Efficiency

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 DIN EN ISO 17769-1. See Fig. 1 Efficiency

Pump efficiency η

• Power output ... Pump power output (P_Q) 
• Power input ... Pump input power (P) 

Mechanical efficiency η_m

• Power loss ... Mechanical power loss (P_L,m) in the pump bearings (e. g. plain and rolling element bearings) and shaft seals
• Power input ... Pump input power (P)

Internal efficiency η_i

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

Hydraulic efficiency η_h

• Power output ... Pump power output (P_Q)
• Power input ... Pump input power (P) minus power loss (P_{L,disc fric.}) caused by disc friction and mechanical power loss (P_L,m) in bearings and shaft seals

Pump set efficiency η_Gr

• Power output ... Pump power output (P_Q)
• 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)