When an elastomeric material fails to return to its original size after release from a constant compressive load, the amount of material that remains compressed is called a compression set. To be effective, o-rings require a complete, continuous seal to form 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 o-ring failure for both static and dynamic seals. Compression set is largely a factor of temperature and time, but a number of other elements can contribute to this type of o-ring failure occurring. Among the frequent reasons for o-ring compression set failure are the following:
- Selection of elastomer with poor compression set properties
- Low heat resistance of material
- Excessive swelling of o-ring material in system fluid
- Too much squeeze to achieve seal
- Incomplete curing (vulcanization) of o-ring material during production
- Operating temperature 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.