Shaft seals are commonly used in gearboxes, which convert high speed input from an electric motor into low speeds that drive various machines or conveyors. A cut-away view of a gearbox assembly is shown in Figure 190.

Typical gearbox applications will have two shaft seal styles: one for the input seal and one for the output seal(s). The input seal is a higher speed (usually 1750 RPM) seal. Because both external and internal contamination can be a problem in gearbox assemblies, new generation, high-tech gearbox seals incorporate additional contamination exclusion, both internally and externally. The input seal is often a TC or TCW design made with fluoroelastomer (FKM). The input seal shown in Figure 191 combines a TC design with an oil side contamination exclusion lip to prevent dirt and metal particles in the oil from reaching the primary sealing lip.

In addition to the input seal, there will also be one (or more) output shaft locations. The output seal usually operates at lower speeds than the input seal. (Actual output speed depends on the internal gear ratios set up in the gearbox.) But because the speeds are typically lower for output seals than for input seals, different cross-sections (designs that would generate too much friction and drag if used as input seals) can be used as output seals.

The cross-section of a typical output seal is shown in Figure 192. Note that this is a QA-style design to exclude heavy contamination. Another possible QA-style output seal design is shown in Figure 193; this design features an even greater number of contamination exclusion lips.

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