For viscosity corrections, previous versions of PUMP-FLO used a set of equations that were derived from Figures 71 and 72 of the Hydraulic Institute Standards (14th edition, Hydraulic Institute, 1983).  Two sets of equations were used: the equations based on Figure 71 were for pumps with a best efficiency point (BEP) of less than 100 US gpm (water performance); the equations based on Figure 72 were for pumps with a BEP greater than 100 US gpm (water performance).

The latest release of PUMP-FLO no longer uses these equations.  Instead it incorporates the viscosity correction method outlined in "Effects of Liquid Viscosity on Rotodynamic (Centrifugal and Vertical) Pump Performance" (ANSI/HI 9.6.7, 2004).

The correction equations in HI 9.6.7 are based on a pump performance. Reynolds number adjusted for specific speed (parameter B), which has been statistically curve-fitted to a body of test data.  The parameter B is calculated as follows:

B = 26.6 * [(n1/2) * (HBEP-W0.0625)]/[(QBEP-W0.375) * (N0.25)]

n = kinematic viscosity in centistokes of the pump liquid

QBEP-W = the water flow rate (US gpm) at the best efficiency point

HBEP-W = the water head (ft) per stage at the best efficiency flow rate

N = pump speed (rpm)

The test data includes conventional single-stage and multi-stage pumps, and covers the following ranges:

1 cSt < n < 3000 cSt

13 US gpm < Q (@ BEP) < 1140 US gpm

20 ft < H per stage (@ BEP) < 430 ft

B < 40

NOTE: PUMP-FLO uses 4.3 cSt for the lower limit of the viscosity range (this corresponds to the lower limit of the viscosity in Figures 71 and 72 of the HI Standards 14th edition, and is the value used in previous versions of the program).

As in previous versions of the software, PUMP-FLO reports the viscosity correction factors at BEP.  At BEP, the head correction factor (CH) is equal to the flow correction factor (CQ); at flow rates other than BEP flow, CH varies.

The correction equations are not exact for any particular pump, but are rather a generalized method based on empirical data.  This method may be applied to pump performance outside the ranges listed above, however the uncertainty of the performance prediction is increased.  In such situations, PUMP-FLO still corrects the pump performance data, then issues a warning to indicate that there is increased uncertainty in the performance prediction.

For a complete listing of the correction equations, please see "Effects of Liquid Viscosity on Rotodynamic (Centrifugal and Vertical) Pump Performance" (ANSI/HI 9.6.7, 2004).