Cave Fills on LP tanks
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Diver-Drex
Contributor
Double post
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Not really. If it was known that overfilling LP steels was unsafe, then you would be correct.
The fact is that there is zero evidence whatsoever that overfilling them is “wrong”...
They are rated for LP because of arbitrary government regulations imposed on the manufacturers of pressurized cylinders that are designed to be commercially transported on the interstate system.
PfcAJ
Contributor
How many data points do you need before accepting that the stamped working pressure on the tanks isn’t at all a realistic value?
20 years? 40? How many tanks? Thousands? Hundreds of thousands?
Things with ratings use safety factors. Whether that's 10:1, 5:1, 2:1, etc. The rating on a tank has an arbitrary safety factor applied. That tanks are hydro'd at a much higher pressure than rated is indicative of that. By overfilling you are simply decreasing the safety margin that has been engineered into the tanks.
For something like a dynamic load where you are hanging from a single suspension point, applying a force much greater than your body applies while static, you may choose to use a higher safety factor than say, picking up a pillow sack full of feathers. Regardless, you are free to apply the safety factor as you wish. In the case of lp steel tanks, I find the rating to be more conservative than required, and am quite comfortable choosing to utilize them at a different operating pressure than is stamped on the tank. I'm simply choosing a less conservative safety factor.
For something like a dynamic load where you are hanging from a single suspension point, applying a force much greater than your body applies while static, you may choose to use a higher safety factor than say, picking up a pillow sack full of feathers. Regardless, you are free to apply the safety factor as you wish. In the case of lp steel tanks, I find the rating to be more conservative than required, and am quite comfortable choosing to utilize them at a different operating pressure than is stamped on the tank. I'm simply choosing a less conservative safety factor.
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Rusty Shackleford
Contributor
He is saying at the rated pressure, it's like using a .357 to shoot 38s when it can safely shoot 357s.
MichaelMc
Working toward Cenotes
As is often the case ..., the devil is in the details:
.357 has a bullet diameter of .357
.38 has a bullet diameter of .357
So, using a .357 to shoot a .38 is quite safe, see .357 Magnum - Wikipedia, as it fits and develops lower pressure. Though if I recall it can foul the cylinder more as the case is shorter. Firing a .357 in a .38 would not be safe, as it develops higher pressure, but the case is longer anyway.
So, on details, do we know the burst limit, and the other limits (elastic, etc) of 3AA LP cylinders?
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This 1970s destructive test study is an interesting read and sheds more light on the standards. But I'm not qualified to comment.
.357 has a bullet diameter of .357
.38 has a bullet diameter of .357
So, using a .357 to shoot a .38 is quite safe, see .357 Magnum - Wikipedia, as it fits and develops lower pressure. Though if I recall it can foul the cylinder more as the case is shorter. Firing a .357 in a .38 would not be safe, as it develops higher pressure, but the case is longer anyway.
So, on details, do we know the burst limit, and the other limits (elastic, etc) of 3AA LP cylinders?
Edit:
This 1970s destructive test study is an interesting read and sheds more light on the standards. But I'm not qualified to comment.
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2airishuman
Contributor
I think the interesting question is: What is a safe fill pressure once you disregard the rating?
"Cave fills" have, from what I understand, crept up in pressure over the course of years. What's a cave fill now on a 3AA2400 cylinder? 3500 PSI? More? Some people say 90% of hydro. The hydro test is at 4000 PSI. Typical yield point is reached at around 4500 PSI. Typical rupture pressures are around 5500 PSI.
I've never quite understood why the same logic isn't applied to HP steels. They have higher pressure ratings because they use higher specification steel. Seems like a HP steel would be just as safe at 4800 PSI as an LP steel would be at 3500. Most regulators will handle 4500, and there's a point of diminishing returns because air behaves less like an ideal gas at those pressures, but still.
If scuba manufacturers listed an MBS for their tanks it would be easy. Pretty standard in the rope access/climbing/lifting/rigging industry. Wouldn't be too hard for the manufacturers to publish, but I bet they'd run into ratings issues with regulatory bodies. I don't know the regulations but I wouldn't be surprised if they were legally obligated to rate tanks at a certain percentage of their maximum.
Basically, tank ratings are the Working Load Limit, with an unpublished safety factor and an unpublished Minimum Breaking Strength. However because we don't know the MBS with any certainty, we can't calculate the safety factor. Basically, we've all just agreed that somewhere between the rating (WLL) and the hydro (less than MBS) steel tanks are safe to fill.
I think it would be interesting to see the differences between a DOT HP steel, and its European 300 bar volumetric equivalent tank, if there is any.
Basically, tank ratings are the Working Load Limit, with an unpublished safety factor and an unpublished Minimum Breaking Strength. However because we don't know the MBS with any certainty, we can't calculate the safety factor. Basically, we've all just agreed that somewhere between the rating (WLL) and the hydro (less than MBS) steel tanks are safe to fill.
I think it would be interesting to see the differences between a DOT HP steel, and its European 300 bar volumetric equivalent tank, if there is any.
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АлександрД
Contributor
I`m talking, that filling tanks up to working pressure - it is Russian roulette - Wikipedia but with EMPTY barrel, without shells.
And overpressured filling, more than testing pressure (that is normally is 1,5 of working pressure), is like play of Russian roulette - Wikipedia but with FULL barrel.
Ok, I will compare US style of filling (according written above, till testing pressure, and more) with Desert Eagle, and our overfilling style (with 10-20% overfilling, and less then testing pressure) with Derringer.
P.S. even empty gun can shot...
(use english subtitles translation) and moment at 2:50
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