Irrigation pipes banging when toilet flushed

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marlonc497

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Hey guys, today while a zone of the sprinkler system was running I flushed a toilet which resulted in a loud banging coming from the pipes and the backflow preventer shaking and expelling water. Once I shut the zone down everything stopped. From what I can observe it sounds like a low water pressure issue but I'm not sure as to what I should do. I've already replaced the backflow preventer, installed a check valve before it, and even added a water hammer arrestor in hopes of fixing the problem but the problem persists. The only thing I have clear is that this issue occurs when i flush the toilet. Any help is greatly appreciated.

Thank you!
Marlon
 

Geofd

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How close to your back flow device is your check valve, is it a spring loaded check I usually install a spring loaded check within a foot of the house side of the device after working on the system or device you need to bleed the air out of the backflow thru the test ports,they are the small flat head screwdriver fittings, open slowly,and bleed until water starts leaking out of the test ports
 

marlonc497

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Thanks for the reply! Yes it's a spring loaded check valve within a foot of the device on the house side. I've also bled the device. The same issue has happened with the past 3 backflow preventers I've had. Another thing I would like to add that could possible give more information is that sometimes if I open the valve right before the backflow preventer sometimes the zone closest to it turns on despite the zone valve being off. Just a little bit more information that could maybe help.

Thanks!
 

Geofd

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Sounds like if your introducing water to the system, and sometimes the zone comes on , I think there are electric valves that control the zones maybe that zone valve is failing,your sprinklers shouldn't work until you time clock energizes them
 

marlonc497

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Yeah it may be a separate issue I suppose. The main issue I want to solve it the loud banging that shakes my whole house, feels like an earthquake. If a zone is running normally and a toilet gets flushed then boom loud banging occurs. I also find that the issue occurs typically at night. Is there any more information I could supply that could help?
 

marlonc497

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I have normal electric zone valves, looks very similar to these:
1619962526315.png
 

JG plumbing

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No such thing as normal. Those look like junk to me.

I don't think you have enough info here to guess what your problem is. You need to have someone there to go through your arrangement and narrow down where it's coming from.
 

marlonc497

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My water pressure is around 50 psi, when the backflow preventer trips it drops to around 23 psi. Whenever a zone turns on I can pretty reliably get a good 2 seconds of pipe banging (backflow preventer shaking and expelling water). More rare but much more severe when it does not resolve itself and just continues expelling water until I shut it off.
 

JG plumbing

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Your zone valve may need modified or swapped for one that closes /opens softly. Aka more money
 

Geofd

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Hey guys, today while a zone of the sprinkler system was running I flushed a toilet which resulted in a loud banging coming from the pipes and the backflow preventer shaking and expelling water. Once I shut the zone down everything stopped. From what I can observe it sounds like a low water pressure issue but I'm not sure as to what I should do. I've already replaced the backflow preventer, installed a check valve before it, and even added a water hammer arrestor in hopes of fixing the problem but the problem persists. The only thing I have clear is that this issue occurs when i flush the toilet. Any help is greatly appreciated.

Thank you!
Marlon
Show us a pic of the backflow device,is it above the highest sprinkler head there are 2 different styles for 2 methods of installation
 

marlonc497

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The only place the check valve could have been installed was behind the wall, the plumber that installed the irrigation system left no room and did not originally install a check valve nor a water hammer arrestor. I have a feeling he didn't do all that great of a job. Should I consider having the plumber redo the backflow preventer portion only or the zone valves as well?

Thanks
 

JG plumbing

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I still think it's a zone valve. But if I came there I would want to see it act up. Or ask to redo it.
 

Twowaxhack

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I’d remove the check valve permanently and leave the backflow preventer in the pic.

Maybe replace the ballcock with a slow close type.

You’re velocity of the sprinkler water feed is probably high when operating.

I think your sprinkler supply pipe is undersized for the volume you’re flowing. This increases velocity and can cause water hammer issues that are unusual for the pressures.......

Or you have a bad zone valve.......


Or I’m just way off base and just ignore me because I’m guessing. 🤣
 
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Geofd

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The only place the check valve could have been installed was behind the wall, the plumber that installed the irrigation system left no room and did not originally install a check valve nor a water hammer arrestor. I have a feeling he didn't do all that great of a job. Should I consider having the plumber redo the backflow preventer portion only or the zone valves as well?

Thanks
If there is a check valve before the backflow within a foot I think you ok,you need an irrigation guy to check the zone valve you think is faulty
 
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