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SurfLung
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Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
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Fun Facts About 38s

Wed Nov 15, 2017 6:32 pm

Fun Facts About "38s"
- I got to wondering about an aircraft oxygen tank my son sent me... Its a fairly modern tank and I was wondering if the usual reducer bushing would convert it to Scuba. What threads are standard on O2 tanks, anyway? I found some specs on the 3AA Steel tanks and copied them. The necks of the tanks will be either 1/2" NPT or 1" NPT thread. My tank is 1" NPT. So, the McMaster Carr High Pressure Reducer Bushings will fit just like my other Scuba conversions.
O2TankSpecs.jpg
Also, I looked at the specs for HST and Service Life. Its 5 years and unlimited. So, why wouldn't any Hydrostatic Testing Facility service tanks whose official lifetime is unlimited?
Image
Interesting... The specs actually name the tanks 38 CF 3AA with capacity of 38.9 cf. I told my son it looks like a "38"? This size of tank has been made in many variations... Round bottoms, conventional bottoms, dimpled bottoms, 5-Bump bottoms, 1/2" NPT thread (Voit), 1" NPT thread (Military surplus and oxygen), 3/4" Straight Thread w/O-Ring (US Divers), 1/2" Straight Thread w/O-Ring (Sportsways).

Ideal Weight: Surprisingly, not all of these 38s weigh the same. Tanks that are 1800 psi are the thinnest and lightest. That's my USD Yellow Twins and Military Surplus. Next up are the 1880 psi tanks by Sportsways. Next again are these 2015 psi oxygen tanks... They take more pressure but have the same capacity. And finally there were some Voit tanks made for 2250 psi which were 45 cf and filled 10% over were close to 50 cf. All of the others fill 10% over to get 42 cf. All pretty much the same dimensions but thicker steel for higher pressure and therefore more weight. For divers, some prefer the more heavy so they don't have to wear as much weight. The lighter tanks are among the few twins you can wear with just a swim suit and still need a weight belt to sink.

I also have a modern version called a High Pressure 80. Same height of tank but 1/4" wider diameter and thicker steel yet. That one gives 80 cf at 3442 psi. Very heavy, too.

Finally, tanks just like this are sold brand new by the SkyOx company. They call it their 40 cu ft cylinder. See http://www.skyox.com/product/SK%2011-40-CV
NOTE: They are valuable. Price is $373.46 if we wanted to buy them new! So, you could make up a new set of Twin 38s from these new tanks for around $800... About the same as it costs to buy new Twin Steel Tank sets from XS Scuba.
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SurfLung
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