A Fundamental Study of a Stepped Pumping Seal

如果密封的低压侧充满液体，则润滑方程是油膜压力的线性函数。因此，可以通过静压油膜力系数、动压油膜力系数、静压泄漏系数和动压泄漏系数来评价密封的润滑和密封性能，并可以预测转速和密封压力的运行特性。另一方面，液体从密封的低压侧泵送到高压侧。然而，由于间隙宽度的增加，存在净泄漏为正的临界转速。由于润滑膜的硬度很高，如果将高压液体的工作间隙设置得很小，就可以密封而不会泄漏。一种新的仪器被用来验证理论预测。由于一种新的方法，即使在旋转状态下也可以连续精细地调整平衡比，如果密封的低压侧被气体包围，则抽油槽中会出现气蚀，并控制抽油强度。从而实现了零泄漏运行。空化边界始终是稳定的，因此没有观察到由于空气注入而导致的密封破裂现象。超过临界转速后，随着缝隙宽度的变化，会出现渗漏现象。实验结果表明，这种变化是由空化的产生或消失引起的。确定了润滑和密封性能的设计准则。

If the low pressure side of a seal is filled with liquid, the lubrication equation is a linear function of film pressure. Accordingly, the lubricating and the sealing performances can be evaluated by hydrostatic film force coefficient, hydrodynamic film force coefficient, hydrostatic leakage coefficient and hydrodynamic leakage coefficient, and operating characteristics can be predicted for revolutional velocity and seald pressure.In this seal, noncontacting operation without wear can easily be attained due to Raileigh-step effect under rotation. On the other hand, liquid is pumped from low pressure side to high pressure side of the seal. However, critical speed exists over which net leakage is positive due to increased gap width. Since the stiffness of the lubricating film is very high, a high pressure liquid can be sealed without leakage if its operating gap is set to be very small. A new apparatus was used to verify the theoretical predictions. Continuous and fine adjustment of balance ratio is possible even under rotation due to a new method.If the low pressure side of the seal is surrounded with gas, cavitation appears in the pumping grooves, and it controlls the pumping intensity. Zero leakage operation is thus attained. Cavitation boundary was always stable, hence seal breakdown phenomenon due to air injection was not observed. Over the critical speed, leakage appears with descrete change of gap width. Experimental results suggests that the change is caused by generation or disappearance of cavitation. Design criteria for lubricating and sealing performances are settled.