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I'm putting in a new bathroom sink in a 37-year-old house in Texas. It seems that the technology has changed, and I can't fit the new sink to the old water valves, but have to replace those.

The gentleman at the hardware store sold me two kinds, so I would have the right kind and return the ones I don't need, but I'm stumped. I'm attaching photos of the current situation, as well as both kinds of replacements. I'm not sure if what's there now will just unscrew, or if I need to get behind the drywall to see more of the plumbing in order to make the switch.

Here's what's currently installed

Here's option A

Here's option B

Can anyone familiar with this kind of work give me any pointers? Thanks in advance.

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First, I don't think you'd have to change the valves. The photos don't show it well (and everything is very dirty), but the outlet connections are probably threaded and will accept appropriate hoses or compression fitting parts. Anyway, it won't hurt to replace them.

You seem to have half-inch copper supplies and sweated (soldered) valve connections. The first valve you show should be correct. It has a compression fitting that mates to the copper supply once you cut the old valve off and clean up the pipe. A good alternative recommended in the comments is the new crop of push-on fittings, such as those from Sharkbite. When installed on properly prepared pipe they're considered reliable.

You'll remove the nut and the tapered brass washer from the valve and slip those over the pipe. Slide the valve onto the pipe until it bottoms out, then bring the brass washer up to it. Thread the nut on and tighten it fairly snugly, but not crazy tight, keeping the valve all the way on the pipe. Be sure to support the valve so as to not apply force to the pipe. Use a wrench on the valve body and one on the nut.

No tape or dope is required. The brass and copper deform to create the seal. This procedure is undoubtedly covered a thousand times on the web, so give it a search if you'd like more detail or a video.

Now you'll simply install either smooth lines using the compression fitting or a washered supply hose to the valve output.

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  • Once I "cut the old valve off and clean up the pipe". Yikes. Thanks for the answer; you certainly seem to know what you're talking about. I'm unsure about cutting off the old valves, though. Do I need special tools for that? What search terms should I use to find online info about this job? – G Tony Jacobs Sep 7 '17 at 4:05
  • You will need a copper tubing cutter to cut the pipe; no hack saw or similar tool. But before you cut the tubing make sure you can clean off any paint and get down to just shiny copper. I would use rolled sand paper made for soldering, Once clean then you can cut the copper close to the existing valve. Then finish with a fine steel wool or crocus cloth, to get the sanding grooves off the copper so there are no leaks when tightening the new compression nut. Then follow "isherwood's" advice. – d.george Sep 7 '17 at 9:45
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    Seriously though, if you went into this not knowing you might have to cut pipes, you might be in over your head. Call a plumber. – NPM Sep 7 '17 at 11:34
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    If you want to replace the valve you need to buy the "mini" version tube cutter because of the space limitation. If you do not know how to solder the copper, you better get a push-connect version of the valve (the sharkbite in HD). You simply push the valve into the copper to connect. – cuteCAT Sep 7 '17 at 13:16
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    Second the recommendation for the push on valves. I can solder and have used the compression fitting valves, but on the last few I've done its worth the time savings and ease to just push on and be done. In tight spaces, even compression fittings can be difficult. – JPhi1618 Sep 7 '17 at 14:11

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