USD Manifold Methods

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SurfLung
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USD Manifold Methods

Mon Jul 03, 2017 11:21 am

USD Manifold Methods
Some Hints for Success in Leak Free Assembly
Image
- I've re-built several sets of Twin Tanks in the past 5 years and all but one (Sportsways 42s) have the USD Twin Tank manifold. The first one I did was my yellow Twin 38s and my buddy Sea Hunt Jerry said, "Whatever you do, don't take the center section apart. You'll never get it to seal again." Then last week on this forum, Allan made a similar comment. So I thought it might be a good forum topic.
- To begin with, I may just be lucky but I haven't had much trouble getting the USD Manifolds to seal. The ball ended connection points for the center valve seem to be what give most folks a difficult time. So, I'll start there.
- What I do is clean and polish the ball ends and their receptacles with 0000 fine steel wool. Then I wipe any dust or steel wool residue off with a paper towel moistened with food grade spray silicon. Finally, when I'm assembling, I put a little high pressure grease on the ball ends... This is to help the ball slip into a nice, even seating pressure without galling... It's a metal to metal seal. This seems to work every time except when the J-Valve end has gasket or thread galling issues.
- Solving J-Valve issues. The center of the ball receptacle on the J-Valve side has an Allan wrench center. You unscrew the receptacle to service the J-Valve. Sometimes, the threads on the receptacle get crossed or galled and you can NOT get it out to do service. This might not be bad if the J-Valve doesn't need service. But I've found that the galling may also prohibit you from screwing the receptacle IN far enough to seal its gasket. The only fix for this is to replace that whole J-Valve side with one that's serviceable. A leak in this case is not the fault of the ball joint. Used USD Manifolds to buy for replacement parts seem to be plentiful and cheap. (This is in fact what had to be done with my first set of Twin 38s).
- Normally, you CAN unscrew the J-Valve ball receptacle and you'll find an old gasket on the end of it. I have replaced this with an O-Ring from my Divers O-Ring kit... Found the usable size by trial and error. With this gasket sealing properly, the ball receptacle will complete the seal. I think this J-Valve gasket may be the culprit in most sealing problems where, no matter how hard you horse on the ball receptacle nuts, you can't stop the leak.
- The outside end of the J-Valve can be serviced as well and there's an old gasket at the end of the screw-in body... There's an O-Ring that fits this. Clean up and very light coating of high pressure grease on the internals here.
- The other outside end of the manifold may or may not have a nut on the end. If it does. I think it was originally for a pressure gauge. Anyway, it has an O-Ring and can be a source of a leak if the O-Ring is bad or the nut isn't tight.
- Solving 1/2 inch Thread and Bushing Leaks. First of all, you need to have a tank vice. I made one from a board and some steel band at a cost of less than $10... I found it on the internet but also posted it on the VDH forum somewhere.
- Second, you need a way to grip the valve with enough leverage to twist the 1/2 inch threads deep into a good seal. A wrench always beats up the appearance of the manifold. What I do is assemble the whole manifold onto the valve I'm screwing in and use the length of the manifold for the wrench leverage I need to properly tighten the valve.
- Third, If you are using a bushing reducer, go to a discount tool supplier and buy a cheap box wrench that fits your bushing tightly. This will be longer than a 12" and cost about $15.
- Fourth, CLEAN the threads inside and out... Smooth clean surfaces will seal easier than rough and dirty ones.
- Finally, use Bill Antique Diver's method of "Six Wraps" of Teflon pipe tape before tightening tapered thread bushings and valves.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

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ScubaLawyer
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Re: USD Manifold Methods

Mon Jul 03, 2017 11:31 am

Great write up Eben. Makes me wish I'd taken Bill up on his offer of the used 1800 psi fire dept tanks a while back. Now that I've rebuilt my Sportsways 38/42 I'm looking to create a roundy-bottom set like yours.
Mark

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captain
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Re: USD Manifold Methods

Mon Jul 03, 2017 11:47 am

I have worked on many of these USD manifolds and can not count the number of jury rigging I have found. Teflon tape on the nut threads, O rings where none are required, incorrect teflon seals,the list goes on. What you find may not be correct, These manifolds use only 2 O rings, one under the J ball seat and the other at the regulator connection. The end plug is a nylon gasket. Bonnet seals are metal to metal. On/ off and J valve stem use teflon seals, no O rings here although I have found f them there.
If you experience trouble getting the J end ball seat out a propane torch and penetrating oil is the tools of choice, it also works on bonnet nuts.

" The outside end of the J-Valve can be serviced as well and there's an old gasket at the end of the screw-in body..." If you found one it was incorrect, this is a metal to metal seal just like the ball joints.
Captain

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SurfLung
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Re: USD Manifold Methods

Mon Jul 03, 2017 4:31 pm

- Thanks Mark. I'm glad to share what I've learned... And am glad to admit I'm still learning! :)

- Thanks for the help Tom. That makes good sense.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

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SurfLung
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Re: USD Manifold Methods

Mon Aug 14, 2017 1:31 pm

- Last weekend, after four years of regular use, the first USD Manifold I rebuilt developed a leak on the J-Valve side. This is my beloved set of USD Yellow 38s. When I got home Sunday, I took the set apart, took the manifold and valve parts off the tanks. On the J-Valve side, I unscrewed the brass ball seat and found the source of the problem: When I re-built these before, I had put an O-Ring on top of the old washer that seals the ball seat.
- So now, I removed my O-Ring but also removed the old washer residue with a brass O-Ring pick. This seat I then cleaned up with #0000 steel wool. After that, I cleaned any remaining dust and particles out with a moist rag, Q-Tip, and by blowing compressed air through it.
- Next, I found a new O-Ring that fit the seat. I lightly greased it with silicone compressor grease, installed it, screwed the brass ball seat back down and tightened it against the O-Ring. That should solve any internal leak from the J-Valve.
- Finally, I cleaned and polished the brass ball seat connectors and brass ball seats with #0000 steel wool. Again, wiped any dust or debris clean with a moist towel. Used a very light coat of high pressure compressor silicone grease on the ball seat surfaces. Assembled and tightened the nuts. Filled the tanks and dunk tested... NO LEAKs. That's a service process with predictable results.
- SwimJim added another plus to the USD Manifold system... There are parts available everywhere.
Image
Here's me with my beloved Twin 38s four years ago Photo by Eric P.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

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captain
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Re: USD Manifold Methods

Tue Aug 15, 2017 11:54 am

I just had 1/2" thread 72's hydroed. For years I have used

https://www.permatex.com/products/threa ... with-ptfe/

It works better than teflon tape, you don't have to use the gorilla arm to remove or install the valve, and I never have experienced leaks and having to remove the valve and reinstall it to stop a leak like I did using teflon tape before I switched. Teflon tape did not exist when these tanks were made, at the time plain old pipe thread dope was used.

I also use it on all my compressor pipe thread connections.
Captain

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georgeaustin
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Re: USD Manifold Methods

Tue Aug 15, 2017 3:18 pm

We've had very good results with PTFE compound in my day job as teflon tape is outlawed in nuclear service due to foreign material exclusion rules. People still use the teflon tape in the oil and gas and municipal water/wastewater industry but I prefer PTFE in ALL applications where formerly tape was used.

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