Abstract: For operating control and safety, a variable-speed close-coupled pump is direct connected to the underflow of the primary separation vessel (PSV). The desired discharge density of the PSV is 70- 80% solids in order to minimize bitumen losses. For a good pumping system, the pump discharge density should be less than 65% solids to avoid settling out of the solids in the downstream conduit. Therefore it is necessary to dilute the PSV underflow before it reaches the pump. Secondary flotation tailings, a dilute stream containing a high proportion of fine solids, is used for this purpose. The solids content of the PSV underflow is monitored by one of two alternative systems-- a torque recorder on the PSV rake shaft or a density gauge on the PSV underflow conduit. The former is used when the PSV is being fed low fines tar sand-- the latter when it is treating high fines tar sand. The close-coupled pump speed is adjusted relative to the solids content measurement to keep it at the desired 70- 80% level.