shaft seal

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 fillers, curing, and product design change the final performance range.

Material	Common Uses	Main Limitations
NBR	Mineral oil, gear oil, general rotary shaft seals	Limited high-temperature and ozone resistance
HNBR	Hot oil, transmission fluid, higher mechanical loads	Higher cost than NBR
FKM	High-temperature oil, fuel, chemical exposure	Higher cost and reduced low-temperature flexibility in some grades
EPDM	Water, steam, brake fluid, glycol	Not suitable for most mineral oils
Silicone and VMQ	Wide temperature range, low friction	Poor oil resistance for many rotary shaft applications
PTFE	High temperature, chemical resistance, dry running, low friction	Less elastic than rubber lips and requires careful installation

If the fluid contains aggressive additives, solvents, fuel blends, or high-pressure oil, choose the material only after a compatibility check. A material can work in one oil at 80 °C and fail in another oil at 120 °C.

Why Shaft Seals Fail

Most shaft seal failures have a mechanical cause before a material cause. The common failure paths are:

Shaft surface finish outside the seal design range
Excessive shaft runout or misalignment
Installation damage to the lip or outer case
Hardening or softening from the wrong material
Contamination from dirt, sand, or process media
High pressure or speed beyond the seal design
Incorrect size or incorrect groove fit

Replacing the seal without correcting these conditions often leads to the same leak. The replacement seal may fail within days or weeks.

Shaft Seal Applications

CORASEALS supports shaft seal selection for gearboxes, hydraulic pumps, electric motors, axles, bearing housings, compressors, reducers, and off-highway equipment. The same shaft seal type is not correct for every shaft. A gearbox may need an NBR or FKM rotary oil seal. A final drive in abrasive conditions may need a floating seal. A dusty agricultural shaft may need a cassette seal.

Related sealing products include oil seals, rotary shaft seals, V-rings, cassette seals, bearing seals, and mechanical face seals. For hydraulic systems, CORASEALS also provides hydraulic cylinder seal kits, rod seals, piston seals, wiper seals, and wear rings.

Requesting a Shaft Seal Quotation

Send the following information to CORASEALS:

Shaft diameter, housing bore, and width or the full ID × OD × width
Seal type or existing part number
Fluid, temperature, pressure, and shaft speed in rpm or m/s
Shaft surface finish and runout if known
Existing drawing, sample photo, or section sketch
Required quantity and target application

Send the shaft seal type, material, ID × OD × width, operating temperature, pressure, medium, shaft speed, drawing, sample photo, and required quantity. CORASEALS will confirm the lip design, case type, and material before quotation.

Frequently Asked Questions

What is the difference between a shaft seal and an oil seal?
An oil seal is one type of shaft seal. The term shaft seal covers rotary shaft seals, V-rings, cassette seals, bearing seals, and mechanical face seals. In many industrial catalogs, oil seal refers to a radial lip seal that seals around a rotating shaft.

How do I measure a shaft seal?
Measure the shaft diameter at the sealing contact area, the housing bore at the seat area, and the installed width. Record the dimensions as ID × OD × width. Also record the lip configuration and case type because the same size can have multiple designs.

Can I use one shaft seal material for all oil types?
No. NBR works with many mineral oils but has limits in hot or aggressive fluids. EPDM is not suitable for most mineral oils but works with water and steam. FKM often suits higher-temperature oil and fuel exposure. Always verify the fluid compatibility with the compound datasheet.

Why does the new shaft seal still leak?
The new seal may leak because the shaft surface is worn, runout is too high, installation damaged the lip, the material is not compatible, or the size is wrong. The previous seal may also have failed from a mechanical condition that was not corrected.

What information should I send for a shaft seal quote?
Send the shaft seal type, material, ID × OD × width, operating temperature, pressure, medium, shaft speed, drawing, sample photo, and required quantity. For rotary shaft seals, also include shaft diameter, housing bore, shaft surface finish, and runout if available.