Please help me to figure out about this pipe.

In our hosue, We have the water pipe coming out from the wall right next to the A/C unit. Recently, the water start running constantly, and I have no know what it is.

The following points are something I am sure about. 1. The water stops running if I turn off the main valve. 2. Water was actually dripping very sometimes like 3, or 4 years ago. It is now running 3 gallons / hours. 3. It is cold water.
4. There are two pipes and joined by some kind of a T socket. 5. The pipes are nothing to do with the A/C unit; it is coming from the ground.

Please anyone give me ideas what it is and how to stop the water.

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  • Location : Dallas TX
    – Ken
    May 8, 2020 at 2:46
  • In your picture, where exactly is it leaking? May 8, 2020 at 5:33
  • I would guess that is some kind of pressure regulator, I have never used a venting or relieving style regulator on a water system but it looks like it was designed this way.
    – Ed Beal
    May 8, 2020 at 14:13
  • Does the water stop flowing if you cut off any check valves other than the main one? That might help locate the source of this pipe. May 8, 2020 at 15:28
  • @Programmer66 Thank you for your comment. It is not leaking. The water is constantly running.
    – Ken
    May 8, 2020 at 16:58

1 Answer 1


Looks like it could be a flow activated trap primer:

A trap primer (or trap seal primer) is a plumbing device or valve that adds water to traps. The water seals in traps are needed to prevent sewer gases from entering buildings, but because this water is exposed to the air, it is subject to evaporation over time in infrequently used floor drains, leading to the release of sewer gas into the environment. The trap primer mitigates this problem by injecting water, either directly or indirectly, into the trap to maintain the water seal indefinitely. - Wikipedia

enter image description here

Example of one here and as well as the source of the above image (link is to a PDF, only picked this one as it was one of the first search results).

Look to see if you can find a make and/or model number on the 'Tee'. You may need to use a small mirror or camera to see the backside.

If it is now constantly flowing, there may be on obstruction inside the valve preventing it from functioning correctly. It could also be broken and in need of replacement. Depending on the valve, you may be able to just replace the internals.

  • Thank you. I have been wondering what this "T" thingy was, now I know it is called Trap Primers. This is huge progress for me. Thank you!!!!!
    – Ken
    May 8, 2020 at 20:03
  • Sounds like a real possibility, should more up votes.
    – Ed Beal
    May 8, 2020 at 20:31

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