Service pressure of Steel 72

[gbray]

I have 2 72's that I usually have filled to 2500 when cooled. one thing to be cautious of is what the burst disk is rated for. You don't want to be surprised after leaving your tanks in a hot place and finding they have no air in them. I find I can have as much bottom time as buddies with al80's if I have a good fill and am conscious of my breathing etc. I like my 72's.

 

[Jim Lapenta]

I routinely take mine to 3000 and they cool to around 2800.

 

[rstofer]

Cool-Thanks, that's the info I was looking for. It sounds like I don't need the Al 80's then.

The steel 72 is actually 65 cf at 2250 psi. it only gets to 72 cf when filled to the '+' rating of 2470 psi. Assuming it has a '+' rating from the last hydro.

To get to 80 cf would require overfilling to a little over 2700 psi.

I wish I had a definitive source for the buoyancy characteristics of the steel 72. They certainly seem less floaty than the Al 80.

Richard

 

[WD8CDH]

What I would really like to see would be an HP cylinder (higher strength steel) of the exact same dimensions as the old steel LP 72's. It would of course still hold 72CF of air at 2475psi, but it would hold 100CF at 3442psi and still be a legal fill. It would still have the nice buoyancy characteristics as an old 72 but I prefer the smaller diameter than the present HP100 tanks.

 

[DA Aquamaster]

I used to own about a dozen of them. Most of them seemed to be about neutral when empty with a K-valve, but a couple were still a pound or so negative when empty and I had one set of doubles that actually floated when empty even with bands and manifold, so they were obviously a couple pounds positive each when empty.

So the odds of getting a definitive source for buoyancy traits on a generic steel 72 are slim and none because they varied so much based on who made them and to a lesser extent when they were made.

 

[DA Aquamaster]

What I would really like to see would be an HP cylinder (higher strength steel) of the exact same dimensions as the old steel LP 72's. It would of course still hold 72CF of air at 2475psi, but it would hold 100CF at 3442psi and still be a legal fill. It would still have the nice buoyancy characteristics as an old 72 but I prefer the smaller diameter than the present HP100 tanks.

If I remember correctly, back in the 1980's Faber made a 2400 psi 75.8 (75.8 cu ft at 2640 psi) that was very similar to the generic steel 72 in dimensions. As I recall it was a fantastic tank but it was competing directly with used 72's that could be bought for a third the price of the new Faber.

Now that steel 72's are drying up somewhat, and with the potential for a 3600 psi over fill in some areas, there may be a strong market for that same LP tank. Or as you suggest a special permit version with a 3442 psi service pressure would make a great alternative to the shorter and fatter E, P and FX series 3442 psi 100's.

 

[rstofer]

So the odds of getting a definitive source for buoyancy traits on a generic steel 72 are slim and none because they varied so much based on who made them and to a lesser extent when they were made.

Maybe before the summer is over I'll quit being so lazy and just measure the tank in the pool. After all, I only really care about the buoyancy of MY tank, not the entire fleet.

It's odd how a particular tank can capture the interest of so many divers yet the tank itself is no longer made. Kind of a retro thing, I imagine.

If all the production steel tanks were lined up and a steel 72 was included at a current price, I would be willing to bet that the vast majority of divers would line up to buy the HP 100.

And yes, I am still looking for another 72. These tanks work best in pairs.

Richard

 

[OldNSalty]

Well for me, part of it is the price, so you are correct. I found one-literally, someone had left it in the parking lot of where I worked. We held on to it for a few weeks and let everyone know that we had it but no one claimed it. Eventually I just took it home. The other one cost me a total of $30. If these tanks were new and say, cost about $180-200 I wouldn't buy it.

Case in point: the Conshelf XIV is still made for about $600-how many of us have bought one new?

I did spot another for just $15 recently but I was a few days late on calling

 

[WD8CDH]

If I remember correctly, back in the 1980's Faber made a 2400 psi 75.8 (75.8 cu ft at 2640 psi) that was very similar to the generic steel 72 in dimensions. As I recall it was a fantastic tank but it was competing directly with used 72's that could be bought for a third the price of the new Faber.

Now that steel 72's are drying up somewhat, and with the potential for a 3600 psi over fill in some areas, there may be a strong market for that same LP tank. Or as you suggest a special permit version with a 3442 psi service pressure would make a great alternative to the shorter and fatter E, P and FX series 3442 psi 100's.

If I remember correctly, that was a 7.25" diameter tank. I would prefer a 6.9" (or smaller) tank. The closest thing that they make is the FX-72 (6.73" diameter), very nice tank, but it's only 72CF at 3442psi. I would think that a 6.9" diameter tank that is at least 80CF would be more marketable.

 

[Killer&Griller]

I have probably 8 in the shop that I filled yesterday......... If I could just remember what I filled them too........

For those wondering about the tub, I bath all my fills so I don't have the 200-300 loss afterward......

I know several that pump them to 4k and 4100, I have a brass set and stop at 3400..... not willing to upgrade to the SS set yet......