Metered Leakage Prediction for Reciprocating Valve Stem Seals

The development of any sealing product invariably involves some form of physical leakage testing, and although this evaluates the performance of the product, it gives no insight to the fundamental sealing mechanism of the design. Elastohydrodynamic lubrication theory was used to study this problem. The study of hydrodynamic lubrication, where there is fluid flow, is, from a mathematical standpoint, the application of a reduced form of the Navier-Stokes equation with the continuity equation. This equation is well known as the Reynolds equation. However, normally, the Reynolds equation is derived from Cartesian co-ordinates where the curvatures of surfaces are ignored. However, a valve stem seal (VSS) works in an axisymmetric environment. This paper discusses the development of the elastohydrodynamic lubrication theory in a cylindrical co-ordinate system and its usefulness in the prediction of metered leakage across a valve stem seal.