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Introduction
The sealing design of a butterfly valve directly affects its shutoff performance, media compatibility, temperature resistance, operating characteristics, and suitability for different applications. Depending on the sealing materials and design, butterfly valves are generally classified into soft-seated butterfly valves and metal-seated butterfly valves.
Soft-seated butterfly valves typically use non-metallic materials such as EPDM, NBR, FKM, or PTFE as sealing elements. They are commonly used in applications involving normal or moderate temperatures, relatively clean media, and requirements for reliable shutoff and cost efficiency. In contrast, metal-seated butterfly valves mainly use metal sealing components and rely on optimized valve design and precise sealing surface contact to achieve reliable shutoff. As a result, they offer greater application potential in demanding conditions involving high temperatures, erosion, wear, or long-term continuous operation.So, what are the main differences between soft-seated and metal-seated butterfly valves, and how should you choose between them?This article compares the two designs in terms of sealing materials, sealing performance, temperature capability, wear resistance, operating torque, cost, and actual operating conditions, helping you select a butterfly valve that better matches your piping system.
Table of Contents
- What Are Soft-Seated and Metal-Seated Butterfly Valves?
- What Are the Main Differences Between Soft-Seated and Metal-Seated Butterfly Valves?
- How to Choose Between Soft-Seated and Metal-Seated Butterfly Valves?
- Which Applications Require Extra Attention?
- FAQ
Keywords: Soft-Seated Butterfly Valve, Metal-Seated Butterfly Valve, Butterfly Valve, Double Eccentric Butterfly Valve, Triple Eccentric Butterfly Valve
You can watch the following videos for a quick overview:
1. What Are Soft-Seated and Metal-Seated Butterfly Valves?
1.1 What Is a Soft-Seated Butterfly Valve?
A soft-seated butterfly valve is a butterfly valve that uses rubber, PTFE, or other non-metallic materials with a certain degree of deformation compensation capability as sealing elements.
Common sealing materials include:
- EPDM
- NBR
- FKM
- PTFE
When the valve closes, the seat material forms a seal with the disc through elastic deformation or controlled contact deformation. This allows the sealing surface to compensate for certain machining and assembly deviations while achieving reliable shutoff.
It should be noted that different soft sealing materials have significantly different properties. For example, EPDM, NBR, and FKM are elastomeric materials, while PTFE has different material characteristics and sealing mechanisms compared with rubber.
Therefore, during valve selection, the specific seat material should be determined according to the medium, temperature, pressure, and other operating conditions.
Typical Characteristics of Soft-Seated Butterfly Valves
- Good shutoff performance
- Relatively low operating torque
- Simple valve structure
- Relatively low manufacturing cost
- Various non-metallic seat materials available
- Suitable for normal and moderate temperature applications
Therefore, soft-seated butterfly valves are commonly used in water treatment, HVAC systems, water supply and drainage, and certain general industrial fluid control applications.
1.2 What Is a Metal-Seated Butterfly Valve?
A metal-seated butterfly valve typically uses metal or other high-temperature and wear-resistant materials as the sealing pair.
Common sealing materials include:
- Stainless steel
- Alloy steel
- Hard alloys
- Composite sealing materials using metal and graphite
- Other high-temperature and wear-resistant materials
Metal-seated butterfly valves mainly rely on precise sealing surface machining, optimized sealing structures, and appropriate sealing contact pressure to achieve reliable shutoff.
Metal-seated butterfly valves are commonly associated with eccentric butterfly valve designs, especially triple eccentric butterfly valves. However, it is important to understand that an eccentric valve structure does not directly determine whether the valve uses a soft seat or a metal seat.
For example, some double eccentric high-performance butterfly valves can use PTFE, RPTFE, or other non-metallic seats. Therefore, determining whether a butterfly valve is soft-seated or metal-seated requires checking both the seat or sealing ring material and the actual sealing structure.
The valve should not be classified solely based on whether it is a concentric, double eccentric, or triple eccentric butterfly valve.
