Calculating the Mechanical and Volumetric Efficiencies for Check-Valve Type, Digital Displacement Pumps

Abstract

Methods for calculating the volumetric and mechanical efficiencies for hydrostatic pumps and motors are well known, and depend upon the precise volumetric displacement of the machine. It is also known that check-valve type, digital displacement pumps undergo an apparent reduction in volumetric displacement as pressures increase, and that this reduction in displacement is realized at both the input and output terminals of the machine. Recent work has been conducted to physically explain and quantify this apparent reduction in the volumetric displacement. In this present paper, the results of this previous work are used to calculate and plot the volumetric and mechanical efficiencies of a digital displacement pump, using measured values of pump efficiency and fluid bulk modulus. It is shown that without accounting for the apparent reduction in volumetric displacement, the volumetric and mechanical efficiency calculations may produce unrealistic results, and be in error by as much as 7%.