A numerical model of an elastomeric reciprocating hydraulic rod seal has been constructed. The model consists of coupled fluid mechanics, deformation mechanics, and contact mechanics analyses, with an iterative computational procedure. The fluid mechanics analysis consists of the solution of the Reynolds equation, using flow factors to account for surface roughness. Deformation of the seal is computed through the use of influence coefficients, obtained from an off-line finite element analysis. The contact mechanics analysis uses the Greenwood and Williamson model. The seal model is used to predict leakage rate, friction force, fluid and contact pressure distributions, and film thickness distribution. Results for a typical seal show that the seal operates with mixed lubrication, and the seal roughness plays an important role in determining whether or not the seal leaks.

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The recent development of an elastohydrodynamic lubrication rod seal model has made possible the simulation of hydraulic seal performance for design and selection purposes. This model consists of coupled fluid mechanics, contact mechanics, deformation, and thermal analyses. The model yields predictions of such characteristics as leakage and the friction force on the rod, as well as film thickness, fluid pressure, and contact pressure distributions. The model has been used in the selection process for the rod seal in a mini-actuator of a fluid power orthosis (orthopaedic device used to improve the function of movable parts of the body). Two alternative seals have been analysed and compared, an O-ring seal and a U-cup, both of polyurethane.