Commonly a sealing lip is provided by a pre-formed moulded component of the seal, often supported radially by a garter spring. However, seals are also known of a kind in which a rubbery element (for example, cut from sheet stock) becomes deformed by interacting components, upon assembly of the seal, to form a suitable lip. This invention can apply equally to both such forms of seal.
Ordinarily the bore (i.e. inside diameter) of a seal is determined upon assembly of the seal and is invariable in use. However, as well as providing potential for improved performance in use, there can also be benefits for installation and maintenance purposes in arranging for a seal to be of variable nominal bore; by the term "nominal bore" is meant here the bore of the seal as it is (or would be) when out of use, as opposed to its bore when in use which would be determined by the diameter of a shaft to which it was applied. In use of the seal, variation of the nominal bore enables variation of the lip/shaft interface characteristics for maximum efficiency of operation. During installation and maintenance, the ability to increase the bore, and so slacken the seal's grip on a shaft on which it is engaged (or to be engaged) can be of benefit in facilitating movement of the seal along the shaft and avoiding damage to the lip.