Atomic Parts Cost

[Geo7]

I thought nitrile is only approved up to 40%, and EPDM and Viton are approved to 100% ?

Apeks / Aqualung use only one type of o-ring: EPDM in 80 shore for low pressure and high pressure. Their o2-compatible regs / parts kits are just cleaned better.

 

[rsingler]

No o-ring is "compatible" with 100% high pressure (3000 psi) oxygen.
It's all about the level of risk you want to accept.
All three compounds will auto-ignite at a high enough partial pressure of oxygen. No grease. No glowing particulates impacting the o-ring at high speed. Autoignition.

Add adiabatic heating from slam-opening of a tank valve, and you might get close to ignition temp of an o-ring in the direct path of that gas for all three compounds. It's maybe one reason why Atomic modified their yoke bolt to keep the o-ring out of the direct gas path when they made their titanium regs "nitrox compatible".
Now add hydrocarbon contaminants from poorly filtered gas.
Now add the U.S. litigation industry or the mysterious requirements of the latest version of European CE standards.
Suddenly, Viton is the ONLY acceptable o-ring. But it will still burn, and release fluorine when it does.
But it breaks more easily, takes a set more quickly, and is less pliable than other compounds at the same durometer, in my experience. In other words, it doesn't seal quite as well, IMO.

Viton is not the only possible o-ring. If you keep your gas clean, service your regs properly, have a reasonable design, and maybe, except for gases over 40% O2 and 3000 psi, some folks think there's a reasonable risk coefficient for an o-ring compound that doesn't tear as easily and seals longer because it's more resistant to long term deformation. Viton isn't the only choice for all diving.

 

[rsingler]

So here's a conundrum. As pointed out above, not a few mfrs use EPDM instead of Nitrile for their <EAN40 kit o-rings, and maybe even for deco concentrations of O2. EPDM has excellent sealing characteristics, and a longer storage shelf life than Nitrile. But the study above, during exposure to pure oxygen at 1500 psi, showed an autoignition temperature lower than nitrile (318F vs 343F), and a higher yielded heat of combustion than Nitrile.
In contrast, the high temperature limit in the table in post #39 above, created from open source data, showed a supposed max temp higher than nitrile. In any case, neither are close to Viton's max temp. And yet EPDM is the choice of manufacturers for elevated oxygen concentrations in not a few regulators.

Second piece of data: Wikipedia shows us that in a 10:1 compression ratio gas auto cylinder, temps reach 900F, well above the 600F limit for Viton from the study above. A scuba first stage can suddenly reach 200:1 compression compared with before the valve was opened, albeit over a longer time.

My point? There's more to the issue of adiabatic heating than meets the eye. I suspect that NBR having only half the max allowable temp of Viton is only a small part of what is behind rare regulator ignition incidents. Our habits are driven by more by lawyers than by physics, though I will concede the added safety of Viton with high pressure oxygen. Its autoignition temperature is double its brethren, while its heat of combustion is only 1/3 to 1/2 of Nitrile or EPDM. But that only matters if it ignites.

But let's start a new thread if we need to continue this discussion. I certainly don't know enough to debate it.

 

[Geo7]

My viton o-rings in the spg swivel look like exploded truck tires... Can't remember if I used Krytox GPL205 or Tribolube71 on them, but it's poor abrasion resistance...

 

[rsingler]

Looks like a batch molding flaw, like this one I had on a Poseidon, that they denied.

 

[-JD-]

My viton o-rings in the spg swivel look like exploded truck tires... Can't remember if I used Krytox GPL205 or Tribolube71 on them, but it's poor abrasion resistance...View attachment 801618

Out of curiosity, do you lube just the barrel/inner interface, just the exterior, or both?

 

[Geo7]

Looks like a batch molding flaw, like this one I had on a Poseidon, that they denied.
View attachment 801643

Good point! I think I have another batch of Viton (but now installed nitrile)...

And mine was an independently sourced o-ring, not from an OEM manufacturer's kit.

 

[Geo7]

Out of curiosity, do you lube just the barrel/inner interface, just the exterior, or both?

I lube the whole thing generously, the o-ring groove and on top of the o-ring (obviously on the side in contact with water, not beyond the the o-rings, where the swivel is in contact with HP air).

 

[ams511]

Deleted

 

[ams511]

Yes I think the companies that raise the prices like that underestimate the effect of the small but vocal group of divers that switch to affordable regs. The whole "Apeks revolution" in the 1990s was driven by cave divers and made that brand. Then Apeks raised prices (was it ever cheap in the US anyway?), and now it seems Deep6 is taking the market by storm. So trying to make a few extra % on the bottom line by raising kits prices (making parts and training hard to access), drives away the serious divers that then influence others.

IIRC the Zeagle branded Apeks regulators were relatively inexpensive compared to ScubaPro and Aqualung offerings. When Aqualung bought Apeks, they jacked the price of the kits so Zeagle couldn't give free parts with service anymore. That's why Zeagle did the trade ins.

When HOG first burst on to the scene, there were quite a few people bashing them as being cheap knock-offs and violating Apeks intellectual property (which long since expired). The funny part was Apeks was basically the same price if you bought from European dive shops.

What I don't think the dive companies get is that they are pricing diving out of the mainstream.