Dyamic Elastomer

The rubber part that has to move to move or flex to compensate for seal face wear or shaft movement.

A rubber bellows is a dynamic elastomer found in low cost seal designs.

It is important that the bellows attaches to the shaft and provides the torque needed at the seal faces, so be very careful about the type of lubricant put on this bellows during the assembly process.

See: rubber bellows seal.


O-rings are usually the best choice because of the wide variety of materials available, ease of installation, and they can flex before they are required to roll preventing some fretting problems.

In this drawing the dynamic elastomer (O-ring) is located between the inner and outer sleeve.

The static elastomer seals the inner sleeve to the shaft.

The squeeze or interference fit of this dynamic elastomer is much less than that shown in conventional O-ring charts.

O-ring charts reference static and reciprocating elastomers. Mechanical seal companies have established their own rules for dynamic O-ring interference fits on polished shafts or sleeves.

The metal bellows seal allows you to eliminate the dynamic elastomer completely.

Most mechanical seal designs incorporate both dynamic and static elastomers. Dynamic O-rings are required to flex and roll with the shaft movement. This means that a very low shaft squeeze is important to prevent seal hang up or hysteresis. They must also be free to flex and roll to compensate for mechanical seal face wear.

Static O-rings do not have to move. They are used as a gasket and are a lot more forgiving than dynamic O-rings because a small amount of swell can be tolerated that might even improve their sealing.



  • On February 15, 2018