MECHANICAL FACE SEAL DYNAMICS SUBJECTED TO MACHINE VIBRATION AND NOISE

Mechanical face seals are wide-spread in many applications, such as centrifugal compressors, submersible pumps, drill-bits for oil and water, hydrocarbon processing equipment, and turbomachinery. Often vibration and noise are unavoidable because of changing environments which can be persistent and forceful. In critical applications when seals fail, they may have significant or even catastrophic consequences. To ensure the safety of such machinery and its associated mechanical components, the vibration and noise must be diagnosed and kept within certain limits. This work focuses on the dynamics of a flexibly mounted stator mechanical face seal that is subjected to combinations of axial broad-band noisy vibrations of the shaft and the housing. The current analysis builds upon the dynamic models that have been developed over the last four decades. In all that body of work, the positions of the housing and the shaft have been considered fixed. The current work relaxes that condition, augmenting the equations of motion to incorporate the said noisy vibrations. While the exact root-causes and sources of machinery vibration are very difficult to ascertain, the current analysis uses some general common causes of noisy seal operation, and provides markers to be observed for diagnosis. While the forcing noises are assumed to originate along the main axis of the seal, because of the strong coupling between the axial and angular modes, the seal is affected (even strongly) in all modes (axial and angular). A numerical simulation ensues, and the results are subject to spectral analyses. Results show that under some design conditions, the seal is largely insensitive to machine vibrations. However, under other design parameters, the seal response exhibits a rich spectral content that stems from various transient phenomena that include (among others) half frequency whirl, synchronous steady-state response, and the natural (eigen) response. Under aggravated noisy conditions the investigated seal exhibits large oscillations and leakage, along with face contact and rubbing. Prolonged rubbing causes faces to wear and leads ultimately to seal failure.