Seal chemical resistance depends on the exact elastomer compound and the complete liquid exposure, including concentration, temperature and contact time. EPDM, NBR and FKM are material families, not universal compatibility approvals.
For cleaning equipment, start with the chemical identity and the equipment manufacturer’s compatibility information. The pH value alone cannot determine which O-ring, sprayer or dosing-pump version is suitable.
How do EPDM, NBR and FKM differ?
EPDM is commonly considered for water and suitable aqueous cleaning duties, while mineral oils and hydrocarbon exposure can be problematic. NBR is often associated with oil-resistant sealing, but it is not a universal choice for aggressive cleaning cycles. FKM offers useful resistance in many oil and chemical applications, yet standard compounds can have important limitations with some alkalis, solvents and steam.
These are screening tendencies, not an approval table. Specialty compounds can differ substantially from general-purpose materials in the same polymer family. Check the exact manufacturer designation, not only the three-letter abbreviation.
Why is pH insufficient for seal chemical resistance?
pH describes one property of an aqueous solution. It does not describe solvent content, oxidising activity, oil content or every ingredient that may attack a seal.
For example, two alkaline cleaners can have similar pH values but different solvents and concentrations. A seal that performs well in one may swell, harden or lose function in the other. Likewise, “acidic” does not identify the acid, its concentration or compatibility with a specific compound.
Obtain the current safety data sheet and the chemical supplier’s material recommendation. A safety data sheet may not disclose every ingredient or provide a finished compatibility assessment, so equipment approval may still be needed.
Why do concentration and temperature change the result?
A diluted working solution and its concentrate are different exposure conditions. Higher temperature and longer contact can reveal differences that a brief room-temperature check does not show. Repeated cleaning cycles also add mechanical and thermal demands.
As an illustrative selection case, a sprayer may be used for a dilute cleaner but stored with concentrate left in the suction system. Assess that retained-liquid exposure as well as the spraying stage. Do not transfer a percentage limit from another supplier’s sprayer guide to every EPDM or FKM product.
How should you select a seal for a sprayer or dosing circuit?
Record the chemical product, intended dilution, maximum liquid temperature, continuous or intermittent exposure, and whether the seal is static or moving. Include rinse and cleaning chemicals encountered during maintenance.
Then check the approved seal compound, dimensions, hardness and equipment version. Body material, hose, check valves and lubricant must also be compatible. If information is incomplete, request written confirmation for the intended duty or a suitable manufacturer-approved test. Changing only the O-ring material does not make the entire device chemically compatible.
Selection reference
| Material family | Initial screening use | Do not assume |
|---|---|---|
| EPDM | Water and suitable aqueous cleaning duties | Universal resistance to oils, solvents or every acid |
| NBR | Many oil-related sealing duties | Suitability for all detergents or aggressive cleaning cycles |
| FKM / FPM | Many oil and chemical duties, depending on compound | Universal resistance to strong alkalis, polar solvents or steam |
Conclusion
Choose the exact compound for the complete exposure. Use compatibility charts as screening information and confirm the finished equipment’s suitability before substituting a seal material.
Frequently asked questions
Is EPDM suitable for both acids and alkalis?
It can be suitable for some, but the exact chemical, concentration, temperature and compound must be checked.
Is FKM always better than EPDM?
No. A more expensive material may be less suitable for the specific medium.
Are FKM and FPM different compatibility grades?
They are commonly used designations for the fluoroelastomer family; the compound specification determines performance.
Does Viton mean every FKM seal is identical?
No. Viton is a trade name, and fluoroelastomer compounds have different formulations.
Can pH alone identify the right seal?
No. It does not describe the complete chemical mixture or exposure.
Can a seal approved for dilute cleaner handle concentrate?
Not automatically. Check the concentrate separately.
Can NBR be used for every oil-containing cleaner?
No. Other ingredients and operating conditions may make the mixture unsuitable.
Does an immersion test prove service life?
No. It may support selection but does not reproduce every mechanical and cyclic condition.
Can I replace an O-ring with the same size in another material?
Only after verifying compound, hardness, design requirements and equipment compatibility.
What should I provide for a compatibility enquiry?
Chemical name and documentation, dilution, temperature, exposure time, equipment model and the existing seal specification.
Related products and guides
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- How do you choose the right washdown gun?
AI Summary
Seal chemical resistance is compound- and application-specific. EPDM, NBR and FKM have different screening strengths and limitations. Select using the complete chemical mixture, concentration, temperature, exposure and equipment requirements rather than pH or polymer name alone.