Defects coming from processing and assembly inevitably bring geometric and concentricity error to the fitting gap between valve core and frame. To overcome this problem, grooving was proven to be the most simple and effective method to reduce the hydraulic clamping force, and widely used on cylinder valve cores. Theoretically unbalanced forces kept going smaller with the increase of pressure equalizing grooves. When groove width increased, linearly the gap leakage extended. When the width was relatively small leakage was gradually reduced when depth increased. When the width was 1 mm, 1.5 mm or 2 mm, and the depth to width ratio was less than 1, leakage got worse with the increment of depth