Pump Operation at Off-Design Conditions

  • Igor J. Karassik
  • Terry McGuire


Theoretically, as long as the NPSH available is greater than the required NPSH, a centrifugal pump is capable of operating over a very wide range of capacities. As explained earlier, the exact operating capacity is determined by the intersection of the pump head-capacity curve with the system-head curve. This operating capacity can be changed by altering either one or both of these curves: varying the pump speed will alter the head-capacity curve, whereas throttling the pump discharge will alter the system- head curve. But at any given speed, the performance of a centrifugal pump is at its optimum at only one capacity point, and that is the capacity at which the efficiency curve reaches its maximum; at all other flows, the geometric configuration of the impeller and of the casing no longer provide an ideal flow pattern. Our definition of “off-design” conditions must therefore be any condition wherein a pump is required by the force of circumstances to deliver flows either in excess of or below the capacity at best efficiency.


Centrifugal Pump Cavitation Erosion Thrust Bearing Total Head Specific Speed 
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Copyright information

© Chapman & Hall 1998

Authors and Affiliations

  • Igor J. Karassik
    • 1
  • Terry McGuire
    • 1
  1. 1.Ingersoll-Dressor Pump CompanyUSA

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