# Loud Thumping/hammering sound



## Tgod288 (Jul 22, 2020)

Sprinklers worked fine yesterday. We got 5 inches of rain in a few hours last night. Ran zone 1 today for one minute and turned it off. Heard very loud thumping sound from backyard and went about my business for 15 minutes before realizing it was coming from this above ground pipe show in photo and water was coming steadily out of the green cap circled. I shut the water main off and sound immediately stopped. This caused the in ground box to fill with water. I emptied out most of the water and tried zone 1 again with the same result.

Any ideas? Thanks!


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## ionicatoms (Mar 8, 2020)

Maybe this helps


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## Tgod288 (Jul 22, 2020)

ionicatoms said:


> Maybe this helps


But would this explain the hammering after the sprinklers run?


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## johnr (Jul 13, 2020)

I had a similiar situation some years ago and it was the regulator in your photo that was the culprit. It was "cycling on and off (open / closed )" which caused the hammering sound. Replaced it and problem solved.


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## johnr (Jul 13, 2020)

I had a similiar situation some years ago and it was the regulator in your photo that was the culprit. It was "cycling on and off (open / closed )" which caused the hammering sound. Replaced it and problem solved. I would start there. I think it was a relatively low cost item to replace but I don't recall if I did it myself.


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## Tgod288 (Jul 22, 2020)

johnr said:


> I had a similiar situation some years ago and it was the regulator in your photo that was the culprit. It was "cycling on and off (open / closed )" which caused the hammering sound. Replaced it and problem solved. I would start there. I think it was a relatively low cost item to replace but I don't recall if I did it myself.


Yes that is what I am thinking at this point. To replace the whole thing is about $100 and looks to be pretty simple. Hopefully that fixes it.


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## BadDogPSD (Jul 9, 2020)

That's the vacuum breaker. You should be able to get a rebuild kit for around $25. If you end up replacing, you might want to consider adding a union (or 2) to make it easier to service in the furure.


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## Tgod288 (Jul 22, 2020)

Just tested other sprinkler zones and none of them caused this problem. Only zone 1 creates the noise as soon as it shuts off. Does that mean the vacuum breaker is working?


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## BadDogPSD (Jul 9, 2020)

Could be the valve for zone 1. Have you tried turning it on manually to see if the same thing happens?


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## Tgod288 (Jul 22, 2020)

BadDogPSD said:


> Could be the valve for zone 1. Have you tried turning it on manually to see if the same thing happens?


I am just running one zone at a time for a one minute test. Yes think that's what you mean.


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## BadDogPSD (Jul 9, 2020)

Are you using a timer to activate the zone or turning it on manually at the valve? If the vacuum breaker seems to nmwork normally with all of the other zones, it may be the zone one valve. Perhaps the solenoid?


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## Tgod288 (Jul 22, 2020)

BadDogPSD said:


> Are you using a timer to activate the zone or turning it on manually at the valve? If the vacuum breaker seems to nmwork normally with all of the other zones, it may be the zone one valve. Perhaps the solenoid?


Oh ok I see. I just opened it manually at the valve. As soon as I shut it, hammering started. So no difference from running the zone at the control panel.


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## Tgod288 (Jul 22, 2020)

I swapped the solenoids on zone 1 (bad zone) and zone 2 (good zone) and zone 2 works still and zone 1 now only hammers once when it gets shut off. Strange. Edit ran a few times and hammers more than once. I think I can also hear the hammer in the underground pipe, not just at the PVB


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## BadDogPSD (Jul 9, 2020)

I'm confused. You swapped solenoids and zone 1 was still bad?


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## Tgod288 (Jul 22, 2020)

Correct


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## BadDogPSD (Jul 9, 2020)

Sounds like a bad valve on your zone 1.


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## Tgod288 (Jul 22, 2020)

How would you go about replacing only one valve? It's all so compact in there, am I going to have to redo the whole thing? Could I just take off the top cap and replace the internals?


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## BadDogPSD (Jul 9, 2020)

Yes, you can try a rebuild kit first.


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## Tgod288 (Jul 22, 2020)

Rebuild kit didn't work. I have a hard time believing it is the valve because the only part of the valve that isn't new is the body and it is just solid plastic they water flows through, no moving parts to malfunction.


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## jht3 (Jul 27, 2018)

what did you rebuild? the vacuum breaker?

buy an identical valve and swap everything but the body. if that doesn't solve anything, you now have spare parts for the next time. and there will be a next time on one of your zones.


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## Tgod288 (Jul 22, 2020)

I rebuilt the sprinkler valve except for the body with no positive results. I then took apart the vacuum breaker and reassembled (waiting on parts to rebuild) and it seems to have made it a lot better. When zone one shuts off I can still feel/hear about 3 hammers in the pipe, but it is very faint. I would prefer no hammer like the other 4 valves, but not sure what else to do.


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## ionicatoms (Mar 8, 2020)

Tgod288 said:


> I would prefer no hammer like the other 4 valves, but not sure what else to do.


This guy has three general suggestions for mitigating water hammer:
• Use a larger diameter pipe to reduce the velocity of the water.
• Close the valve more slowly.
• Supplement with an anti-surge device.

This guy has 4 suggestions that overlap the first guy: https://www.thebalancesmb.com/solve-water-hammer-issues-844851


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## BadDogPSD (Jul 9, 2020)

Strange that it's just that one valve that causes the issue.


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## Tgod288 (Jul 22, 2020)

Agreed. Think I will try a water pressure reducing valve at the backflow pipe.


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## Tgod288 (Jul 22, 2020)

except if the pressure is fine for the 4 other valves, then why wouldn't it be ok for the zone 1 valve? The pressure is about 75 psi.


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## RVAGuy (Jul 27, 2020)

I suspect Zone 1 may have higher flow than your other zones or is further away than your other zones from the PVB. This creates more water moving in the pipe at a greater velocity. It's the sudden "stop" of the column of water that creates the water hammer, not the static operating pressure of the water itself. You can see this in a roll of garden hose when you open the handle quickly and the hose roll jumps. Now imagine putting that in a straight line in a rigid pipe. All of the water hammer is directed in one direction (unlike the hose) and that's what you are hearing.


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## Tgod288 (Jul 22, 2020)

Yes zone one is furthest and most sprinklers. I installed a water pressure reducing valve and it is still hammering. Don't know what else to do at this point.


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## Tgod288 (Jul 22, 2020)

If I stand at the valve box, I can faintly hear the hammer in the pipes underground when valve one closes. Is that worth worrying about?


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## RVAGuy (Jul 27, 2020)

As mentioned by others, you can install a mechanical water hammer arrestor. Don't do a length of pipe with air in it, because over time air diffuses into the water and becomes useless. Another option is to split zone 1 into two zones to reduce the speed of the water column doing the hammering. It's your call on whether to do it or not. If you've had your system for some time and haven't had any main breaks, I'm inclined to leave it alone.


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## ionicatoms (Mar 8, 2020)

Maybe swap to lower flow sprinklers and water for a longer duration.


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## johnr (Jul 13, 2020)

@Tgod288 Perhaps you are dealing with a simple and common "water hammer" problem. That is, the water shuts off abruptly in your lawn system and sends a shock wave thru the plumbing. More details in linked article. Also note that the article mentions a 'simple' fix of just turning off the household water and draining your system, which clears the air chambers in your system, and you are ready to go. Hopefully one of us can help.

https://www.thespruce.com/fix-water-hammer-pipes-4126485


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