The ball valve seat is one of the most critical components for ensuring a bubble-tight shutoff. It acts as the primary seal between the movable ball and the stationary valve body.
There are three main categories of seats: soft seat, hard seat, and metal seat for different service conditions. Soft seats are more flexible and provide effective sealing, while hard seats are ideal for harsh conditions like high pressures. Metal seated trunnion ball valves excel in mechanical strength, suitable for extremely high-temperature and abrasive media settings.
This guide will help you choose the right material by understanding the concept of balancing chemical compatibility, temperature ranges, and pressure limits.
PEEK: The Choice for High-Pressure Hardness
PEEK (Polyether Ether Ketone), belonging to hard seats, is a high-performance thermoplastic polymer with excellent thermal, chemical, and mechanical properties. PEEK seats are widely used in applications that need dimensional stability even under extreme conditions.
PEEK offers excellent mechanical strength and resistance to high temperatures (performing well within the range of -56°C to 315°C, as well as steam service up to 260°C). It is much harder than standard PTFE or reinforced Teflon. This hardness makes them suitable for high-pressure applications up to CL6000. Onero Valve ensures our PEEK materials comply with NORSOK M-710 or ISO 23936-2 standards, ensuring safety in explosive decompression environments.
However, the stiffness of this material requires a higher torque to achieve a perfect seal. Moreover, it can be brittle compared to elastomers and may fail if the fluid contains large solids. Engineers often use PEEK for oil and gas production, where pressure rapidly fluctuates, providing a durable barrier against explosive decompression.
Viton vs FFKM: Comparing Elastomer Resilience
The elastomers for the valve soft seat market offer many options for specific gas and liquid services.
One of them, Viton (Fluorocarbon elastomers, FKM, or FPM), is inherently compatible with a broad spectrum of chemicals. Because of this, which spans considerable concentration and temperature ranges, Viton has been widely accepted as a material for constructing knife gate valve seats.
This material can be used in most applications involving salt solutions, mineral acids, petroleum oils, and chlorinated hydrocarbons. Its temperature rating is from -29°C to 149°C, in colors gray, black, or red, and may be used on bleached paper lines. Viton is not suitable for steam or hot water, but some O-ring grades work in hydrocarbon lines with hot water, depending on the type.
FFKM (Perfluoroelastomer) is a much better alternative to Viton for extreme environments. It remains stable at temperatures up to 327°C (620°F), depending on the specific grade. This makes it the superior choice for aggressive acids and ethers that would degrade standard FKM (Viton) seals.
FFKM also offers excellent resistance to aggressive chemicals such as acids, ketones, esters, and solvents, along with strong performance in steam, water, weathering, and sunlight exposure. Compared with FKM, it provides slightly better electrical resistance and short-term resilience, making it suitable for critical sealing applications in harsh industrial environments.
Matching Seat Materials to Severe Service Conditions
When fluids contain sand or metal chips, a metal-seated trunnion ball valve is necessary. Metal seats use hard coatings like Tungsten Carbide to resist erosion and are an ideal choice for temperatures exceeding the limits of polymers. Soft materials would, unfortunately, simply melt or wash away in these extreme conditions.
Below is a comparison table that summarizes the key performance metrics for common seat materials that were discussed above. Understanding this will narrow down the options and select the right material.
| Materials | Types | Temperature Range | Chemical Resistance | Best Applications |
| PEEK (Polyether Ether Ketone) | Hard seat thermoplastic | -56°C to 315°C (steam up to 260°C) | Excellent resistance to hydrocarbons, steam, and other aggressive chemicals. | High-pressure oil & gas service, fluctuating pressure systems, and CL6000 applications. |
| Viton (Fluorocarbon elastomers, FKM, or FPM) | Soft seat elastomer | -29°C to 149°C | Good resistance to oils, fuels, mineral acids, salt solutions, and chlorinated hydrocarbons, but limited for steam or hot water. | General chemical service, petroleum processing, knife gate, and ball valve soft seats. |
| FFKM (Perfluoroelastomer) | High- performance elastomer | -15°C to 205°C | Near-universal chemical resistance, including acids, ketones, esters, solvents, steam, and water. | Extreme chemical processing, high-temperature sealing, and critical and corrosive environments. |
Selection logic must also consider the glass transition temperature of plastics. If the material becomes too cold, it loses its ability to seal. If it becomes too hot, it loses its mechanical strength and flows out of the seat pocket. Therefore, always verify the specific grade of the material with your supplier.
Conclusion
Choosing the right seat material needs a deep understanding of the operating environment. PEEK offers the hardness needed for high-pressure gas, while elastomers like Viton and FFKM provide flexible sealing. For the most abrasive or high-heat services, a metal-seated trunnion ball valve remains the industry standard.
Onero Valve provides expert guidance on material selection for all our industrial valves. We ensure that seat materials such as PEEK and advanced elastomers are matched to the required pressure, temperature, and chemical conditions.
Supported by our integrated manufacturing system, including CNC machining and multi-stage inspection, we maintain a strict quality management process to ensure all our products comply with API 6D and other international standards.
