Numerical analysis of a hydraulic rod seal: Flooded vs. starved conditions

• Coupled fluid mechanics, contact mechanics and load support analyses.
• Starved conditions lead to a higher friction force than with flooded conditions.
• Starvation occurs during instroke if sealed pressure during outstroke is low.

A numerical analysis of a reciprocating hydraulic rod seal, considering both flooded and starved boundary conditions, has been performed. It consists of coupled fluid mechanics, contact mechanics and load support analyses. The fluid transport, friction force, film thickness distribution, contact pressure distribution and fluid pressure distribution in the sealing zone have been computed for a polyurethane U-cup seal. Starved conditions lead to a smaller region of pressurized fluid in the sealing zone, higher contact pressures and a higher friction force than with flooded conditions. If the fluid deposited on the rod during the preceding outstroke is insufficient to fill the sealing zone, starvation will occur during the instroke. If, however, sufficient fluid is deposited, flooded conditions will occur.