Butterfly Valve Seat Materials: EPDM vs Buna-N vs Viton

The seat, not the disc or body, is what actually decides whether a butterfly valve survives your service. Get the seat material wrong and the valve fails early, no matter how well it was installed or how good the disc and body are.

This guide covers the three elastomers you'll run into on wafer butterfly valves — EPDM, Buna-N, and Viton — at the level of established, published reference information, and is honest about what Apex actually stocks today versus what we can source on request.

Written by the Apex Flow Solutions technical desk — twenty years of industrial distribution experience behind every guide.

Quick answer: which seat for your service

EPDM: the water and general-service seat

What it is: ethylene propylene diene monomer, a synthetic rubber built for water and weather resistance. It's the default seat on Apex's stainless-disc (SE) butterfly line.

Good for: potable and non-potable water, hot water, steam service, dilute acids and bases, alcohols, and general HVAC duty.

Poor for: petroleum oils, fuels, and hydrocarbons — EPDM absorbs them and swells, which destroys the seal.

Typical temperature range: roughly -40°F to 300°F, compound-dependent — a general reference figure, not a guarantee for a specific manufacturer's formulation.

Product block: EPDM ships as standard on every stainless-disc (SE) valve in our line, gear and lever alike — for example the 4 in. wafer butterfly valve, stainless disc, EPDM seat, gear operated (9650G4SE), the 6 in. wafer butterfly valve, stainless disc, EPDM seat, lever operated (9650L6SE), and the 8 in. wafer butterfly valve, stainless disc, EPDM seat, gear operated (9650G8SE).

Buna-N (nitrile): the oil, fuel, and air seat

What it is: nitrile rubber (NBR), the standard elastomer for petroleum-based media. It's the default seat on Apex's ductile-iron-disc butterfly line.

Good for: petroleum oils, fuels, hydraulic fluid, compressed air, and natural gas.

Poor for: ozone and weathering exposure, strong oxidizers, and chlorinated water or hypochlorite — Buna-N hardens and cracks under sustained oxidizer exposure. This is one of the most common misapplications we see: a Buna-N valve installed on a chlorinated water or hypo dosing line.

Typical temperature range: roughly -40°F to 250°F, compound-dependent.

Product block: Buna-N ships as standard on every ductile-iron-disc valve in our line — for example the 4 in. wafer butterfly valve, ductile iron disc, Buna-N seat, gear operated (9650G4), the 6 in. wafer butterfly valve, ductile iron disc, Buna-N seat, lever operated (9650L6), and the 3 in. wafer butterfly valve, ductile iron disc, Buna-N seat, lever operated (9650L3).

Viton (FKM): the aggressive-chemistry seat — and where our butterfly line stands today

What it is: fluoroelastomer (FKM), the seat material of choice when the media is hot, aggressive, or oxidizing — exactly the service where Buna-N fails.

Good for: chlorinated water, sodium hypochlorite, ozone, most oils and fuels, and higher-temperature service generally.

Poor for: hot water and steam service, where EPDM performs better and costs less; also some polar solvents and ketones.

Typical temperature range: roughly -15°F to 400°F, compound-dependent.

The catalog-reality note: our wafer butterfly line doesn't currently include a Viton-seat option — both disc/seat sub-lines are fixed pairings (stainless disc with EPDM, ductile iron disc with Buna-N), and there's no Viton butterfly SKU on the site today. If your service genuinely calls for FKM — hypochlorite, ozone, or another oxidizer at meaningful concentration — tell us the chemical, concentration, and size and we'll source it rather than sell you a seat that's the wrong material for the job. We do stock Viton-seated check valves today; see our Buna vs. Viton check valve seats guide for how we handle that comparison where the product exists.

Comparison at a glance

*General reference ranges for standard compounds. Actual limits vary by manufacturer formulation — see "When to ask us" below.

Decision panel

When to ask us

Everything above is standard, widely published elastomer reference information — the kind you'd find in any manufacturer's compatibility chart. What it isn't is a guarantee for your specific service: chemical compatibility depends on concentration, temperature, exposure duration, and the exact formulation of the elastomer, and a general reference table can't responsibly promise any of those for your application.

Plain water, general HVAC, or a straightforward oil/fuel application? The guidance above is enough to order with confidence. Dosing a specific chemical — hypochlorite at a particular concentration, an acid, a caustic, a solvent, anything outside plain water or general oil/fuel service — tell us the chemical and concentration and we'll confirm the right elastomer, sourcing it if it's not already on our shelf, before you order.

Where this connects

Choosing a seat material is only part of picking the right valve — see our butterfly valve selection guide for body style and our broader valve seat material guide for how EPDM, Buna-N, Viton, and PTFE compare across ball, check, and butterfly valves generally. If a seat has already failed, our troubleshooting guide covers how to read the failure and whether it's a repair or a replacement.

Frequently Asked Questions

What is the difference between EPDM and Buna-N butterfly valve seats?

EPDM is built for water, steam, and dilute chemical service and handles hot water up to roughly 300°F. Buna-N is the choice for petroleum-based media — oils, fuels, hydraulic fluid, and natural gas. EPDM swells when exposed to petroleum products, and Buna-N hardens and cracks under sustained chlorine or ozone exposure. Mixing them up is a common cause of early seat failure.

Does Apex sell a Viton-seated butterfly valve?

Not on the shelf today — our current wafer butterfly line pairs stainless discs with EPDM seats and ductile iron discs with Buna-N seats, with no Viton option in either. If your service needs FKM, tell us the chemical, concentration, and size and we'll source it rather than sell you a seat that isn't right for the job.

Can I use an EPDM butterfly valve on a chlorinated water line?

Yes — EPDM has good resistance to chlorinated water at typical potable and municipal concentrations, and it's the standard seat for that service on most butterfly valves, including ours. Viton becomes the better choice at higher hypochlorite concentrations or with continuous ozone exposure; if you're not sure where your application falls, tell us the concentration and we'll confirm.

Why does a Buna-N butterfly valve fail quickly on a hypochlorite line?

Buna-N (nitrile) has poor resistance to oxidizers. Sodium hypochlorite and ozone attack the rubber's chemical structure, causing it to harden and crack rather than swell. The failure can happen within months on a continuously dosed line — well established across elastomer reference material — which is why hypochlorite service calls for EPDM or Viton, not Buna-N.

What temperature range can a butterfly valve seat handle?

It depends entirely on the seat material: EPDM covers roughly -40°F to 300°F, Buna-N roughly -40°F to 250°F, and Viton roughly -15°F to 400°F, all compound-dependent general reference figures. Confirm against the manufacturer datasheet for your exact valve, especially near either end of the range.