What Size Tanks work onUSD Solid Twin Manifold with J Valve

[dso]

I tried to use a new/old stock USD solid twin manifold w/J valve with twin 63cf Al tanks and the tanks do not seem to align correctly.

Very slightly closer at shoulder of tanks than bottom, top band does want to fit around tanks at top.

Any ideas?  Were these manifolds only for 6.9 dia tanks?  Can't see how that would affect alignment.

Thanks for any help...

Phil

[SeaRat]

I don't think it's a problem with the manifold, as I have a set of small AL tanks that work.

IMG_1460 by John Ratliff, on Flickr

I think it may be your bands that are incorrect.

John

PS, I love those smaller doubles.

[dso]

SeaRat...when you say "small"....what is the diameter of your bottles [cf?]...what bands did you buy?

Thanks....Phil

[vance]

Hello, and welcome to the forum. I don’t have any personal experience with small aluminum tanks, but I’m sure there are members who can help get you sorted. Be sure to read the tech section instructions on how to post photos.

[eberwolf]

I've also come into possession of a NoS US divers doubles manifold. I found a pair of Faber Steel 40 steel tanks that fit nicely on the manifold.

A tech diver here looked at it and asked how do the tanks get tightened to the manifold beings how new twin tank manifolds separate.

I wasn't sure on the answer. Any input?

[james1979]

Nov 13, 2023 12:15:06 GMT -8 eberwolf said:

I've also come into possession of a NoS US divers doubles manifold. I found a pair of Faber Steel 40 steel tanks that fit nicely on the manifold.

A tech diver here looked at it and asked how do the tanks get tightened to the manifold beings how new twin tank manifolds separate.

I wasn't sure on the answer. Any input?

Not to be a smart aleck, but "one at a time".  With modern tanks (O-ring seal on the neck) it's the O-ring that does the sealing.... just thread the manifold onto one tank, then thread the other tank onto the manifold.  Good and snug should be plenty, and the bands add extra insurance against loosening.

Respectfully,

James

[SeaRat]

Nov 13, 2023 12:15:06 GMT -8 eberwolf said:

I've also come into possession of a NoS US divers doubles manifold. I found a pair of Faber Steel 40 steel tanks that fit nicely on the manifold.

A tech diver here looked at it and asked how do the tanks get tightened to the manifold beings how new twin tank manifolds separate.

I wasn't sure on the answer. Any input?

Most twin tank manifolds separate. The U.S. Divers Company solid manifold eliminated two contact points, which a lot of times leak. The tanks are sealed to the manifold by O-rings, which do not require tightening. Hand tight is enough to make the seal. Actually, over tightening is bad for both the tank and the manifold.

DA Aqualung-2 by John Ratliff, on Flickr
Here's an example of the U.S. Divers Company doubles manifold that is older than the solid manifold. Note that it has three separate sections, and that the center section needs to be sealed. These seals are actually not O-ring, but are brass-on-brass fittings which must be wrenched very tight. But they have one advantage over the solid manifold, in that the center section can be tilted a bit so the double hose regulator sits better on my back.

IMG_1453 by John Ratliff, on Flickr
These are what I refer to as my "jump tanks," as they are converted CO2 bottles. Note that the manifold not only separates, but also doesn't use O-rings to seal the manifold to the tanks. Instead, it used a valve with 1/2 inch tapered threads, which were sealed with teflon tape. This took some knowledge to get the seal right (wrap the teflon tape around the threads correctly), and get them tightened way down. A lot of force was necessary for this connection.

142309158_5274939835851296_4955705790799075275_o by John Ratliff, on Flickr
The reason I called them "jump tanks" is that these were the tanks we used in USAF Pararescue for parascuba jumps. Here Airman Eldridge Neal poses in the door of a HU-16B Albatross amphibian in the equipment he jumped on the Gemini VIII mission.

'Hope this explanation helps. Basically, the solid manifold simplified hooking the twin tanks together, and eliminated two potential leak sites.

John