Start with the medium: mineral oil, water, glycol, fuel, steam and aggressive chemicals require different materials.
Temperature, pressure, movement, extrusion gap and required lifetime are equally important. A material family is not a complete specification.
NBR is widely used with mineral oils; EPDM is often selected for water and glycol systems but is generally unsuitable for mineral oil. HNBR offers improved heat and ageing resistance over many NBR grades.
FKM suits many oils, fuels and elevated-temperature applications. FFKM may offer broader chemical resistance, but compatibility must still be verified for the actual grade.
PU is often chosen for wear-resistant hydraulic sealing, while PTFE offers low friction and broad chemical resistance but behaves differently from elastomers.
Comparison of common sealing materials
This table is general guidance, not material approval. Actual temperature limits and compatibility depend on compound, hardness, exposure time and operating conditions.
How the medium affects material selection
Mineral oil and hydraulic oil: NBR is a common starting point. HNBR, FKM and selected PU grades may be appropriate depending on temperature, wear and pressure. EPDM is generally unsuitable for mineral-oil-based fluids.
Water and water-glycol: EPDM is often a useful starting point, but inhibitors, concentration and temperature must be assessed. Other compounds may work with specific mixtures.
Fuels and solvents: FKM can be suitable for many fuels, but not all solvents. Verify the exact chemical formulation before selecting a compound.
Aggressive chemicals and high temperatures: FFKM or PTFE may be considered, but neither is universally suitable. PTFE also requires an appropriate seal design.
Five questions before ordering
- What is the medium, including concentration and additives?
- What are the continuous temperature and short-term peaks?
- What are the operating pressure, pressure spikes and motion?
- What geometry, dimensions and hardness are required?
- Are test reports, certificates or specific approvals needed?
Common material selection mistakes
Selecting a material from a generic temperature chart alone. A compound may tolerate a temperature in air but not in the actual medium.
Assuming all NBR, FKM or EPDM grades have identical properties. Compounds within the same family can differ substantially.
Replacing a seal with a more expensive material without checking groove design, squeeze, friction and mechanical properties.
General technical guidance, not approval for a specific application. Confirm material grade, dimensions and suitability for actual operating conditions.
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