Centrifugal pumps usually handle most liquid pumping services at plants. Indeed, the pumps, which come in vertical and horizontal configurations, are ubiquitous at most sites. However, such pumps do not suit highly viscous liquids; these liquids require positive displacement pumps. Unfortunately, some engineers still specify positive displacement pumps for many water services and some medium viscosity liquids in the hope of, say, greater flexibility or operational advantages. In most such cases, though, variable-speed centrifugal pumps are better choices.
Ordinary centrifugal pumps usually can tolerate solids’ levels up to around 7% — with appropriate corrections on the pump curves. Specially designed centrifugal pumps can handle up to about 15% solids. For levels exceeding approximately 20%, specially designed positive displacement pumps, such as screw pumps, often are preferable.