Rules of Thumb

A Simple Guide to Understanding O-Ring Compression Set

Technical drawing of o-ring compression set

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. 


Have more questions about o-ring compression set? 

Ask one of our engineers today.