New 63 Equals Vintage 72?

[SurfLung]

New 63 Equals Vintage 72?
Generally speaking... It's my understanding that the original steel "72" was really about 65 cf at 2250 psi and reached 72 psi at 10% over or 2475 psi. The reason I mention this is because the present day aluminum "63" is said to have almost the same buoyancy characteristics as the original steel 72 (aka 65). And, you can rent a present day aluminum 63 from most dive operators.

Here's a USD 72 Description from the 1963 catalog...

"Should sink slowly when full. +1.7 lbs positive when empty will float".

And, I looked up the buoyancy of an aluminum 63...
Full is -2.4 lbs (sinks slowly?)
500 psi + 1.7 lbs (floats)

I downloaded the 1963 USD catalog from the Vintage Double Hose website, courtesy of the late Bryan Pennington.

[ScubaLawyer]

That's interesting Eb. I always found steel 71.2 tanks to be neutral at 500 psi. I guess it makes sense that they could be slightly positive at 0 psi.

M

[SurfLung]

Yes and I think it's also been shown that not all tanks were made the same. Among my 38s, 42s, and 50 there is quite a difference in buoyancy. The 1800 psi USD 38 tanks have thinner steel and are more floaty than the 1880 psi Sportsways 42 tanks. And my 2250 psi Voit 50 tank is absolutely HEAVY. After I posted the above, I saw some other data from the Basic Scuba book that didn't agree with it. I heard that bit about the aluminum 63s being similar to the steel 72s and I've found the 63s to be comfortable diving tanks.

[rhwestfall]

What I like about the AL63 is the length. Using it with a DH, I can wear the reg in the correct place, and have nothing even remotely close to my legs. Also, unlike the HP80 steel, they do not make me overly head heavy.

I have a pair of 63's on a solid bar military manifold.