This paper describes an investigation into the effects of fluid properties on piston pump flow losses through experimentation and modeling. The case drain and pressure compensator control flow rates of a variable-displacement axial piston pump were measured under a wide range of conditions. Synthetic ester, high bulk modulus, VI-improved and single grade mineral oils were evaluated. The high bulk modulus fluid exhibited 20% lower flow losses than a conventional mineral oil of the same viscosity grade. The modeling effort extended the flow loss analysis of Jeong to account for compensator control of the pump displacement. Comparisons between model predictions and measured flow losses showed good agreement. Stepwise regression analysis of the model parameters disclosed that the compressible flow term had a greater coefficient of determination than the turbulent or laminar flow terms. These findings demonstrate the potential of combining comprehensive fluid analysis with modeling to optimize fluids for the efficient transmission of power.

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