Tank buoyancy numbers

[Bob DBF]

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

And don't forget the old Faber 3000# service +10%, MP 3300# service, and new 3442# service 72's.


Bob

 

[2airishuman]

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.

There is no one "best" hydro shop here. They all have their drawbacks.

All Safe in Wyoming, Minnesota is closest for you. They do a great job with shot blasting, and they will + rate PST LP72s, but not Norris LP72s. They will put a VIP sticker on your cylinder following hydro test for a few dollars extra. Their rates are very reasonable and they accept walk-in customers. However they will not follow the round-out procedure that PST recommends for HP galvanized cylinders so you will not want to give any such cylinders to them, or there is a good chance they'll be condemned for no good reason. (The same potential problem also exists for 3AA HP galvanized cylinders from any maker). All Safe is willing to shot blast cylinders, without hydro testing them, again for very reasonable rates.

Any Norris LP72s you have will have to go to Weber & Troseth if you want + ratings. As far as I know, they don't accept walk-in business, but several of the LDSs subcontract their hydro work to them. For this reason they end up being more expensive, and they don't do shot blasting. They do a good job on any cylinder including PST HPs.

You can also use Nardini, which is on the north edge of the cities. They will not + rate anything but are a good choice for PST HP cylinders, 3AL cylinders, and any Worthington or Faber cylinders made under a special permit. They accept walk-in customers and are easy to work with, and have reasonable rates.

Would that be "Lesser Minnesota?"

Heh. I'm actually in Northfield, just south of the Twin Cities.

 

[2airishuman]

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.

I've run into it more than once. It depends on the dive shop and on who is running the fill station that day.

 

[Andrew Donn]

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.

I'm surprised that the test facility would test the cylinder back to back like that. This sets up a potentially dangerous situation. If the tank did truly fail a proper test then it is likely that it would pass a subsequent retest. Since the test is measuring permanent expansion the first test has already "permanently" expanded the tank and the permanent expansion on the second test is going to be less and probably in spec. If there truly was a problem with the test setup with air in the lines than your tank is probably OK but that should be picked up in the run up to a proper test.

 

[guruboy]

Regulations allow for a retest if the first test had an error

 

[JamesBon92007]

I'm surprised that the test facility would test the cylinder back to back like that. This sets up a potentially dangerous situation. If the tank did truly fail a proper test then it is likely that it would pass a subsequent retest. Since the test is measuring permanent expansion the first test has already "permanently" expanded the tank and the permanent expansion on the second test is going to be less and probably in spec. If there truly was a problem with the test setup with air in the lines than your tank is probably OK but that should be picked up in the run up to a proper test.

That makes me question the whole process--if they are testing for expansion and the recovery from the expansion and the tank was "permanently" expanded then wouldn't a second test indicate that there was very little expansion in the metal?

 

[BRT]

That makes me question the whole process--if they are testing for expansion and the recovery from the expansion and the tank was "permanently" expanded then wouldn't a second test indicate that there was very little expansion in the metal?

I think they do not stop having permanent expansion. This is the problem. They deform without returning to size therefore getting bigger and bigger and weaker and weaker.

 

[guruboy]

Does anyone know if the scuba specs tables online are giving salt water buoyancy numbers?

 

[Kharon]

Does anyone know if the scuba specs tables online are giving salt water buoyancy numbers?

Which tables - there are many.

 

[guruboy]

I weighed two of my Norris LP72 at the hydro shop today.

No boot, no valve-
26.5 lbs
28 lbs