<div class="htmlview paragraph">Fine solid particles in a lubricating oil affect the sealing characteristics of oil seals, and their lives are shortened by the wear of oil seals and shafts created by the particles.</div> <div class="htmlview paragraph">Tests were carried out by using various kinds of foreign matters. The results showed that foreign matters in oil film between the sealing lip and the shaft surface directly caused the leakage. Consequently, it was reconfirmed that the practical application of dust lip and the countermeasure in the construction of seals or their housings were indispensable to obtain the long life and the stable operation of oil seals.</div>