Anyone got some Kel-F (PCTFE) to spare?

[oxyhacker]

I am looking into replacing the nylon valve puck on a tank valve seat with Kel-F (to improve O2 safety). Only thing is, I can't find anyone who will sell me Kel-F with less than a $100 minimum. Anyone got a little they might part with - 10mm, 7/16" or larger rod, or 4mm flat stock, or know of a supplier with reasonable minimums?

 

[pescador775]

Petes's sake, just pick up some scrap teflon.

If not, these people have 30 buck minimum for KEL-F:
Kel-F Rod - KEL F PCTFE Sheet- Order Online

 

[WD8CDH]

Check mcmaster.com

 

[oxyhacker]

I'm not trying to reinvent the wheel, but just make a few O2-safe valve seats. I can't think of valve manufacturer who is using teflon for 02 valve seats, so there may be some reason why not. Most of them were using Kel-F for their "nitrox" valves, and nylon6 for everything else, but now all seem to have switched to nylon due to concerns about the fumes that kel-f puts out should it combust. I did find some cheaper sources since I posted, but still a lot of money when I only need an inch or two.

Oh, I can't find any PCTFE at M-C. Lots of PTFE, but no PCTFE.

 

[pescador775]

KEL-F contains chlorine so there is reason for concern. Nylon is OK for seats, even in oxygen, but not the "best". However, teflon is just about oxygen proof. Also some concerns for combustion fumes but no more so than the kitchen pot on a hot stove. Look, who knows why these manufacturers do things? One day, the experts are making assertions of one sort and the next they are jerking us around and back to square one. I suspect that nylon is preferred over teflon because nylon is hard as a brick. Teflon makes an excellent valve seat, price is reasonable and the material is readily available. It is soft, so a knife edge orifice could implant a sharp groove in the material. Just don't muscle the valve knob. If that is unsuitable, glass filled teflon is available from the same source:
TEFLON - TEFLON - GLASS FILLED ROD & SHEET -Order Online

Use the excess to make spares for Cale or somebody.

 

[pescador775]

EBay might be a source of glass filled teflon:
Teflon ® Balls PTFE Basic Shapes

 

[oxyhacker]

Teflon is also too soft to be easily machined, which may have something to do with why it is not always used for valve seats, and why it doesn't seem like a good choice in this case, where I just want to make one or two.

Soft is not necessarily better for knife edge pistons or valve seat crowns, they can get stuck in it enough to cause erratic opening, or even, blockage (seem to recall the SP Mk15 had some trouble with this).

Anyhow, if I cannot find a bit of Kel-F I'll just use nylon.

I suspect that nylon is preferred over teflon because nylon is hard as a brick. Teflon makes an excellent valve seat, price is reasonable and the material is readily available. It is soft, so a knife edge orifice could implant a sharp groove in the material. Just don't muscle the valve knob.

 

[pescador775]

I don't get the concern over "fumes" from combustion. If there is a fire in the tank or valve then one has larger problems than fumes. A burnt valve seat won't seal anyway. Not likely. If there were a plume of combustion gas in the tank and a mask was placed on an unconscious patient a problem could then arise. How likely is that? Seems far fetched. If such weird happenstance were feared the operator could check the oxygen flow for odor before employing the mask.

I have a couple of Heiser, 45 cf cylinders filled with O2 to 2500 psi. I cleaned neither the tanks nor the Thermo valves all of which were brand new. The tanks were sparkling inside and the valves looked fine. I did install Viton rings on the neck thread. It's been two years since I jammed them with oxygen. (I use a Haskel so "jam" is the right word). The valve's seats are standard issue SCUBA stuff and have had no problems with that or anything related.

Some years ago, a guy on SB claimed that oxygen caused slow erosion of nylon seats. One of these days, I'll drain one of the tanks to check. BTW, are the mfgrs using nylon 6 or nylon 6/6?

 

[pescador775]

Hello to this old thread. Now, I need some plastic rod as the HP seat on a condensator drain has gone south. After looking at the thermal concerns associated with KEL-F I reviewed some literature on other plastics. It looks like combustion products from PEEK are less noxious. Mechanical properties are good and flammability is comparable to other materials, slightly better than nylon. Anyway, I ordered a small quantity from these guys. Fingers crossed.

SmallParts.com: - /

 

[mhinagoya]

The HP seat on my coalescer went south too. I replaced it with some HDPE and it has been working flawlessly ever since.

If you want a small piece of rod (.250 inch diameter), PM me your address and I'll drop it in the mail. I will even cut it to length for you first if you tell me how long you want the rod.

Bill.