Butterfly Valve Seat Types, Materials, and Selection Guide

Butterfly valve seats are generally classified into soft seats and metal seats. The fundamental difference between the two lies in how sealing is achieved and the service conditions they are designed for.

Soft-seated valve seats rely on the elastic deformation of non-metallic materials such as rubber or PTFE to create a seal. They offer excellent sealing performance and strong tolerance to assembly deviations and minor pipeline deformation. As a result, they are commonly used in water supply, wastewater treatment, and HVAC systems operating under low to medium pressure with water-based media.

Metal-seated valve seats achieve sealing through metal-to-metal contact. Their performance depends more heavily on structural design and machining accuracy, making them suitable for harsher service conditions such as high temperature, high pressure, or media containing solid particles.

In practical selection, there is no absolute “better” choice between the two. The key is whether the seat type is properly matched to the media characteristics and operating conditions.

For a detailed comparison and clear selection guidelines for these two seat types under different operating conditions, please refer to the full article "Soft-Seated vs Metal-Seated Butterfly Valves: Differences and Selection Guide."

The impact of temperature and pressure on different valve seat materials

In butterfly valve applications, temperature and pressure directly affect sealing behavior and service life during long-term operation. Different seat materials respond to thermal and pressure loads in very different ways.

1.EPDM seats
As temperature continues to rise or approaches the material’s upper limit, EPDM gradually hardens and loses elasticity. Prolonged high pressure or frequent pressure fluctuations can also lead to permanent deformation.

For these reasons, EPDM is best suited to water system applications where temperature and pressure remain relatively stable.

2.NBR seats
Compared with EPDM, NBR has lower heat resistance and aging performance. When exposed to elevated temperatures or sustained higher pressures, NBR hardens and ages more quickly.

 Its use is therefore more appropriate for oil-based media where both temperature and pressure are well controlled.

3.PTFE seats
Under continuous pressure fluctuations or elevated temperatures, PTFE is prone to cold flow (creep), which can reduce contact force at the sealing interface.

PTFE is well suited for corrosive media, but mainly in applications where operating conditions—especially pressure and temperature—are extremely stable.

4.FKM seats
FKM sacrifices some elasticity in exchange for excellent resistance to high temperatures and aggressive chemicals. When temperature or pressure remains close to the material’s upper limits over long periods, sealing performance may gradually decline.

 Even so, FKM remains a preferred choice for high-temperature oils and complex chemical media.

How to choose the right butterfly valve seat

Once the main seat types and their differences are clear, practical selection should return to engineering reality. The decision should start from the type of media, which is the core factor, rather than simply comparing material performance data in isolation.

First and foremost, the seat material must be compatible with the media. This is the most basic—and also the most critical—principle in butterfly valve selection.

1.Water-based systems (potable water, raw water, wastewater, HVAC)
→ EPDM seat is the preferred choice
EPDM is specifically optimized for water service. It offers good elasticity, stable long-term sealing performance, and a well-proven track record in engineering applications. For water systems, it remains the most common and lowest-risk option.

2.Raw water with sand or abrasive particles
→ EPDM as the standard choice; upgrade to wear-resistant seats (e.g. PU) when abrasion increases
In extremely abrasive intake conditions, especially where maintenance access is limited, metal-seated solutions may be considered as a further upgrade.

3.Oil or fuel media systems
→ NBR seat is preferred
NBR is designed for oil-based media and is not recommended for long-term water service.

4.Chemical or strongly corrosive media
→ PTFE or FKM seats are preferred (to be confirmed based on the specific media)
In these applications, chemical compatibility is the primary concern, rather than elastic sealing capability.

Common selection pitfalls

Misconception 1: “Higher-grade material means wider applicability.”
Using an expensive FKM seat in a standard cold-water pipeline is a waste of performance. For this type of service, EPDM is usually the more appropriate and efficient choice.

Misconception 2: “PTFE can handle everything.”
While PTFE offers excellent chemical resistance, it is vulnerable to abrasion. In water containing sand or solid particles, PTFE seats can wear out very quickly.

Misconception 3: “Metal seats are always more advanced.”
Installing a metal seat in a conventional concentric butterfly valve often results in poor sealing performance. True metal-to-metal sealing requires a double-offset or triple-offset valve design to work properly.

Summarize

At its core, butterfly valve seat selection is an engineering judgment, not a simple comparison of materials. Only by fully understanding media characteristics, the effects of temperature and pressure on material behavior, and the limitations of the valve structure itself can seat selection truly support long-term, stable system operation.

At Union Valve, we approach seat selection from real project conditions. By matching material properties, operating conditions, and valve design, we help customers identify potential risks early and ensure reliable, long-term valve performance.

If you are selecting a butterfly valve seat for a specific service condition, or would like to verify whether your current selection is appropriate, we welcome you to get in touch and discuss your application with us.

Related Articles:

• Soft-Seated vs Metal-Seated Butterfly Valves: Differences and Selection Guide
• EPDM vs PTFE Butterfly Valve Seats: Selection Guide
• How to Replace a Butterfly Valve Seat
• Understanding Butterfly Valve Seats: The Differences Between Hard, Soft and Rubber Lined