Viscous Slurry (Non-Settling) When pumping highly viscous slurries, standard HR and ER calculations cannot be used. Using figures on the next page, the head and efficiency ratio correction factors can be calculated using the yield stress or plastic viscosity of the slurry. Note that one pascal-second (Pa.s) is equivalent to 1000 centipoise (CP) for viscosity units. These correction factors will ensure that the motor has enough speed and power for the pump to perform at the required duty. It is also important to remember that the pump must be primed in order to pump. In highly viscous slurry applications, friction losses on the suction side can prevent slurry from flowing into the eye of the impeller under gravity alone. In addition to having a large enough suction pipe to minimize friction loss, one method used by deep cone thickener operators is to start the pump operating with diluted slurry and slowly increase the viscosity of the slurry while the pump is running. This way the pump will be constantly prime