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Largo
05-28-2010, 19:53
Please allow me to preface this by saying, please only reply if you are certain of your facts.

No disrespect is intended.

I keep finding Steel 72s for almost nothing. But, they are often rusted, or have something nasty inside.

Assuming I have them cleaned, and the rust removed; what is the likelihood of a Steel 72 failing hydro?



(Never mind threads, I've got that covered)

navyhmc
05-28-2010, 20:36
It's been a while since I tangled with a 72, but the last one I'm aware of was 20 years out of hydro and took about 4 tumbles to getthe rust out-minimal pitting though. It passed hydro!

Not a hydro tech, but I will go out on a limb and say the 72 that was found in a garage after 20 years is more likely to pass a hydro than the one that was used every day for 20 years. The oldest tank I have seen pass a hydro to date was a 1958 steel 63.

Largo
05-28-2010, 20:40
I'd like to expand on that, and argue that a hydro causes more wear and tear than normal use.


The reason that I'm asking is that, I recently had a hydro technician brag that he regularly passed air cylinders that were more than 100 years old.

That's all I know about that, but I'd like to know more.

Rileybri
05-28-2010, 20:53
I have and regularly use 5 ST 72's the oldest is 68' and is going strong. Two I had tumbled due to rust and both are mint now and have passed there hydros fine. I have no mmore then $50 into any one of the 5 tanks I own.

navyhmc
05-28-2010, 20:55
I agree on the hydro causing more wear and tear than a regular fill as it's 5/3 the working pressure (at leat that's what I've been told...) so the extra tension is extra w/t. Not seomthing I want to de EVERY year to say the least.

As to the 100 yo tank passing, I can also believe that given a few things: 1. They would over build it as a safety precaution and 2. the pressures would be lower as the technology to produce the 4000 psi on a regular basis sans steam was not there so a 1500 psi cylinder would not have a significant pressure in it to test.

BUT::::: I would question as to how the tech knew what pressure to test said 100 yo cylinder. The marking system that we have today would not have been around then to know what to test for. I am sure that it would have been inidicated somewhere, but I would ask...

eta: I would also wonder what and who would use a 100 yo tank. the only thing I can think of is maybe, maybe a fire extinguisher.

Largo
05-28-2010, 21:01
The air cylinders were used in mid-America during the oil boom of the turn-of-the century.

navyhmc
05-28-2010, 22:00
I understand that, I just wonder as to how they tested them, what was the standard and how did they identify what the working pressure of those early pressure cylinders was? I honestly don't know when the DOT testing standard that we follow today came out. I'm not that into the history of the pressurized air tank.

Which could be why you asked to begin with and have had to read the rantings of some strange guy in Kansas......

Largo
05-28-2010, 22:08
I understand that, I just wonder as to how they tested them, what was the standard and how did they identify what the working pressure of those early pressure cylinders was? I honestly don't know when the DOT testing standard that we follow today came out. I'm not that into the history of the pressurized air tank.

Which could be why you asked to begin with and have had to read the rantings of some strange guy in Kansas......


Word.

It's just struck me that maybe I should try to put some of these ST 72s into service. They come out of nowhere!!! And they are basically free.

Am I in error in saying that there isn't that much difference in bottom time between a ST72 and an AL80?

navyhmc
05-28-2010, 22:35
Am I in error in saying that there isn't that much difference in bottom time between a ST72 and an AL80?

This pause brought to you by mathematical calculations.

Well, a steel 72 is actually 71.2 cu ft vs. the AL80's 77.4

If your SAC is .5 cu ft/min, and you're at 60', with a 500 psi safety: The 72 will last 39-40 minutes and the 80 will last 45-46 minutes.

increase the depth to 90': 29-30 for the steel, 34-35 for the AL

at rec limits-130': 22 minutes steel, 26 minutes AL

at 30': 58 minuntes steel, 67 minutes AL

So it's relative to what you want to say much difference is...

Me, I say some but not much. :smiley20:

daZZ
05-29-2010, 02:56
got a 72 here. the oldest test date i can make out is 1975, there may be two older but i cant read them.

it hadn't been tested for approx ten years prior to my acquisition. it passed no problems.

we hydro every year over here

Lake Michijim
05-29-2010, 13:20
I dive vintage often and I have a nice collection of 72's. Remember, a 72 is not a 72 unless it's filled to it's + rating, a 10% over fill. 2475 psi. A 72 filled to 2250 is around 69 cubic feet if memory serves correctly. Like any steel tank they need to be tumbled every few seasons as the flash rust builds up. IMHO, they are the best tank ever made. Excellent dive characteristics, especially when compared to an AL80 which floats like a cork at the end of a dive. I use 72's for my double set ups and have plenty of air to complete the kind of dives I do. great tanks.

navyhmc
05-29-2010, 14:16
Interesting there LM. I have always calculated a 72 at 71.2 That's what I was told it was at 2250. I've been living a lie for 36 years? OH the shame!

brojack17
05-29-2010, 17:09
I picked up a steel 72 very cheap, but my LDS said not to mess with it because it was "lined". What should I do? It was MFG'd in 85 and hydro'd in 89 but sat in a garage basically since.

navyhmc
05-29-2010, 19:10
I picked up a steel 72 very cheap, but my LDS said not to mess with it because it was "lined". What should I do? It was MFG'd in 85 and hydro'd in 89 but sat in a garage basically since.

There was a short lived run of tanks that had a lining in them to supposedly keep them from rusting. The porblem is that the lining didn't always fo it's job and it was impossible to tumble with the lining in it. There is a process out there to remove it, but I ca't recall it off the top of my head.

http://www.gmcscuba.com/pdf/tank%20cleaning%20&%20tumbling%20tips.pdf is a guide of sorts for tumbling and cleaning tanks. pages 7-8 talks about linings. Hopefully that will help.

chilly willy
05-29-2010, 19:38
I've got a couple of 72's that I got for nothing, one I tumbled and the other was fine as far as rust goes. The older one of the two has a manufacture date of '63, the "newer" one is a '69. Both passed hydro and are great tanks for a total of $70 for testing. I see no reason to pass up a 72 unless there are obvious flaws with the tank, a large amount of rust inside would cause some concern but if there is only light amounts no problem.

Lake Michijim
06-01-2010, 10:39
Just sort of a side note. Be sure the shop you take them to for service understands the concept of steel tanks. There was a shop here that only wanted to deal with aluminum and professed that steel tanks should be outlawed. They finally went out of business. Imagine that.

navyhmc
06-01-2010, 20:43
I can believe that Lake! I've seen some stuff similar to that in now out of business shops.

captain
06-02-2010, 07:23
I have 10 steel 72's the oldest being 1957. They all pass hydro just fine.
I have seen commercial oxygen cylinders made in the late 1890's still in service 100 years later with hydro stamps every 5 years. Most are ICC (DOT) 3A specification cylinders.
As said 72's are 72 at 10% overfill which is 2475 psi. Getting them +10% rated is problem because today most all hydro facilities do not have the required REE documentation for them.

Lineman Larry
06-02-2010, 07:48
I own and dive with 4 Steel 72's. All are mid 1960's vintage and all are plus rated. I just had 3 of them O2 cleaned for "partial pressure" filling. The fourth is out for tumbling but should be back soon.

BSea
06-02-2010, 07:56
I also have 4. 2 are doubled & o2 cleaned. My oldest is a 67. But I also have a set of doubled 38's from 61. All have current hydro's, but none are + rated.