Ball Valve Seats and Seals Help 1

[302Hugo]

I'm trying to purchase some low temp valves and I'm having a hard time determining what seats and seals I should get. It seems the main Seat materials are PTFE/RTFE, Devon, Nylon, PEEK, Viton-A, and Metal-Metal. The Seal materials are Buna-N, HNBR, PTFE, and Viton-A.

So my problem is that I was told not to use Buna/HNBR/etc because the benzene in our product eats through that too easily, and I need low temp capabilities (-40) so that puts out Viton-A. The valves are higher than 300 ANSI so PTFE is out. And I talked to a few people and they said not to use Nylon because it's too soft and doesn't work well.

What do I do? At this point it seems that I either go with Buna-N and hope it lasts, or go with Viton-A and hope the line is never shutdown long enough for the temp to get that low.

Is it as important for the seat material to be low temp as it does the seal material? In the valve specs it doesn't list the seat material as low temp or not, but in the seal material it lists which material is good for low temp.

Thanks.

 

[SNORGY]

Crittenden:

See attached...perhaps it will help?

By your reference to "Devon", I assume you mean "Devlon". When I specify that, I usually specify "Devlon V API Grade".

This "valve elastomer selection" stuff is truly a black art, in my mind.


Regards,

SNORGY.

 

[rneill]

Not sure I understand your comment about teflon being limited to Class 300. Reinforce Teflon (RTFE) is commonly used well above class 300? When I've checked in the past, ball valves with teflon seats have typically had full flange rating up to Class 600 and it can be used above this rating as well but the manufacturer will derate the valve to something below the flange rating. Since full flange rating is not always required (especially at higher classes) the valve with RTFE seats may still meet your required design pressure. Of course, this depends on the specific valve design so you might want to check with a variety of suppliers. RTFE is always my preferred choice due to its wide temperature range and chemical compatibility.

There are a wide variety of other grades of Viton that I didn't see listed such as Viton Duro 90 and Viton GLT. I believe the Viton GLT has the -40 rating you are looking for but I don't believe the other Vitons do.

Snorgy, good reference info. Agree about the "Black Art". Never quite know exactly what chemicals may be used in the actual operating environment when we spec the valves (chemical inhibitors, dewaxers, well workover chemicals coming back with production, etc.).

 

[302Hugo]

Thanks for the replies and attachments guys, I can always count on you two guys giving me an answer. I appreciate that! I still need to run through my last question thread and thank you guys!

I agree with you SNORGY about it being a black art. I've found also that there is so much varying information out there (for instance some sites I have been to says Viton-A and PEEK are only good to -17C, but others have said they are good to -50C...Dupont has Viton-A listed as -17C). I assume the vendor is confused with Viton-A and a different low temp Viton?

Rneil, I've since noticed that some manufacturers allow PTFE higher than Class 300. I was originally looking at PBV and according to their temp/press chart the glass filled PTFE is only good to Class 300...however I just was looking at KF and they have their Teflon (I assume plan PTFE?) showing up to Class 900.

I have actually talked to my supervisor here and he said that he is fine with just using Viton-A in our valves, even though it's only good to -17C. He noted that the chance of our lines going down long enough to reach -17C and be fully pressurized is very unlikely, so that has to be taken into consideration.