Numerical Analysis of Lateral Forces Acting on Spools of Hydraulic Components

This paper deals with the analysis of pressure distribution within the fluid film in the clearance between spool and sleeve of hydraulic components, in order to predict the value of the locking force induced by unbalanced pressure acting on tapered geometries. Particular care is devoted to the investigation of the lateral force dependency on clearance and eccentricity of the spool. Some theoretical results are presented, obtained solving (by the finite difference method) the two dimensional Reynolds equation for the fluid film. These results are then compared to those deriving from a generally adopted predictive formula. Results show remarkable differences, up to 70 %, in presence of high values of eccentricity. Moreover, an analogous Reynolds' based solution is performed for a tapered geometry of the spool with one balancing groove, with particular attention to the influence of its length and position on resulting locking force and leakage flow. Also the locking force reducing effect of a balancing groove is characterized, and a saturated behavior when the groove is placed very close to the high pressure spool side has been found.