Design checkpoint
Start with the operating envelope
List the continuous temperature, short excursions, media, pressure, and motion first. A material that survives a headline temperature may still fail when those conditions overlap.
1. Separate continuous temperature from peaks
The first pass is to document the temperature the seal sees for most of its service life, then record the highest short-term excursion. FKM is a strong default for many oil, fuel, and chemical environments up to roughly 200-250°C, while FFKM is reserved for the most aggressive combinations of heat and media.
Silicone remains useful when flexibility, cleanliness, and a broad low-temperature range matter more than abrasion resistance. Its performance should be checked carefully where dynamic wear, sharp edges, or high tear loads are expected.
2. Compare the trade-offs that change the result
A compound may look suitable on a temperature chart but behave differently once pressure, media, and movement are added. Review compression set, gas permeability, and dynamic friction alongside the headline service temperature. That wider view keeps the material recommendation tied to the application rather than a single data-sheet line.
| Compound | Temperature window | Best strengths | Watch for |
|---|---|---|---|
| FKM | -20 to +250°C | Heat, oils, fuels, many chemicals | Cold flexibility and hot steam |
| FFKM | -15 to +325°C | Extreme heat and chemical resistance | Cost and lead time |
| Silicone | -60 to +200°C | Flexibility, cleanliness, weathering | Tear and abrasion in dynamic duty |
3. Validate the compound in the real media
When the media is unfamiliar, a short immersion and compression-set test can expose a mismatch earlier than a field failure. Share the actual fluid blend, concentration, cleaning cycle, and pressure pulse with the compound supplier so the test reflects the real duty cycle.
Document the accepted compound, cure system, hardness, and test conditions on the drawing or purchase specification. Clear documentation is the simplest way to keep an approved material consistent across suppliers and plants.
Key takeaways
- Separate continuous temperature from short peaks
- Check media, pressure, and motion together
- Treat compression set as a life indicator
- Validate unfamiliar media before production