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Efficiency (η) is generally understood as a ratio used to characterise the quality of power conversion in energy applications.

In particular in the case of "work-producing" machines (e. g. pumps, compressors, fans) and prime movers (e. g. turbines), efficiency describes the ratio of power input to power output, where the power output is the power input minus power losses:

In centrifugal pump engineering, the three terms (power output, power input and power loss) have different meanings depending on the type of efficiency being described in accordance with EN 12723. See Fig. 1 Efficiency

Efficiency: Losses, efficiencies Fig. 1 Efficiency: Losses, efficiencies

Pump efficiency η

Mechanical efficiency ηm

Internal efficiency ηi

  • Power output ... Pump power output (PQ)
  • Power input ... Pump input power(P) minus mechanical power loss (PL.m) in pump bearings and shaft seals

Hydraulic efficiency ηh

  • Power output ... Pump power output (PQ)
  • Power input ... Pump input power (P) minus power loss (PL,disc fric.) caused by disc friction and mechanical power loss (PL,m) in bearings and shaft seals

Pump set efficiency ηGr

  • Power output ... Pump power output (PQ)
  • Power input ... Drive input power, measured at a location to be agreed (e. g. terminal box of the electric motor, start of an underwater cable)