Typical Characteristics of Metal-Seated Butterfly Valves
- Suitable for high-temperature applications
- Good wear resistance
- Strong resistance to media erosion
- Suitable for certain demanding industrial environments
- Higher requirements for sealing surface machining and manufacturing accuracy
Therefore, metal-seated butterfly valves have significant application value in demanding conditions involving high-temperature steam, thermal oil, erosive media, and other severe industrial services.
2. What Are the Main Differences Between Soft-Seated and Metal-Seated Butterfly Valves?
Soft-seated and metal-seated butterfly valves do not have an absolute relationship of one being better than the other. Instead, they represent two different sealing solutions designed for different operating conditions.
In practical applications, valve selection should not focus only on whether the seat is “soft” or “metal.” Instead, factors such as sealing performance, temperature, media characteristics, wear, operating torque, and maintenance cost should all be considered.
2.1 Sealing Performance and Leakage Requirements
Soft sealing materials typically have a certain degree of elasticity or contact deformation capability. Therefore, when the valve closes, the seat can conform more closely to the sealing surface of the disc.
As a result, soft-seated butterfly valves often provide advantages in applications involving relatively clean media, moderate operating conditions, and higher requirements for shutoff performance.
In contrast, metal-seated butterfly valves mainly rely on sealing surface machining accuracy, sealing structure, and appropriate sealing contact pressure to achieve reliable shutoff.
Modern high-performance metal-seated butterfly valves can also achieve excellent sealing performance through optimized designs and advanced manufacturing processes. Therefore, it is incorrect to simply assume that “soft-seated valves never leak while metal-seated valves always leak.”
Actual leakage performance should still be confirmed according to the specific valve design, leakage class, and applicable standards.
2.2 Temperature Capability and Media Compatibility
Temperature is one of the most important factors when selecting a sealing design.
The temperature capability of a soft-seated butterfly valve mainly depends on the specific seat material. For example, EPDM, NBR, FKM, and PTFE have different temperature limits and media compatibility characteristics.
Therefore, even among soft-seated butterfly valves, the actual application range can vary significantly depending on the sealing material.
At elevated temperatures, standard rubber sealing materials may experience aging, hardening, softening, or permanent deformation, which can eventually affect sealing performance.
In comparison, metal sealing materials are generally more suitable for high-temperature environments. Therefore, metal-seated butterfly valves can be considered for applications involving high-temperature steam, thermal oil, and high-temperature gases.
However, the actual temperature capability of a butterfly valve still depends on the specific materials, sealing structure, and product design parameters. It should not be determined solely by whether the valve is classified as soft-seated or metal-seated.
2.3 Wear, Erosion, and Service Life
When the medium contains solid particles, dust, or has strong erosive characteristics, the wear resistance of the sealing surfaces becomes particularly important.
Soft sealing materials may wear over time under continuous erosion and friction, which can gradually affect the valve’s sealing performance. Therefore, for media containing particles or with significant abrasive properties, the wear resistance of the soft seat material should be carefully evaluated.
Metal sealing materials generally offer higher mechanical strength and better wear resistance. Therefore, under high-temperature, abrasive, erosive, or long-term continuous operating conditions, a properly designed metal sealing structure may provide better durability.
However, it should not be assumed that a metal-seated butterfly valve will always have a longer service life.
The actual service life of a valve can also be affected by factors such as:
- Media characteristics
- Operating frequency
- Pressure differential
- Sealing materials
- Manufacturing quality
- Installation conditions
- Maintenance practices
2.4 Operating Torque and Actuator Selection
Soft-seated butterfly valves generally provide good sealing conformity and, under appropriate design and operating conditions, often require relatively low operating torque.
Therefore, they can usually be combined with pneumatic or electric actuators to provide an economical automated valve solution.
In comparison, metal-seated butterfly valves may require greater sealing contact pressure to achieve reliable shutoff. As a result, under the same valve size and operating conditions, their operating torque may be higher.
