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Post by pearldiver on Nov 13, 2008 4:28:58 GMT -8
Hey, here is a set of twin 72's I just picked up. They are 1955 USD steel w/ 1/2 inch valves. The harness is not cotton webbing, it's nylon and has clasps that are similar to a alligator clip, no D-rings. The harness does not look homemade. The guy I got these from said they are military tanks. Any idea if that is true or not? I'll have Linda put the photo on here and try this.  tinypic.com/view.php?pic=5of1u8&s=4  |
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Post by Nemo on Nov 13, 2008 13:12:42 GMT -8
Any way we could see larger pictures?
VBR,
Pat
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Post by SeaRat on Nov 13, 2008 18:03:51 GMT -8
I doubt very much that the harness is original, or from the U.S. Navy. Even in the 1967, the harnesses had a larger shoulder portion sewn on for comfort. The U.S. Navy would never allow the alligator clips either (at least, the people I knew of wouldn't). The harness is not threaded correctly in the slots on the metal bands too. This looks to be jerry-rigged, but a well-done jerry-rig.
John
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Post by pearldiver on Nov 13, 2008 18:36:27 GMT -8
Hey Sea Rat, I knew you'd have an answer for me. I had the same thought when I saw it. The bands are original, but the straps aren't. It is a very good job. They aren't alligator clips per se, you put the strap through a slot and a clip with alligator teeth grip it. They are spring loaded. The tanks are nice though along with the manifold. Question. If these things pass hydro, do I need to change the burst disc? These are original ones from 1955 and aren't the BB kind. They look like a regular tiny bolt in there and on the top of it, it looks like a spot of melted metal. Is the BB under there ready to blast off somewhere? And will a newer burst disc fit this? I think they should be at least updated. ?? Hey, I dunno, I was only born a year after these tanks were made!!
PS: The sad thing is the guy who had these is 80 yrs old. He said they were his in the UDT in WWII. The second I saw them I knew they weren't, but I just said. "Uh huh, cool." Poor guy, I don't even think they were his.
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Post by duckbill on Nov 13, 2008 19:28:44 GMT -8
Nice looking set, pearldiver.
Definitely change the burst discs if you plan to use them. The dive shop would likely insist you do anyhow. That melted metal in the hole is lead, or some alloy of lead. They are designed to melt in a fire and allow the air to escape before the tanks blow. They aren't really burst discs, per se, and I don't think I've ever seen any BBs in any of them. However, they have been known to blow the lead plug out and it is just like a bullet. I don't know how much velocity they can really attain in the quarter inch or so they travel through the plug, but I sure wouldn't want to be hit by one.
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Post by pearldiver on Nov 13, 2008 19:57:12 GMT -8
The old Healthways tank I had, did have a burst disc with a BB in it with a spring on top. You could see it in there and it looked just like a copper BB. I'll get them changed out for sure. I like your set of twins on your photo there. Nice. Thanks for the info... Love you guys.
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Post by Captain on Nov 14, 2008 7:24:52 GMT -8
No such equipment used in WW II, the 1955 date rules out WW II the Navy didn't get the Aqua Lung until about 1948-49 although they could be ex-Navy.
There were burst discs behind the lead plugs. Newer burst disc will work, I have a manifold just like it on my work bench right now that I put new burst discs in.
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Post by SeaRat on Nov 14, 2008 11:05:06 GMT -8
Just after WWII, the U.S. Navy was using DA Aqualung regulators (Broxton) and triple tank systems. Here are a series of photos of these scuba units being used:     (These photos were all listed as "Official US Navy Photos" in the books, and so are not copyright protected) In the 1960s, they switched to twin 72s. Here's a few photos of those sets:  Note: If you look at the harness of the diver in the hatch, it may actually more closely match the one in question than I previously believed. The harness is not a standard military harness, as it attaches in the wrong place, and looks to have a D-ring at the bottom tank band. If you look at the diver with the mask, he has what appears to be a cross-chest strap with a metal quick disconnect on it, which again is non-standard for a military harness. This indicates to me that non-standard harnesses were used by the U.S. Navy in the 1960s. Also, this diver appears to be wearing a capillary depth guage, which would not work at all in a submarine hatch situation (pressurized air would be in the tube, and so it would not indicate depth).  Then the U.S. Navy switched again to the infamous twin AL 90s with the plug in the bottom, which means that they cannot legally be hydrostatically tested--I think all of these are now out of circulation, and the U.S. Navy now has gone to modern tanks.     Note: the instructor was using twin 72s on this deep dive (120 foot qualifying dive off Key West, Florida).   John |
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Post by Captain on Nov 14, 2008 12:47:05 GMT -8
It is not illegal to hydro test the aluminum 90's, any pressure vessel can be hydro tested, they just can not be stamped or legally used in commerce because they do not have a DOT specification code such as 3AL stamped on them, sort of like an automobile without a VIN is not street legal.
