sweating theory

Hi -- I've been sweating in a copper shower, and have done pretty well with everything, except for the 6" 1/2" pipe between the mixer and transfer valves. On my first try, I must not have doped the pipe well enough, or screwed it in tight enough, but it leaked a little bit. But both solder joints held well. I had to sacrifice both joints to get it out, Subsequently, I tried sweating one or the other threaded fittings on the bench. I wrapped the valves and, as much as possible, the fittings, with wet towels, but I always seem to loose the joint I soldered on the bench. I also tried sweating them both one after the other as I originally had done, but one joint in the transfer valve fitting failed. The only difference I can tell from my first attempt is that the mixer valve below had water in it from the test, but it definitely was not up into the threaded converter.

Eventually I had to go for pex. Can someone tell me what tricks of the trade might have helped me get this all copper?

best,
areselle

I would have installed the nipple between the valves first, then anchored the valves. You put the cart before the horse.

You must have an opening in the system. If the valve is closed when you solder the last joint, the expanding air (and especially water vapor which expands a huge amount from liquid) will put a pinhole in the joint to relieve the pressure.

Hey, you got it done. That counts for something in my book.

Jim -- do you mean that the steam could melt the solder, or the pressure mechanically break the seal?

Kingsotall -- Yes, I got it done, and it's withstood an upgrade to from 50 to 90 lbs pressure with a city line change, and holding. BUT, I feel like I copped out using Sharkbite fittings and pex, which felt like plumbing or dummies (great for this dummy, I guess!)D. I'm sort of old school, and working on developing my plumbing skill set!

While the solder is still liquid, the steam or high pressure air from inside the pipe can blow a path through it and ruin the joint. So, if you have the valve or some other opening so the pressure can't build up inside the pipe, it should be okay.

Ahhh! I get it! Thanks, Jim.

If you want to just use copper in the set-up you pictured above, you could pre-sweat all the male adapters let them cool, dope and tape them and screw them in place.

For the small pipe between the two units, use a copper coupling in the middle as the last sweat joint after you have screwed in all the adapters.

And like they said above....open a valve somewhere so the expanding pressure from the heating won't blow open the sweat joint before it cools.
Good luck.

Mario -- I actually considered the joint in the middle, but gave up out of frustration. The steam thing I missed completely. Thanks! Just a small piece of pex. The rest made it to copper.

Removing the cartridge from the valve would have helped...

The first rule of plumbing

1) The last joint soldered in a closed system will leak.

If you have ever boiled water on the stove, you will know that steam will lift the lid.
When you solder, the hot air will blow a air hole through the solder and leave a path for the water.

You can try this on your own.
Take a length of copper pipe and try to solder two caps on it.

Or another example.
Try running 2" copper lines in a retirement home to the new 200 gallon water tanks run in parallel with pumps and thermostats for mixing.
Don't keep the check valve open while soldering.
Then wait until two hundred seniors have been waiting for the water to be turned back on for hours.
And then tell them, that the last joint soldered blew a hole in the joint.

I had one very red faced plumber working for me that day.
I had told him that it would leak if he tried to solder in a closed system.
He was out to prove me wrong.
Boy, did he look dumb.
So four plumbers spent two more hours draining everything down so we could take out the bad fitting and try it again.
And the retirement home had to wait, because sometimes even plumbers don't know the first rule of plumbing.

1) The last joint soldered in a closed system will leak.

Those galvanized clamps will create galvanic corrosion.

That piece of PEX is now going to serve as a restriction against mfg. specs for inside diameter most likely.

Retirement home stories...
OK, here's one for you.

I was called out one fine day to a nice little retirement home to fix a leak in a ceiling causing some ceiling tiles to get spotted with water stains.
Not a very large leak in fact it took quite a while to find it.
It wasn't until my flashlight caught the fine mist just right in the light that I could follow it back to the source....a pinhole in a 1/2" copper pipe.

Piece of cake....right?
I turned off the water, drained it down, cut the pipe right on the pinhole and cleaned up a 1/2" copper coupling and the pipe ends, fluxed everything and started to solder.
Should have been end of story right there. Home in time for breakfast.
It was about 8 A.M.

That's when it all went south.
The retirement home was under new management and had outsourced all maintenance work...(that's why they called me).
They had hired a 20 year old girl to be the new manager and she laid off the entire maintenance crew to "save the wasted money".
They took all the keys to everything with them, including the keys to the fire alarm system.

You see where this is going now?

The soldering of a single 1/2" copper coupling set off the smoke detector that was at least 10 feet away.
(I know now I should have covered it with a wet cloth) Live and learn.
A shrieking alarm and strobe lights went off all over the complex, little old men and little old ladies came running out of their rooms in total panic yelling "where's the fire"...

I was all done soldering when the alarm went off, so I went back to the office to have the new manager girl shut off the alarm and call in the "all clear" to the fire department.
The box to the alarm system was locked....
The hundred or so keys she did have on a couple of rings got tried over and over with no matches found.

The fire department showed up, alarms and sirens blazing, strobe lights and little people still in the halls....
They tried every key on the rings....again.
The manager girl tried calling the maintenance guys she had just laid off.
No luck, no way, no how.

The fire department, after being on the scene for at least a good hour maybe two had to break into the building's alarm system control box with an axe to shut the alarm off.
At this point all the people went back to their rooms, the fire department did their final checks resetting the system and left.
The "manager girl" and myself went to the office to sign the bill, and I just couldn't resist mentioning to her at that point...
"Bet you're wishing you hadn't laid off those maintenance guys now... eh?"

I went on to tell her that I... "still had one questionable fitting on those copper pipes that could stand to be replaced even though it was not leaking now, but this time it was right by a sprinkler head ".
When I got to the part explaining to her how the little red vials of liquid under the sprinkler heads were temperature reactive, and if they got too hot this time they might trigger the entire sprinkler system to douse the whole building with water....she finally lost it.
She came completely unglued, started shouting and screaming and called my company begging them to get me out of there and never let me come back.

Served her right.