However, actual valve torque is not determined by the sealing design alone. It can also be affected by valve size, operating pressure, differential pressure, media characteristics, valve design, and operating frequency.
Therefore, pneumatic and electric actuators should be selected based on the actual calculated valve torque, with an appropriate safety factor included.
2.5 Pressure Capability and Actual Operating Conditions
Soft-seated and metal-seated butterfly valves are often simplified as “soft seats are for low pressure and metal seats are for high pressure.” However, this statement is not entirely accurate.
In certain high-temperature, high differential pressure, or demanding industrial applications, metal-seated butterfly valves may offer greater application potential.
However, the actual pressure capability of a butterfly valve is not determined by the sealing design alone.
Valve pressure capability is also related to:
- Valve body design
- Pressure rating
- Body and trim materials
- Stem and disc strength
- Sealing structure
- Applicable design standards
Therefore, it is incorrect to assume that soft-seated butterfly valves can only be used at low pressure or that metal-seated butterfly valves are automatically suitable for high-pressure applications.
For high-pressure or high differential pressure applications, the specific valve model and technical specifications should always be confirmed.
2.6 Cost and Maintenance
From the perspective of initial purchase cost, soft-seated butterfly valves often have an advantage.
Because of their relatively simple structure and the mature application of non-metallic sealing materials, they generally provide good cost efficiency in conventional industrial projects.
Metal-seated butterfly valves usually require higher-grade materials, greater machining accuracy, and more demanding manufacturing processes. Therefore, their initial purchase cost may be higher.
However, the purchase price alone does not represent the total lifecycle cost.
For valves used in high-temperature, abrasive, erosive, or difficult-to-maintain systems, selecting an appropriate metal-seated structure may help reduce maintenance frequency and replacement requirements.
Therefore, valve selection should consider:
- Initial purchase cost
- Expected service life
- Maintenance intervals
- Downtime costs
Soft-Seated vs. Metal-Seated Butterfly Valve Comparison
| Comparison Item | Soft-Seated Butterfly Valve | Metal-Seated Butterfly Valve |
|---|---|---|
| Sealing Material | EPDM, NBR, FKM, PTFE, and other non-metallic materials | Metal and high-temperature or wear-resistant materials |
| Shutoff Performance | Generally provides good sealing performance under conventional conditions | Depends on sealing structure, machining accuracy, and valve design |
| Temperature Capability | Depends on the specific seat material | Generally more suitable for high-temperature applications |
| Wear Resistance | Depends on sealing material and media characteristics | Generally better suited for abrasive and erosive conditions |
| Operating Torque | Usually relatively low | May be higher depending on the valve design |
| Pressure Capability | Depends on valve design and pressure rating | Also depends on valve design and pressure rating |
| Service Life | Affected by material, media, and operating conditions | May provide better durability in high-temperature and abrasive applications |
| Initial Cost | Usually lower | Usually higher |
| Typical Applications | Normal or moderate temperatures, clean media, and general industrial services | High temperature, erosion, wear, and demanding industrial applications |
3. How to Choose Between Soft-Seated and Metal-Seated Butterfly Valves?
For most users, the most important question is not simply understanding the definitions of the two sealing designs, but determining which solution is more suitable for the actual operating conditions.
Therefore, the following factors should be considered during valve selection.
Butterfly Valve Seat Selection Guide
| Operating Condition | Recommended Evaluation Direction | Additional Factors to Confirm |
|---|---|---|
| Normal temperature and clean media | Evaluate soft-seated designs first | Media compatibility, pressure rating, leakage requirements |
| High shutoff requirements | Soft-seated designs often offer advantages | Specific leakage class |
| High-temperature media | Evaluate metal-seated designs | Actual temperature, materials, pressure rating |
| Particle-containing, erosive, or abrasive media | Evaluate wear-resistant metal-seated designs | Particle size, concentration, and flow velocity |
| Frequent operation | Do not select based only on seat type | Valve structure, torque, seat wear, actuator configuration |
| High differential pressure | Evaluate according to the specific valve structure | Pressure rating, torque, cavitation, and erosion risks |
3.1 Selection Based on Operating Temperature
Operating temperature is an important factor affecting sealing material selection.
