Help for calculating the correction factors for centrifugal pump water performance due to viscosity

Applets are programs based on the java language that are designed to run on your computer using the Java Run Time environment.

Centrifugal viscosity correction factors are based on tests that were done by the Hydraulic Institute www. and this help page gives a brief description of the method devised to calculate the viscosity correction factors. You can find more information in The Hydraulic Institute's Standards book.

This applet is designed to help you do corrections to the data on the water performance curve due to the effect of viscosity. Centrifugal pumps are tested with water. The results of these tests is plotted on a graph of flow vs total head called the characteristic curve or performance curve. Superimposed on this curve is the value of the efficiency for various operating points. The fluid's viscosity will affect the performance of the pump. The viscosity of water is 1 centiStoke(cSt) at 60 degrees Fahrenheit. Fluids that have a higher viscosity than water, say 4 cSt and higher, will have an influence on the pump's performance and will adversely affect the flow, head and efficiency. Therefore, three correction factors have to be determined: flow, head and efficiency. This help page will explain how to calculate these three correction factors.

First, establish the operating or design point, that is total head and flow for the viscous fluid of the pump, based on your system requirements. Using the characteristic curve of the pump establish the efficiency at the operating point. Enter these numbers in the - Viscous Performance Design Point - frame of the applet. The program can only do calculations for flows between 10 and 10000 gpm and between 6 and 600 feet of total head. The program will let you know if you are outside these limits.

Next enter the viscosity of the fluid in centiStokes and it's specific gravity. The viscosity limits are between 4.3 and 3300 cSt.

If the flow is higher than 100 gpm another textbox called - % flow of B.E.P. - (Best Efficiency Point) will appear. B.E.P. is the best efficiency point of the pump for a given impeller size and speed. If possible, it is desirable to select a pump model, impeller size and speed in such a way that the design point corresponds to the B.E.P. It is not always possible to find a pump where this occurs and sometimes the flow rate will be slightly more or less than the flow rate at the B.E.P. For your selection, establish the percent of flow of your design point with respect to the flow at the B.E.P. and enter this into the - % flow B.E.P. - textbox. The program has data for the head correction factor that correspond to: 120%, 100%, 80% and 60% flow of B.E.P.. if you enter data that is outside of 60 and 120% the program will warn you. If your data is in between these values, for example 105%, the program will choose the closest data to your % flow of B.E.P. value. When you have entered all the data, press the Calculate button.

For flows between 10 and 100 gpm, the pump is assumed to be running at it's B.E.P. so there is only one correction factor for head.

The correction factors are based on the following charts from the Hydraulic Institute, please do not copy or otherwise distribute these charts, they are available in the Standards book at they are provided here to justify the source of the information. I have done a regression analysis on each one of the lines and curves of the graphs whcih provides a formula that the program can use to calculate the correction factors and save you some time and effort.

For more information on viscosity correction see the Goulds pump catalogue Technical Section.

Viscosity data of common liquids can also be found int the Goulds pump catalogue.

The Goulds pump catalogue also provides more information on atmospheric pressure vs. elevation.