Whenever a shaft rotates, it needs a bearing arrangement for smooth and effective operation. Wherever there is a bearing, you will always find a seal helping it to reach its maximum service life and reliability. The most common types of seals used in bearing arrangements, are radial shaft seals for use in general industrial applications with shaft diameters up to 200 mm or 8 inch respectively. The large diameter seals, for shaft diameters above 200 mm, provide special features and are intended for use in heavy and large-size engineering applications, which require either very large or specially designed seals. In general terms, a radial shaft seal is a barrier with four main functions (images 1-4).