buna o-rings

[noknife]

well i'm thinking of making some stainless valves and selling on ebay or something. i work at a machine shop and the design is very basic. the only problem is that ptfe o-rings are hard to find and expensive. i found some buna n 70 o-ring that are coated with teflon on ebay but it states that the teflon is fragile. now i think i remember reading that buna is safe it self. any thoughts?

http://www.ebay.com/itm/AS568-006-O-Rin ... 2ebcb6b790" onclick="window.open(this.href);return false;" rel="nofollow

[Richard7]

Its all covered right here under rule #8 http://homedistiller.org/forum/viewtopi ... =35&t=5090

[noknife]

oh sorry thought i did a good enough search.

[noknife]

oh i thought it was a new fandagled plastic or something ha. but what about ptfe. I thought everyone trusted that.

[Richard7]

Well, to be honest that is a gray, area being ptfe coated.

[dad2five]

Richards point is that under the rules we live by, if it ain't copper. SS, PTFE, or recently pickled brass; u don't want it exposed to hot ethanol.... (Rule . And those o rings, even tho Teflon coated, don't count.

Now nobody sez u gotta follow the rules; but I would think you'd veer from them at your own risk. U're suggestin to veer from them at your customer's risk.

But hey, I'm new here

[Richard7]

Pure ptfe = no problem.

[noknife]

oh ok. that's kinda what i thought. but i remember some brew shop selling buna gaskets. and they were more expensive than the ptfe. just plain dumb. that's where i read it, just remembered. thanks guys

[Richard7]

i remember some brew shop selling buna gaskets.

Yea, you gota look out for them brew shop guys, they love to sell turbo yeast and rubber components

[noknife]

ha no kidding, except rubber doesn't smell as bad.

[Soggy Bottom Boy]

PTFE encapsulated seals should be OK as long as the O-rings are not overly compressed so that it could tear the PTFE layer. Also, the PTFE part of them should not be subject to mechanical abrasion or over-flexing from the valve mechanism by repeated cycles of use.

EPDM encapsulated o-rings would be a much better choice, as EPDM has a much better chemical resistance to ethanol than that of Buna-N (aka Nitrile).

Buna-N has very poor chemical resistance for ethanol.

I would suggest extended, accelerated usage cycle trials, and monitor for failures of the encapsulation before you decide to market anything like this.

[noknife]

yeah I think I'll stick to pure ptfe. if i wouldn't use it I wouldn't want to sell it. might just by some ptfe sheet and make my own. sounds cost effective.

[noknife]

ok another issue. sorry guys. i didn't even know there were more than 1 grade of ptfe. there is virgin and mechanical grade i guess. the first site i used to check it out said that mechanical grade is not food grade. i know i'll probibly get different answers depending on where i go so i thought i would ask you guys what you think about that. and one more thing. is all ptfe tape virgin? i never knew about it before. i have used it for several things on my stills. thanks ahead of time for any help.