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viscosity correction


    The performance data provided by pump manufacturers are valid for water. If another fluid is pumped this has an influence on the performance of the pump. The viscosity has an effect on the pump head, the power absorbed and the capacity (flowrate). It is no surprise that, for a higher viscosity, all effects are in an unfavourable direction: The power increases, the flowrate decreases and the head also decreases. These effect are all mainly a result of the increased 'disk friction' that the impeller experiences.

    The Hydraulic Institute published two charts with correction factors that cater for this: one for a flowrate up to 100 Gallons per minute and one for the range from 100 to 10 000 gallons per minute. Reading them is not too difficult, takes a bit of time and requires that you carry the charts with you. This routine returns them, which is faster, more accurate and more convenient.

    To use them, the correction factors can be applied using:

    viscosity corrections

    This gives you a point on the pump curve for the viscous fluid, with:

  • QViscous = Capacity of the pump using viscous fluid
  • HViscous = Head of the pump using viscous fluid
  • etaViscous = Efficiency of the pump using viscous fluid
  • PViscous = Pumping power using viscous fluid
  • CQ = Capacity correction factor
  • CH = Head correction factor
  • Ceta = Efficiency correction factor
  • QWater = Capacity of the pump for water
  • HWater = Head of the pump for water
  • etaWater = Efficiency of the pump for water
  • PWater = Pumping power for water
  • The values returned are related to the best efficiency point (BEP) of the pump curve. With these values the curves can be re-drawn for the higher viscosity.

    To use the free online calculation routine click on viscosity corrections

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