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For decades, valve manufacturers and valve users have suffered from the limited availability of ball valve seat materials. PEEK and PTFE are the two go-to materials of choice. So much so, that the habitual use of these two materials has left a void in performance, both physically and financially. Advances in materials processing techniques and quality processes are now starting to create alternatives that have clear competitive advantages for ball valve performance.
Given the stringent safety and quality requirements for valve seats, the selection of PTFE and PEEK has become an easy option as they have a proven track record and are recognised across the industry. This though does not come without it’s challenges. All too often PEEK is supplied under pricing pressure, which has caused the trusted use of PEEK on specifications to suffer from many quality and poor manufacturing practices;
This is an important subject but for now, let’s consider what is good about PEEK and PTFE and where their place is and isn’t for ball valve seats.
PTFE – what is it good for, where does it struggle
- Good chemical resistance, low coefficient of friction, low moisture absorption, and high electrical resistance. but its flexibility at low temperatures is a key feature.
- PTFE mechanical properties are low compared to other polymers and is very soft and cannot be used for higher pressures.
PEEK – what is it good for, where does it struggle
- Outstanding chemical resistance, very low moisture uptake, good fire performance, excellent mechanical strength across a broad temperature range, and good dimensional stability.
- Relatively High Cost. It is very hard and difficult for valve companies to seal with.
So what is the gap?
Typically as pressure increases PTFE can no longer resist deformation well enough to perform long term, so PEEK is employed as the seat material of choice. Stepping from PTFE to PEEK causes a significant leap in price for valve seats. It also creates challenges around seal performance given that PEEK is so much harder and resistant to the slight deformation needed to seal against imperfections on the sealing face. Therefore, in a highly competitive landscape, moving to PEEK and the associated improvements in adjacent components and actuation can be the difference between winning and losing an opportunity. This is coupled with the influx of lower quality PEEK materials flooding the market, which can cause unreliable performance, prolonged testing due to quality issues and ultimately damaged brands and unplanned delays.
Is it about time to consider other materials as a potential solution?
Advanced material processing techniques are utilising physical properties of materials and creating high-performance characteristics without the problems with seal performance and extortionate price tags.
How can we address this challenge which is faced across the valve industry and what new developments are on the horizon?
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Teflon vs PEEK valve seats
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(Mechanical)
(OP)
19 Dec 18 16:24Hi guys,
I am purchasing some valves for a client using their datasheets.
1. The CL 150 valves specify RPTFE seats however the supplier is providing filled PTFE and High performance PTFE seats.
2. The CL 600 valves specify PEEK seats however the supplier is providing Teflon seats.
Are these acceptable alternatives? What properties should I compare to deem these materials as acceptable alternatives?
(Automotive)
19 Dec 18 17:01Teflon is the brand name for PTFE, so it looks like whatever your supplier you're using is only supplying one type of seat (PTFE) regardless of what is specified. RPTFE is just Reinforced PTFE - in order to determine what was specified vs. supplied you would have to consult the specs for the exact material specified to determine the filler material (probably glass) and what percent fill.
I know its not helpful but it is highly dependent on your application. I can say though that if an application calls for PEEK, PTFE will very likely not be an acceptable alternative. PTFE has excellent chemical resistance over a broad range of chemicals, but PEEK has far superior mechanical properties - especially so at high temperatures. I believe though PTFE being a fluoropolymer has slightly better chemical resistance than PEEK. "Better" is a relative term here though - you would have to again look at the material specs for each to determine if whatever chemical(s) in your working fluid is compatible with the material specified.
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