In order to accurately predict the reverse pumping rate of rotary lip seals, a mathematical model of lip seal under steady state was developed adopting the JFO cavitation boundary condition based on mass conservation. The lubrication governing equation was solved by streamline upwind finite element method. Then, the effects of operating parameters and microundulation structural parameters on the reverse pumping rate were investigated. The results show that the reverse pumping rate increases with the rotary shaft running speed, while decreases with the sealed pressure, or even turns to leakage rate. The reverse pumping rate increases with the microundulation circumferential amplitude, wavelength and the maximum circumferential deformation, while decreases with the microundulation axial profile amplitude. The lip seal shows reverse pumping effect only when the location of the maximum circumferential deformation is close to the oil side, and the closer it is to the oil side, the larger the reverse pumping rate is.

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