Discuss how pumping water differs from pumping 40% Propylene Glycol. Does the impeller have to change trim to produce the same flow and head with a more viscous solution?

Answer: 

          Centrifugal pumps work best on relatively “thin” (i.e. low viscosity)fluids. The fluid velocities inside the passages of centrifugal pumps are generally much higher then in positive displacement pumps – and higher velocities mean more viscous drag, i.e. lower efficiencies. Typically, centrifugals are not used above 100 cP or so, although there are exceptions. Hydraulic Institute Standards have a chart to de-rate the pump flow, head and efficiency (which then allows you to calculate horsepower), as a function of viscosity.

Using this chart, a new (de-rated) H-Q and efficiency curves can be constructed. The impeller diameter is then determined as usual, using the affinity laws.