radial shaft seal

Radial Shaft Seals: Sizing, Material Selection, and Application Guide

Quick Answer: A radial shaft seal is a lip seal installed between a rotating shaft and a stationary housing. The seal keeps lubricant in and blocks dust, water, and contamination. For a quotation, send CORASEALS the shaft diameter, housing bore, seal width, material, fluid, operating temperature, shaft speed, and required quantity.

A radial shaft seal is also called a rotary shaft seal, oil seal, or lip seal in many industrial markets. CORASEALS supplies radial shaft seals as part of the oil seal and rotary shaft seal product range. This guide explains sizing, material selection, installation conditions, and the information needed for a radial shaft seal quote.

What Is a Radial Shaft Seal?

A radial shaft seal has a flexible sealing lip that contacts the rotating shaft. The OD fits into the housing bore. A metal or rubber outer shell holds the seal in position. A garter spring usually keeps the lip in contact with the shaft surface. The seal prevents lubricant leakage and keeps dust, water, and abrasive particles out.

Common specification terms include ID, OD, width, shaft diameter, housing bore, lip type, garter spring, dust lip, and seal profile. The seal ID is normally smaller than the shaft diameter. This lip interference creates the sealing contact. The OD must match the housing bore with the correct fit.

Where Radial Shaft Seals Are Used

Radial shaft seals are used on gearboxes, pumps, motors, axles, bearing housings, transmissions, and rotating equipment assemblies. Buyers use these seals in automotive, agriculture, mining, construction machinery, and general industrial equipment. If a shaft rotates and lubricant is present, a radial shaft seal is often the correct sealing element.

How to Measure and Specify a Radial Shaft Seal

Measure the shaft diameter at the sealing contact area. Measure the housing bore where the seal outer diameter sits. Measure the available width in the housing. Specify the size in this order: shaft diameter x housing bore x width, or ID x OD x width. Confirm the unit in millimetres or inches.

Do not order by a TC, SC, BA, or VB code alone. These profile codes change between seal catalogs. Always confirm the outer surface type, lip configuration, spring position, dust lip, and dimensions. Send a drawing or sample photo if the old seal is worn or unmarked.

DIN 3760 and ISO 6194 are common dimensional references for radial shaft seals. Use the supplier drawing to confirm lip design, spring position, and OD construction.

Material Selection for Radial Shaft Seals

Seal material must match the oil, grease, chemical exposure, temperature, and shaft speed. NBR is the most common material for mineral oil and gear oil. FKM works where higher temperature and chemical resistance are needed. HNBR offers good oil resistance and improved wear in many industrial drives. EPDM suits water and some brake fluids but is not suitable for most mineral oil environments. Silicone has a wide temperature range but lower wear resistance. PTFE lip seals can handle chemical attack, dry running, and low friction, but they require careful shaft surface and runout control.

Material	Common Selection Reason	Main Limitation
NBR	Good mineral oil and grease compatibility	Limited high temperature and polar fluid resistance
FKM	High temperature oil and chemical resistance	Higher cost, not suitable for all steam or ketone environments
HNBR	Good oil resistance and improved wear	Not suitable for strong polar solvents
EPDM	Good water and brake fluid resistance	Not suitable for mineral oil
Silicone	Wide temperature range	Lower wear resistance and tear strength
PTFE	Chemical resistance, low friction, dry running	Requires shaft surface and runout control

Temperature limits and chemical resistance change with compound formulation, fluid additive packages, and seal design. Always request compound-specific data from CORASEALS for the actual fluid and operating temperature.

Design Differences and Installation Conditions

A standard single lip radial shaft seal with a garter spring covers most oil retention jobs. A double lip version or a seal with a dust lip adds protection in dusty or wet environments. A PTFE lip seal may suit dry or low-friction applications. A cassette seal offers a complete sealing unit for severe dirt, mud, or oil contamination.

Before installation, check the shaft surface condition, hardness, chamfer, runout, and housing bore condition. Shaft wear grooves, spiral lead, scratches, and excessive runout cause early leakage. The housing bore must be clean and round. If the seal is installed backwards, the lip will not seal the intended fluid side.

Pressure, Speed, and Temperature Limits

Standard radial shaft seals are designed for low-pressure lubricant retention. If the system has internal pressure, choose a pressure-supported design or a PTFE lip seal. Confirm the pressure limit in bar or MPa with the supplier.

Shaft speed should be checked in m/s at the lip contact. Allowable speed depends on material, shaft hardness, surface finish, lubrication, and temperature. High speed with poor lubrication shortens lip life.

Common Failure Causes

Lip wear from high speed or abrasive contamination
Shaft wear groove at the old contact position
Hardened or cracked lip from heat or chemical attack
Incorrect size or damaged outer shell during installation
Excessive shaft runout or poor surface finish
Wrong material for oil, fuel, water, or chemical exposure

Radial Shaft Seal Quote Requirements

Send CORASEALS the following information for a radial shaft seal quote:

Seal type or profile: single lip, double lip, spring loaded, PTFE lip, cassette, or unknown sample
Material: NBR, FKM, HNBR, EPDM, silicone, PTFE, or unknown
Dimension: shaft diameter x housing bore x width
Operating temperature in °C or °F
Pressure in bar or MPa, if any
Fluid or medium: oil type, grease, water, chemical, fuel, or other
Shaft speed in rpm and shaft diameter
Drawing, sample photo, or old seal markings
Required quantity

If you do not have all dimensions, send the equipment model, pump model, gearbox model, or old seal photo. CORASEALS can help identify the seal size and material for many industrial rotating equipment applications.

Frequently Asked Questions

What is the difference between a radial shaft seal and an oil seal? The terms are often used interchangeably. An oil seal usually describes a shaft lip seal for oil retention. A radial shaft seal specifies the sealing direction from the rotating shaft to the stationary housing.

How do I measure a radial shaft seal? Measure the shaft diameter at the lip contact area, the housing bore where the seal OD fits, and the available width. Provide the size as shaft diameter x housing bore x width.

Which material should I choose for mineral oil? NBR is the most common material for mineral oil and gear oil. FKM is an option for higher temperature and chemical resistance. HNBR is an option for improved wear in oil applications.

Can a standard radial shaft seal handle pressure? Standard radial shaft seals are designed for low pressure only. Pressure-supported designs or PTFE lip seals are needed when the seal must handle pressure.

What causes a radial shaft seal to leak early? Common causes include lip wear, a shaft wear groove, wrong material, incorrect size, poor shaft surface finish, excessive runout, and installation damage.