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I just bought a house in the Las Vegas area and we are replacing a vanity cabinet. When we removed it, we discovered this u-shared copper pipe with some "device" in the enter coming out of the wall under the normal water and drain pipes. What is it?

Image of u-shaped copper pipe coming from the wall

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    Looks like a pressure regulator. See homedepot.com/p/….
    – popham
    Commented Dec 25, 2023 at 5:39
  • Is this on an outside wall? Is there an outside faucet on the other side of this wall? If so this could be an inside cutoff valve for an outside water faucet. This might be a tap into the cold water line to the vanity to get supply for an outside faucet. Commented Dec 25, 2023 at 11:27
  • OK so it is not a valve, but is a pressure reducer. Does it go to an outside irrigation system which operates at low pressure? Commented Dec 25, 2023 at 17:06
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    @Jim, that was one of my thoughts. I have a drip irrigation system that operates at 30 psi behind a similar regulator. In Las Vegas I would definitely expect it to be installed outside, though. Maybe if the system was goofed by excluding the regulator initially, the path of least resistence was putting the regulator inside? Countering noises from a refrigerator line on the opposite side of the wall is my second "other side of the wall" theory.
    – popham
    Commented Dec 25, 2023 at 18:25
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    @JimStewart This is not an external wall, and there is no faucet on the other side of the wall. The other side of the wall is the master bedroom.
    – Aron M
    Commented Dec 26, 2023 at 0:34

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That's a pressure regulator. My best guess based on the image is that it regulates the pressure of the vanity's cold water. That seems odd, so I would cut into the drywall to examine the pipe configuration. Maybe the additional information can rationalize the pressure regulator's existence.

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    Given that this doesn't look like a diy hack job, I'd leave the drywall where it is and only start cutting if there was an issue other than curiosity. That's just me and my dislike of drywall repair, though. Commented Dec 25, 2023 at 15:34
  • Could be on the water inlet to the house, which just happens to be right there.
    – Jon Custer
    Commented Dec 25, 2023 at 17:21
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    @Aloysius, any drywall repair would be behind the new vanity. Having a pressure regulator without understanding its exact purpose (beyond pressure regulation) seems a little nuts. And I would want to be rid of those push fittings, so I would be looking to remove the pressure regulator. Those particular push fittings are probably just the tip of the iceberg, though. 25 years. Tick tock.
    – popham
    Commented Dec 25, 2023 at 18:28
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    the push fittings are at least accessible... beats burried propress. Commented Dec 26, 2023 at 0:12
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    tape a microphone to it or use a mechanic's stethoscope to listen to see what appliances make water sounds in it when flowing water. that will tell you what it's doing, but not why.
    – Jasen
    Commented Dec 26, 2023 at 13:53

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