Mechanical Seal Secondary Materials – Quick Selection Guide
Choose the right sealing material for your pumping application.
1. Material Selection at a Glance
| Material | Best Applications | Typical Temperature* | Avoid / Caution |
|---|---|---|---|
| NBR (Nitrile / Buna-N) | General water, mineral oils, diesel, hydraulic fluids | -30°C to +100°C | Steam, strong chemicals, high temperatures |
| EPDM | Hot water, steam, seawater, glycol, mild acids and alkalis | -40°C to +150°C | Petroleum oils, diesel, fuels |
| FKM (Viton®) | Hot oils, fuels, hydrocarbons, many chemicals | -20°C to +200°C | Steam, prolonged hot water, ketones, amines |
| PTFE (Teflon®) | Aggressive chemicals, acids, solvents, pharmaceutical and chemical processing | -200°C to +260°C | Limited elasticity; special seal design required |
| Flexible Graphite | High-temperature service, steam, hot oils, metal bellows seals | Grade and design dependent | Strong oxidisers; limited flexibility |
| FFKM | Aggressive chemicals combined with high temperatures | Up to +300°C (special grades) | High cost |
Temperatures are approximate material capabilities, not guaranteed operating limits for a complete mechanical seal.
2. Quick Selection by Pumping Media
| Pumping Media | Recommended Secondary Seal Material |
|---|---|
| Clean water (ambient temperature) | NBR (standard), EPDM |
| Cold water / General water pumps | NBR |
| Hot water | EPDM |
| Steam | Steam-grade EPDM / Graphite for suitable high-temperature designs |
| Seawater / Salt water | EPDM or NBR |
| Wastewater / Sewage | NBR or EPDM |
| Mineral oil / Lubricating oil | NBR, FKM for higher temperatures |
| Hot oil / Thermal oil | FKM, Graphite for suitable high-temperature designs |
| Diesel / Fuel oil | NBR or FKM |
| Petrol / Gasoline | FKM |
| Glycol / Water-based coolant | EPDM |
| Mild acids / Alkalis | EPDM or PTFE, depending on concentration |
| Strong acids / Aggressive chemicals | PTFE, FFKM where required |
| Chemical solvents | PTFE; FKM or EPDM only if compatible |
| Food / Beverage processing | Food-grade EPDM, FKM or PTFE, depending on media |
| Pharmaceutical processing | PTFE or approved sanitary-grade elastomers |
| High-temperature industrial processes | Graphite, PTFE or suitable high-temperature elastomers, depending on media and seal design |
3. Simple Rules to Remember
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NBR – First choice for general-purpose water and oil pumps.
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EPDM – First choice for hot water, steam and water-based applications.
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FKM / Viton® – Choose for fuels, hydrocarbons, hot oils and compatible chemical services.
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PTFE – Choose when broad chemical resistance is the main requirement.
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Flexible Graphite – Consider for high-temperature applications where conventional rubber is unsuitable.
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FFKM – Consider for demanding chemical and temperature combinations.
Important Notes
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Normal-temperature water does not automatically require EPDM. NBR is widely used and often more economical.
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For seawater, both NBR and EPDM may be suitable. Metallic component corrosion resistance must also be considered.
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Standard FKM is generally not recommended for continuous steam or hot-water service.
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PTFE and flexible graphite are non-elastomeric secondary sealing materials. They are not always direct replacements for rubber O-rings.
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Carbon seal faces are different from flexible graphite secondary seals. Carbon/graphite seal faces should be selected separately.
Final material selection must consider the exact liquid, chemical concentration, operating temperature, pressure and seal design. Always confirm compatibility for critical applications.