If the media temperature is relatively low or within a conventional temperature range, a soft-seated butterfly valve can be evaluated first.
If the operating temperature is higher, the temperature resistance of the sealing material should be carefully confirmed. For applications involving high-temperature steam, thermal oil, or high-temperature industrial gases, a metal-seated structure can be further evaluated.
3.2 Selection Based on Media Characteristics
For clean water, air, and other relatively clean industrial media, soft-seated butterfly valves can usually meet most flow control and shutoff requirements.
However, if the medium contains solid particles, dust, or presents significant erosion and abrasion risks, greater attention should be given to the wear resistance of the sealing materials.
In such cases, a metal-seated butterfly valve designed for the specific operating conditions may be a more suitable option.
3.3 Selection Based on Leakage Requirements
If the system has high requirements for shutoff leakage performance, soft-seated designs often offer good advantages.
However, if the application also involves high temperatures, erosion, wear, or long-term continuous operation, leakage requirements should not be the only consideration.
A more comprehensive evaluation should include:
- Leakage class
- Operating temperature
- Media characteristics
- Valve structure
- Sealing materials
- Maintenance intervals
Only by balancing these factors can a more suitable butterfly valve solution be selected.
3.4 Selection Based on Operating Frequency
For automated systems involving frequent operation, it should not be assumed that either soft-seated or metal-seated designs are automatically more suitable.
Frequent operation may affect sealing surface wear, operating torque, and actuator service life.
Therefore, valve selection should consider the valve structure, sealing materials, actual pressure differential, and actuator configuration.
3.5 Selection Based on Lifecycle Cost
The purchase price is only one part of the total valve cost.
For relatively mild operating conditions, soft-seated butterfly valves generally provide lower initial costs and good overall cost efficiency.
However, for systems involving high temperatures, erosion, abrasion, or difficult maintenance conditions, maintenance costs, seal replacement frequency, and equipment downtime costs should also be considered.
Therefore, proper valve selection should not focus only on the initial purchase price but should evaluate costs throughout the entire service life of the valve.
What Parameters Should You Provide When Consulting KST About Butterfly Valve Selection?
To help engineers select the most suitable butterfly valve, it is recommended to provide the following information when consulting KST:
- Medium name
- Maximum operating temperature
- Normal operating pressure and maximum pressure
- Pressure differential across the valve
- Pipe size
- Connection type
- Leakage requirements
- Operating frequency
- Manual, pneumatic, or electric actuation
In addition, for soft-seated applications, the required seat material should also be specified.
For high-temperature, erosive, or other demanding industrial applications, the sealing structure and material configuration should be further confirmed.
Compared with simply specifying “a soft-seated butterfly valve” or “a metal-seated butterfly valve,” providing complete operating parameters makes it easier to determine the most appropriate valve structure and configuration.
4. Which Applications Require Extra Attention?
Under certain special operating conditions, selecting a butterfly valve based only on whether it is soft-seated or metal-seated may not be sufficient. Additional technical evaluation is often required.
4.1 High-Temperature Applications
High temperatures can affect not only the performance of soft sealing materials but also the strength, thermal expansion, and sealing surface contact of metal components.
Therefore, for high-temperature applications, the following factors should be confirmed:
- Actual operating temperature
- Maximum and normal operating temperatures
- Temperature fluctuations
- Sealing materials
- Valve pressure rating
4.2 High Differential Pressure Applications
High differential pressure may increase valve operating torque and increase the pressure and erosion risks acting on the sealing surfaces.
Therefore, valve suitability should not be determined solely by whether the valve is soft-seated or metal-seated.
