Experiments and modeling of zero leakage backward pumping mechanical face seals

Abstract

There is an ever-growing interest in developing face seals with zero leakage. Environmental concerns, clean operation requirements, and zero maintenance requirements provide a need for zero leakage, long-life oil seals. There are several types of designs that can be considered for such applications. The interest in this paper is a face seal having backward-pumping face features. Such seals can be designed to operate with zero leakage against some pressure. In this paper the design of one such zero-leakage seal is described. The seal was manufactured and numerous experiments were conducted. Many different problems were identified and the solutions were implemented. It was shown that such seals can operate with zero leakage under most conditions, but some small leakage traces might occur in some instances. A backward-pumping seal develops liquid cavitation regions in the sealing interface. Modeling of the seal shows that the predictions are very sensitive to assumed boundary conditions. Considerable modeling difficulty arises when using conventional cavitation assumptions. In this paper a lubrication model based on a fluid consisting of foamy or bubbly oil is developed. Solutions provide continuity of gas and liquid flows. Nonlinear equations are developed and solved. The model is applied to the zero-leakage seal above, and the predicted results are consistent with the known experimental results. Conclusions are made showing that the model has potential for use in other air/oil sealing applications.