737 destroyed by O2 explosion

[stuartv]

I think the $70 refers to these:
DGX Premium O2 Pro Valve, Right (Typical Side) | Dive Gear Express®

Good point. And they are only $59!

I am kind of hoping that @rsingler finds that the AP valves have fine threads, like the DGX valves. I think fine threads and a needle valve sound like the ultimate safest setup. But, I won't mind too much if they don't and I can be satisfied with $60 valves, instead of $150 ones.

 

[rsingler]

While tearing down one of the new AP valves will have to wait a few days until I get some time to play, I thought I'd at least show you the comparison between the standard max dive valve seat, the Dive Gear Express oxygen valve seat and the new AP diving valve seat.
As you can see, both the DGX and AP oxygen valves have fine threads, decreasing the speed of valve opening.

Additionally, you can see the novel design of the AP Diving needle valve seat. How this works to slow the pressure rise in an oxygen first stage may become clearer when I tear down one of the valves later this week.

 

[rsingler]

 

[stuartv]

View attachment 587374

PM me with a price for 4 when you know what you can sell them for.

 

[mderrick]

This thread has an implication that the problem with oxygen fires is the valve. The main cause of oxygen fires is heat from adiabatic process that ignites a kindling chain that starts with contamination. The valve itself is unlikely to be the cause of a fire, even the speed the valve is opened is unlikely to be the cause if it's a threaded opening design (slow opening or not) as long as it's not a quarter turn ball design. There are lots of designs for oxygen valves, the typical CGA 540 cylinder valve opens as fast or faster than the typical SCUBA valve. The rapid opening Thermo nitrox scuba valves actually passed the V9 ignition tests for 3000 psi service pressures (which means they were tested for ignition with instantaneous open at 5000 psi.) No valve that says it can be used with any nitrox mixture greater than 23.5% oxygen is going to have an improper gas path.

Discarding natural selection in the operator handling the oxygen cylinder, in my experience its contamination of the DIN fittings on scuba valves and regulators that is the usual cause of oxygen fires. The contamination isn't something obscure or the wrong o-ring... its lube on the threads, even oils from your fingers and hands, but I suspect the worst offender is polyester lint from clothing. (Blow out the valve before coupling the DIN fitting to the outlet.) The valve design does very little to protect from contamination (although eliminating chromed surfaces can help). The other area I often encounter contamination is in the neck threads, especially where the neck threads were lubed (the kind of lube doesn't really seem to make a difference.) I've seen as many fires that started in the neck threads from a right angle impact on the valve, as I've seen start in the outlet/regulator interface. I've also seen fires that started inside 1st stages. When servicing valves and regulators over the years I've seen evidence of many fires in valve outlets and 1st stages where the kindling chain never escalated. Want to know where I've never seen an oxygen fire start? Inside the valve, although I'm sure it happens I've never seen it.

If it makes you feel safer to have a particular valve on your scuba cylinder full of oxygen, go ahead, but don't delude yourself into thinking that will somehow significantly reduce risk of an oxygen fire.

 

[stuartv]

This thread has an implication that the problem with oxygen fires is the valve. The main cause of oxygen fires is heat from adiabatic process that ignites a kindling chain that starts with contamination. The valve itself is unlikely to be the cause of a fire, even the speed the valve is opened is unlikely to be the cause if it's a threaded opening design (slow opening or not) as long as it's not a quarter turn ball design. There are lots of designs for oxygen valves, the typical CGA 540 cylinder valve opens as fast or faster than the typical SCUBA valve. The rapid opening Thermo nitrox scuba valves actually passed the V9 ignition tests for 3000 psi service pressures (which means they were tested for ignition with instantaneous open at 5000 psi.) No valve that says it can be used with any nitrox mixture greater than 23.5% oxygen is going to have an improper gas path.

Discarding natural selection in the operator handling the oxygen cylinder, in my experience its contamination of the DIN fittings on scuba valves and regulators that is the usual cause of oxygen fires. The contamination isn't something obscure or the wrong o-ring... its lube on the threads, even oils from your fingers and hands, but I suspect the worst offender is polyester lint from clothing. (Blow out the valve before coupling the DIN fitting to the outlet.) The valve design does very little to protect from contamination (although eliminating chromed surfaces can help). The other area I often encounter contamination is in the neck threads, especially where the neck threads were lubed (the kind of lube doesn't really seem to make a difference.) I've seen as many fires that started in the neck threads from a right angle impact on the valve, as I've seen start in the outlet/regulator interface. I've also seen fires that started inside 1st stages. When servicing valves and regulators over the years I've seen evidence of many fires in valve outlets and 1st stages where the kindling chain never escalated. Want to know where I've never seen an oxygen fire start? Inside the valve, although I'm sure it happens I've never seen it.

