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Braze copper pipe with brass rod?

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  • Braze copper pipe with brass rod?

    I'm adding an after cooler on my compressor. To keep costs down, I'm thinking about splitting the 3/4" OD soft copper tube running from pump to tank, and brazing modified brass or copper fittings on the ends. I can then run 3/4" type L pipe over to the radiator and back I figure doing this will save at least $50-75 in fittings and tube because I already have all the fittings except the -8AN to 1/2NPT adapters, which I may make as well. The air is really hot coming out of the pump and I'd just feel better with a brazed joint instead of soft soldered. For brazing the type L pipe and fittings, can I use the brass rod and flux I already have for my gas welding setup or do I need to track down some version of that copper/silver/phos rod? I was going to do a test, but I haven't had a chance and if I need to order stuff I want to get on it soon.

  • #2
    Copper to copper and copper to brass is done in the HVAC business all the time, 5-15% Silvaloy rod is the standard, with no flux needed. The brass rod you have will probably melt way to close to the melting point of the copper, hard to say if the rod or the fitting will melt first but it would be real close, thus not a good method.

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    • #3
      I think Spark is right. You will probably have trouble with what melts at what temperature.

      If you still need to braze these joints - PM me. I can send you some HVAC braze rod (called Silfos) that is much better than soft solder but melts at a temperature below the copper.

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      • #4
        Originally posted by cxagent View Post
        I think Spark is right. You will probably have trouble with what melts at what temperature.

        If you still need to braze these joints - PM me. I can send you some HVAC braze rod (called Silfos) that is much better than soft solder but melts at a temperature below the copper.
        Sorry for the delay. Reply sent. I'll take any help I can get. 😁

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        • #5
          I will put some in the mail.

          You will need oxy-acetylene torch. Or maybe I should say I can't use anything less to braze with Silphos.

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          • #6
            Originally posted by cxagent View Post
            I will put some in the mail.

            You will need oxy-acetylene torch. Or maybe I should say I can't use anything less to braze with Silphos.
            That's generous of you!

            I've got nothing to add to this topic but your name caught my eye... any experience with chemical warfare agents? CX is truly nasty stuff...

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            • #7
              Originally posted by cxagent View Post
              I will put some in the mail.

              You will need oxy-acetylene torch. Or maybe I should say I can't use anything less to braze with Silphos.
              Thanks! I've got fresh oxy-acetylene tanks.

              Would TIG work with these rods as well? I saw a utube where he did it with silicon-bronze rod and one that used copper ground wire from some Romex.

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              • #8
                Originally posted by gzig5 View Post
                Thanks! I've got fresh oxy-acetylene tanks.

                Would TIG work with these rods as well? I saw a utube where he did it with silicon-bronze rod and one that used copper ground wire from some Romex.
                The Silfos rod is a brazing operation, you need a somewhat wide heat area for the rod to flow into the joint, Tig could work but is more of a pinpoint heat so you would have to walk it around a bit and not melt the base metals. I have seen the bare ground wire from Romex used BUT that was a TIG welding operation of copper to copper, not brazing. The difference here is between laying a bead and it wicking into the joint.

                Tig would work but have to keep the heat down and keep it moving so as not to melt the base metal. The oxy-acetylene is a better choice, much wider heat area.

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                • #9
                  I would agree with Sparky_NY comments. I have to keep the oxy- acetylene torch moving to keep from melting the copper tube or fittings. I suspect TIG would get plenty hot but you would need to develop some great skills to melt only the braze rod and not the copper.

                  I put a note in the box about flux. No flux needed on copper to copper joints. I looked up the manufacturer's recommendations for flux just to be sure. Harris said they did recommend flux when joining copper to brass. I included the link on the note. As always - what you do is up to you.

                  Fasttrack - nothing to do with CX gas. Most of what I do for work is building commissioning which is abbreviated CX. (I don't know why) I did work in the defense industry for over a decade so I had some experience with NBC design requirements. Everything had to be designed so it could be cleaned after contamination. Never had to deal with during exposure.
                  Last edited by cxagent; 09-27-2021, 12:33 PM. Reason: spelling error

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                  • #10
                    Originally posted by cxagent View Post
                    I would agree with Sparky_NY comments. I have to keep the oxy- acetylene torch moving to keep from melting the copper tube or fittings. I suspect TIG would get plenty hot but you would need to develop some great skills to melt only the braze rod and not the copper.

                    I put a note in the box about flux. No flux needed on copper to copper joints. I looked up the manufacturer's recommendations for flux just to be sure. Harris said they did recommend flux when joining copper to brass. I included the link on the note. As always - what you do is up to you.

                    Fasttrack - nothing to do with CX gas. Most of what I do for work is building commissioning which is abbreviated CX. (I don't know why) I did work in the defense industry for over a decade so I had some experience with NBC design requirements. Everything had to be designed so it could be cleaned after contamination. Never had to deal with during exposure.
                    I have used many many pounds of it doing copper to brass on AC units, never with flux and never a problem. I do clean the joints first though. All the ac units have brass valves that the copper pipe attaches to, I never heard of anyone in the trade using any flux.

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                    • #11
                      Originally posted by cxagent View Post

                      Fasttrack - nothing to do with CX gas. Most of what I do for work is building commissioning which is abbreviated CX. (I don't know why) I did work in the defense industry for over a decade so I had some experience with NBC design requirements. Everything had to be designed so it could be cleaned after contamination. Never had to deal with during exposure.
                      Got it! Looks like you're a fairly new member here so, in case others haven't said it yet, welcome aboard! Glad to have you here.

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                      • #12
                        Originally posted by Sparky_NY View Post

                        I have used many many pounds of it doing copper to brass on AC units, never with flux and never a problem. I do clean the joints first though. All the ac units have brass valves that the copper pipe attaches to, I never heard of anyone in the trade using any flux.
                        No argument here. My experience matches yours. If I were handing this Silphos to the person and maybe demonstrating its use I would have said the same thing (no flux needed). But I have not / will not meet this person much less demonstrate what I do. So I referenced the manufacturer's web site for more information. And I never contradict a more knowledgeable source like the manufacturer even if my personal experience is different.

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                        • #13
                          Without side tracking the OP too far... have any of you guys in the trade heard of the need ( requirement?) for filling the tubing with inert gas before brazing to prevent the formation of oxides that could flake off and plug/ damage AC components? Seems like over kill to me based on what I have see as common industrial practice. Maybe on the space shuttle !!!

                          Joe B

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                          • #14
                            Originally posted by JoeCB View Post
                            Without side tracking the OP too far... have any of you guys in the trade heard of the need ( requirement?) for filling the tubing with inert gas before brazing to prevent the formation of oxides that could flake off and plug/ damage AC components? Seems like over kill to me based on what I have see as common industrial practice. Maybe on the space shuttle !!!

                            Joe B
                            Yup, standard practice. There are pinhole openings in areas of a system plus its like having sand in your motor oil, very bad for the compressor, definitely not over kill. It can be the difference if a system lasts 5 years or 20 years.

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                            • #15
                              I flow propane through systems when brazing, works just as well as argon or nitrogen. No need to lug a tank around.

                              As for using 5 to 15% silphos for copper to brass.. It sort of works. Its not reliable. Still get a brittle joint.


                              You dont need oxy acyetalene, i have brazed 3/4" pipe with two propane torches and ceramic fiber insulation. 1/2 pipe can be done with 1 torch..

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