Mechanical seals are sealing components used in rotating machines such as pumps, compressors, agitators, etc. They are used to seal every types of fluid (liquid, gas, paste, etc) in all industrial domains from nuclear to food industry.
As can be seen, on the first figure, a seal is basically composed of a rotating ring linked to the shaft and of a static ring linked to the housing, one of this link being flexible to allow a good alignment of the faces. The rings are pushed in close contact under the action of elastic elements and the pressurised fluid. A thin fluid film of about one micrometer can build-up and generally separates the seal rings avoiding wear and increasing reliability. This film must, on the other hand, remain sufficiently thin to prevent leakage. The thickness of the lubricating film depends on many interacting physical phenomena as illustrated on the second figure. The central point is lubrication which controls the fluid flow of the fluid, the pressure distribution and the asperity contact. Because of the flexible link, the floating ring can encounter vibrations. Moreover, the geometry of the faces and thus the fluid film thickness is greatly affected by elastic distortions due to the pressure loading and thermal distortions resulting from the heat dissipated by friction in the contact. In some situations, phase change can take place in the contact. Another key parameter which is not illustrated here is the wear of the surfaces.