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Sweating on copper fittings


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I need to lengthen a water supply line to a sink.  The ½” copper supply line routs up through the bottom of the cabinet. 


1)      To lengthen the supply line I wanted to add a coupling, an extension, and a shut-off valve.   What is the minimum distance I should try to maintain between the sweated on coupling and the sweated on shut-off valve?  When I sweat on the shut-off valve I do not want to create a leak at the previous sweated on coupling .

2)      What is the minimum distance I should have between the cabinet floor and the shut-off valve?  I do not have anything which is fire retardant to help protect the cabinet from the torches heat/flame.

The coupling and supply extension will be installed after the old cabinet is removed and before the new cabinet is installed.  The shut-off valve will be installed after the new cabinet is installed.  I want to be able to sweat the fittings, but I only have a few successes under my belt.  I am willing to learn and do.  Looking for your advice.  Thanks  


Edited by Ron Dudelston
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I am not a plumber!!!!!!!!!!!!!!!!!!!!!!!!!!!!


If you are going to any plumbing around the house, I'd spring for one of these-


These heat blankets are available at plumbing supply places and the BORGS


You can minimize the distance between the old and new connections by wrapping a wet rag around the existing connection to prevent it from heating up to the melting point. 


I put my shutoff valves about mid point between the bottom (inside) of the cabinet and the highest easily accessible point- if it's under the sink then about half way between the cabinet inside floor and the bottom of the sink.


The "tricks" to sweating connections are- CLEAN-CLEAN-CLEAN- using emery cloth or a pipe brush on both piece to be connected. The outside of the pipe and the inside of the fitting/valve must be shiney. FLUX- to further clean when heat is applied. Apply flux to the pipe and fitting.  HEAT- heat the fitting/valve not the pipe. Move the flame around the fitting/pipe to heat all sides. SOLDER- apply the solder where the pipe/fitting meet. The fitting/valve should be hot enough to melt the solder as the solder touches the touches it. Run the solder completely around the connection.  If you get a leak, drain the water down below the fitting, reheat and add solder again.



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Dan...Lew has covered most everything you need to do, especially buying the Flame-Heat-Protector...If you have a Menards close by, they carry them in the plumbing section.


The only thing I'll add when attaching new plumbing to an existing pipe besides clean, clean, clean (with emery or at least 150 grit), when you put the heat to an existing run, no matter how well you have drained the pipe, water will wick and travel to the heat point. Any water will most likely cause a poorly soldered joint. To counter act this, buy a cheap loaf of white bread or buns (more dense than wheat).


Embed the bread/bun over the open end of the existing pipe as if you were using it as a cookie cutter. I typically do this 3 or more times to ensure enough bread has been forced into the open pipe. The bread will act as a dam and both block and absorb any water while you're soldering. Once the connection has been made and water flowing again, the bread will dissolve. It's always a good idea to remove any aerators from the faucet prior to running your water in case a solder ball or other debris needs to flow out. Just saves plugging the aerator screen.


One other thing, buy only solid core lead free solder and use a good paste flux compatible with the solder to tin the joint. Coat the inside of the fitting(s) and OD of the pipe. When the proper amount of heat is applied, you'll see the pipe and fitting tin, then flow your solder. Always best to over solder a little (not too much) rather than under solder. I have confidence you can so this!


A kit like this should be enough to do the job for you and is available at the BORGS....



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Whenever I had fittings that were close together, I would sweat them at the same time and never had a problem due to one melting the solder in the other. But I did see a trick that may help if you're worried about it, wrap a wet cloth around the fitting you don't want affected, it will keep the temps low enough that the solder won't melt. Also, look into getting pre-soldered fittings ( I think that's what they are called). They already have a ring of solder in the appropriate place...all you do is flux, assemble, and heat.

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