7500 ft private water line with 438 ft elevation drop - are my multiple PRVS causing water hammer?

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ballardFan

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I have a water line that is approximately 7500 feet long from the meter to my property. The meter is a 1.5" service. My line is 2" and is a mixture of 5400 ft HDPE, a small bit of sch 40, and about 2000ft sch 80 PVC at different points.

Pressure at the meter is about 100 PSI.

Over the 7500 ft distance the line descends from 468 ft to 30 ft final elevation which adds ~202 PSI to the starting pressure. I know there are other factors like friction loss to factor in but either way the pressure on this line is huge so I have a lot of equipment to deal with it.

I have multipe PRVs on the line now.

PRV 1: Right after the meter to drop the start pressure to 50 PSI before it runs down the slope.

PRV 2: 2500 ft distance after a drop of about 90 ft in elevation. It again drops back to ~50PSI.

Another 3500 ft down the line I have a service hose bib and checked the pressure and it is 120 PSI. The increase in pressure at this bib is from the elevation drop and all tracks about right.

PRV 3 is about 100 ft from my first house tap at the 30 ft elevation. I am estimating input pressure is around 180PSI (120 psi measured plus elevation drop adding about 61 PSI). I don't have a great way to measure input pressure.

I just replaced PRV#3 with a new Zurn Wilkins 600 XL2 which has the integrated check valve. As far as pressure control it is holding perfect for my whole property at 50 psi after this PRV.

My Issue: I am having a problem since I replaced PRV3 where when I have all flow shut off at my house it will blow out the line back up the hill.

It did not occur before i replaced the PRV. It will not occur as long as I have some flow going either.

My understanding is the spring loaded nature of the PRV is basically causing a water hammer to run "back" up the pipe. I assume this higher quality PRV is hitting the line harder (e.g. the spring is reacting faster then the old one did).

Question:

Is my assessment accurate? What should I do? Add another intermediate (4th) PRV? Add a mega hammer arrestor or a series of them like these: Zurn Wilkins Z1700-600 #600 Shoktrol Water Hammer Arrestor?
 

Valveman

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It is not the spring but the speed that the valve closes. When it closes too fast it is like dropping a boulder in front of a speeding freight train. A slower closing PRV would help, and a diaphragm tank on a tee before the PRV could give it a little more cushion to work with.

Also an expansion tank in the house will be needed because of the check valve feature.
 

ballardFan

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It is not the spring but the speed that the valve closes. When it closes too fast it is like dropping a boulder in front of a speeding freight train. A slower closing PRV would help, and a diaphragm tank on a tee before the PRV could give it a little more cushion to work with.

Also an expansion tank in the house will be needed because of the check valve feature.

Thank you.

Should I replace with a PRV that does not have the check valve in your opinion?

I'm not sure how to assess the speed the PRV closes on different PRV units?

I bought the Zurn Wilkins 600xl because it was a higher grade unit (higher flow rate and is all bronze body). I live by salt water and everything metal that isn't SS316 or bronze wears out quickly. My other 2 PRV are Watts units that are rusting out in the dome area of the PRV and the screws are a pain compared to the Zurn screw on design. But I can't have these blow outs taking my water service down so I will replace anything I need.

I was going to put in one more PRV to drop the pressure further between current location of PRV2 and PRV3. Do you think that will not help?

I will add WH expansion tank as well. It is not required here, but you make a good point. I definitely have some overflow from my side release valve that I wasn't sure why I was getting.
 

Reach4

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I was wondering about putting a pressure relief or a pressure tank/ thermal expansion tank) up stream off the PRV that seems to blow out pipes. Unfortunately the tanks I am familiar with are only rated up to 150 psi.

Yard hydrants are typically rated to a max of 125 psi. That would have given you a good pressure sampling port if it could take the pressure.

PRV to drop the pressure further between current location of PRV2 and PRV3
Makes sense to me.

