Cave Fills on LP tanks

[PfcAJ]

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.

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.

What’s up Pinellas County bros!

 

[NAM001]

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

I dont know if that is a reasonable path to argue on. Yes steels are more forgiving of over filling than al tanks are. (cracking) Yes you can over fill lp's them a lot,, because of the protection factor used in US allowed tanks,,,with out achieving any real dangers. Sustained fillng to those pressures and occasional pressures are 2 different factors. And yet with all that there are those that will not over fill a 3400 psi tank to 4k but will a lp tank to 4k. Different tanks different beliefs. What seams to be constant is that you dont pack al tanks to high pressures. Its probably as mistifying as 3442 is a lp tank and a 3500 tank is a HP tank. Most likely the same tank only a different stamping.

 

[NAM001]

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.

Again you are talking moot aspects of things. how about the oms 108 that is really 122 or the oms 121 that is 125. those differeences IMP are non mattering issues.

 

[NAM001]

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.



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.



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.

Your last comment is a valid one. You need to understand that those that are cave filling are doing so based on a tank not based on all tanks. The cavers do a good job of not taking un neccesary risks. As such i dont know about cavers taking lp 50's and cave filling them to 4k to explore caves. the need for the extra gas negates the use of a small 50 tank you are discussing. Its like what if you fell out of an airplane and you only had on one ice skate.

 

[BRT]

I dont know if that is a reasonable path to argue on. Yes steels are more forgiving of over filling than al tanks are. (cracking) Yes you can over fill lp's them a lot,, because of the protection factor used in US allowed tanks,,,with out achieving any real dangers. Sustained fillng to those pressures and occasional pressures are 2 different factors. And yet with all that there are those that will not over fill a 3400 psi tank to 4k but will a lp tank to 4k. Different tanks different beliefs. What seams to be constant is that you dont pack al tanks to high pressures. Its probably as mistifying as 3442 is a lp tank and a 3500 tank is a HP tank. Most likely the same tank only a different stamping.

I guess I never considered a 3442 HP100 a low pressure tank.
Faber Stealth HP100 Steel Tank

 

[NAM001]

I guess I never considered a 3442 HP100 a low pressure tank.
Faber Stealth HP100 Steel Tank

Im not sure what the actual designations are now days but at one time something about a 3500 psi tank required a different dinn valve than <3500. I probably don't have that right but it is vaguely in my mind of being a catagory change at 3500. The point was really " 60 psi changes the world view" Kind of like a motorcycle race a 199cc is the 200 class but a 201 is in the 250 class. And like bikes you buy them for their class size , not actual size which making comparisons often confusing.
again its like getting a oms 121 tank and it is actually a 125.

It may be the line where 232 or 234 bar is. one is under and the other is over.

 

[Jack Hammer]

IIRC, one of Sheck's books mentions overfilling tanks by 50%. Possibly in Taming of the Slough. Pretty sure ive also seen it mentioned somewhere in Cave Diving Articles and Opinions.

 

[Diver-Drex]

Your last comment is a valid one. You need to understand that those that are cave filling are doing so based on a tank not based on all tanks. The cavers do a good job of not taking un neccesary risks. As such i dont know about cavers taking lp 50's and cave filling them to 4k to explore caves. the need for the extra gas negates the use of a small 50 tank you are discussing. Its like what if you fell out of an airplane and you only had on one ice skate.

This was my whole point. Experienced divers with the ability to make sound judgements can do as they see fit and will likely be fine.
But there are people getting the advice on open forums that don’t have the experience and sound judgement to apply the advice correctly. Someone will take it one step further. How far is too far for a 40 year old 72? What is the limit for a lp50? Same as lp85 right?

 

[kensuf]

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 started cave diving in 1994. I distinctly remember a shop in Branford, FL that offered ice cold fills in a chill bath to 3600 psi. The biggest problem we had was the chance of blowing a burst disk as the cylinders warmed up during the drive to the dive site.

 

[LiteHedded]

overfillin lp50s here checking in.

have not exploded yet