Steel 72 Doubles

[allenw1972]

I have a couple questions regarding setting up a set of steel 72's for doubles from a DIR perspective:

1. Can anyone think of any reason a set of steel 72s would be a bad idea? I really don't know what the weighting would be, but I assume they would get a little light empty. I assume a "V" weight could solve that issue.
2. Do many people run these to up to higher pressures than 2200? Could one run them up to 2500 or even 3000 without issue? Has anyone done this without problems? I understand the from a liability standpoint, this is not smart, but from a practical standpoint, would this present an issue over time with the tanks? (I know this is not really a DIR question, but I am here already)

Thanks all!

 

[b1gcountry]

Just curious...what threads do they take? Could you find an isolation manifold for them?

I would not myself feel comfortable running these above their rated pressure.

They don't provide much more gas than a single HP130, and they weigh a lot more I'd imagine. Unless you are using them for redundancy, they don't seem to give much benefit.

Tom

 

[allenw1972]

Just curious...what threads do they take? Could you find an isolation manifold for them?

I would not myself feel comfortable running these above their rated pressure.

They don't provide much more gas than a single HP130, and they weigh a lot more I'd imagine. Unless you are using them for redundancy, they don't seem to give much benefit.

Tom

The threads are the same standard size that nearly all tanks use today.

Yes. They take the standard isolation manifold as long as you have the correct bands (the tanks are 6.75" dia.)

Good point on the gas volume, but I was planning to use them for dives where less than 130 cf is needed. My equipment is setup for doubles and I would rather dive two 72's vs. one 130. Plus, I already own the 72's.

Your reply is much appreciated.

 

[SparticleBrane]

There's plenty of information about ye-olde steel 72s in the tanks forum, but I'll post some general information here.

Up until 1958 they were made with 1/2" pipe thread and didn't utilize and o-ring, after that they used standard 3/4" NPSM like most other cylinders. They are within 2-3lbs of Al80s, hold 71.cf of gas at 2475psi, and are 6.9" in diamater. Depending on the manufacturer they are ~5-6lbs negative fill and -1lbs to neutral when empty.

Steel 72s are rated for 2250psi, and 2475 with the +. Many people bring them to 3,000 with no issues. They're built to the same 3AA specs as any other LP cylinder, so logically there's no reason they wouldn't be able to sustain just as much of an overfill, proportionally.

With that being said, my girlfriend and I have a set -- she's fairly small in stature so they make a nice lightweight set of doubles for her to use. We bought her cylinders in very good condition and we want them to last forever, so we don't bring them above ~2700psi warm when filling so they usually end up around 2500psi in the water (no sense in having them fail hydro if they aren't made anymore, right?)


As to the DIR answer, it would be "balanced rig." In this particular case with steel doubles, that probably means "drysuit."

 

[Jim Lapenta]

I dive a set of steel 72's and regularly fill them to 2800 or so. The buoyancy characterisitics are great for diving wet. They make a nice set. They are just about neutral empty and in my 5 mil I wear no weight can easily swim them up and at 2800 psi which is 81.45 cu ft per tank I'm carrying 162 cu ft of gas. That's a bit more than a single 130. Mine have passed hydro for the last 25 yrs or so. Even before I got them I knew the guy who had them and he regularly gave them "good fills". Now mind you they don't set around much when they are filled.

ANd the benefits are numerous besides the increased capacity. Less weight, even dry I wear only 4lbs extra with them as opposed to my dbl85's. Then have a very nice low profile, and the set only weighs about 75-80 lbs with manifold and regs. Redundancy is also nice. Yeah you can put a Y valve on a 130 but if the tank oring goes it makes little difference. I also have a couple older 72's with the pipe thread. They pass hydro every time and the yget good fills as well. One is from 1955 and the other from 1957. THey give me the same volume as an al80 without the huge buoyancy swing, more compact, and waaay longer lifespan.

Those of us who know 72's love em and I'd put another set together in a heartbeat. Joel at TDL used to sell the right bands and a 200 bar convertible manifold can be gotten pretty cheap. I paid 130 for mine new on ebay.

 

[b1gcountry]

I stand corrected. Seems like a decent alternative to a set of AL80s. How does the dry weight compare between an AL80 and a 72?

Tom

 

[Jimmer]

I love my 72's. I dive them more than any other tanks right now. I'm even using them for my Intro to Tech class, and have absolutely no trouble getting trimmed out and maintaining buoyancy in my drysuit without a ton of weight. I generally fill them to about 2600, but did once put 3000 in them when I walked away from the compressor to talk to a customer and I maxed out on the regulator. No problem with that, I just took them diving and breathed them down. They are a great size, and weight for mid range dives with redundancy, plus I love being able to tell people that they are almost twice as old as me and have less rust

 

[Jim Lapenta]

Bathroom scale grown legs but as an old butcher I can tell you the 72 I have sitting here is a good 4-5 lbs lighter than the new al80 next to it.

 

[Jimmer]

I stand corrected. Seems like a decent alternative to a set of AL80s. How does the dry weight compare between an AL80 and a 72?

Tom

A 72 with a boot on it and 1300 PSI weighs 33.2 pounds, an al80 without a boot, and 2200 PSI weighs 37.4.

 

[AndyNZ]

Ah, the answer to all your dreams is the Faber 300bar 10 litre tanks! 300 bar is a rated fill of 4300psi or so, and they take the same manifold and bands as the Faber 12 litre tanks, so really easy to get hold of.

I've got a set of 232 bar 10 litres, so still 3300 psi, and the only problem with them is that the weight distribution is a little too high when I swap from my 12s to the 10s - they trim out really well with an aluminimum plate, mind you.

Not sure what the hydro and/or filling requirements are in the US - but import some of these babies from the UK and you'll love them.