Variation of Cavitation Pressure with Liquid and Operating Conditions in Mechanical Seals

Abstract

A series of experiments is conducted to investigate the cavitation pressure P_cav in the sealing film of a mechanical seal. To generate negative pressure, a reversed Rayleigh step is produced on the sliding surface, and the formation of cavities in the sealing film is observed. The pressure in the cavitation region is directly measured using a pressure sensor installed under a pinhole on the sliding surface. Various lubricating oils with similar kinematic viscosities are used as sealing fluid. The results show that pressure in the cavitation region is related to the operating conditions. P_cav decreases with increasing sliding speed in all oils and all sealing gap, i.e. minimum distance between two sliding surfaces of mechanical seal. When the sealing gap is the same, P_cav at each sliding speed is slightly different depending on the type of lubricating oils. When the lubricating oil is the same, small dissolved air results in low P_cav. In addition, two sealing gap are tested under the same sliding speed and the same oil, revealing that thin sealing gap results in low P_cav. Further, a model of cavitation in the reversed Rayleigh step is proposed based on the experimental results.