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Pump efficiency

Pump efficiency (η) is also referred to as coupling or overall efficiency and characterises the ratio of pump power output (PQ) to power input (P) for the operating point in question:
Pumpenwirkungsgrad_Formel_1

Pump efficiency (η) is the product of mechanicalm) and internal efficiencyi).

Pumpenwirkungsgrad_Formel_2

The best pump efficiency (ηopt) is the highest efficiency for the rotational speed and fluid handled as specified in the delivery contract.

For centrifugal pumps whose mechanical design does not clearly separate the pump shaft from the drive shaft, such as is the case with close-coupled pumps and submersible motor pumps, the efficiency of the pump setGr) is specified in place of pump efficiency (see DIN 24 260) (Gr stands for group). This figure describes the ratio of pump power output (PQ) to the power consumed by the driver (see Drive), which is measured at an agreed position (e.g. at the terminals of the motor or where an underwater cable starts).

Achievable pump efficiency is very much a function of specific speed as well as the size and type of the pump and increases as these two variables increase. Reference values for achievable efficiency of modern centrifugal pump types are based on statistical analyses of the values for existing
pumps. See Figs. 1 and 2 Pump efficiency

Pump e_ciency: Attainable efficiency η of single-stage volute casing pumps without diffuser, and efficiency gain Δη Fig. 1 Pump efficiency: Attainable efficiency η of single-stage volute casing pumps without diffuser, and efficiency gain Δη by using a diffuser, as a function of specific speed ns Pump efficiency: Attainable efficiencies η of multistage high-pressure pumps (acc. to KARASSIK) as a function of specific speed Fig. 2 Pump efficiency: Attainable efficiencies η of multistage high-pressure pumps (acc. to KARASSIK) as a function of specific speed ns