The following parameters should also be confirmed:
- Valve pressure rating
- Allowable differential pressure
- Operating torque
- Relevant fluid conditions
4.3 Media Containing Particles or Strong Erosion
If the medium contains solid particles, dust, or other abrasive substances, the wear rate of the sealing surfaces may increase significantly.
In such applications, the following factors should be evaluated:
- Particle size
- Particle concentration
- Media flow velocity
- Valve operating frequency
- Wear resistance of sealing materials
Metal-seated structures may offer advantages in these applications, but the final selection should still be based on the specific characteristics of the medium.
4.4 Strict Leakage Requirements
If the system has clearly defined leakage requirements, the valve should not be selected based only on whether it uses a soft or metal seat.
The following parameters should also be confirmed:
- Leakage class
- Testing standards
- Test medium
- Operating pressure
- Actual operating conditions
Especially under low-pressure, high-temperature, or special media conditions, actual sealing performance may be affected by multiple factors.
Typical Application Examples
Typical applications for soft-seated butterfly valves include:
- Normal-temperature water treatment
- HVAC systems
- Water supply and drainage
- General clean fluid applications
Typical applications for metal-seated butterfly valves include:
- High-temperature steam
- Thermal oil
- Industrial media with significant erosion or abrasion risks
However, industry names or application names alone cannot replace detailed operating parameters.
Final valve selection should still be confirmed according to temperature, pressure, differential pressure, media characteristics, and leakage requirements.
5. FAQ
1. Which is better: a soft-seated or metal-seated butterfly valve?
Neither is absolutely better than the other.
Soft-seated butterfly valves are generally more suitable for normal or moderate temperatures, relatively clean media, and applications where reliable shutoff and cost efficiency are important.
Metal-seated butterfly valves are more suitable for evaluating demanding conditions involving high temperatures, erosion, abrasion, or long-term continuous operation.
The final selection should still be based on the specific valve design, materials, and actual operating conditions.
2. Is a PTFE butterfly valve considered soft-seated or metal-seated?
In most cases, butterfly valves using PTFE seats or sealing materials are classified as soft-seated or non-metal-seated valves.
However, PTFE has different physical characteristics compared with elastomeric materials such as EPDM and NBR.
Therefore, not all soft-seated materials should simply be described as elastic materials. The actual valve structure and sealing configuration should also be considered.
3. Is a double eccentric butterfly valve always metal-seated?
No.
Double eccentric refers to the structural design of the valve, while soft-seated or metal-seated classification mainly depends on the seat and sealing materials.
Some double eccentric high-performance butterfly valves can use PTFE, RPTFE, or other non-metallic seats. Other designs may use different sealing structures.
Therefore, a butterfly valve should not be classified as metal-seated simply because it has a double eccentric design.
4. Are metal-seated butterfly valves always suitable for high-pressure applications?
Not necessarily.
Metal-seated butterfly valves offer greater application potential in certain high-temperature, high differential pressure, and demanding industrial applications.
However, the actual pressure capability of a valve still depends on the valve body design, pressure rating, material strength, sealing structure, and applicable product standards.
Therefore, it is incorrect to assume that every metal-seated butterfly valve is automatically suitable for high-pressure service.
5. Do metal-seated butterfly valves always have a longer service life?
Not necessarily.
Under high-temperature, abrasive, erosive, or long-term continuous operating conditions, a properly designed metal sealing structure may provide better durability.
However, actual valve service life can also be affected by media characteristics, operating frequency, pressure differential, sealing materials, manufacturing quality, installation, and maintenance.
Therefore, service life cannot be determined solely by whether the butterfly valve is soft-seated or metal-seated.
6. Should water systems use soft-seated or metal-seated butterfly valves?
For most normal-temperature water treatment, water supply, drainage, and HVAC systems, soft-seated butterfly valves can generally be evaluated first.
However, if the water temperature is high, the medium contains particles, significant erosion is present, or special durability requirements exist, the sealing structure and materials should be further evaluated according to the actual operating conditions.