Abstract: Dewatering solid suspensions such as gypsum semihydrate in water of varying concentrations down to a low residual moisture by flowing the suspension into a hydrocyclone to partially dewater the suspension and then to a pusher centrifuge to produce solids of low residual moisture and controlling the volume inflow to the hydrocyclone to maintain, despite variations in concentrations of solids in the feed, a constant amount of solids per unit time. Variations in power consumption of the pusher centrifuge or specific gravity of the suspension before it enters the pusher centrifuge may be used to determine changes in volume inflow to maintain a constant solids content per unit time entering the hydrocyclone. Reduction of the solids to a uniform and low residual moisture content and avoidance of operating difficulties such as clogging or inadequate separation of the water results.