Pulp and paper applications create some of the most challenging problems for pumps. Fluids change viscosity as they move through the system, and starches and clay wreak havoc on pump rotors. Tony Peters, managing director of AxFlow Limited, explains how to best tackle these tough-to-handle slurries and choose the best pump for your application. A dilatant liquid is one in which the viscosity increases with shear. Its opposite, a thixotropic material, thins with shear. Within the paper and pulp industry, the problem that dilatancy poses is that it can lock up the pump. As a result, both the pump and its mechanical seal can be damaged. Starch, clay, and other slurries made up of fine particles become dilatant when they reach a certain, product-specific concentration. Starch slurries generally become dilatant at concentrations above 4% w/w solids; some coating slurries become dilatant at around 70% w/w solids.
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