Leaking Radiator Elbow at npt thread after 3 tries

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BenDanger

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So I recently moved a radiator and I had to re-pipe the existing valve and elbow with new 1-1/2 pipe. I used ptfe pipe dope the first time I installed the original radiator union elbow. After a day I discovered a slow leak. Took it all apart and this time used both pipe tape and pipe dope. Leaked imidiately this time and worse. Finally I used pipe tape and jb weld epoxy putty. I put the putty all over the female hub, and some over the male thread that had tape. After tightening I formed it around the seam.

.....still leaks very slowly. I actually had a similar problem on the valve side and the jb weld is holding fine there. The threads all seem pretty clean, but is it possible that I bent the bronze hub when I had it in the vice? Is the tape maybe messing up the jb weld? Should I try one more time with just jb weld? I'm not even sure if I can get this app art after the jb weld, I was going to try heating it up with a torch. I also looked but I can't even find replacement angle unions that large if I wanted to replace it.
 

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Jadnashua

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Tape on a union can make it leak. A little pipe dope on the mating surface can sometimes help. If the mating surface is deformed, it may never seal. Over tightening a union can make it tough to get it to seal if you take it apart. The threaded nut does not seal, it is used to compress the mating surfaces together, and does not need any tape or pipe dope, only the mating surfaces, and when new, it shouldn't need that. JB Weld complicates your problem...it shouldn't be used in this situation.
 

BenDanger

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Tape on a union can make it leak. A little pipe dope on the mating surface can sometimes help. If the mating surface is deformed, it may never seal. Over tightening a union can make it tough to get it to seal if you take it apart. The threaded nut does not seal, it is used to compress the mating surfaces together, and does not need any tape or pipe dope, only the mating surfaces, and when new, it shouldn't need that. JB Weld complicates your problem...it shouldn't be used in this situation.

No I meant that the leak was at the tapered thread on the bottom of the elbow joining to the pipe coming out of the floor. The union itself is sealing fine without anything on it.
 

Jadnashua

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Unless the threads are all messed up, pipe dope and/ or tape should make a good seal. Is it possible that the radiator casting might have a pinhole or has cracked?
 

BenDanger

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Unless the threads are all messed up, pipe dope and/ or tape should make a good seal. Is it possible that the radiator casting might have a pinhole or has cracked?
It worked without leaks before I took it appart. The leak is definitely coming through the threads. Maybe the are worn. I'm going to the plumbing supply place today to see if I could find another union elbow to replace it with. I'm hoping I can find one that matched the union already in the radiator. If I can't find a new one I think I'm going to do one more try with just jb weld. I'm thinking it might not have bonded well with all the tape on the male pipe.
 
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