When an elastomeric material is unable to return to its original size after being released from a constant compressive load, the amount of material that stays compressed is called a “compression set”. To work effectively, o-rings must form a complete, continuous seal between sealed surfaces. Because compression set produces flat surfaces on both sides of an o-ring’s cross section, it significantly reduces the joint’s sealing potential.
Common Causes of O-Ring Compression Set
Compression set is one of the most common causes of both static and dynamic o-ring failure. Compression set is largely a factor of temperature and time, but a number of other elements can contribute to this type of failure occurring. Among the frequent reasons for o-ring compression set failure are the following:
- Selection of an elastomer with poor compression set properties
- Low heat resistance of a material
- Excessive swelling of an o-ring material in system fluid
- Too much squeeze occuring to achieve seal
- Incomplete curing (vulcanization) of an o-ring material during production
- Operating temperature that is too high for the rubber used
Suggested Solutions
Compression set can be avoided by employing the correct materials and ensuring compatibility between parts on a given project. In order to avoid or correct o-ring compression set failure, look to the following solutions:
- Employ a low set elastomer
- Specify an o-ring material that resists both operating and friction generated heat
- Re-check o-ring material compatibility with system chemicals
- Reduce o-ring squeeze if possible
- Inspect incoming o-rings for correct physical properties
- Employ a low-set elastomer or higher temperature rated material
Ensuring o-ring and gland compatibility is key to preventing compression set failure. Before installing an o-ring, verify that it is of the correct size, material and chemical compatibility for your situation.
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