#1 Why do O-rings swell?
An O-ring swells when it comes into contact with a chemical to which it is not resistant.
The lack of resistance of O-rings manifests itself in two ways
- The O-ring absorbs the medium (swelling)
- The O-ring is destroyed by the medium (dissolving)
Example of swelling
A simple test example is EPDM. This is because EPDM is not resistant to vegetable and animal oils and fats. If you place EPDM in commercially available fish oil, for example, the O-ring will swell to two to three times its original size.
Tip: As this media test is safe and easy to perform, this test is ideal for testing EPDM as a material.
Assuming a mistake was made and an NBR instead of an FFKM O-ring was used with the chemical aqua regia (concentrated hydrochloric acid and nitric acid), it can be observed how the O-ring literally dissolves in the chemical.
Against this background, media resistance is crucial for the longevity of an O-ring. We therefore have a comprehensive and well-structured media resistance list on our website.