Steel tank volume question...

[rhlee]

[I know this is silly, but....]

I purchased a pair of used steel tanks and was told they were steel 72's. However, I'm now trying to calculate SAC/RMV using recent logged dive data, and it occurred to me that I read somewhere that on steel tanks, the advertised volume sometimes includes the 10% overfill (i.e. 2400+ tanks that are marketed as 85cf are 85cf when filled to 2400 + 240psi?)?

In any case, I'm trying to figure out how much air is actually in my tanks when I go diving (I get fills to 3000psi). The neck reads:

DOT-3AA 3000-85/9007/103 M 8303 FABER ITALY 1 A 85+

The cylinder measures 21" from the bottom of the boot to the neck of the tank (not incl. valve) and approx 21.5" in outer circumference.

Anyway, any help would be appreciated.

 

[DA Aquamaster]

The lenght, diameter and service pressure all indicate that it is a Faber 71.4 cu ft tank. (The other Faber tanks have a service pressure of 2400 psi.)

The Faber 71.4 holds 71.4 cu ft at 3300 psi. (a 10% overfill) and holds 64.9 cu ft at it's 3000 psi. service pressure which gives you 46.21 psi per cu ft.

It appears to have had it's initial hydro test in January 1985 and would have a galvanized finish.

They are -11.3 lbs bouyant when full and are still -5.9 lbs bouyant when empty, so they reduce the amount of weight you need to carry on a weight belt by 10 pounds compared to an AL 80.

I am not sure of Faber tanks of that vintage but newer ones have an REE number stamped on them. That number makes it relatively easy to obtain the plus rating needed to get 10% overfills. The test to the required tolerances can be done at the next hydro test, but usually has to be specifically requested.

 

[rhlee]

Thanks for the info. This will be very useful in figuring out my air consumption numbers.
I do have one follow-up question though, about the bouyancy numbers. Both

http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

and

http://dive.scubadiving.com/html/200010_tankchart.html


List the Faber 72 as being -8.4 to -3.7 negative. Where did you find your figures? I'm going on a trip where the boat will be providing AL80s (which I don't usually dive with), so I'd like to get an idea of how much extra weight I'll need with my normal gear/wetsuit configuration.

thanks.

 

[DA Aquamaster]

The difference in specs from various sources are usually due to the valve being either included or excluded from the calculation. I suspect the stats used on those sites are without any valves, which is a common way for tank manufacturers to do it.

The specs I used were specs for Fabers sold through Scubapro and are figured with a K-valve attached.