Odd ball tank

[time2dive]

I have one of the Navy tanks. It is now gathering dust in my collection of oddball tanks.
The markings on mine are:

9-65
EE 61-4 CC
700 cu in

Test 5000 PSIG

No. 1243F
Non Magnetic
3000 PSIG (SPUN)
RE 91

I tested it to see if it was safe to fill and filled it once. I did not stamp it with a current hydro stamp (not allowed, no DOT markings).
I do not know what I will ever do with it.

[ovalis]

The big question for me is, are there any Navy cylinders out there that do not have the plug in the bottom? I have few of what I think is a navy cylinder and none of them have the plug.

[antique diver]

The big question for me is, are there any Navy cylinders out there that do not have the plug in the bottom? I have few of what I think is a navy cylinder and none of them have the plug.

It is entirely possible that some are not made the same way, but the ones I have seen were not that easy to spot anyway. They were smoothed off to be completely flush with the rounded bottom of the cylinder, then the primer and paint filled in the small circular ring where the plug and cylinder bottom meet. To be sure you would probably have to completely remove the paint and primer from that area.

Having found a number of cracked 1970's and 1980's Aluminum cylinders is the cause of my concern about the unknown Aluminum alloy and possible stress cracking at valve opening and/or the plug opening if there is one.

I'm sure that I have expressed my concern about the 6351 alloy more times than most of you want to hear, but I have seen what an exploding cylinder can do to a dive shop.

[luis]

The Navy tanks were made from a 6061-T6 aluminum alloy seamless pipe. They were rolled to form both ends.

My understanding is that the metal was rolled to form a unit with the plug.

A while back I sent the Mil specs (for these tanks and the steel 72) to Bryan. You can find PDF copies in the download section.

I have seen some of these tanks and I could not see any indications of a plug from the outside. I did see a clear indication of the plug during an internal visual inspection.

If I recall correctly, the Mil spec calls for welding the plug. If it was actually welded, they either had to heat-treat the AL 6061 back to a T6 condition, or the weld had to be controlled to minimize the heat affected zone.

[kgehring]

have looked in 3 or 4 of these tanks and the plug is very hard to see internally. You cant tell from the exterior.

[captain]

On the outside you can see a faint semi-circle outline of the plug



The bright round spot is the plug inside.
I stripped both of mine down to bare metal before painting. The plug is visible on the outside if you look closely, inside it is obvious.

Something must have changed I can't seem to direct post a picture from Photobucket using URL or Img?

// ADMIN NOTE:
I edited your tags for you Tom, so that it would appear in the post
// END ADMIN NOTE

[crimediver]

Thanks for the pics Captain. I have tried to take some of the inside of a cylinder and it was a bit tricky.

[ovalis]

That's good info. I always assumed (Never Assume!) the plug was clearly visible on the exterior. I received this tank in question and if you look at it very carefully on the exterior, the plug is barely visible. From the inside, the plug is clear as day.
There's not too much other info on the tank though. It just has the working pressure, test pressure, serial #, hydro date (10-61), and Pressed Steels "PST" stamped on it. The physical dimensions of the tank matches the other 3 that I have. I have a 1965 & 1967 tank that has a lot more info stamped on it with Non Mag, Mil Spec and all that other stuff on it. I do have another from 1956 that came with a 1/2" tapered opening that pretty much has the same info stamped on it as this 1961 version.

[Ron]

I am throwing out a SWAG, but I bet the original run of aluminum tanks that PST did for the Navy didn't have all the specs on it as per the MILSPEC. When you submit stuff for the Navy to review (we have done this at my company), then you typically submit a product or sample of a large run of a product that is "pre-systems acquisition." I would bet that these early run tanks, like the two that Mike has, are pre critical design review (or what Navy did in the 60's), hence their early date, lack of a nonmag marking, lack of a contract number stamp, and lack of US Governent property stamp. I would guess these were early tanks made by PST to have Navy demo during a request for proposal or somethig similar. The MILSPEC was probably formalized later in the acquisition process. If the tanks as a whole were rare (I am guessing), then the pre-initial operational capability ones would be quite a bit more rare. This is all in accordance with how government procurement works now, so I am not sure if it was markedly different in the 60s. Bear in mind that I am not an expert in how the Navy procured defense materials in the 60s.