If it makes you feel safer to have a particular valve on your scuba cylinder full of oxygen, go ahead, but don't delude yourself into thinking that will somehow significantly reduce risk of an oxygen fire.

Isn't the whole point of the slow-opening valve to lessen the chance that contamination downstream will ignite? By reducing the velocity of the impact of that contamination on whatever it gets blasted into when the valve is first opened?

I.e. there's a piece of lint in the opening of the 1st stage reg. If you open the valve instantly, that lint gets blown into the 1st stage with a lot of force. If you open the valve slowly, that lint gets blown into the 1st stage slightly more gently. So, slow opening reduces the chance of the lint catching on fire. Yes? No?

 

[mderrick]

Isn't the whole point of the slow-opening valve to lessen the chance that contamination downstream will ignite? By reducing the velocity of the impact of that contamination on whatever it gets blasted into when the valve is first opened?

I.e. there's a piece of lint in the opening of the 1st stage reg. If you open the valve instantly, that lint gets blown into the 1st stage with a lot of force. If you open the valve slowly, that lint gets blown into the 1st stage slightly more gently. So, slow opening reduces the chance of the lint catching on fire. Yes? No?

Like most things, Yes AND No. Sure velocity of impact makes a difference... but the valve would need to open maddeningly slow to make a significant difference in practice. Flow restrictions too can be practical in rebreather valves, but are less practical in open-circuit applications. Don't mean to imply that speed of opening the valve doesn't make a difference, because it absolutely does... but the design of the valve is much less a factor than the speed the operator actually opens the valve. Trying to correct the problem of the operator who opens the valve too fast by designing a valve which opens slowly by design has merit... but if the operator is ignorant or careless enough to benefit from the feature that still doesn't address the underlying issues of ignorance or carelessness. I've found it's really difficult to design out ignorant or careless operators in almost any system. If contamination is present, while opening slowly might reduce the risk, the risk is still much more about contamination than about the speed the valve opens. Just the friction of gases passing through the flow path is enough to cause contamination to ignite if the conditions are right.

 

[stuartv]

Like most things, Yes AND No. Sure velocity of impact makes a difference... but the valve would need to open maddeningly slow to make a significant difference in practice. Flow restrictions too can be practical in rebreather valves, but are less practical in open-circuit applications. Don't mean to imply that speed of opening the valve doesn't make a difference, because it absolutely does... but the design of the valve is much less a factor than the speed the operator actually opens the valve. Trying to correct the problem of the operator who opens the valve too fast by designing a valve which opens slowly by design has merit... but if the operator is ignorant or careless enough to benefit from the feature that still doesn't address the underlying issues of ignorance or carelessness. I've found it's really difficult to design out ignorant or careless operators in almost any system. If contamination is present, while opening slowly might reduce the risk, the risk is still much more about contamination than about the speed the valve opens. Just the friction of gases passing through the flow path is enough to cause contamination to ignite if the conditions are right.

I feel like I get what you are saying. I try to be careful. I put caps on my CCR 1st stages when the cylinders come off. I open the valves slowly (even though I don't really need to on the dil side).

But, even though I try really hard to remember and do everything right, every now and then I do forget and crack the O2 open that first turn too quickly. So, even though I know how I am supposed to do it, and I'm pretty good about it, and it probably makes VERY little difference compared to all the other important things, I will still spend some bucks for slow-opening valves for my O2 cylinders... I'm not GENERALLY ignorant or careless. But, I will make a mistake every now and then....

 

[dogbone]

I always thought planes used oxygen candles to avoid stuff like this...not compressed o2...dont know why I thought that...but I recall being told that, or reading it at some point...

 

[Aquanomad]

Or the Nautec OSEL is carrying with a claimed 20 year service life on the seat for ~90 euro. Rebreather Safety Improvement: Progressively opening Oxygen Cylinder Valve Seat