Properties of Liquids Section 1

Determination of Pump Performance When Handling Viscous Liquids

The performance of centrifugal pumps is affected when handling viscous liquids. A marked increase in brake horsepower, a re-duction in head, and some reduction in capacity occur with moderate and high viscosities.

Fig. 5. (Performance Correction Chart) provides a means of determining the performance of a conventional centrifugal pump handling a viscous liquid when its performance on water is known. It can also be used as an aid in selecting a pump for a given app Fig. 5. (Performance Correction Chart) are averaged from tests of conventional single stage pumps of 2-inch to 8-inch size, handling petroleum oils. The correction curves are, therefore, not exact for any particular pump.
When accurate information is essential, performance tests should be conducted with the particular viscous liquid to be handled.
sect d3 fig5
                                                           Figure 5

Limitations on Use of Viscous Liquid Performance Correction Chart

Reference is made to Fig. 5. (Performance Correction Chart) This chart is to be used only with in the scales shown. Do not extrapolate.

Use only for pumps of conventional hydraulic design, in the normal operating range, with open or closed impellers. Do not use for mixed flow or axial flow pumps or for pumps of special hydraulic design for either viscous or non-uniform liquids.

Use only where adequate NPSH is available in order to avoid the effect of cavitation.

Use only on Newtonian (uniform) liquids. Gels, slurries, paper stock and other non-uniform liquids may produce widely varying results, depending on the particular characteristics of the liquids.

Symbols and Definitions Used in Determination of Pump Performance When Handling Viscous Liquid.

These symbols and definitions are:

Qvis = Viscous Capacity, gpm
The capacity when pumping a viscous liquid.

Hvis = Viscous Head, feet
The head when pumping a viscous liquid.

Evis = Viscous Efficiency, per cent
The efficiency when pumping a viscous liquid.

bhpvis = Viscous Brake Horsepower
The horsepower required by the pump for the viscous conditions.

Qw = Water Capacity, gpm
The capacity when pumping water.

HW = Water Head, feet
The head when pumping water.
sp gr = Specific Gravity

CQ = Capacity correction factor

CH = Head correction factor

CE = Efficiency correction factor

1.0 QW = Water Capacity at which maximum efficiency is obtained.

The following equations are used for determining the viscous performance when the water performance of the pump is known:

sect d3 equat1
C0, CH and CE are determined from Fig. 5 which is based on the water performance.

The following equations are used for approximating the water performance when the desired viscous capacity and head are given and the values of CQ and CH must be estimated from Fig. 5 using Qvis and Hvis, as:

sect d3 equat2