When you blow a pipe, that has to give you an impressive water bill. :-(
 

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It may not be the PRV's. Have you changed any faucets or valves in the house recently? The PRV's are reacting to an increase in pressure caused by a decrease in flow. If you close a faucet too fast, the resulting pressure wave could travel through all three PRV's as they as in the open position when you close the faucet. Something like a solenoid valve on a washing machine, which are notorious for causing water hammer, could be the problem. If you close things in the house slowly, the PRV's will close slowly, and the pipe won't pop. A large expansion or pressure tank in the house would give the PRV's time to close when you close a faucet too fast. I don't know how large a tank you need, but I would use something with at least a 1" opening.
 

Fitter30

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Your system needs to design / mechanical engineer that deals with prv. Try talking to a manufacturer rep or tech. Have a 2" valve is great for design flow but someone opens a bath room sink faucet at 1 gpm regulator might not regulate correctly. Thats where two prv in parallel 2" and 3 /4" set just a different then you don't have a 2" valve slamming shut.
 

ballardFan

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No valve changes but I did add an irrigation system with automated valves at the same time I put in the replacement 600XL PRV to replace a Watts of questionable functionality (it was blowing by/off/making noise). The irrigation system is protected by an RPZ for what is worth.

And to @fitter30 I have seen those types of bypasses with different primary and secondary sizes. That could be a good idea. I need to find a pro - the equipment on this property is in the 10s of thousands just in pipe and fittings and regulation devices. The problem is it is on an island in the middle of the ocean without many engineering level water works folks.
 
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Fitter30

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No valve changes but I did add an irrigation system with automated valves at the same time I put in the replacement 600XL PRV to replace a Watts of questionable functionality (it was blowing by/off/making noise). The irrigation system is protected by an RPZ for what is worth.

And to @fitter30 I have seen those types of bypasses with different primary and secondary sizes. That could be a good idea. I need to find a pro - the equipment on this property is in the 10s of thousands just in pipe and fittings and regulation devices. The problem is it is on an island in the middle of the ocean without many engineering level water works folks.
A engineer doesn't have to see the problem if the info is correct they can fix the problem. Thats a better reason to start with a manufacturer and if they won't help maybe they can recommend someone. Guessing how to fix a problem can get expensive and still not work.
 

jadnashua

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Note that a PRV creates a closed system, so the pipe between the PRVs will be subject to pressure changes caused by temperature changes, too, in addition to the pressure from the elevation changes. If the valves in the end are holding, a PRV won't prevent the pressure from rising due to the temperature...do you have at least one expansion tank after the last PRV? When you try to push water back through a PRV, sometimes, the valve in it can make some noises if it is excessive. Some PRVs have a bypass valve in them, but that won't help unless there's someplace for the water to expand into if it gets pushed back.
 

Valveman

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but I did add an irrigation system with automated valves at the same time

This could be your problem. Irrigation valves closing too fast cause a lot of pipe breaks. Going from high flow to zero flow quickly when an irrigation valve closes, the PRV's are still wide open when the shock wave blows right back through them. I always look for what was changed before the problem started.

As for finding a engineer to help, good luck with that. Most of the people I knew who could solve this problem are either retired or long dead and gone. I can count on one hand the number of young engineers I know who "might" be able to figure this out. A lot of engineering firms call me with problems like this. The pool of experienced engineers is pretty low if they are calling an old farm boy like me to help figure it out. :)
 

John Gayewski

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I didn't read this whole thread but I'll give you some info to think about. Prv's have a minimum and maximum flow rates that need to be met or held down to. Your need to make sure the prv you put is is designed to do as little and as much as you need it to. The manufacturer will help you. I like caleifi for this they are good.
 

John Gayewski

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Never heard of Caleifi? Did you mean Cla-Val? If so, I agree and have names of a couple of good people there.
Calife (not sure that's spelled right) it's the largest brass manufacturer in the world. They recently have started pushing their north American wing harder. They are moslty hydronic focused, but they are a top Italian manufacturer and have been breaking into the plumbing stuff more and more. Their help department has some great guys that worked in the field for many years. I listen to their podcast. Ask caleifi
 
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