Reynolds Equation and Elastohydrodynamic Lubrication in Metal Seals

Oil film profile and pressure distribution between a metal seal and a reciprocating hydraulic jack rod have been measured. A rapidly diverging oil film, which would normally be expected to cause rupture of the fluid and severe cavitation, was observed near the centre of the contact, but the corresponding pressure in this region was found to be high; the two measurements therefore appeared to be incompatible. A re-examination of the inverse Reynolds equation, however, shows that in certain circumstances rapidly diverging oil films are consistent with high values of hydrodynamic pressure; these circumstances are defined. Experimental results are presented which demonstrate that a metal seal may satisfy these conditions. A numerical solution of the elastohydrodynamic equations is described briefly, and the theoretical results are compared with those from the experiments. Reasons why these unusual conditions should exist in the seal are discussed. It is concluded that working in this elastohydrodynamic régime is undesirable.