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rsv (Mechanical) (OP)
28 Nov 05 18:21
I have asked this in the Material forum but, I am not sure whether it is better to ask the Q here.
Can anyone tell me what the Maximum recommended pressures & temperatures are for continuous use for the following valve (ball or butterfly) seat  materials?

Nylon, PTFE, RPTFE, Devlon & PEEK

Are there any pressure / temperature tables available?
I know there are chemical compatability issues as well but, I have found charts for them whereas nothing on the press. temp issue.
NGiLuzzu (Mechanical)
29 Nov 05 3:46
rsv,
       at first instance, I usually consider the recommended service temperature range only (from the soft materials catalogues and/or data-sheets); but for more delicate applications and accurate information I'd suggest to refer to the Supplier directly. Some of that information can be found on the web...  

       Du Pont - Dow (elastomers division) - for example - provides a "Chemical Resistance Guide" that may be downloaded after a free registration: see   http://www.dupontelastomers.com/Header/index.asp
       As far as I remember, pressure and temperature values (as well as composition of the service fluid) are input data for this program...


       You can also try visiting:

            http://www.angst-pfister.com/english/defaulte.htm

            http://www.busakshamban.com

            http://www.plastics.saint-gobain.com



Hope this helps,                'NGL
Sircrashalot (Mechanical)
29 Nov 05 7:49
The valve manufacturer will generally determine the limits on these by experiment using their designs.

Generally ANSI pressure ratings where I have seen these materials used:
PTFE 150 to 600
Nylon 150 to 600
RPTFE 150 to 900
Devlon 300 to 1500
PEEK 600 to 2500 & API 10,000

It also depends on the valve size - a 4" 600# valve may be OK with a Nylon seat, but at 20", it needs PEEK.  Again, it goes back to what the manufacturer has qualified in their R&D department.

Andy
JimCasey (Mechanical)
29 Nov 05 9:09
The pressure/temperature ratings for a material generate a reasonably complex curve.  The rating for a part is not only determined by a material but by how it is designed and supported in the assembly.  One globe valve manufacturer has PTFE seats rated for 6000 psi, due to some clever design. OTOH: I wouln't trust a PTFE Faucet washer at 100 psi. If you have a specific valve in mind it would be best to consult the literature for that product.  
jsummerfield (Electrical)
29 Nov 05 9:23
Use Google.

Google Nylon, PTFE, RPTFE, Devlon & PEEK.  Some sites will include many plastics that you should consider.  You will find lots.  Consider a few thoughts beyond the valve manufacturer.

The plastic manufacturer provides most data to sell their product.  PEEK is good for continuous service up to about 480 degree F.  Go to the Victrex site for PEEK, Dupont for PTFE, etc.  Look for the trade name like Nylon and the generic like polyamide.  Isn’t Devlon a modified polyamide?  Also obtain data from other plastics companies who may take the basic components like PTFE to make the glass reinforced PTFE.  For some trade names it may be difficult to identify the generic.  Isn’t  Kel-F a.k.a. PCTFE or polytetrachorotrifluoroethylene but requiring spelling correction?

You may also find standards that exist such as BS6564 for carbon reinforced PTFE.  Most of the material standards apply to the metals.  Fewer standards apply to soft goods.

John

rsv (Mechanical) (OP)
29 Nov 05 18:23
Thanks for the help & web sites - I will look thru' them.
I thought it would not be as straight forward as press. temp curves.

The reason for the post was so I could clarify manufacturer's data as they seem to differ & I need to order ball valves up to 36" and press/temp ratings of 4350psi at 250F & 1350psi at 460F
Sircrashalot (Mechanical)
30 Nov 05 8:17
At these sizes, pressures and temperatures I would ask for a reference list of where they have supplied like valves before.  You definately want to be sure that they have done something similar in the past...

Andy
rsv (Mechanical) (OP)
30 Nov 05 17:06
Good info on the web sites thanks
I have also found info on cooper cameron valve website which directly links temp. and valve class.
I believe they have a good reputation.

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