737 destroyed by O2 explosion

[bletso]

I get your problem with the term hydrocarbons, but it is what we have. Give me another term. I do know O2 doesn't like buna rubber and hydrocarbon base oils and greases. Actually, it doesn't like a lot of things in the presence of heat. Turn on is almost always the flash point whether adiabatic compression, particle impingement or whatever. Even NASA had problems.

You just have to respect O2, especially under pressure. Here is another pic. I heard this one - phsst, turned off the O2. It was hot. Pressure maybe 140 psig.

 

[stuartv]

Non-problem? I would disagree.
Rare, yes.
But the key difference between Scuba and CGA 540 oxygen valves is the engineering to remove sharp corners and bends that promote impact ignition. Design is why the other valves do so much better. And yes, cleanliness. But there's a reason why no scuba valve is CGA rated for high pressure 100% oxygen service, even though we use them that way. And even if the valve were perfect, where does it go next? Into a complex labyrinth that accentuates the adiabatic heating issue.
So if we're stuck with a twisty-turny gas path for scuba, at least we can use a valve design that opens ultra slowly.
It's worth the extra $80 to me, for one or two valves. To each his own, unless you're on my boat and you don't choose the extra safety margin.

$80 extra? That would be nice.

From SilentDiving, these valves are $150! The valves I'm using are from DGX. $40.

OXYGEN REBREATHER CYLINDER VALVE - Silent Diving LLC

DGX Compact In-Line Valve, Green Handwheel | Dive Gear Express®

I have 3 or 4 I want to replace, now that I have just learned about these progressive-opening valve. But, $450 - 600 is going to hurt!

What about these "Premium O2" valves from DGX? They say they have "finer threads, making the initial opening action of the valve more gradual and requiring several more turns to fully open than the standard SCUBA valve."

DGX Premium O2 In-Line Valve | Dive Gear Express®

Would one of these give as much safety margin as the AP needle valve? If the AP valve can still go to fully open in, say, 1/2 a turn, it seems like these DGX valves might actually be better? I don't know. That's why I'm asking.

 

[rsingler]

The DGX valves are a step in the right direction but an order of magnitude different in effect. The AP diving valves go to full pressure over two minutes. Where the DGX is at least an improvement, is in the speed of opening. But the threads nonetheless pull the entire seat face away from the orifice, albeit a smaller distance per turn. The AP diving valve, on the other hand, is a needle valve. This obviously means that the pull away surface area is much smaller early on in valve opening.

I'm working with Silent Diving to perhaps become a dealer for these valves. Perhaps we can work a deal for ScubaBoard members if this comes to fruition.

 

[Norwegian Cave Diver]

Does an unserviced, stiff to open valve, add to the problem?

 

[kelemvor]

Why not just create some kind of adapter and use regular medical o2 valves?

 

[rsingler]

Does an unserviced, stiff to open valve, add to the problem?

If it's clean but just stiff, and therefore opens really slowly, that's a good thing. But the reality is that it's stiff because of accumulated corrosion outside the gas path, and ??? accumulated ??? inside the gas path.
More likely, with extra effort required to open, the initial cracking may come with a bit of a "jump", increasing the risk of sudden pressurization, adiabatic heating and impact ignition.

As a separate item, I've gotten a positive response regarding offering these valves to my SB brethren. Send me a PM if you want info re: pricing.

 

[rsingler]

Why not just create some kind of adapter and use regular medical o2 valves?

Only half of the problem is in the valve.
You can have an oxygen-stable seat, and a valve thread that opens very slowly, but you still have the potential for solid hydrocarbon debris immediately downstream in the first stage. Therefore, sudden compression can still create the potential for ignition inside the first stage. That's why I think significantly delayed speed of opening is an exciting safety development for divers.

 

[stuartv]

The DGX valves are a step in the right direction but an order of magnitude different in effect. The AP diving valves go to full pressure over two minutes. Where the DGX is at least an improvement, is in the speed of opening. But the threads nonetheless pull the entire seat face away from the orifice, albeit a smaller distance per turn. The AP diving valve, on the other hand, is a needle valve. This obviously means that the pull away surface area is much smaller early on in valve opening.

I'm working with Silent Diving to perhaps become a dealer for these valves. Perhaps we can work a deal for ScubaBoard members if this comes to fruition.

Please forgive in advance my ignorance on this.

Are you saying that the AP needle valve restricts flow even when fully open? That is counter to my understanding and also seems to be counter to the video that was shown of the AP valve demo.

From the thread you posted earlier:

They have an O2 needle valve feeding one regular hose and one hose with a flow limiter. The regular hose gets to full pressure in roughly 13 seconds and the one with the flow limiter is not far behind.

But, my real question is not directly about that. It is, does the needle valve restrict flow when all the way open?

If it does not, and it takes a "normal" number of turns to open it all the way, then a person who opens it quickly gets no benefit from the needle valve, right?

OTOH, if you open a DGX valve quickly, well, it still opens slowly because of the threading.

And if the AP valve does ultimately restrict the flow, even when open all the way, is that a safety hazard? Maybe not. I don't feel knowledgeable enough to say for sure.

What it seems like - to my novice point of view - is that the needle valve is helpful if you remember to open it slowly. But, if you don't, it makes no difference. On the other hand, the DGX valve seems like it would help whether you open it slowly or quickly. And, what would be ideal, is a combo of the two. A needle valve AND finer threads to make it take more turns to open.

 

[nadwidny]

I get your problem with the term hydrocarbons, but it is what we have. Give me another term.

In the lab we called that type of contamination "oil" or "oil mist".

 

[Blue Horizon Diving]

If you ever do an oxygen technicIan course with the likes of PSI-PCI, you see some crazy things in videos and photos of what has happened.