AS and SA radial oil seals

Radial oil seals are designed for sealing shafts in bearing housings. Providing long-lasting sealing efficiency, they consist of a rubber sealing lip, metal case and a stainless steel garter spring plus an external dust lip. We offer two radial seals that are mirror images of each other. 

  • Misalignment for shaft diameters up to and including 100 mm is approx. 3°

  • Works for speeds of up to 10 m/s

  • Made of nitrile rubber (NBR) that withstands up to 90°C

  • Stainless steel garter spring

AS Seal

The Radial AS seal type is pressure-tight, by the pressure of the grease the lip will pressed closer to the shaft as shown in the illustration. Therefore it can not be greased through the seal, the seal has to be used in combination with a CS or CC seals or as AS-AS / AS-VK assembly used on places with none abrasive surrounding just to close and become a maintenance free bearing unit.  It is necessary that if you do the initial greasing, to keep the cap a little bit open. to ensure that air can escape.

SA Seal

SA oil seals are designed with asymmetric lip angles as shown in the illustration. The angle α between the shaft and lip on the air side is smaller than the angle β on the lubricant side to prevent lubricant from leaking out of the system. When grease is used, the difference in angles is less important and often reversed to provide better sealing against contaminants from outside. We call this seal version SA. Leakage is less of a concern here due to the consistency of grease, which prevents excessive loss of lubricant. Therefore the main purpose of the grease seal is to keep contaminants out.

To improve bearing life by the correct use of bearing shaft seals, it is recommended to use an automatic lubricator or lubricate regularly. Only a small quantity of grease is necessary when slowly flushed into the bearing cavity to force dust and moisture away from the seal lips.

Note – SA seal is not for food applications

The SA seal is not suitable for applications where high hygiene is demanded because the cavity in the lip can act as a chamber for collecting dirt. For high hygiene applications, use our CC design. The AS seal and, to a lesser extent, the SA seal are not suitable for applications where there is a risk of contamination from abrasive materials. For this type of application, use our CS design


In some configurations, the bearing units from Extreme Bearing are pressure-tight. Therefore it is necessary to keep the cap a little bit open while you do the initial greasing. Otherwise problems like in the picture shown here can occur.

In addition, whenever it is necessary to add some more grease later, you should always take care not to create overpressure in the housing. The Extreme Bearing units are pressure-tight when used with the following configurations of seals: AS/AS, AS/VK, CL/CL and CL/VK.

Please inform your maintenance crew about this special service operating instruction. It could be helpful to dismount the grease nipples and exchange them with a standard stainless screw, so it will be impossible to make mistakes.


The small gap between the seal lip and the shaft provides sealing against contaminants. The grease in the vicinity of the seal lip and grease in between the two sealing lips also provide a sealing action.

The gaps between the lips and the stator of the seal must be greased to keep out dust and water. To improve bearing life for bearing shaft seals, it is recommended to use an automatic lubricator or to lubricate regularly. Only a small quantity of grease is necessary when slowly flushed into the bearing cavity to force dust and moisture away from the working parts.

Examples of grease diagrams using AS seals

If the contamination is only on one side of the bearing unit, a seal combination can be chosen that is based on refilling the grease on this side. In this way, the contamination along with the grease shall flow away from the sealing lips. An example of such an assembly, a CS-AS combination, is shown in one of the illustrations with the path of the grease shown by the red arrows.

VK-AS seal assembly

AS-AS seal assembly

CS-AS seal assembly

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WAIVER: Our opinion and our advice are not guaranteed and Extreme Bearing shall not be liable for the consequences of any damages caused by incorrect advice or the contents of this website. The customer is responsible for checking that the right choice of Extreme Bearing product has been made to match their actual working conditions and dimensions.