The closing and opening characteristics of the diffused self-pumping hydrodynamic mechanical seal

The closing and opening characteristics are crucial in determining whether the diffused self-pumping hydrodynamic mechanical seal (DSPHMS) can separate the seal rings and maintain non-contact steady-state operation. Assuming critical opening film thickness, this study investigates how these characteristics change with variations in the effective radius of the bellow, bellow stiffness, medium pressure differential, and rotating speed. A steady-state operation control equation for the DSPHMS, consisting of medium pressure, an elastic element, and a fluid film on the end faces, was established. Based on the axial force balance criterion, the impact of these factors on the steady-state operating rotating speed range under variable film thickness conditions was analyzed. Results indicate that the opening characteristics positively correlate with the effective radius of the bellows, the medium pressure differential, and the rotating speed, but negatively correlate with the bellow stiffness. However, the closing characteristics show positive correlations with the bellow stiffness and medium pressure differential and a negative correlation with the effective radius of the bellow. Rotating speed has minimal effect on closing characteristics. Additionally, the steady-state operating rotating speed range narrows with increasing effective radius and medium pressure differential, but broadens with the greater bellow stiffness. These findings suggest that improving opening performance reduces adaptability to variable and extreme operating conditions. The results provide a theoretical basis for designing the lift-off rotating speed and steady-state operating rotating speed range and optimizing the operating condition range of the DSPHMS.