PTFE for high performance butterfly valve 4

[bao2ye]

My friend needs PTFE material for his high performance butterfly valve. Can anyone help him to define the specification for the PTFE material? What phycial, chemical, and mechanical properties need to be considered and specified.
The valve should be used below 300 psi and 410 F.

 

[kenvlach]

Lots of info on PTFE on the Internet.
Your biggest worry will be creep -- PTFE tends to flow under pressure, especially with higher T. Useful as a protective coating or with lots of filler.

 

[StoneCold]

bao2ye
I have used several different kinds of teflon coated butterfly valves. I prefer the Neotecha from Tyco. They are more money than some others but hold up very well. I think the last one I got was a PFA coated valve.

Regards
StoneCold

 

[NGiLuzzu]

bao2ye,
the value of +410°F = +210°C is, more or less, the upper limit of the usual temperature range considered for PTFE.

In any case, I feel that the world of polymers in general, and of PTFE in particular, is very complicated, almost an... "undiscovered country" for non-experts. For example: many specify "virgin" PTFE without deep knowledge the meaning of such a requirement (for many applications "modified" PTFE is better) and many supply "virgin" PTFE without further details...

So I would suggest you to define the chemical features of your application and check them with one or more Expert Suppliers.

For some references, you may want to browse into:
-

http://www.teflon.com/

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http://www.impreglon.co.uk

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http://www.smaltiriva.com/rivestimenti2e.htm

Hope this helps, 'NGL

 

[terje61]

Hi bao2ye,

The Norwegian specification: Norsok M-630 gives you the requirements for many materials including PTFE. You can use this as an example/reference.

http://www.standard.no/pronorm-3/data/f/0/03/78/9_10704_0/M-630.pdf

Look for page 59/85 - Datasheet P22

Regards,
Terje

 

[bao2ye]

Thanks you all for those valuable information.

 

[JimCasey]

The Neotecha is not a "High Performance" valve. HP in the butterfly valve world refers to double-offset. The TYCO product meeting that description would be the Keystone K-Lok.

Anegri's comments about virgin TFE are worth a star. There are so many "Teflons" on the market, but only one of them is PTFE. PTFE is probably the most inert but TFM and PFA are melt-processable, where PTFE has to be compression-molded or machined from billet. Sometimes these are generically referred to as "Fluoropolymers".

Also particularly valuable for butterfly valve seats are additives to stabilize the polymer dimensionally. Glass fibers, Carbon particles, and/or mineral fillers are used. I asked a guy at Worcester once what the composition of Polyfill(r) is. He asked:"What size valve?" It has TFE, Glass, and Carbon in it, at least but they use different recipes for the seat materials so that the properties of the seats are optimized for the specific conditions to be encountered.

 

[azertyuiop]

For that pressure and this temperature, 100% PTFE is out of limits, since pure PTFE temperature resistance ends at 200dC, and you operate at 210dC.
PTFE expands 10x more than stainless steel when heated at it's max temperature, and as such creep in between spaces and does deform permanently, if it doesn't clog up some of your valve mechanisms.
If you absolutely want to retain PTFE at your specified operational range, then demand to use a 'stansit' seat and seal, it is a 50% PTFE and 50% SS316 mix, and as such has far less creep and far more resistance against deformation, with the added benefit of temperature resistance up to 260dC at 40bar (1bar = 15psi). Stansit has been around since the 1980's and is a true tested material.
The alternative seal material replacing PTFE as inert seat and seal is PEEK. It is harder while also being totally inert, has far better P/T capabilities than PTFE, but costs a bit more.
At this pressure and temperature, I also advise to ask for a trunion mounted ball valve, since if you use a floating ball valve, the proces pressure will push the ball against your PTFE seat, and deform it permanently if you use pure PTFE.
A trunion mounted ball is kept into place on top and bottom of the ball, and the process pressure press the seat against the fixed rotating ball, reducing seat deformation enormously, since the pressure area of a seat is far smaller than a closed floating ball.

 

[NGiLuzzu]

See also thread408-105701 and thread408-166397...

Ciao to All, 'NGL

 

[ytse]

300 psi @ 400F already exceeded the pressure - temperature limits for polymer seats of HP butterfly valves. 410F is approaching the limit of polymer seats. Even Glass reinforced (RTFE) are only rated up to around 450F.

I don't think you can find a valve with polymer seat that is rated at that temperature and pressure. At 410F, the best you can hope for is around 200 psi rating. However, since pressure rating drop off rapidly as temperature increases, if your design temperature is reduced to, say, 350F, then there are a few HP butterfly valves that can meet the 300 psi rating (e.g. Keystone, Durco, Bray, etc).