# Like Water Hammer but probably not



## tmmabey (Jan 10, 2020)

Greetings

When a particular valve turns on in my irrigation system, I am getting a loud thump and pipe movement in part of my system. I have thoroughly digested Jess Stryker's tutorial on water hammer issues, and it doesn't seem to be addressed.

A sketch is worth many long-winded paragraphs, so please see attached. I recently installed a new irrigation system as part of a front yard total redo. It ties into an existing backyard system.

When valve 4 turns ON, there is large pipe movement and a thump in the section of pipe that runs in my crawl space underneath the house to the backyard. (This was installed by prior owner). It seems very odd that the pipe that is experiencing the movement has ZERO WATER FLOW when this occurs. Valve 4 is for the front yard, and none of this water flows through the pipe in question.

When other valves turn on, there is also smaller movement, but nothing as large or violent as valve 4. It seems like the valve with the highest flow rate would produce the biggest problem, but this is not the case. Valve 4 carries about 1.9 gpm, while Valve 5 carries 3.2 gpm, but the effect of Valve 5 is only slight in comparison.

Any thoughts on the cause and the remedy?

Thanks
Todd
Torrance, CA


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## g-man (Jun 15, 2017)

Do your valves have a flow control? If so, dial down valve 4.


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## Movingshrub (Jun 12, 2017)

I have two separate meters, one for the house and another for the irrigation. When I would turn on my irrigation, I would get a thump inside the house. My thought was that the vacuum created by the sudden consumption of water by the irrigation system created a void/cavitation, which was them promptly filled by the water system, resulting in an equivalent result to water hammer. Either way, I changed the flow control like g-man suggested which resolved the issue in my case.


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## tmmabey (Jan 10, 2020)

Thanks for the suggestion. This reduced the noise and movement a great deal.


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## TSGarp007 (May 22, 2018)

When I was researching for my project, I never considered looking for valves that had flow control built in to them. Makes sense and provides some good flexibility.


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## g-man (Jun 15, 2017)

When the valve opens, if it opens very fast, the line will see a pressure drop with an acceleration of the water until the feed line resupply. This causes a shockwave thru the pipes. It is similar the water hammer when the valve closes and stops the flow of water.

Another thing to check is your heads. If the heads drain out of water, then the rush water is faster. Having heads with check valves keep the pipes full of water, this reducing the rush of water movement.


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## TSGarp007 (May 22, 2018)

@g-man , others: Doesn't help on the first valve opening, or the last, or when ''cycle and soak' is activated for that matter, but is the minimize water hammer option in Rachio a good idea to use, even if you don't notice water hammer? Always depends on specifics... I have a master valve and line (thanks to you guys getting me in that direction!) that is a 1" valve and manifold with 1.5 inch PVC piping to the valve boxes. When both zones are open briefly to minimize water hammer, I'm assuming the flow rate though the manifold, master valve, and master pvc line will increase drastically. If both zones got what they wanted it would at max be 25 gpm. It's on a 3/4 irrigation supply separate from the house supply. I estimated my gpm at maybe 17 gpm if I recall correctly, but that was out of a hose bib, so it could be more. The velocity though the master valve could be way more than 5 ft/sec. Thoughts?


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## g-man (Jun 15, 2017)

I turned mine on. It helps when it goes from one down to the next. It basically opens both zones at once and it drops the pressure a lot. Then ~30sec later it closes one of them.

Check your psi. If it is too high, consider a pressure reducing valve. Your washer, dishwasher will thank you.


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## TSGarp007 (May 22, 2018)

g-man said:


> I turned mine on. It helps when it goes from one down to the next. It basically opens both zones at once and it drops the pressure a lot. Then ~30sec later it closes one of them.
> 
> Check your psi. If it is too high, consider a pressure reducing valve. Your washer, dishwasher will thank you.


Pressure is fine I think, under 60 psi. I'm assuming my separate supply for the house is the same, but not sure. My pressure reducer there is my whole house water softener, LOL.

Do you think there is a problem with so much water going through the master valve, albeit briefly? The water from two zones will be trying to go through it for at least 10 seconds. Maybe not an issue...?


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## g-man (Jun 15, 2017)

I don't think there is a problem thru the master valve. When both valves are open, the pressure/flows drops, but the master valve should still see the similar flow as a single valve.


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