Hydraulic Lock Forces on Tapered Pistons

Abstract

When a piston subject to an axial pressure drop has to be moved periodically along a bore sticking often occurs owing to hydraulic locking between the piston and the bore. The locking is caused by the hydrostatic pressures acting along the annulus between the two surfaces. The hydraulic instability may be reduced by using a piston tapered to give a converging film shape in the direction of flow, and this paper considers a large number of tapered configurations. The hydraulic pressures are calculated by a solution of Reynolds' two-dimensional equation using a digital computer, and the resultant force and its line of action are obtained. From these results empirical equations for the locking force and its line of action are derived which are valid for a wide range of conditions. The values predicted by the equations agree well with experimental and theoretical results given in the literature.