See the picture below, it is a mud hopper. Its function is to mix bentonite ,polymer. Usually it is powered by a centrifugal pump for mixing.
Working principe: Dry materials are added through the mud hopper to provide dispersion, rapid hydration and uniform mixing. Liquids are sometimes fed into the mud by a hose placed in the hopper. centrifugal pump that flows the mud at high velocity through a venturi nozzle (jet) below the conical-shaped hopper.
To combine the mud hopper with centrifugal pump, we called it jet mixing unit.