Growing energy costs continue to motivate the use of variable-displacement pumps in hydraulic systems with varying flow requirements. This study presents an analysis of the internal pressure-distribution in variable-displacement vane-pumps, and of the resulting forces and torques applied to their mechanisms and shafts. This analysis is essential to the study of the pump dynamics and control, the pump design, and the selection of the pump bearings. These forces are shown to be a function of the line pressure, the pump eccentricity, the shaft rotational speed, the fluid bulk modulus, the fluid viscosity, and the design geometry. These forces are composed of two periodic components: a continuous component due to the exposure of chambers to the line port, and an intermittent component due to a hydraulic-lock phenomenon. A design criterion is formulated which eliminates magnitude variations in the continuous component of the radial shaft-load.

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