Cave Fills on LP tanks

[PfcAJ]

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?

This all started with you saying cave fills haven’t been going on for 30 years. Now the goalposts have been shifted to “well they weren’t REAL cave fills like we have today”.

The fact is people have been blowing past 2640psi for decades without incident.

 

[2airishuman]

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.

What's your point? 3AA cylinders that are plus rated are hydro tested to 1.51515 of their actual working pressure (5/3 adjusted for the 10% overfill), while exemption cylinders are hydro tested to 1.52528 of their actual working pressure (because of the derating to 3442 psi. If you consider the actual working pressure to be 3500 then it would be 1.50000). Essentially the same.

I've read every word the 3AA specification and the Faber, Worthington, Asahi, and PST special permits. And the 3A specification. Please don't lecture me on the basics.

Before you spout off about "safer" you would need to cite at least one actual injury from a "cave" overfilled cylinder.

The fact that there haven't been injuries yet doesn't mean the practice is safe. There never should be an injury from a ruptured 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.

And we still get people who want to "cave fill" LP72s and other thin walled cylinders (such as LP50s) because there has been no reasonable, fact-based discussion of what the limits of safety actually are once we decide to disregard the regulatory framework.

 

[2airishuman]

This all started with you saying cave fills haven’t been going on for 30 years.

That's not what I said.

 

[PfcAJ]

That's not entirely true because the early "cave fills" were much less ambitious than today's "cave fills." The evidence for the safety of filling an LP steel to 3600 hot and letting it cool to 3200 or whatever does not go back 30 years, because that wasn't routinely done 30 years ago.

Episode of the twilight zone

Cuz we all know 3200psi fills are a recent development in the diving world. In the early 90s al80s (with a 3000psi service pressure) were only filled to 2700 because compressors couldn’t handle the hai prezzure.

 

[Caveeagle]

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.

Umm, nobody would fill a LP tank to 3200 on purpose. At that range, you want it to cool down to at least 3300. ...or 3600. To make your 1/3s math easier.

 

[2airishuman]

OK, fine, so pressures have to be divisible by 3 for rule of thirds, and from @kelemvor's post we see that 3600 is now customary. How long has that been going on? Was it 3300 before? 3000? I don't know -- maybe someone else does -- but I stand by my original assertion that early "cave fills" were made to lower pressures than today's "cave fills." It is based on this that I do not believe that the practice of what are now called "cave fills" can be considered to have a 30 year accident-free history. The actual history is in fact shorter.

 

[kelemvor]

OK, fine, so pressures have to be divisible by 3 for rule of thirds, and from @kelemvor's post we see that 3600 is now customary. How long has that been going on? Was it 3300 before? 3000? I don't know -- maybe someone else does -- but I stand by my original assertion that early "cave fills" were made to lower pressures than today's "cave fills." It is based on this that I do not believe that the practice of what are now called "cave fills" can be considered to have a 30 year accident-free history. The actual history is in fact shorter.

I certainly can NOT attest to the history of cave fills. I'm only regurgitating what I've been told by otherwise reputable sources in person when I talk about how many years it has been going on. I've only been diving for 7 years, and have only owned my own tanks for 6. When I bought tanks, my LDS explained the details about overfilling LP tanks and that's why I bought the tanks I have.

In the cave country "area" (as apposed to the store of the same name) you don't have to ask for cave fills. If you pay for a fill on a steel tank, you get a good cave fill. Most of the fills I've received have been in the 3600 range... I did get a 3800 once that made me nervous, and I've seen several at 3500. Now, I don't live in cave country. However, my LDS is run by a long time cave diver. He also gives cave fills, and he will ask me what pressure I want to end up with.

I also tend to get what I'd call "light cave" fills in the east coast area (jupiter to blue heron bridge) without specifically asking. I usually end up with 3100-3200 cold in my lp tanks when those guys fill tanks. In this region they like to bank "slightrox" at 30%. Personally, I prefer blending to best mix but you take what you can get when you're out.

The Florida Keys have the worst gas stations in Florida in my opinion. 2800ish most of the time, and they even cost quite a bit more. I encountered one station that would only give me 2640 hot. This is the only region where I've ever had to pay by the cubic foot for nitrox. I try to avoid getting fills in the keys unless I'm there for a multi day trip. If I dove in the keys more often, I'd buy additional tanks so I could avoid the situation.

 

[PfcAJ]

OK, fine, so pressures have to be divisible by 3 for rule of thirds, and from @kelemvor's post we see that 3600 is now customary. How long has that been going on? Was it 3300 before? 3000? I don't know -- maybe someone else does -- but I stand by my original assertion that early "cave fills" were made to lower pressures than today's "cave fills." It is based on this that I do not believe that the practice of what are now called "cave fills" can be considered to have a 30 year accident-free history. The actual history is in fact shorter.

NSS-CDS newsletter from 1982 references 4500psi compressors and overfilling lp104s.

 

[NAM001]

I haven't seen anything definitive on the alloys, metallurgy, specs, wall thicknesses, safety factor, etc regarding the US tanks vs Euro tanks.

My point was specifically that the situation is different here and there. Fully valid opinions about tanks in Europe/Russia may not apply to US tanks as they're different tanks.

Agree there are other factors involved tat what i understand it is in the safety factor of hte tanks. the US uses a factor of 4 other nations use 3 or 2.5 to determine working pressure. NOt that this is 100% true if an LP tank was designated under a factor of 2.5 its working pressure would be 3840 and not 2400 psi wth a factor of 3 it wold be 3200 and not 2400.

 

[rddvet]

I did get a 3800 once that made me nervous

You're in largo. I'm in st Pete. If yo're really looking for a butt puckering thrill, you can come by my house. I've got a couple pumped up to 4200 in my garage.