What size tip to sweat 3″ copper pipe?

[dvecci]

I have a 3″ pipe with a pin hole leak. I’ve never worked with copper pipe larger than 3/4″. What size acetylene torch tip should I use? A no. 6 ? The leak is in the hot water line in a public school. I have a rubber clamp on the leak for now.

I read that I should start at the bottom and fill upward, creating a solder dam to build up from. Is that right?

As a second question, related to this same sweat project; will I need to shut off the cold and hot water? I ask this only because I noticed that on a earlier bathroom sink repair, that when I turned on the cold water faucet of neaby sink, water ran out of the hot water pipe that I was repairing. So I had to turn off the branch cold water also, just to insure noone turned on the cold water while I was working. I assume there are hot water recirculating valves in the building that I don’t see, and these devices allow hot and cold water to crossover at certain points or times, but I have more to learn about those.

[Retired plbg1]

First thing are you a Plumber. You dont need a # 6 tip, a #4 is ok. but you dont use a welding flame you trodel it down, also you have to get all the water out, when you open a faucet are valve some where you give it air and it releases water. You better have help because i think you might have aproblem, heat the whole fitting slow and watch you dont burn out solder with too hot of a flame, after it gets hot to melt solder start at bottom and feed solder in and go to top fill in, take rag and wipe solder up to top of fitting. Let me know.

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Art retired plbg

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