Lubricant and Seal - How Do You Check Compatibility?
The wrong oil or grease makes seals swell, shrink or harden, causing leaks and failure. This guide shows how to test lubricants against NBR, FKM and EPDM, which volume change ISO 1817 allows and how an immersion test works.
View lubricantsWhy does not every oil suit every seal?
Seals are made of elastomers whose molecular network reacts differently to each base oil. An unsuitable lubricant penetrates the material and makes it swell, or it extracts plasticisers so the seal shrinks and hardens. Both effects rob the seal of its preload and cause leakage.
Polarity is the key. Non-polar mineral and PAO oils suit non-polar NBR and FKM well but attack EPDM heavily. Polar ester and glycol oils are compatible with EPDM but make NBR swell. A slight swelling of a few percent is actually wanted because it lightly presses the seal - only large volume changes become critical.
- Swelling: the elastomer absorbs oil, softens and loses strength.
- Shrinking: the oil leaches out plasticisers, the seal hardens and cracks.
- Extraction: dissolved components contaminate the lubricant and circuit.
- Hardening by additives: EP and antioxidant additives can attack elastomers.
Which seal material suits which lubricant?
NBR (nitrile), FKM (fluoroelastomer) and EPDM cover most applications. The right pairing depends on base oil, temperature and medium. The overview below shows typical suitability.
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Read the guideHow does an ISO 1817 compatibility test work?
The standard test is immersion of elastomer samples in the lubricant per ISO 1817. Standardised specimens are stored for a defined time at raised temperature, then the change in volume, mass and hardness is measured. Typical conditions are 168 hours at 100 °C or values close to the real application.
- Volume change: usually -3 % to +15 %, often +/- 10 % per supplier limit.
- Hardness change (Shore A): guideline within +/- 10 points.
- Mass change as a check value for the volume measurement.
- Tensile and tear strength must not drop significantly.
- Visual check for cracks, blisters, sticky surface and discolouration.
Frequently asked questions
Is a slight swelling of the seal bad?
No, a small positive volume change of a few percent is even desirable because it lightly presses the seal and prevents leakage. It becomes critical only with heavy swelling above about 15 percent or with shrinking.
Can I simply replace NBR with FKM?
FKM is more chemically and thermally resistant but more expensive and less flexible at low temperature. Before switching, check the groove dimensions and cold resistance, as FKM turns brittle below roughly -20 °C.
Why must EPDM not contact mineral oil?
EPDM is non-polar and absorbs non-polar mineral and PAO oils strongly. The seal swells massively, loses shape and strength and fails. Mineral oil needs NBR or FKM; EPDM is only for glycol, water and brake fluid.
Is the data sheet enough or do I need my own test?
For standard pairings such as mineral oil with NBR the maker approval usually suffices. When switching to bio oils, special elastomers or aged installed seals, an ISO 1817 immersion test with sample specimens is recommended.
Unsure about lubricant selection?
We supply oils, greases and cleaners with documented elastomer compatibility and advise on the right pairing with NBR, FKM and EPDM.
Verified compatibility
Approvals and test values per ISO 1817 documented.
Correct pairing
Base oil and elastomer matched to your application.
Failure avoided
Swelling and shrinking kept safely within limits.
Expert advice
Specialists support you with critical media.