What Exactly Did I Just Get? 1950s twinset

[AfterDark]

Cool set!! I have a SCOTT air tank a little newer 1960 it has the original valve and that measures a .01 or so above 1" so like your tanks it would have required bushings for any size SCUBA valves of the day likely 1/2". My guess is your tanks are probably the same neck size as the SCOTT tanks. I think and someone who knows for sure correct me, there are now 1" valves used for SCUBA? Would those fit on the OP's tanks?

 

[2airishuman]

I believe what you have is a pair of what are usually called LP53s with 1" NGT necks. I have one (a single cylinder) that I use for shop air, but it has a standard neck.

The capacity is around 52-53 cf at 1980 PSI. However, since those particular cylinders do not appear to have been + rated at the time of manufacture, they would have only held around 48 cf, at 1800 PSI.

The buoyancy on these is around +5 empty, +1 full. I took mine on a couple of dives and found the buoyancy problematic.

If you replace the bushings, I would recommend using proper HP ones, which you can get from McMaster-Carr and similar sources. The big box home center plumbing department ones aren't cut with much precision and you'll have trouble getting them to seal.

If you use them for shop air, an annual VIP isn't required. They are lightweight. Sometimes I end up transfilling mine if we end up calling a dive early and have an HP cylinder that is nearly full.

 

[2airishuman]

Just remove the bushing when they are taken in for requalification.

That sounds easy but may require a large impact wrench to accomplish.

 

[James79]

Cool set!! I have a SCOTT air tank a little newer 1960 it has the original valve and that measures a .01 or so above 1" so like your tanks it would have required bushings for any size SCUBA valves of the day likely 1/2". My guess is your tanks are probably the same neck size as the SCOTT tanks. I think and someone who knows for sure correct me, there are now 1" valves used for SCUBA? Would those fit on the OP's tanks?

Tank threads are typically pipe measurements... which go off of the inside diameter of the pipe. So modern valves are 3/4 NPS (National Pipe Straight), which actually measure just over 1 inch outside diameter on the valve threads. If your SCOTT tank uses an O-ring on the valve, it's probably the same as modern tank valves. A 1 inch NPT (National Pipe Taper) like the 38's I'm working on are about 1 and 1/8th at the opening to the tank. 1/2 inch NPT ends up being about 7/8 inch at the fat part of the taper. My money is that you have a modern thread tank. Still horribly dangerous and should be sent to me for proper disposal! lol
Respectfully,
James

 

[James79]

Why would an ABO cylinder be galvanized? Aren't most ABO cylinders 3HT rather than 3AA?

Regarding galvanizing, I know people strip and then paint these old tanks with cold galvanizing paint (like galvalite) relatively often. As for the 3AA vs 3HT, I believe 3AA predates 3HT (and 3HT have a total service life limit due to being thinner walled for weight savings). I also know some of these same style tanks started life as Navy liferaft CO2 cylinders (which would explain both galvanizing and less weight concerns). Mine are actually 3A1800's (not 3AA). Incredible some of the variety that's out there, and the ingenuity of the early divers.
Respectfully,
James

 

[Sam Miller III]

I suppose, I think, I believe .........

 

[captain]

Here is a pallet of aviation O2 cylinders recently removed from scrapped Navy Lockheed SP 2-H antisubmarine patrol aircraft. I have many hours as a crewman on these aircraft. Notice they are wire wrapped, the wire was removed when used for diving. Dr. Sam hit the nail on the head.

 

[PBcatfish]

I had a pair of twin 50 steels up until the 1980's, when I took them into a scuba shop in Hyannis MA for a hydro test. The shop keeper informed me that they failed simply for having pipe thread in the necks. He kept my tanks & only gave me my bands & valves back. When I insisted that I wanted my tanks back, even if they could not be filled again, he told me that it was illegal for him to give me back unsafe tanks. I was young, trusting & uninformed back then, so I just took his word for it. Later I came to find out that pipe thread thanks could indeed be recertified & put back into service. I now consider that man to be a thief.

 

[PBcatfish]

...
The word went out SoCal and the rest of the emerging diving world
"DO NOT fill any tank with a brass reducing bushing"...
...began supplying stainless steel reducing bushings rated according to Leo for over 10,000 PSI-
...

Reducing bushings come in many different forms with many different ratings. You can get bushings that are rated for hydraulic use in a few different materials. The hydraulic ones are rated for pressures that exceed anything I have seen in a scuba tank.

Being able to tell the good ones from the low pressure ones, after they are installed in a tank, is not always easy.

 

[AfterDark]

I had a pair of twin 50 steels up until the 1980's, when I took them into a scuba shop in Hyannis MA for a hydro test. The shop keeper informed me that they failed simply for having pipe thread in the necks. He kept my tanks & only gave me my bands & valves back. When I insisted that I wanted my tanks back, even if they could not be filled again, he told me that it was illegal for him to give me back unsafe tanks. I was young, trusting & uninformed back then, so I just took his word for it. Later I came to find out that pipe thread thanks could indeed be recertified & put back into service. I now consider that man to be a thief.

I still dive a pair of US divers steel 50's as ID's. Light to carry around but, empty they are VERY buoyant and take a lot of lead. I'm refinishing the outside with cold galvanized paint and they are due for hydro this year which I expect them to pass. I take my tanks straight to the hydro tester bypassing the LDS that has a vested interest in selling new tanks.