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In order to clarify the sealing mechanism of radial lip seals, a new test apparatus with a hollow glass shaft was developed, and the fluid behavior under sealing condition was observed by using the Laser Induced Fluorescent (LIF) method. In this paper, the description of the test apparatus and first measurement results are shown. A laser dye dissolved in synthetic oil below the seal lip was excited at a wavelength of 427nm by a SHG solid state blue light laser. The fluorescence was detected by a CCD camera through an optical filter. The fluid paths of the oil beneath the seal lip appeared ahead of each rib as soon as a shaft started to rotate. Furthermore, the intensity of the fluorescence, which is related to the fluid film thickness, increased with shaft speed increasing. First measurement results obtained with the LIF method were in good agreement with other measurement results.

The correlation between the micro surface roughness and sealability of O-rings was experimentally analyzed. We developed a SMLA (Seal Micro Leakage Analyzer) for observing the contact of micro asperities using a micro-prism glass plate, and a micro-leakage measurement device for O-rings. Using the SMLA, the contact of micro asperities of O-rings surfaces ranging from 1.6 microns to 16.3 microns was clearly visualized. We also measured the contact area and leakage amount at the same time, and studied the sealing mechanism. The visualized images of the contact area were analyzed by image processing. The results showed that the micro asperites on the O-ring surfaces were squashed elastically to form a band which sealed in the fluid.