filling 72's

I didn't realize there were concerns with filling LP72's to the standard NFL cave fill- 3600psi... that being said, do you know which shops will or won't fill past the indicated working pressure? Also what are some of the most recent documentations of LP72's exploding if this seems to be the concern. I tried to have them filled today without luck and the concern seems to be thinner sidewalls with this age of tank. I wasn't aware of these issues till now... can anyone fill me in? I didn't find any threads on this forum after searching...

-Matt

Hey Matt!

Are you talking about the old school 2250+ steels?

Safe diving,

Rich

both actually... I have a couple of each

Some 72 sized tanks have a fill pressure of 1800 psi. Be careful! I don't fill mine over 2900, ever.

I have old ones, from the 1970"s. I only fill to 2400psi. I just don't feel comfortable over filling something that old. If I need more gas I just use a larger tanks.

Weak necks. 2400psi max.

I have an old 72 from my uncle that dates to the late 1960's. He had it filled for years down in the West Palm area but after Frank's dive shop closed he could no longer find a place to fill it.
He gave it to me and I brought it up to my home in the north Florida area where we had it fully inspected -- hydro and VIP -- and it passed with no problems and I've been filling it ever since with no issues.
I try to keep it at or under 2500 psi.

Ironically I filled my sidemount 72s yesterday,and the fill person asked me about the pressure,but normally I will sit with those tanks until I know they are aware they are 72s,and no higher than 2400.

I've been filling mine (1972 and a 1973, 2250+) to 3000 on a regular basis for years....maybe I'll back off! I did get a fill to 3600 in cave country once by mistake (filling several different tanks and I got to talking, not paying attention...). I draned them down to 3000 before leaving the shop.

-skip

I like mine to be at 3k...makes math real easy to use it as a stage, and gives me slightly more gas than an 80.

But, I fill slow and don't do the whole "overfill then let it cool" thing. And, I try not to let it sit for forever at 3k before I use it.

I do have to tell fill guys that it's a 72 though, on busy days, they sometimes lose track.

I have some early 70's 2,250 psi steel 72's that I've owned since new. They are clean inside and have never even needed to be tumbled. I fill them to a max of 3,000 psi and they have always passed hydro. While I'll slam my 85's and 108's I go easy on the 72's.

Got some late 60's that I fill to 3000 but then I have had the tanks since I was 12 and they still pass hydro and are rated at 2250.

SLIM

All great points... just dissapointing, I should have done my homework... I really had no idea there were issues with these older tanks. But thinking about it, we got them for doing shallower caves (50' deep or less) and compared to diving a set of 80's, when pumped to 3000 you've got a 33% overfill and 96 cu ft of gas... I was doing 2 hour long dives in mexico at similar depths, so I think these will work great for some of the river caves we like to visit... especially that they are easier for my girlfriend to lug and she doesn't breathe half the time anyway, so it is probably overkill for her :-)

Matt,
The bouyancy chars of steel 72s are also much much better for sidemounting than AL 80's, and that has been the primary reason i use them for short [or shallow or small] cave and river cave dives. I also fill my own, and dont bring them past 2600 warm, about 2400 cold. And, if you think of it, the gas volume difference is really small between 80's and 72s. If both are full (80 and 72 cubic feet) and you are diving thirds (one third = 26.7 and 24 cubic feet), the gas diff is less than 3 cubic feet, and if youre SAC is between 0.5 and 1, thats only a few minutes extra of gas, which is usually less than 200 ft swimming distance.

Sorry for the long exp... but dont fill them past 2400 cold!

don't get me wrong... i'm still keeping them around and planning to use them for the same locations as I originally intended... I was just dissapointed to find out it isn't wise to pump them like my other steels... with a cave fill you could spend hours on two little tanks like that. no worries though!

Quote:

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Originally Posted by IowaCaveDiver

? Also what are some of the most recent documentations of LP72's exploding if this seems to be the concern.

-Matt

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I tried to find some info about it with no luck

Quote:

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Originally Posted by akcaver

Matt,
And, if you think of it, the gas volume difference is really small between 80's and 72s. If both are full (80 and 72 cubic feet) and you are diving thirds (one third = 26.7 and 24 cubic feet), the gas diff is less than 3 cubic feet, and if youre SAC is between 0.5 and 1, thats only a few minutes extra of gas, which is usually less than 200 ft swimming distance.

