Unususal Cylinder

[time2dive]

I have acquired an unusual scuba cylinder. I can use a little help in finding information about it.
Here are the markings:
on one side
NO.1243F
NON-MAGNETIC
3000PSIG (SPUN)
RE91

one the other side
TEST 5000PSIG
9-65
EE 61.4.CC
PE .0-CC
VOLUME 700 CU IN

The cylinder appears to be aluminum, it has a round bottom. It is 7 1/2"x26".
It has roughly the same internal volume as a steel 72. The expansion at hydro was 66cc.
It has a 3/4"neck...standard scuba.

The good news is that it passed hydro, the bad news is that I can't stamp it (no ICC or DOT)

[macado]

I think Luis answered a question about these cylinders before on another board. Not sure if they're the same tanks.

Those are Navy non-magnetic aluminum tanks. They were custom made from 6061-T6 aluminum tube for the Navy. They were made by PST (Pressed Steel Tanks).

They ends of the tube were spun shot and at the bottom there is an aluminum plug that was formed as part of the tank to close them off. The plug may not be visible from the out side. On many of these old tanks the plug tends to leak.

The tanks are not DOT approved (or stamped) so they can not be legally tested for use as a DOT tank. Most hydro stations will not (and maybe should not) test them. If they test it they can only stamp the date not their DOT ID number.

Structurally they are probably perfectly good tanks if they are not leaking from the plug and pass a hydro test. The hydro test would also detect any leaks.

A few divers are using them, if you have your own compressor, but I would strongly recommend having them hydro tested before putting compress air in them.

Since they are spun tanks, I would also perform a very detail visual inspection of the neck and bottom areas to look for cracks (and maybe even eddy current inspection of the neck). Cracks may be present without showing up in the hydro test results, therefore a detail visual inspection imperative.

I think the tanks are 90 cu ft each and I believe the Navy only used them in double sets.

The Navy needed non magnetic tanks for dealing with magnetic mines long before aluminum tanks were commercially available for Scuba.

These are at least great collector tanks. They are rare.

http://www.scubaboard.com/forums/vintag ... tanks.html

[captain]

You can stamp the date the hydro was done, you just can't stamp the hydro shop DOT identifier number. In the pass before the DOT number was in existence hydro shops made up their own symbol to identify themselves.
I have a set set of the Navy non mag aluminum doubles and they have several hydro dates and shop symbols stamped on them from the 1960's. In most cases the Navy used regular dive or hydro shops to test the tanks and the shops stamped the tanks the same as any other tanks. Notice the dive flag stamp. The eagle stamp is the Department of Defense acceptance stamp.