USD Manifold Methods
Some Hints for Success in Leak Free Assembly
- 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.