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Irrigation Backflow preventer water hammer?

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marlonc497

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Hi guys, quite puzzeled right now. Today woke up early in the morning to a terrible constant pipe banging sounds coming from the pipe leading to the irrigation valves. The sound was quite audible from outside where the backflow preventer is. The backflow preventer was leaking a lot water from the top. This was all happening while the sprinkler system was running. I had to close the valve feeding the system from inside the home to stop the banging. What could be the cause of this? The backflow preventer seems to be quite similar to this https://i.ebayimg.com/images/g/QZEAAMXQU6tQ~gRM/s-l300.jpg

Thanks!
 

Geofd

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what you need is a spring loaded check valve no more than a foot in front of the back flow any time I install a backflow device I do this it stops the valve from chattering the zone valves are electric and open very quickly
 

marlonc497

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Thanks for the reply! So I would put spring loaded check valve between the backflow preventer and the zone valves. Also would a sharkbite inline check valve work? Thanks again for the reply!
 

Geofd

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Thanks for the reply! So I would put spring loaded check valve between the backflow preventer and the zone valves. Also would a sharkbite inline check valve work? Thanks again for the reply!
no...I goes in front of the back flow device the rush of water and the loss of pressure from the zone valves opening affects it...also you could put a hammer aresstor after the backflow that would also help
 

marlonc497

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Hi guys, everything has been working well until this morning. I woke up at 4am to intense loud banging coming from the pipes. The check valve seemed to have helped but once again the problem is present. What is my next step? Should I also install a water hammer arrestor? Thanks!
 

marlonc497

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The way everything is setup I'm not sure if I would be able to do that. I do want to fix this problem though. What could cause all of this?
 

Nukedaddy

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Yes. The drawing shows no protection for the water service and the main. A low pressure condition on the main could cause water contaminated with soil and garden chemicals to be drawn into the main and delivered to all the downstream customers! Very dangerous setup! A proper arrangement has the RPZ protecting both the irrigation and the potable lines. An even better setup uses two RPZs protecting the main from irrigation and the potable from irrigation separately. (This also protects the main and irrigation system from garden hoses, boiler feeds, some water softeners, some commercial dishwashers and etc.
 

Jamesplumbing06

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I am by no means a back flow expert. But the 10 times I have experienced this. There was the tiniest piece of trash in the seals of backflow. I mean super tiny. Once was a pipe dope finger print. If it worked as it stands before. It will continue to work as is. Just clean it.
 

marlonc497

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Okay, so far I've put in a check valve and a water hammer arrestor and the problem just happened again today. Im not really sure what else I could possibly do. I think I should note that this doesn't always happen, sometimes it works just fine but other times it doesnt. Should I attempt to clean it or just replace backflow? Wondering if it just is a faulty backflow. When it happens just to be clear the pipe is shaking and banging heavily, curiously enough water continues to go out the sprinkler head but at a reduced pressure. From what I can tell I assume that this problem occurs when the zones switch. The rest of the water is flowing out of the backflow. I am truly puzzled.
 

Geofd

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Okay, so far I've put in a check valve and a water hammer arrestor and the problem just happened again today. Im not really sure what else I could possibly do. I think I should note that this doesn't always happen, sometimes it works just fine but other times it doesnt. Should I attempt to clean it or just replace backflow? Wondering if it just is a faulty backflow. When it happens just to be clear the pipe is shaking and banging heavily, curiously enough water continues to go out the sprinkler head but at a reduced pressure. From what I can tell I assume that this problem occurs when the zones switch. The rest of the water is flowing out of the backflow. I am truly puzzled.
James plumbing is correct when you take it apart look at the rubber disks in the check valves if the rubbers are Grover or cut change out the rubber disks
 

CraigHutton

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I have an irrigation related hammer issue. Hammering when irrigation system is on. First had plumber replace water pressure damper with Zurn Wilkins:
"Pressure Reducing valve with integral by-pass", Model NR3X
Hammering continued, but at lesser intensity.DamperBackflowValves.jpg
Then plumber replaced backflow prevention unit with Zurn Wilkins model 720A 3/4" Pressure Vacuum Breaker 'for back siphonage protection'.
But still hammers when irrigation on, less vibration/sound but still enough to wake a person.
Plumber isn't aware of what else to check, he's surprised that new quality water pressure damper and backflow prevention unit didn't cure the hammering.
Any ideas what else to check, or a possible corrective action??
Thanks,
Craig
 
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Geofd

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Yes put a spring loaded check valve within 1 ft of the street side of the device
 

marlonc497

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Just an update as it may help someone. I switched my irrigation schedule start time from 3am to 10 pm and haven't had any issues since. I suspect this means that high water pressure was causing the problem.
 

CraigHutton

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We found the problem with continued but much diminished hammering after both the water pressure damper and backflow prevention units were replaced. Also the irrigation system was using water and dripping on the bushes outside of the system operation hour on the timer.
When the PVC pipe was cut to install the new backflow prevention unit, saw shavings/cuttings from both the old PVC pipe and the new PVC pipe entered the irrigation water flow and clogged up the irrigation valve. The landscaper had seen this before. He simply turned off the irrigation water, took the top/cap off the irrigation valve (you could see the white PVC shavings/cuttings in the irrigation valve), cupped his palm over the top of the open valve, then had me turn on the irrigation water. Pressure built up and he removed his hand and a spurt of water cleaned out the PVC shavings. He put the valve top/cap on and the problem was cured. He said that many plumbers don't sand their PVC new pipe saw cuts, or be careful that shavings/cuttings from the old PVC pipe saw cut don't enter the irrigation water flow, and then the irrigation valve gets plugged with shavings/cuttings & doesn't function correctly.
One lingering issue. There is a small spout (see picture) from the garage wall behind the water pipes (similar to AC condensation drip spouts, but this isn't one). It is dripping about two cups a day, and has never dripped before. The landscaper says that some valve within the house may have been damaged by the initial violet hammering. Does the slow-dripping spout make any sense to anybody? On the other side of the wall, in the garage, is the control panel for the home fire sprinkler system, now 23 years old. Thanks,
Craig. Drip112120.jpg
 
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