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HDPE Pipe Vacuum Problems

 
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Old 10-01-2010, 05:31 PM   #1
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HDPE Pipe Vacuum Problems


Hello,

Does anyone have experience with gravity flow water systems using HDPE (10") pipe?? I installed a 3.5 mile long line to bring water down to a golf course. It was to be laid in an existing water ditch (and not excavated). Engineer calculated a 10 inch would get us sufficient water (675 gpm). Seemed to work well the first year or two, but last few years has not been able to flow more than 500 gpm without the pipe collapsing due to vacuum. It seems like the pipe strength has diminished over the years. Pipeline was supposed to be a low pressuree pipe, not a vacuum pipe. Does anyone know what may be causing the problem or have heard of problems with hdpe like this??

Thank You in advance,

Mark
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Old 10-01-2010, 10:30 PM   #2
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Re: HDPE Pipe Vacuum Problems


Sounds like you have some type of restriction at the "head" of your pipe. If input falls short of out put, the water in the pipe will start pulling on the pipe itself. Sort of like breathing in air and then covering half of your mouth with your hand........your cheeks will collapse!!!

That's my guess

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Old 10-02-2010, 10:01 AM   #3
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Re: HDPE Pipe Vacuum Problems


Thank you. We have pulled the fish screen off and tested without it. It seems to make no difference. We did think that that may have the problem, but it did not test out. We think it has something to do with more friction loss than avaliable head pressure. We did raise the water level in the creek 2 feet (by building a raised dam), and did not see any changes in flow rate. This is puzzling. Thank you for the advice.

Mark

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Old 10-02-2010, 03:32 PM   #4
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Re: HDPE Pipe Vacuum Problems


What thickness is your pipe is it DR9 DR11 DR17? . Are there low areas where the gravity flow actually has to go uphill for short distances?. Any chance of buildup in the pipe such as scale or algae?
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Old 10-02-2010, 04:29 PM   #5
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Re: HDPE Pipe Vacuum Problems


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Originally Posted by shaper View Post
What thickness is your pipe is it DR9 DR11 DR17? .
This is a very good question. Maybe the engineer specified the wrong thickness.
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Old 10-02-2010, 10:54 PM   #6
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Re: HDPE Pipe Vacuum Problems


Interesting question. Since the pipe functioned as desired the first few years, and it was designed to be a low pressure system, not a negative pressure system, it seems your friction losses have become greater than anticipated in recent years. Most likely you're getting buildup of some kind on the interior of your pipe. Or maybe the water has some mildly corrosive properties.
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Old 10-05-2010, 08:53 PM   #7
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Re: HDPE Pipe Vacuum Problems


Quote:
Originally Posted by turfguy13 View Post
We did raise the water level in the creek 2 feet (by building a raised dam), and did not see any changes in flow rate. This is puzzling. Thank you for the advice.

Mark

Another 2 feet of head gets you less than 1 psi additional head pressure - not much there to measure.
Almost all the low pressure DR-11 HDPE sewers I've built have had a dual function air/vacuum air-release valve designed into them. That might be an easy fix for the issue. "Google" Apco, Crispin or Val-Matic.
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Last edited by PipeGuy; 10-05-2010 at 09:00 PM.
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Old 10-06-2010, 09:57 AM   #8
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Re: HDPE Pipe Vacuum Problems


Thanks for the input all. The pipe is DR 26, and was specified to be low pressure application. I now wish we would have used a much thicker pipe, however the bending of the historic ditch probably would not have accomidated the thicker pipe. We are able to break the pipeline open at every 1000 feet as we installed flanges. We have recently flushed the pipe with approx. 1500gpm to remove any sediment that may have gotten through the fish scree. There deos not seem to be any scale or sediment in the pipe.

Thanks again guys,

I am learning and all comments have been very helpful.
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Old 10-06-2010, 08:43 PM   #9
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Re: HDPE Pipe Vacuum Problems


Ok I'll throw my nickel in.

HDPE is negatively affected by sunlight, what those affects are I do not know.

However if you suspect that the pipe is being affected by vacuum that reduces the flow, would that also change the profile of the pipe?

Is it possible to monitor the pipe to see if it is collapsing and causing restriction?

I realize you have 3.5 miles of pipe, maybe there is a specific area that would be more prone to damage/subject to vacuum than the rest of the line.
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Old 01-26-2011, 12:46 PM   #10
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Re: HDPE Pipe Vacuum Problems


Being dr 26 I would say is a large portion of the problem. HDPE is not affected by sunlight like PVC is. What are you using to pull the vacuum? Why not push it with a pump instead?

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