Cave Fills on LP tanks

[PfcAJ]

You were there, you tell me. Other people who were there have told me that the typical pressure of a "cave fill" was lower then.

I wasn’t there. I was still wearin underoos then.

But I do know a bit about the dives that went on during that period. I’m pretty confident that guys weren’t sticking to 2640psi fills.

 

[rjack321]

14 pages and we got no "cave filled" LP cylinder explosions (in good condition) and no DOT cave fill citations/tickets held up as evidence yet. I know facts have gone out of style - but try harder - my popcorn is getting stale.

 

[LiteHedded]

14 pages and we got no "cave filled" LP cylinder explosions (in good condition) and no DOT cave fill citations/tickets held up as evidence yet. I know facts have gone out of style - but try harder - my popcorn is getting stale.

Sounds like we’re about due then, no?

 

[2airishuman]

HP130 (130@3442) filled to 3600psi = 135cuft of gas
LP108 (108@2640) filled to 3600psi = 147cuft of gas

I'd be carrying less gas with the HP130.

Am I doing the math wrong or are you suggesting a higher overfill pressure on the HP130?

There are a couple of minor things wrong with your math. Most LP108s typically don't hold 108 cf at 2640. They're the same dimensions as cylinders sold as LP104s by other manufacturers and that is what they will typically hold. Air isn't an ideal gas between 2640 and 3600 PSI, and so you lose a few cf there. Then again HP130s hold 130 cf at 3500, not at 3442. ::shrug:: I would guess that with careful measurement you'd see a typical difference closer to 8 cf than 12 cf. Manufacturing tolerances may move that a few cf either way for a comparison of any two actual real-world cylinders.

I don't advocate overfilling either cylinder, but if 147 cf of gas is what you need to make your world go around, you'll be safer putting it in an HP130 than in an LP108, whatever the pressures work out to be. If I really need 147 cf of gas for a dive, I bring a twinset (pair of LP72s for 144 cf or pair of HP100s for 200cf) or an HP120 and a stage. Or go on two separate dives.

I don't understand why it's important to have more than 130cf of gas on a recreational dive unless you are shore diving with a long distance to cover to get from shore to the area of interest.

 

[rjack321]

Sounds like we’re about due then, no?

Did I hear a boom?

 

[2airishuman]

Can you show some incidents of LP steels that were in hydro and viz rupturing? If not, where do you get your risk?

Nope, I can't.

I don't believe that makes it a safe practice.

 

[2airishuman]

I wasn’t there. I was still wearin underoos then.

But I do know a bit about the dives that went on during that period. I’m pretty confident that guys weren’t sticking to 2640psi fills.

Is this going to be another one of your posts where you just state that someone has their facts wrong without actually stating what you believe the correct facts to be?

I don't believe they were sticking to 2640 either. But I don't believe that they were filling to pressures as high as those used for "cave fills" today. Do you disagree with that, or are you just quoting my post to disagree with something I didn't write?

 

[rjack321]

I don't advocate overfilling either cylinder, but if 147 cf of gas is what you need to make your world go around, you'll be safer putting it in an HP130 than in an LP108, whatever the pressures work out to be. If I really need 147 cf of gas for a dive, I bring a twinset (pair of LP72s for 144 cf or pair of HP100s for 200cf) or an HP120 and a stage. Or go on two separate dives.

I don't understand why it's important to have more than 130cf of gas on a recreational dive unless you are shore diving with a long distance to cover to get from shore to the area of interest.

Oi so many things wrong with this post.

a 3442psi hp130 is built to an exemption standard and hydro tested to 3/2 working pressure. 5250psi in the USA

a lp108 is built to a 3AA standard which dates to somewhere around WW1. In WW2 they realized that they could easily add 10% and ship 10% more gas to our Allies. Note that most USDOT 3AA cylinders are also dual rated in Canada by TC and rated to 182 bar or 2640 without any + baloney. 3AA cylinders are hydro tested to 5/3rds working pressure. 4000psi for a 2400+ cylinder in the USA.

Before you spout off about "safer" you would need to cite at least one actual injury from a "cave" overfilled cylinder. There are definitely some failed lp72s on record. As 2250+ rated 3AA cylinders they are hydrotested at 3750psi which is easily reached by most shops and especially shop banks. They are also thin walled and haven't been made in decades so rust pitting or corrosion are certainly valid reasons for them to have exploded independent of their overfill status.

 

[rjack321]

Nope, I can't.

I don't believe that makes it a safe practice.

Just making sure this is memorialized...
So in despite a couple decades of shop wisdom, and no actual facts to the contrary, you have a baseless opinion. Praise be!

 

[BRT]

Nope, I can't.

I don't believe that makes it a safe practice.

I am an electrician by trade. I see changes in the code where the reason for the change was the theoretical possibility of something happening that has never happened. While this might have been fine if they would have figured it out 75 years ago, after so long with no issues the risk is obviously negligible. There is risk in life. If you want to mitigate diving risk you should ban driving to dive sites. That is a proven killer. In hydro, in visual, overfilled steel LP tanks do not have an extremely low failure rate like aluminum tanks of one in several million sold. They have NO failure rate. We are not talking about the risk of DCS. We are not talking about the risk of CO in your air. We are not talking about the risk of an accidental pure O2 fill. This is not the chance of all your regulators failing at the same time. All of those things have a risk that is so close to zero that it is hard to calculate the risk. For the overfilled LP tanks it is impossible to calculate because it has not happened in the history of diving so far as anyone knows. If you think this is unsafe how do you ever leave your house?