Specs on steel 72 ?

[Matt S.]

I was going over my dive log for my first OW dives, looking at my weighting and calculating SAC... My instructor said that we were using steel 72s, but my starting PSI of 2200-2400 doesn't seem to match the 72 cf steel tanks I have found on reference charts--they are all 3000+. (eg http://www.techdivinglimited.com/pub/tanks.html)

Was I using an underfilled tank, or is there some kind of low pressure steel 72 cf tank that I haven't found the specs for? And is the true volume 72 cf, or is that rounded up, like an Al 80?

Thanks!

 

[Thalassamania]

Steel 72 is 71.2 at 2475 PSI. Rated pressure is 2250+

 

[rjack321]

The old 2250 psi (+10% = 2400 psi) 72s aren't made anymore. The numbers on the site you looked at are a different type of tank, usually called a "medium pressure 72"

 

[Matt S.]

Ah ha, no wonder I can't find specs anywhere!

Would either of you happen to know the rough buoyancy swing for that tank, or does it vary too much by manufacturer? EDIT: nm, found the specs in another thread now that I have better search terms.

 

[captain]

About 5 # negative full and neutral to 1# positive empty

 

[Dan Gibson]

Are you refering to the old 2250 psi 72s? I have a set but have never bothered to check out the actual buoyancy characteristics.

About 5 # negative full and neutral to 1# positive empty

 

[captain]

Are you refering to the old 2250 psi 72s? I have a set but have never bothered to check out the actual buoyancy characteristics.

Yes, old 72.

 

[Dan Gibson]

Thanks.

Yes, old 72.

 

[Luis H]

From a previous post of mine:

This data came from one of my US Divers 1970's maintenance and repair manuals:

72 cu ft Standard

Service pressure, psi : 2250
Actual air capacity, ft3 (at 2475 psi): 71.55
Outer diameter, in: 6.81
Length without valve, in: 25.12
Empty weight, lbs (w/o valve): 26
Buoyancy Empty, lbs (w/valve): 0
Buoyancy Full, lbs (w/valve): -5.4

They are not all the same. As mentioned above, there were at least two manufacturers of this cylinders, and they were built for many years. They came with 1/2" tapered pipe thread, 3/4" straight pipe thread, and some even had 1/2" straight pipe threads (mostly Sportsways).
Out of all my 72's one in particular is taller than the rest. There are also other smaller variations.

 

[Dan Gibson]

My set has 3/4" thread so new manifolds work great with it. Someone is borrowing them right now so I don't know who manufactured them. When not cave diving, I really like to use this featherweight set. It gets tiring carrrying around 104s for everyday quarry dives.

From a previous post of mine:

This data came from one of my US Divers 1970's maintenance and repair manuals:

72 cu ft Standard

Service pressure, psi : 2250
Actual air capacity, ft3 (at 2475 psi): 71.55
Outer diameter, in: 6.81
Length without valve, in: 25.12
Empty weight, lbs (w/o valve): 26
Buoyancy Empty, lbs (w/valve): 0
Buoyancy Full, lbs (w/valve): -5.4

They are not all the same. As mentioned above, there were at least two manufacturers of this cylinders, and they were built for many years. They came with 1/2" tapered pipe thread, 3/4" straight pipe thread, and some even had 1/2" straight pipe threads (mostly Sportsways).
Out of all my 72's one in particular is taller than the rest. There are also other smaller variations.