Between my sprinkler system solenoid valve and indexing valve there is a T connector that adds some sort of metal piece on top of the pipe.

Side of unidentified part

Top of part, showing markings

I could not find a similar part on any of the sprinkler system parts lists or guides I've looked through, and google searching for any of the writing on top didn't bring up anything. I can make out the letters CFM 13.5, which makes me think it may be some sort of regulator, but I don't see how that would work since it is attached on the side of the pipe.

The part leaks water when the system is turned on, which makes me think it may be broken and needs to be replaced. Any ideas what it is?

  • Hello, and welcome to Home Improvement. Looks like an anti-siphon valve to me. Jul 12, 2020 at 14:22
  • @DanielGriscom, Thanks! I was thinking it could be an anti-siphon valve, but it looked very different to every product I had seen available. Thanks for the welcome and the link to the tour.
    – Daniel
    Jul 12, 2020 at 14:30
  • 1
    Does it only leak briefly as the system starts, or does it leak continuously as long as the system is on? The first is normal or at least not uncommon until the valve seats as pressure builds, and the second would be cause to replace it.
    – Ecnerwal
    Jul 12, 2020 at 17:50
  • It looks like it flows out quickly when it first starts, but slows to a trickle afterwards.
    – Daniel
    Jul 14, 2020 at 20:52

1 Answer 1


That's an anti-siphon (or vacuum breaker) valve:

enter image description here


It prevents dirty yard water from being sucked back into the potable water system if the water pressure fails.

  • 1
    Also Known As: a "vacuum breaker" (as by breaking the vacuum, no siphoning happens....)
    – Ecnerwal
    Jul 12, 2020 at 16:18
  • Thank you! Any idea why water is leaking out when the system starts up? Is that normal or cause to replace it?
    – Daniel
    Jul 12, 2020 at 16:48
  • It should be a one-way valve, letting air in if the water pressure goes below ambient, and shutting when the water goes back above ambient. So, sounds like it's worn and needs a new gasket, or replacement. Jul 12, 2020 at 16:52
  • 1
    @Daniel you might try searching for "sprinkler anti-syphon valve" or "sprinkler vacuum breaker" to specify one for a sprinkler system, or try at a plumbing supply store, instead of your local big-box national chain store.
    – FreeMan
    Jul 12, 2020 at 17:37
  • 1
    ...or an agriculture/horticulture/farming/greenhouse supply store/website.
    – Ecnerwal
    Jul 12, 2020 at 17:51

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