A blister is an enclosed cavity that protrudes from, and thus deforms, a rubber surface (see Figure 155). Blisters can form on a shaft seal’s lip due to inconsistencies during the manufacturing process or, in some cases, due to excessive heat during storage or transport.

A blister at the contact point on the primary lip of a shaft seal designed to retain oil or grease can be critical. This is because the blister can limit the lip’s ability to maintain proper contact with the shaft. Without good followability between the lip and the shaft, a leak path can develop. A blister on an oil or grease seal’s secondary (dirt) lip, flex section, O.D., or endface can also decrease sealability, though not typically to a critical extent.

See Table 49 for a diagram of these seal components.

POSSIBLE MANUFACTURING DEFECTS MAIN PAGE