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This paper reports a theoretical and experimental evaluation of the pressure transients in a hydraulic servo used to position a mass when the oil volumes on the two sides of the jack are substantially different. Application of small perturbation theory to the closed loop shows that the pressure transients are smallest when the oil volumes are equal. The worst condition is shown to be at the stroke ends, the peak pressure increasing as the volume ratio increases. Predicted values obtained by analogue computer are in good accord with measurements made on an experimental rig. An approximate guide is suggested for the relationship of peak pressures in the unequal and equal volume conditions.