#1 When is a material resistant to a medium?
The media resistance indicates how compatible an O-ring material and a medium are. If a material is highly resistant to a medium such as water, for example, this means that the O-ring does not absorb any of the medium (swelling).
If an O-ring is not resistant to a medium, the O-ring will absorb the medium after a certain time and swell as a result. This is a very common damage pattern, but it is easy to recognize. The O-ring has increased in volume and now feels quite squishy.
If you simply want to try this out yourself, use an animal oil and an EPDM O-ring . Leave the O-ring in the oil overnight and the next day you will be surprised at how swollen the O-ring will be. EPDM can cope with animal and vegetable fats/oils so that the EPDM O-ring absorbs them like a sponge.
#2 How do I check the media resistance of my O-rings?
We have a tool for you, which gives you information about the resistance of over 450 media in combination with all common O-ring materials.
A = Excellent media resistance
B = Good media resistance
C = Moderate media resistance
D = No media resistance
Important to know: All media resistance lists are based on room temperature (20°C). The design must take into account that a medium becomes more aggressive with increasing temperature. If a material in a list only has a “C = moderate media resistance” and the application assumes 120°C, then the resistance will not be given.