartment 38, Fig. 1, provided with radial lifter bars 39 and an annular opening and separated from a grinding zone by a discharge grate 34. Extra diluent to decrease the viscosity of pulp is added to the discharge compartment through an annular outlet. The mill is typically operated with a high pulp density, e.g. more than 75% and diluent to facilitate discharge is added via a line 41, rotatable hub 42, lines 43, T-junctions 44, Fig. 2, and nozzles in each sub-compartment of the discharge compartment formed by the lifter bars 39. The hub is arranged so that diluent is supplied to the compartment only during the last 45‹ of rotation of the mill, and the nozzles are closed by spring-loaded valves Fig. 4 (not shown) to prevent ingress of pulp when the diluent supply is off. In a second embodiment, the mill has two discharge openings and water is supplied at one side as described and at the other via a pipe 64, Fig. 5, an annular chamber 65 communicating with a partitioned chamber and pipe lines 70 which supply nozzles 72. In a further embodiment, the mill has a dual-outlet peripheral discharge, Fig. 8 (not shown) and diluent is supplied only at the lower part of the array of discharge nozzles.