It is basically the same situation with personal tanks that are filled by the owner, they don't have to be hydroed.
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Post by SeaRat on Nov 14, 2008 13:43:15 GMT -8
Captain,
My understanding is that, because of the manufacturing process of the time, they were made for a specific time period, and to be discarded thereafter. Apparently, the plug on the bottom does not handle overpressure well. DOT only regulates interstate commerce, so in that you are correct. They probably don't need a hydro for an individual who fills it themselves, but I don't know of a dive shop which would fill an unstamped cylinder.
About twenty years ago, some of these cylinders were bought as a military surplus at auction by a school to be used for practice welding on aluminum. But someone recognized them as diving cylinders, and brought one to a LDS. They called me, and my advice was that they be drilled so that they could not hold air, which was done. Because I also consulted on safety and health matters with that school district, I also went to them and talked to the welding shop instructor. After explaining the situation, he decided to drill the rest of these cylinders.
While they probably can be legally hydrostatically tested, they were never designed to do so. Because of their limited lifetime, I would not consider them to be safe for filling now. But, you may have more knowledge than I, and if that is true, please give us some more information.
John
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Post by Captain on Nov 14, 2008 14:26:45 GMT -8
These cylinders were made just for the Navy of 6061 alloy the same as today's aluminum cylinders are. The early cylinders were threaded for the old 1/2" pipe thread manifolds and later ones for the 3/4" straight O ring valves.
The main difference is the manufacturing method. The cylinders were made using 6061 aluminum tubing, both ends were rolled closed just as today cylinders are rolled closed on one end.
Being the rolling process does not completely close the bottom of the cylinder the hole was threaded and plugged. There were cases of the plugs leaking, a hydro test would discover this. The opposite end was threaded for the valve. The cylinders are stamped 3000 psi working pressure and 5000 psi test pressure. I am sure the Navy had them on some type of test schedule, what it was is not stated in the Navy diving manual. Just because they were not using normal civilian testing regulations doesn't mean they were not periodically tested.
Once the aluminum cylinder became commercially available the Navy had no need to continue having them specially made. As long as they can pass the 5000 psi hydro test and visual inspection I see no valid reason they could not be used other than the problem of having them filled if you can't do it yourself.
Several years ago a pair of them, new in the box, less the manifold appeared on ebay, I am sorry I did not bid on them. They went unsold with a $100 opening bid.
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Post by SeaRat on Nov 14, 2008 14:36:21 GMT -8
Interesting, thanks Captain. This is more than I knew before.
John
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Post by pearldiver on Nov 14, 2008 16:11:26 GMT -8
SeaRat, Thanks for those photos. I think the first picture of the man standing with gear on was used in a few other books to learn how to scuba. He looks real familiar. Sure don't know about those tanks. They came in a trunk with a Dacor double hose attached. So you know that regulator wasn't used in WWII. So, tomorrow I'm diving and going to check with my buddy to see if he wants to use these twin 72's. If not, I'll think about it and we'll see what I decide to do. They might be more valuable to someone as twins in the shape they're in and to find 1/2 inch valves in good condition might be just as expensive to buy a new tank. I cannot in any way use these for real unless I put them on in the water after someone drags them down there for me. My poor neck just can't handle it after just getting released for my disc problem. Sure like the photos. And I like the info. By the way, the straps on the tanks are not cotton, they are nylon webbing. I can also see where the bands were taken off and moved. The tanks were hydro'd once after 1955 and the date is 1966. So..?? Don't know. But they are in very nice condition on the outside. No boot marks either.
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Post by Linda on Nov 14, 2008 19:27:32 GMT -8
Hiya Gayle. I was traveling yesterday and didn't have time to get your pic up until today. Sorry for the delay! Linda  |
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Post by Seahuntjerry on Nov 18, 2008 20:27:54 GMT -8
Hi ,
Wishing everyone Happy Thanksgiving and Merry Christmas.
Kemp's Cow
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