Abstract:This paper researched the stiction and action delay phenomenon occurred in spool valve based on the analysis of valve motion mechanism, and proposed that the radial clearance could change in service time. The unproper designed clearance is the reason of stiction. Utilizing elastic theory and thermal deformation theory, a formulation of valve sizes was induced with consideration of surface residual stress. And the maximum deformation of valve with diameter 13 mm was calculated as 2.9μm in extreme temperature. In order to consider the valve sleeve deformation induced by oil pressure, a finite element model of static structural was developed. The real fitting clearance should be larger than the total deformation 5.19μm which approximately is 5μm. Furthermore, the leakage versus clearance was calculated. The maximum radial clearance was set to be 8μm to satisfy the expected leakage. The design method and idea employed in this paper could be useful in design new spool valve.