Looking at a couple of used tanks; help needed

[2airishuman]

For my own education, is that a normal working pressure for a steel 72?

The vast majority of them are rated 3AA2250, and can be filled to 2475 with a plus rating, giving around 71.5 cf actual capacity.

Anything rated 2400 PSI is probably an LP85, not an LP72.

Anything with a 3A rating is really not useful for diving by today's standards because these cylinders are extremely heavy for their capacity.

Anything with a 3AA1800 rating is going to be really floaty and therefore not useful except as a shop air cylinder.

There are other oddball ratings out there, who knows, some may be useful for diving, most are not.

There are also a very few shorter 3AA2250 cylinders out there that have a capacity of around 60 cf, that are useful for the same situations that an AL63 is useful for.

 

[JamesBon92007]

Ditto on everything that 2airishuman said, however I think $75 for two tanks is a bit high. All of my steel tanks are from the 60s and 70s and they are fine (but I only own seven). I prefer the galvanized tanks but sometimes they will be galvanized and then painted and that is fine with me except sometimes the paint/coating can be difficult to remove. I seem to have better luck with the valves than 2airishuman but currently I'm trying to get a 1/2" J-Valve to stop leaking. It is the only valve I have that will fit a particular tank. I recently took my old Craig's List tanks (I paid about $15 each) to the local Fire Extinguisher shop and they said it would be $20 ea to inspect and hydro them but they ended up not charging me! All of the tanks passed. As for getting them filled, I have my own compressor but I have heard that many shops will not fill old tanks. At 2475 psi you get about 71.2 cu/ft of air. Since they test them at 3750 psi I am comfortable filling them to 2600 which gives me nearly 75 cu/ft. An aluminum 80 filled to 3000 psi is (usually) about 77.4 cu/ft. Steel 72s are very close to neutral buoyancy then empty and weigh a few pounds less than a typical aluminum 80. The aluminum 80s are typically about 4-5 pound positive when empty. In all this means several pounds that you don't need to carry or wear which I find desirable, especially for shore diving. .So far none of the tanks that I have bought have the "liner" so I'm happy about that. My fire extinguisher place will not hydro the old aluminum tanks and was considering not testing new aluminum tanks made in China.

I also remove the boots and look for dents, gashes, and really bad corrosion etc. Don't pass up any usable boots as they can be hard to find these days.

 

[Birddog1911]

@2airishuman I'm including a couple of pics. Given your experience, do these valves look like the standard types you were referring to?

 

[Doby45]

Bottom tank is a PST, good tank to get fer shure.. The top tank is a Norris. Both galvanized and externally look great.. I would replace both valves just off the get go with DGX valves..

 

[JamesBon92007]

@2airishuman I'm including a couple of pics. Given your experience, do these valves look like the standard types you were referring to?

View attachment 413913

View attachment 413914

Cool! With that J-Valve you won't even need a SPG!

I don't recall seeing tanks with such big numbers (second picture).

 

[Birddog1911]

Cool! With that J-Valve you won't even need a SPG!

I don't recall seeing tanks with such big numbers (second picture).

Must be so I won't need my glasses to read it.

Maybe I should pair them and get a double rig.

 

[Doby45]

Maybe I should pair them and get a double rig.

There are people that do exactly that as a recreational doubles setup. So, not exactly a bad idea.

 

[JamesBon92007]

There are people that do exactly that as a recreational doubles setup. So, not exactly a bad idea.

Unfortunately double-tank bands are kinda pricey these days.

 

[Doby45]

Unfortunately double-tank bands are kinda pricey these days.

Gotta keep yer eyes peeled!

 

[2airishuman]

Bottom tank is a PST, good tank to get fer shure.. The top tank is a Norris. Both galvanized and externally look great.. I would replace both valves just off the get go with DGX valves..

Doby speaks my mind. Those have standard neck threads.

The valves do have the older burst discs, the kind that resulted in $2500 damage to my truck.

I don't recall seeing tanks with such big numbers (second picture).

I have a PST with big numbers like that from the same era.

Maybe I should pair them and get a double rig.

I've done that. 6.9" bands are hard to find but they are out there. LP72 twinsets are not large enough to be broadly useful for technical diving, but they are useful as an alternative to a pony cylinder for solo dives and for coldwater dives where freeflows are a major concern.