Understanding overall efficiency of hydrostatic pumps and motors


  • Gustavo Koury Costa Department of Mechanics, Federal Institute of Science and Technology of the State of Pernambuco, Recife, Brazil
  • Nariman Sepehri Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB, Canada




overall efficiency, hydraulic motors, Hydraulic pumps


Pump and motor efficiency is a complex subject, to such an extent that most of the available models describing efficiency today rely on experimental data. In spite of that, mathematical models relating efficiency to pressure and angular speed have been proposed throughout the years. In all these models, volumetric and mechanical efficiencies are separately built from flow and torque losses relations. The overall efficiency model is then obtained by multiplying the volumetric and the mechanical efficiency equations. In this paper, we show that the overall efficiency equations must be developed from an energy balance and show that the simple multiplication of mechanical and volumetric efficiencies can potentially lead to inaccurate results. We then obtain a generalised equation relating the overall efficiency to pressure and angular speed for both pumps and motors and show how the resulting model can be fitted to actual experimental data.


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Author Biographies

Gustavo Koury Costa, Department of Mechanics, Federal Institute of Science and Technology of the State of Pernambuco, Recife, Brazil

Gustavo Koury Costa works at the Federal Institute of Education, Science and Technology in Recife-PE, Brazil. He received his MSc and DSc degrees from the Federal University of Pernambuco, Brazil. He did his Post- Doctorate in the University of Manitoba, Canada, having become adjunct professor for the Faculty of Mechanical Engineering.

Nariman Sepehri, Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB, Canada

Nariman Sepehri is a professor with the Department of Mechanical Engineering, at the University of Manitoba, Canada. He received MSc and PhD degrees from the University of British Columbia, Canada. His research and development activities are primarily centred in all fluid power-related aspects of systems, manipulation, diagnosis, and control.


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