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Thread: soldering copper pipe

  1. #1
    DIY Junior Member gink's Avatar
    Join Date
    Oct 2005
    Austin Texas

    Default soldering copper pipe

    In soldering a copper ball valve to a copper pipe, replacing stuck gate valves, I understand I mustn't overheat the valve, so as not to damage the seals, but what sort of flux is best? I know acid flux should not be used, but is flux using ammonium chloride or zinc chloride acceptable, or might they cause corrosion in the long run? I won't really be able to flush the pipes very well, this is part of a hydronic heating system. I suppose resin flux would be acceptable in that it would not cause corrosion, but can one be reasonably sure it will prepare the surfaces well enough for a good joint?

    The books and articles one finds don't seem to really address this issue. I'm familiar with soldering electronics, but not yet with soldering pipes.

    thanks very much for your help.

  2. #2


    For a hydronic heating repair or replacement an acid type flux is fine. There is still a large yet silent debate about whether or not flux contributes to faulty copper piping.

  3. #3
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    I don't know one flux from another, but you don't use the same solder for copper pipes that you use for electronics. All you need is ordinary flux that every plumbing shop has. Oatley and Dutch Boy are brands that come to mind, but there are others. Clean the pipe ends and the inside of the fitting well with sand paper, emery cloth, or the special wire brushes that are made for this purpose. Solder immediately after the cleaning process. Apply the flux, heat the joint until solder flows when touched to the opposite side the flame is on. Let the joint cool before moving it or applying water. You can use a damp rag to wipe the excess flux from the joint while it is still fairly hot. Since this is a valve, be careful that the valve is horizontal while soldering so that molten solder doesn't run into the valve seat.

  4. #4


    don't know all the differences, but for sure you can't use an acid flux on electronics, but shouldn't matter for plumbing - your goal is to get a clean surface for a good bond. I learned here (and first hand!) that the new water-based fluxes don't behave the same as the old petroleum-based fluxes. Fortunately I found some of the old stuff in a box and was able to use it. One suggestion - I like the "tinning" fluxes. oh - and make sure the solder is lead-free.

  5. #5


    Just so we understand the primary purpose of FLUX is to remove oxygen from the area which would otherwise leave you which a carbon (black and powder like) residue that solder cannot stick to. The cleaning of the pipes was another cool idea put together by the makers of flux products.
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