A numerical and experimental friction analysis of reciprocating hydraulic 'U' rod seals

This article is focused on the comparison between experimental and numerical friction forces obtained for a typical hydraulic 'U' rod seal. The numerical results are obtained by the inverse hydrodynamic lubrication method. The experimental results have been obtained on an original experimental device capable of measuring the friction force between a rod and two seals. The reciprocating rod speed, the temperature and pressure in the test cell are controlled. Despite the fact that the numerical results correspond to an idealized hydrodynamic problem for smooth surfaces, it was found that the numerical model agrees with experimental data when the predicted film thickness is higher than the rod roughness but largely lower than the seal roughness. This suggests that the roughness of the seal disappears under the pressure in the sealed contact and do not play an essential role in the lubrication mechanisms. However, it is clear that for very small film thickness, the full film lubrication theory for smooth surfaces is not convenient. This may imply that in these conditions mixed lubrication cannot be ignored or that adhesion phenomena, not taken into account by the lubrication theory, can appear in the contact areas.