KEL-F .vs. Nylon 6/6 seats.... question...

[Genesis]

Ok, here's a good one.

Deco regs. High F02 mixes.

All the seats I've seen appear to have been made out of nylon - even those intended for Nitrox service.

Well folks, that ain't the best material for high FO2 mixes, and what's worse - maybe a lot worse - is that the HP seat orifice is likely sonic during actual use.

In laymen's terms this means its where you could get an ignition event with a high FO2 mix.

It doesn't seem to happen very often, so the question becomes - is there some reason that seats aren't made out of something like KEL-F, or it just that the real issue is more one of cleaning than material compatability?

Ditto for valves - finding a manufacturer that will actually specify that a particular valve has O2-compatable components (leave O2-clean out of it - I can do that myself) is a real problem! Thermo, for example, has their "nitrox" valves, but then turns around and says "up to 40%" (!) and the seats in those (I own several) sure as hell look like the old Nylon 6/6 again!

I know that there HAVE been valve flash incidents with high FO2 deco mixes when valves were turned on. Chickdiver had one, for example.

So what's the poop here? I've seen "official" manufacturer documentation and its nearly completely silent on this point, or falls back on the "40%" stuff.

Obviously people ARE using deco tanks, and ARE using deco regs. So is there some "secret" source for compatable seats, or is this whole thing somewhat overblown - make darn sure its O2-clean....

I know there are folks who are perfectly comfortable with regs from both Apeks and SP being used in deco service - the LP side I'm not concerned with. Its the HP side. Having looked at the kits, including the so-called "nitrox" ones that some manufacturers sell, all they appear to be doing is putting in either EPR or Viton O-rings, and most manufactuers appear to have gone to either EPR or in some cases polyurethane (where hard, extrusion-resistance is required - ala the HP piston ring on a SP Mk25) instead - thus, all the "nitrox kit" appears to be, in many cases, is a bezel or trim ring that says "nitrox" with the same stuff in it that would otherwise be in a standard kit!

(Yes, I know there is no such thing as a soft good such as a seat that won't ignite or decompose if temps get high enough in a high FO2 atmosphere, and that temps at a "blind corner" can reach 1500F or more if you're injudicious about how fast you own valves and such. Just wondering what's REALLY being done here by the various manufacturers... because what I can SEE from inspection looks like they're not going as far as they might be able to.)

 

[truva]

I have always wondered why I never see a regulator made from Monel.



Truva

 

[Genesis]

I have always wondered why I never see a regulator made from Monel.



Truva

Atomic M1, factory high FO2 ok up to 70%. There is one. I have no access to their parts though and while a friend of mine has a B2, I don't have the right spanner to take the end cap off and see what the seat is made out of.

Iconel is another good O2 compatable metal. Its god-awful expensive though, but the actual amount required to make a reg body wouldn't be that much. Further, Iconel and Monel are damn near impervious to corrosion in the marine environment.

(BTW I had Iconel exhaust collectors quoted for my big boat. $5,600 each. OUCH! Ok, now I know why people use SS and deal with replacing them every 5-7 years!)

Actually, brass is about as good as you can get for high FO2 gas. Brass will not burn in 100% O2 at pressures under about 10,000 psi - which is way, way beyond anything you'll ever see in a scuba tank.

For this reason when there is a flash the brass in the valve or reg is not the problem - its the other stuff, usually an O-ring or seat that ignites.

 

[captain]

Maybe checking with a company that services O2 welding regulators will provide some answers on materials. After all there are tens of thousands of them being used every day with 100% 02. I worked around welders every day for 30 years and can't recall any incidents and I would say the regulators don't exactly get tender loving care.

Captain

 

[DA Aquamaster]

Ok, here's a good one.

Deco regs. High F02 mixes.

All the seats I've seen appear to have been made out of nylon - even those intended for Nitrox service.

Well folks, that ain't the best material for high FO2 mixes, and what's worse - maybe a lot worse - is that the HP seat orifice is likely sonic during actual use.

In laymen's terms this means its where you could get an ignition event with a high FO2 mix.

I agree the rapid compression in the high pressure parts of the reg when the valve is turned on can generate enough heat for ignition resulting in a flash fire in the first stage. It's a good idea to turn the valve on slowly and leave the purge button slightly depresed while doing it.

However during normal use the exapansion of the gas as it moves through the first stage requires that a lot of heat be absorbed and the temperature of the gas as well as the seat will remain low even with high velocities and sharp corners. For example just a few brief taps on the purge valve in a reg will cool the nylon HP seat well below freezing.

If the gas were moving through the reg at high velocity with no drop in pressure, then the nylon seat would crispy fry in short order.

 

[Genesis]

Yeah, you got a point there.

When you PP mix a tank using a needle valve, it gets REAL COLD, and that's at very low flow rates (I fill at ~60psi/min) - well below what you'd be taking it out at given normal breathing rates.

I guess the real issue is during the turn-on, and perhaps in the valve, where there is no drop in pressure of significance......