Tank buoyancy numbers

[JamesBon92007]

My PST steel 72's must be different from what ever you have. Mine say 2400 which gives 2640 with the 10%.

Could you post a picture of one? Please include the 3AA stamp at the top of the tank and the first hydro date.

 

[JamesBon92007]

I have 11 LP72s manufactured between 1962 and 1978 by PST and Norris. I used to have more, including some made by Kidde which I have since sold due to local difficulties in getting the hydro shops to issue a + rating for them. They all bear a service rating of 3AA2250..

I only have, and have only seen (that I recall) one steel 72 that had a second "+" stamped after a hydro re-test. I tried to ask the hydro guy last time about getting the "+" stamp and didn't get a usable response. I'm going to ask again next time. I was under the impression that if it got the "+" sign the first time it was good for life, but that is contrary to what I remember being taught when I was originally certified.

 

[guruboy]

I only have, and have only seen (that I recall) one steel 72 that had a second "+" stamped after a hydro re-test. I tried to ask the hydro guy last time about getting the "+" stamp and didn't get a usable response. I'm going to ask again next time. I was under the impression that if it got the "+" sign the first time it was good for life, but that is contrary to what I remember being taught when I was originally certified.

It needs to qualify for + at each hydro.

 

[JamesBon92007]

It needs to qualify for + at each hydro.

That's what I was originally told but it seems like at least some of the tanks would be re-certified for the "+."

 

[guruboy]

Shop needs to know the REE number and how to do it.

 

[Boiler_81]

As far as I know the PST tank is the only one which has a known published REE number. If someone has documents for other manufacturers please post them.

I have had the hydro shop stamp the + on PST tanks using the published REE number.

 

[2airishuman]

There are some shops that don't issue + ratings because they don't know how. There are some shops that don't issue + ratings because the testing equipment they use is not precise enough for them to be authorized to issue + ratings.

The cylinder may be filled 10% over rated only if there is a + at the most recent hydro.

Every 3AA cylinder I've seen has a + rating at the time of manufacture.

+ ratings may be issued even if the previous hydro test did not include a + rating.

To issue a + rating, the hydro shop needs to know the REE value for the cylinder. On most newer (1990s and later) cylinders, the REE is stamped on the cylinder by the manufacturer. Otherwise, the REE value must be provided by the manufacturer. The situation for LP72s is messy because the manufacturers are out of business (or at least out of the scuba cylinder business) and there are differences of opinion about the validity of the documents that are still in circulation. The PST one is widely available but has a typo so some shops won't accept it. Some shops apparently have REE values for Norris cylinders. I haven't found anyone who does for Kidde cylinders.

There is a process for determining the REE by measuring the cylinder wall thickness with ultrasound equipment, but it is involved and, as far as I know, no one but @Luis H has had any luck with this approach.

I have 11 LP72s, all PST and Norris, and all of them have + ratings.

 

[Andrew Donn]

My PST steel 72's must be different from what ever you have. Mine say 2400 which gives 2640 with the 10%.

You will find both 2250 rated and 2400 psi rated steel 72s.

The other important thing to consider is the difference between "spec" numbers and marketing data. It is unlikely that you will see true published specification numbers from a tank manufacturer on their website or in brochures. What you are more than likely seeing is something that has been "messaged" by the marketing department. How else do you get 77.4 cu.ft. rounding to 80 cu.ft?

 

[Kharon]

You will find both 2250 rated and 2400 psi rated steel 72s.

The other important thing to consider is the difference between "spec" numbers and marketing data. It is unlikely that you will see true published specification numbers from a tank manufacturer on their website or in brochures. What you are more than likely seeing is something that has been "messaged" by the marketing department. How else do you get 77.4 cu.ft. rounding to 80 cu.ft?

Yep - and a 360cc Honda motorcycle that has an actual displacement of 326cc. LOL

 

[JamesBon92007]

There are some shops that don't issue + ratings because they don't know how. There are some shops that don't issue + ratings because the testing equipment they use is not precise enough for them to be authorized to issue + ratings.

The cylinder may be filled 10% over rated only if there is a + at the most recent hydro.

Every 3AA cylinder I've seen has a + rating at the time of manufacture.

+ ratings may be issued even if the previous hydro test did not include a + rating.

To issue a + rating, the hydro shop needs to know the REE value for the cylinder. On most newer (1990s and later) cylinders, the REE is stamped on the cylinder by the manufacturer. Otherwise, the REE value must be provided by the manufacturer. The situation for LP72s is messy because the manufacturers are out of business (or at least out of the scuba cylinder business) and there are differences of opinion about the validity of the documents that are still in circulation. The PST one is widely available but has a typo so some shops won't accept it. Some shops apparently have REE values for Norris cylinders. I haven't found anyone who does for Kidde cylinders.

There is a process for determining the REE by measuring the cylinder wall thickness with ultrasound equipment, but it is involved and, as far as I know, no one but @Luis H has had any luck with this approach.

I have 11 LP72s, all PST and Norris, and all of them have + ratings.

Well, that explains a lot. The hydro guy that just tested my tanks was going to condemn one of them but tested it again after testing the other tanks. He said there was "air in the line" so some of the water didn't get sucked back into the tank when the pressure was released (I think that's how it works). The setup didn't appear to be very sophisticated.

So, as we now know, dive shops are only supposed to fill the tanks to the rated pressure if it didn't receive a new "+" stamp on it's most recent hydro. However, in my 48 years of getting tanks filled I can recall only one time where the dive shop did not fill my 72 to 2475 and I'm pretty sure they all only had the "+" stamped on the original hydro and not on the subsequent hydros. When I questioned the guy about that he filled it to 2475.

Who does your hydro tests in Minnesota? Should I bring my tanks with me this summer so I can get the "+" stamps on them? Where is "Greater Minnesota?" You mentioned Twin Cities. I'll be staying somewhere near Scandia. Would that be "Lesser Minnesota?"