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I have a soldered copper water pipes that terminate in a 3/4" male thread adapter. That is screwed into a brass gate valve female-female. The valve won't close fully.

I want to cap the pipe. I can use a pipe plug on the brass valve or remove the valve and use a pipe cap on the copper thread adapter. I don't want to un-solder the thread adapter for a sweat cap.

Shopping around, I find plugs and caps in PVC, galvanized iron or black iron. Copper threaded caps seem nonexistent and brass ones are rare and expensive.

I don't want to use solder because it involves soldering.

I don't want to use brass or copper because the stuff is expensive. Can I get away with PVC? This is all on cold pipe. What's my best choice to avoid galvanic corrosion problems?

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3 Answers 3

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You could cut off the threaded adapter so you have plain copper pipe, then push on a Shark-Bite cap (they're about $6-8 at most home centers or hardware stores).

Otherwise, a stainless steel cap could be used if you're having a hard time sourcing an affordable brass threaded cap.

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a brass plug with thread tape should be sufficient. Removing the valve and capping the copper male fitting would also work just as well but requires turning off the water supply.

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  • Do you think a PVC plug with threaded tape would work instead? It's a lot cheaper and easier to find.
    – Harper - Reinstate Monica
    Aug 22, 2016 at 2:46
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    @Harper It may work in the sort term. In my experience, mixing metal and plastic threads almost never ends well.
    – Tester101
    Aug 22, 2016 at 10:28
  • Well... Iron is right out. Not the answer I was hoping for, but I sure don't want to do this job twice. Thanks.
    – Harper - Reinstate Monica
    Aug 23, 2016 at 14:30
  • Harper could not find a way to contact you through a private message. I'll gladly PayPal you eight dollars so you can buy you a brass plug. m.homedepot.com/p/…
    – Alaska Man
    Aug 24, 2016 at 17:39
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    If the existing adapter had female threads, you could probably use a PVC plug. However, when male metal threads are used with female plastic fittings, the metal typically expands the plastic enough as it's threaded together to cause a leak. When you go the other way (female metal with male plastic), the metal tends to compress the plastic instead and makes an okay connection.
    – William S.
    Dec 27, 2016 at 21:23
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Solder a cap on a short nipple, then solder the capped nipple into a female threaded to sweat adapter. Then thread the whole mess onto the male threaded fitting.

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