Buna-N vs EPDM vs FKM vs PTFE: Valve Seal Material Guide
Best low-cost choice for many oils, fuels, greases, and hydraulic fluids.
Best common choice for water, steam, caustic, ozone, weathering, and many aqueous services.
Best upgrade for higher-temperature oil, fuel, solvent, and demanding chemical service.
Best chemical barrier for aggressive chemicals, high purity, seats, liners, and diaphragm faces.
| Material | Also Called | Strong In | Weak In | Common Parts | Best Use Case |
|---|---|---|---|---|---|
| Buna-N | NBR, Nitrile | Petroleum oils, fuels, greases, hydraulic fluids | Ozone, weathering, steam, many ketones, esters, chlorinated solvents | O-rings, seals, gaskets | Cost-effective oil and fuel sealing |
| EPDM | EPR, ethylene propylene | Water, steam, caustic, ozone, weathering, many aqueous chemicals | Oils, fuels, hydrocarbons, many solvents | O-rings, seals, diaphragms | Water and wastewater chemical service |
| FKM | Fluorocarbon, Viton-type | Oils, fuels, high heat, many solvents, many aggressive chemicals | Steam, hot water, strong bases, amines, ketones | O-rings, seals, seats | Higher-temperature chemical and hydrocarbon service |
| PTFE | Teflon-type fluoropolymer | Broad chemical resistance, aggressive acids, oxidizers, high-purity service | Creep, cold flow, permeation in certain media, low elasticity | Seats, liners, diaphragm faces, packing | Chemical barrier and purity-critical service |
| Application | Best Starting Material | Why |
|---|---|---|
| Potable water | EPDM | Strong fit for water and many aqueous services |
| Wastewater | EPDM | Common elastomer for water/wastewater valves |
| Hot water / steam | EPDM | Better starting point than alternatives in steam service |
| Petroleum oil | Buna-N or FKM | Buna-N economical; FKM upgrades temperature margin |
| Diesel / fuel oil | Buna-N or FKM | Hydrocarbon service generally points away from EPDM |
| Gasoline | FKM or Buna-N | FKM often preferred for higher performance |
| Caustic soda | EPDM | EPDM often strong in aqueous caustic service |
| Sodium hypochlorite | Application-specific | Check concentration, temperature, off-gassing, valve design |
| Aggressive acid | PTFE or FKM | Must verify acid type, concentration, temperature |
| Solvents | FKM or PTFE | Solvent family decides the answer |
| High-purity chemicals | PTFE / PFA-wetted | Low contamination and broad chemical resistance |
| Outdoor ozone/weathering | EPDM or FKM | Buna-N usually weaker outdoors |
Sodium Hypochlorite — Do Not Use the Generic Hierarchy
Variables requiring investigation include concentration, temperature, valve body material, O-ring material, seat material, diaphragm material, off-gassing behavior, and valve construction type. Sodium hypochlorite can involve oxidizer exposure, off-gassing, trapped cavity pressure, and crystallization concerns. Always verify the complete valve construction before selection.
What Happens When the Wrong Seal Material Is Specified
- Wrong material enters service
- Chemical attack begins
- Seal swells, hardens, cracks, or creeps
- Torque increases
- Bubble-tight shutoff is lost
- Internal leakage begins
- External leakage or body-joint failure follows
- The valve brand gets blamed
- The same wrong spec gets reordered
Most recurring valve failures are not mysterious. The valve is often doing exactly what the material spec allowed it to do.
Start with Buna-N or FKM.
Start with EPDM.
Start with FKM.
Evaluate PTFE, PFA, or PTFE-faced construction.
Stop and verify the full valve construction.
Frequently Asked Questions
Is Buna-N the same as NBR?
Yes. These terms refer to nitrile rubber for oil, fuel, grease, and hydraulic-fluid applications.
Is Buna-N better than EPDM?
Not universally. Buna-N suits petroleum oils and fuels. EPDM suits water, steam, caustic, and aqueous services.
Is EPDM better than FKM?
Only in the right service. EPDM excels with water and caustic. FKM excels with oils, fuels, solvents, and higher temperatures.
Is FKM the same as Viton?
FKM is the material class. Viton is a trade name. Use FKM generically unless specific compounds are needed.
Is PTFE better than FKM?
PTFE offers broader chemical resistance but lacks FKM's elasticity. PTFE works as seats and liners; FKM works as O-rings.
Which seal material works best for sodium hypochlorite?
There is no one-word answer. Sodium hypochlorite selection depends on concentration, temperature, pressure, valve type, off-gassing, body material, seat material, O-ring material, and diaphragm construction.
Which seal material works best for caustic soda?
EPDM is often a strong starting point for sodium hydroxide and caustic soda service, but the concentration and temperature still need to be confirmed.
Which seal material works best for oil and fuel?
Buna-N and FKM are usually better starting points for oil and fuel service than EPDM. FKM is often considered when temperature, solvent exposure, or chemical severity exceeds Buna-N's comfort zone.