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Shaft Seals and Rotary Shaft Seals: Types, Sizing, Materials, and Selection

Quick Answer: A shaft seal retains lubricant and blocks contaminants around a rotating or reciprocating shaft. The correct shaft seal depends on shaft diameter, housing bore, width, shaft speed, temperature, fluid, pressure, and surface finish. CORASEALS supplies rotary shaft seals, oil seals, radial lip seals, V-rings, cassette seals, bearing seals, and mechanical face seals in metric and inch sizes.

What Is a Shaft Seal?

A shaft seal closes the gap between a moving shaft and a stationary housing. The seal lip contacts the shaft surface and retains oil, grease, or another fluid inside the equipment. At the same time, the outer case seals against the housing bore. A shaft seal also blocks dust, dirt, water, and other contaminants from entering the bearing or gear chamber.

Shaft seals appear in gearboxes, pumps, motors, axles, bearing housings, compressors, reducers, and hydraulic systems. When a seal is selected without checking the application conditions, the common result is early leakage, lip wear, shaft grooving, or overheating.

Common Shaft Seal Types

• Rotary shaft seals and oil seals: Radial lip seals with a metal or rubber case. These seals are widely used for rotating shafts in gearboxes, pumps, and motors. Many oil seals are dimensioned according to DIN 3760 or ISO 6194.
• V-rings: Axial face seals that rotate with the shaft. They work as flingers and secondary seals. V-rings are useful in dusty or wet conditions and can tolerate some shaft misalignment.
• Cassette seals: Sealed assemblies that combine the seal, sleeve, and multiple barriers. Cassette seals suit heavy contamination, agricultural equipment, off-highway axles, and bearing positions that need longer life.
• Bearing seals: Seals designed for bearing positions. They can be integrated with the bearing or installed in the housing next to the bearing.
• Mechanical face seals and floating seals: Face contact seals used in abrasive conditions. These seals are common in final drives, track rollers, and mining equipment. Floating seals use two metal rings and elastomer belleville members.

Oil seal codes such as TC, SC, TB, and similar designations are not identical across all manufacturers. The same code can describe different lip arrangements in different catalogs. Always compare the section drawing, lip configuration, case type, and dimensions before ordering.

How to Specify and Measure a Shaft Seal

Shaft seals are normally specified by shaft diameter, housing bore, and width. The dimension order is usually ID × OD × width for rotary shaft seals. Always confirm this order with the supplier. Measure the shaft diameter at the contact area. Measure the housing bore at the seat area. Measure the installed width or the available groove width.

Recording only the old seal dimensions is not enough. One seal size can have multiple lip configurations, case designs, and material options. The same ID, OD, and width can use a single lip, double lip, dust lip, rubber OD, metal OD, or a garter spring. Send the old drawing or a sample photo when the seal is coated or heavily damaged.

For new applications, also record shaft speed, runout, surface finish, oil type, temperature range, and external contamination. These factors decide whether a standard NBR lip seal works or whether the application requires FKM, HNBR, PTFE, or a cassette seal.

Shaft Seal Material Selection

Material choice controls temperature resistance, oil compatibility, low-temperature flexibility, and chemical resistance. The table shows common material groups used for shaft seal lips. Use these values as a starting point. Confirm exact compound limits with the datasheet because fi