# Water hammer from irrigation system on second meter?



## Movingshrub (Jun 12, 2017)

I have two water meters.

I *think* the second one is tees off the same line, as in, one line from the main, splits, and feeds both meters. Now, that might not be correct considering when I did call before you dig, the utilities marked two parallel blue lines in my yard between the meters and the street.

Whenever I run an irrigation cycle, I get a noise/banging on my copper pipes. This did not occur last year, to my knowledge.

I assume I am having water hammer, but I wouldn't think it would be an issue with two meters. Thoughts?

I forgot to add. This occurs on every zone. One zone is 22GPM while the smallest is 4GPM. Also, I am starting to hear the noise for almost every fixture/appliance in the house; noise with washing machine or toilet ceases demand for water.


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## g-man (Jun 15, 2017)

Check your static pressures. Maybe they increased them.


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## Movingshrub (Jun 12, 2017)

g-man said:


> Check your static pressures. Maybe they increased them.


My plan was to check static and see what it spikes when I close a valve. It might be time to finally install a pressure regulator.


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## Movingshrub (Jun 12, 2017)

Yes I know that's high. With that being said, it's been that level for the last three years and the noise started now.


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## unclebucks06 (Apr 25, 2018)

What size pipe are you flowing 22gpm in? Might be exceeding the velocity limit of the pipe.


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## g-man (Jun 15, 2017)

The PSI was the same value 3 yrs ago?


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## Movingshrub (Jun 12, 2017)

unclebucks06 said:


> What size pipe are you flowing 22gpm in? Might be exceeding the velocity limit of the pipe.


The entire system, supply line, and all the branch lines, are 1.25" SCH 40 PVC, using Rain Bird DVF 1 in. FNPT Valve with Flow Control.

I have five zones and based off the rainbird irrigation design manual, that puts the water velocity as:
Sidewalk Strip - 8.48 GPM - between 1.71-1.92FPS
Front yard - 24.69 GPM - between 5.14-5.57 FPS
North half of back yard - 21.49 GPM 4.28-4.71 FPS
South half of back yard - 22.90 GPM 5.14-5.57 FPS
Driveway strip - 7.28 GPM 1.49-1.71 FPS

For the 20+GPM zones I understand I'm pushing the FPS limit of the pipe. The design called for class 200, where as I went with SCH40 due to the amount of tree roots and chipmunks I had tunneling around my yard, and by switching to SCH 40 with a smaller ID, it increased the FPS velocity of the water to above 5 FPS.

If I were to change the 5000 series rotors to 5004 PRS rotors, it would change the GPM and FPS to
front yard 22.8 GPM between 4.71-5.14 FPS
N. back yard 21.96 GPM between 4.28-4.71 FPS
S. back yard 20.37 GPM between 4.28-4.71 FPS

So, it might be value added to change those rotors to PRS style rotors to reduce my GPM and FPS, but the GPM and FPS isn't the cause in my opinion because I get a bang inside the house when any of those irrigation valves close, including the 7.28GPM and 8.48 GPM valves. I was actually able to watch the exterior hose sillcock vibrate when the irrigation valve closed. The irrigation system is on a different water meter as well. I assume that the two meters are connected via a T rater than a separate tap into the main line. I may dig up around the meter and confirm.


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## Movingshrub (Jun 12, 2017)

g-man said:


> The PSI was the same value 3 yrs ago?


Yes. I bought the house April 2015 and the PSI was really close like 84, 87. Either way, 80+PSI.


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## g-man (Jun 15, 2017)

It could be that one of the internal pipe hooks became loose. I would install a pressure regulator. 80PSI is too much.


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## Movingshrub (Jun 12, 2017)

g-man said:


> It could be that one of the internal pipe hooks became loose. I would install a pressure regulator. 80PSI is too much.


I went and talked to the local utilities to confirm it wasn't an issue with the meter backflow on the second meter. Their suggestion was, no matter what, install the PRV. I'm trying to figure out what the interior pressure should be after installation. 75PSI? 50PSI?


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## g-man (Jun 15, 2017)

60psi


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## Movingshrub (Jun 12, 2017)

g-man said:


> 60psi


Noted.

There are about a billion different pressure reducers out there. Any particular features I need to seek out before I pull the trigger? I currently have on the work bench a Watts LF25AUB-Z3 PRV. I am waiting on pressure gauges to arrive before installing.


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## Movingshrub (Jun 12, 2017)

When you want to make sure you can still read the gauges at 100/ordering the gauges without reading the dimensions.

That's 3/4 copper pipe, for some perspective.


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## Movingshrub (Jun 12, 2017)

As part of diagnosing the water hammer noise, I calculated the water velocity of the irrigation system.

Now that I'm done with the pressure reducing valve, I wanted to confirm whether I need to make changes on the irrigation system.
My static water pressure is 80PSI. The irrigation is on it's own meter.

I used rainbird's GPM performance charts, which only go up to 65 PSI for the rotors I'm using. Using the GPM at 65PSI numbers, I end up with velocities by zone of: 1.71, 2.14, 4.59, 4.92, and 5.28. At 80PSI, is it safe to assume that the GPM is higher

Do I do nothing? Put in a pressure regulator on the supply side? Replace a handful of rotors with pressure reducing rotors, which with their lower GPM requirement, will reduce the velocity? Use the flow control feature of the valves and reduce the water flow?


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## Greendoc (Mar 24, 2018)

What I would do is decrease the GPM drawn and consequently the velocity in the system. Drawing more than 4 FPS of water through copper pipes routed through your house will cause audible water hammer. Fast closing valves do not help either in regards to water hammer. For irrigation systems operating at high pressure, my preferred valve is the Buckner Superior all brass valves. Yes, they cost more than plastic valves, but they are slow closing. They are also repairable. At 80 PSI incoming pressure, I would not want a regulator inline with the irrigation system. A 3/4 regulator has a rather sharp pressure/volume curve. I have seen irrigation systems have severe problems once such a device has been installed. They are very good for reducing static pressure, but maintaining adequate dynamic pressure is where they fail.


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## Movingshrub (Jun 12, 2017)

Greendoc said:


> What I would do is decrease the GPM drawn and consequently the velocity in the system. Drawing more than 4 FPS of water through copper pipes routed through your house will cause audible water hammer. Fast closing valves do not help either in regards to water hammer. For irrigation systems operating at high pressure, my preferred valve is the Buckner Superior all brass valves. Yes, they cost more than plastic valves, but they are slow closing. They are also repairable. At 80 PSI incoming pressure, I would not want a regulator inline with the irrigation system. A 3/4 regulator has a rather sharp pressure/volume curve. I have seen irrigation systems have severe problems once such a device has been installed. They are very good for reducing static pressure, but maintaining adequate dynamic pressure is where they fail.


Two separate issues. I've fixed the water hammer inside. That issue seems to be resolved.

The second issue, if that's even fair to call it such, is determining whether the GPM requirement on my irrigation system, is going to lead to damage to the PVC, since the water velocity is over 5 FPS.


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## g-man (Jun 15, 2017)

I think the recommendation for a pressure reducing valve should also be installed to the irrigation system. Dont confuse PSI with GPM. Operating at 80PSI is not ideal.

https://www.irrigationtutorials.com/gpm-psi-municipal-water-source/


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