EPDM vs NBR vs FKM (Viton) Valve Seats: Selection for Water, Oil and Chemicals
Technical guide · Supreme Valves India · Updated 2026-10-25
Resilient-seated butterfly valves, soft-seated ball valves, knife gate valves and many check valves depend on an elastomer or polymer seat. The body may be ductile iron or stainless steel, but if the seat material is wrong for the fluid the valve will leak within weeks. The three elastomers on most datasheets are EPDM, NBR and FKM (often called by the trade name Viton), with PTFE as the main polymer alternative.
Quick comparison
| Material | Good for | Avoid | Typical temperature range |
|---|---|---|---|
| EPDM | Water, potable water, sea water, glycol, low-pressure steam, dilute acids and alkalis, outdoor exposure | Oils, fuels, hydrocarbons, most solvents | About -30 to +120 °C |
| NBR (Buna-N, nitrile) | Mineral oils, diesel, fuel oil, hydraulic oil, LPG, compressed air with oil, water at moderate temperature | Ozone and sunlight, ketones, strong acids, steam | About -20 to +90 °C |
| FKM (Viton) | Hydrocarbons including aromatics, many acids, hot oils, many chemicals | Hot water and steam, ketones, amines, some esters | About -20 to +200 °C |
| PTFE / RPTFE | Almost all chemicals, high-performance butterfly and ball valve seats | Abrasive slurries; creeps under high load and temperature | About -50 to +200 °C, depending on pressure |
Temperature ranges vary by compound and by pressure, so treat these as guide values and confirm with the valve's pressure-temperature chart.
EPDM
EPDM is the default seat for water: municipal and drinking water, cooling water, HVAC chilled and heating water, fire water, and seawater. It resists ozone and weathering, so it is also used outdoors. Peroxide-cured grades handle hot water and low-pressure steam better than sulphur-cured grades. Its weakness is oil: even small amounts of oil in compressed air or water lines can make EPDM swell.
NBR
NBR is the general-purpose oil-resistant elastomer. It is the usual seat for fuel and lubricating oil, diesel, hydraulic systems and LPG. It ages in sunlight and ozone, and its upper temperature limit is lower than EPDM's, so it isn't used for hot water or steam. Hydrogenated nitrile (HNBR) extends the temperature range and improves ozone resistance where needed.
FKM
FKM keeps its properties at higher temperatures and resists hydrocarbons, including aromatics such as benzene and toluene that attack NBR, along with many acids. It is the step up for hot oils, fuels with aromatic content and many chemical services. It is more expensive and performs poorly in hot water, steam and some polar solvents.
PTFE and lined valves
PTFE resists nearly all chemicals and is used as the seat in high-performance (double offset) butterfly valves and in most ball valves. For aggressive chemicals, fully PTFE, PFA or FEP lined valves isolate the fluid from the body entirely. PTFE is less resilient than elastomers, so it needs a design that maintains seat load, and it can creep under high load and temperature.
Common selection mistakes
- EPDM on oily compressed air. Compressor carry-over oil swells the seat. Use NBR.
- NBR in hot water. The seat hardens and cracks. Use EPDM.
- FKM in steam. It degrades. Use EPDM for low-pressure steam, or a metal-seated or high-performance valve.
- Ignoring cleaning chemicals. In food, pharma and water treatment, check the seat against the cleaning and disinfection chemicals as well as the process fluid.
- "Rubber lined" with no grade. Always state the elastomer and, for drinking water, the required approval.
What to include in an enquiry
Fluid and concentration, normal and maximum temperature, pressure, any cleaning chemicals, and approvals needed (drinking water, food contact). For butterfly valves, also give the body and disc material and flange drilling.
Frequently asked questions
Can EPDM seats be used for diesel or oil?
No. EPDM swells and softens in mineral oils, fuels and most hydrocarbons, and the seat will fail. Use NBR for oils and fuels at moderate temperature, or FKM for hydrocarbons at higher temperature or with aromatic content.
Which seat material is suitable for drinking water?
EPDM is the usual choice for potable water. The specific compound must carry the drinking water approval required at the site, for example WRAS in the UK or NSF/ANSI 61 in North America, so ask for the approval certificate rather than just 'EPDM'.
Is FKM (Viton) suitable for steam?
Generally not. FKM compounds have good dry heat and chemical resistance but degrade in hot water and steam. For low-pressure steam and hot water, a peroxide-cured EPDM is normally used; for higher temperatures, use metal or PTFE-based seats.
Related products & guides
Continue to RFQ
Contact / RFQ form · Quotation checklist · EPC supplier · AEO SEO GEO hub
Project RFQ: EPC · Fire · How to buy · Lead hub · Contact / RFQ