Sorry for the long exp... but dont fill them past 2400 cold!

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And as the "80" are only 77.4 the difference is even lower

Some LP 95's are as old as some of the last steel 72's, and all are designed to the same 3AA engineering standard.

As for "old" there are still welding tanks from pre-WWI (1910, etc) that I have seen pass hydro and still qualify for a plus rating. As long as rust does not claim it, a steel tank will essentially keep going forever as they do not have the same fatigue or SLC issues as aluminum tanks.

I've never heard the "thin neck" thing before, and no offense, but it sounds like BS/urban legend. The necks on my steel 72s are no thinner than the necks on my LP 95s.

When you consider that we "cave fill" 2400 psi 3AA steel tanks to 3600 psi (a 150% fill) it would suggest that filling a steel 72 to 3375 psi would give the same 150% fill. Obviously you would not want to fill it to 3600 psi, but fills in the 3000-3200 psi range are at least as reasonable as filling 2400 psi tanks to 3600-3700 psi.

At 3000 psi a steel 72 holds 80.9 cu ft, at 3200 psi it holds 86.3 cu ft, at at 3375 psi it holds 91 cu ft.

They are essentially equal to an AL 80 when filled to 2850 psi (76.9 cu ft), and that is only a 127% overfill.

But prejudice and misnformation being what it is, it is still hard to get them filled to more than 2250 psi in many places even in N FL. The bottom line is that a 150% overfill in any 3AA tank is going to be safer based on condition than on service pressure. I'd rather fill a very clean steel 72 to 3375 psi than fill a ratty looking LP 95 to 3600 psi.

Quote:

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Originally Posted by IowaCaveDiver

All great points... just dissapointing, I should have done my homework... I really had no idea there were issues with these older tanks. But thinking about it, we got them for doing shallower caves (50' deep or less) and compared to diving a set of 80's, when pumped to 3000 you've got a 33% overfill and 96 cu ft of gas... I was doing 2 hour long dives in mexico at similar depths, so I think these will work great for some of the river caves we like to visit... especially that they are easier for my girlfriend to lug and she doesn't breathe half the time anyway, so it is probably overkill for her :-)

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I use mine as sidemount in shallow caves (<50ft, ave 20) and for initial investigation. and sometimes just because they make it so easy.

I dove them backmount for awhile and that too was like wings on your back, not tanks.


Originally Posted by IowaCaveDiver http://www.cavediver.net/forum/image...s/viewpost.gif
? Also what are some of the most recent documentations of LP72's exploding if this seems to be the concern.

-Matt

I too would like to know; is there a list of tanks that have exploded that also shows size, original hydro, material, volume, etc.? who keeps the records? DOT?

-skip

Quote:

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Originally Posted by DA Aquamaster

I've never heard the "thin neck" thing before, and no offense, but it sounds like BS/urban legend. The necks on my steel 72s are no thinner than the necks on my LP 95s.

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No offense taken. I've always thought the same thing, but was told the same story by several different divers for whom I have a lot of respect.

Mine passed hydro earlier this year and have been getting filled to 2800-2900 since.

Quote:

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Originally Posted by SuPrBuGmAn

Mine passed hydro earlier this year and have been getting filled to 2800-2900 since.

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Dont get me wrong, I "accidently" filled a 72 to 3100 this summer at the shop, and nothing happened, just havent done that since

The neck isn't as big an issue as wall thickness. 72s have thinner walls than most other steel tanks.

As for exploding, the only ones I have heard of exploding were due to heavy rust inside the tanks. The incidents went way down when the VIP program started. Since they walls are thin, it wouldn't take very much rust to weaken them.

If they pass hydro, they held 3750psi for 30seconds.
I have an old set of 72 but I don’t fill more than 2500psi. The best way to judge the health of your tanks is by getting the % permanent expansion from your hydro tester.
Keep in mind that DOT allows 10% permanent expansion, most tanks will show 0.2 to 0.8% mine are at 4% this is why I don’t go pass 2500psi.