Impeller Replacement or Trimming

In situations where the output of the existing centrifugal pump is found to be excessive for the demand in the system, and where the replacement of the pump or installation of a variable speed drive is not feasible, pump capacity can be reduced by replacing the impeller with a smaller one or reducing the outside diameter of the existing diameter. Most pump casings and shafts can accomodate impellers of different sizes. In cases where a smaller impeller is not avaiable, the existing impeller can be trimmed to reduce the impeller diameter. This will reduce the impeller tip speed, and thereby also the flow and head that is delivered by the pump.

Excessive impeller trimming may have negative subsequences. Consequently, reducing impeller diameter below 70% of original size is rare.

Development Status Products

Impeller Replacement or TrimmingCosts & Benefits

Parent Process: Pump Systems
Energy Savings Potential

Efficiency improvements that can be obtained with this measure are estimated to be as following: (UNIDO, 2010):
• 20% for low efficiency base cases
• 15% for medium efficiency base cases
• 10% for high efficiency base cases

Electrical and primary energy savings potential of this technology for different countries are estimated as following (UNIDO, 2010):

  Final* (GWh/y) Primary* (TJ/y)
US 9984 109621
Canada 2979 37108
EU 7166 67326
Thailand 556 5598
Vietnam 208 2970
brazil 817 9109


CO2 Emission Reduction Potential

Total emission reduction potential, as kt CO2/y, for different countries are estimated as following (UNIDO, 2010): 

US 6017
Canada 1481
EU 3124
Thailand 289
Vietnam 102
brazil 119


Estimated typical capital costs of this measure for different system sizes (S) are:
• US $5000  for S < 37 kW;
• US $10000 for 37 kW < S < 75 kW;
• US $15000 for 75 kW < S < 150 kW;
• US $20000 for 150 kW < S < 375 kW;
• US $25000 for 375 kW < S < 745 kW; (UNIDO, 2010)

Cost of conserved energy, expressed as US $/MWh-saved, are estimated as following: (UNIDO, 2010)

US 57.0
Canada 55.5
EU 59.3
Thailand 35.5
Vietnam 33.6
brazil 37.2

Impeller Replacement or Trimming Publications

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Impeller Replacement or Trimming Guidelines

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