Old steel tanks?

[KGNickl]

I just picked up 4 old steel tanks and put a bunch of info below and have a few questions.

Questions
1. If anyone has any info such as tank brands or to verify size of the tank let me know? ANSWER: 1978 PST 72 cu ft. steel tank
2. How do these tanks compare to the standard 80 cu ft. rental tanks I'm used to? Say I'm diving at 40 ft. w/ one of these vs. 40 ft. w/ the standard 80 cu ft. rental tank, what will my air time difference be assuming breathing is the same on air? ANSWER: Below...
3. They have 2250 valves on them now and I'm wanting to put some pro valves on them (I want to use my din regulator, but also have the option to hookup a yoke regulator occasionaly). Can I put a 3000 PSI pro valve on it? Or does it have to be a 2250 PSI valve? Anyone know of where I can get a 2250 PSI pro valve or companies that make them? ANSWER: Below...
4. What thread type does this tank have? 3/4 NPS? Pictures added below.

Tank Info
3 out of 4 are filled with air, one isn't. They are in great looking condition on the outside. They aren't rusted and are free of scratches and dents. I'm hoping the 3 filled tanks are in as good condition inside as outside, the third tanks since its empty and been sitting I really haven no expectations for it. Right now 3 have Sherwood Selpac K valves on them, and one has a US Divers K valve.

The tanks read DOT 3AA2250 and then a # which I'm guessing is a serial # (ex: 25431U). The most recent fill sticker on the tanks is from 2002 and the oldest stamp on the tanks is 2C78+. I'm guessing they are 72 cu ft. tanks. They are about 22" around (approx 7" diameter) and about 25" tall. The guy I bought them from got them in a lot of equipment and doesn't dive local so they have been sitting in his basement. The shops sticker that is on the tank is no longer in business.

 

[captain]

The valve itself does not make a difference only the rating of the burst disc, so yes you can put a 3000 psi valve on them with a 2250 psi burst disc. As you determined they are most likely 72's however they contain 72 cubic feet when filled to 2475 psi (2250 +10%) and about 65 cubic feet at 2250 psi. An AL 80 is actually about 77 cubic feet at 3000 so the difference is 12 cubic feet if the AL 80 is filled to a solid 3000 psi which usually isn't the case. Most were made by PST or Norris.
I use steel 72's exclusively, I have 9 singles and one doubles set. They have better bouyancy characteristics than the AL 80.

 

[skdvr]

Damn you beat me to his house by about 15 min... I was on my way to get them... I would be pretty sure too that you have 72's. I would take them into TGADC and let Mark take a look at them. I would guess that the 3 with air are still probably just fine to use, the 4th could be ify. I am not sure about valve thread sizes and so on with these. Again I think that Mark at TGADC would be a good source of info on these, as far as what your options are for putting valves on to use your DIN regs with. Godo luck with them...

Phil

 

[Peter Guy]

Captain -- you wrote

They have better bouyancy characteristics than the AL 80.

Would you please elaborate?

I have two old 72's that I'm thinking about using for "monkey diving" and I'm curious as to how negative they are when full -- how positive they are when empty. I've been unable to get good info on their buoyancy characteristics so I'm quite interested in your response.

Thanks.

 

[KGNickl]

Damn you beat me to his house by about 15 min... I was on my way to get them... I would be pretty sure too that you have 72's. I would take them into TGADC and let Mark take a look at them. I would guess that the 3 with air are still probably just fine to use, the 4th could be ify. I am not sure about valve thread sizes and so on with these. Again I think that Mark at TGADC would be a good source of info on these, as far as what your options are for putting valves on to use your DIN regs with. Godo luck with them...

Phil

Yah, I got lucky (as long as the tanks pass and work out......). I had just got home from the gym and the email came when I was in the middle of checking my email. I called and walked out the door to pick them up a few minutes later.

I think I'm going to empty the tanks and pull the valves and look inside. If they look good I'll get 2 of them hydro and if they pass I'll throw new valves on and have them tumbled. If the first 2 tanks work out I'm undecided on what to do with the other 2 since I really only need 2 tanks. My ideas are sell them for what I bought them for (as is), get hydro and sell them for the price I paid + price the hydro cost me, or I might just throw new valves on and have them cleaned and setup for enriched air.

 

[captain]

Captain -- you wrote Would you please elaborate?

I have two old 72's that I'm thinking about using for "monkey diving" and I'm curious as to how negative they are when full -- how positive they are when empty. I've been unable to get good info on their buoyancy characteristics so I'm quite interested in your response.

Thanks.

The steel 72's generally are about 0 to 1 pound positive empty and 4 to 5 negative when full compared to an AL 80 which about 4.5 pounds positive empty and 1.5 negative full.
Which means you can drop 4.5 pounds of lead off your belt when using the steel 72. And the steel 72 empty weights the same as an AL 80 empty, 31 pounds.

 

[KGNickl]

All my original questions are answered, but I've added a new question regarding thread size. Also added pictures to help with that. Hoping its 3/4 NPS so I can put pro valves on the tanks if they pass inspection and hydro.

 

[DA Aquamaster]

Pro valves will work fine as they share the same thread as an AL 80.

 

[matt t.]

These are great tanks! I have a set with original hydros of '60 and '66. DO NOT OVERFILL THESE!!! They are thinner than new tanks and will not do well with overfilling. Enjoy them!

 

[KGNickl]

These are great tanks! I have a set with original hydros of '60 and '66. DO NOT OVERFILL THESE!!! They are thinner than new tanks and will not do well with overfilling. Enjoy them!

What happens if the tanks are overfilled? Would it just put stress on the steel and raise the chances of failing visual or hydro in the future?