I understand that rotary pumps perform well when handling viscous liquids. How does the performance change as the liquid viscosity increases?
A. A pumped fluid’s viscosity typically affects pump ratings as follows: The net positive inlet pressure required (NPIPR) increases with increasing viscosity, as shown in Figure A. The required pump input power (Pp) increases with increasing viscosity, as shown in Figure B. The maximum allowable pump speed (n) decreases with increasing viscosity. The pump slip (S), as shown in Figure C, decreases with increasing viscosity. Exercise care in applying these generalities to non-Newtonian fluids, as the viscosity may change within the pump due to shear. When the apparent viscosity of a non-Newtonian fluid can be determined, then these generalities can be applied. Because the exact relationship between viscosity and pump ratings depends on the pump design and on the application conditions, refer to the pump manufacturer’s published data for a particular pump, or consult the manufacturer when considering viscous fluid pump applications. Energy put into a fluid to overcome resistance to shear
