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Old 02-18-2010, 03:34 AM   #1
tranelch
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Default Water Meter Going Backward

Shortly after finishing construction on our new home, the utilities company called to question our meter reading. Through experimentation with the department of public works, we discovered that sometimes when the outdoor spigots (water only meter) were running, the indoor meter (water and sewer) would turn backward. We never had air in the pipes, so we concluded that the meters were installed so close to the supply "T" (see attached photo), the turbulence was causing the meter to turn backward (in addition, if water was actually flowing backward, it would have to go back through the meter and would cancel out the backward flow). When I relayed our conclusion to our plumber, he responded that:

Quote:
The check valve will actually be installed on the vertical pipe before it tees off...This is something that is not covered under our warranty because there is absolutely nothing piped wrong. ...The negative static pressure is not related to the plumbing system, but instead is caused by the city.
That just didn't make sense to me (the negative static pressure comment, if I understand it correctly, would suggest that the head pressure is pushing harder than the supply to the house when the outdoor spigots are running--we know that water is not flowing out through the meter), and I was not convinced that paying to install a check valve on the supply before the "T" would solve our problem. I then asked another local plumber to have a look at it. He agreed that the meters were too close to the "T"

I am wondering if the unbiased folks on this forum could break the tie and share there opinion on what is likely causing our meter to run backward.

Thanks in advance,
Chris


meters.JPG  
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Old 02-18-2010, 01:36 PM   #2
tbart16
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wow that is crazy! I would install a check valve between the tee and the reversing meter. Good luck



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Old 02-18-2010, 02:12 PM   #3
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Very strange situation. The Water company I worked for had geared meters that could not run backwards. If your meters allow reverse movement, you need two check valves, one installed before each meter. One, on the vertical pipe will not deter the situation.

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Old 02-18-2010, 03:11 PM   #4
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It is piped improperly.

Those meters are installed in a "series" and should have been installed in "parallel".

The flow rate from your irrigation system is so great it is causing turbulence and turning the gears of the meter. If the meters were piped parallel instead of in a series the flow would not even be close enough to do so.

The simplest fix is to install vented dual check between the two meters. This will allow any back flow or turbulence to be mitigated before it can affect the "main" meter.

I would also be sure your back flow preventor on your irrigation system is installed and working properly. You do not want to drink your irrigation water, and these systems are tied together in such a way that it would only take a small loss in city water pressure to create a backflow scenario. The ASSE recommends a RPZ (reduced pressure zone valve) in your situation.
sourced from the ASSE Residential Cross Connection Manual 4th Edition 2008

p.s. It's been my experience that metal clamps on plastic pipes are a bad idea. They expand and contract at different rates and can cause cracks. And I hate to nit-pick the guy, but why would you put a galvanized tee in between all that copper and brass. For three or four more dollars he could have used a brass tee and saved a future corrosion issue.

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Old 02-19-2010, 02:57 AM   #5
tranelch
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Default Thank you

Thanks for the detailed feedback everyone. It has been a crazy experience--I think the utilities company thought I was tampering until they saw the meter turn backwards themselves. If anyone else reads this, I would welcome more opinions as well--I have gotten such a wide variety of opinions, it would be nice to get closer to a consensus.

Chris

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Old 02-19-2010, 02:34 PM   #6
majakdragon
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The only way to solve the problem is to isolate the meters from each other. The easiest way to do this is with check valves. This prevents flow to the unused meter while the other one is operating.

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Old 02-19-2010, 10:20 PM   #7
SilverBack4Jack
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Definitely check valves before each meter. NOT just on the vertical line. 2 check valves not 1.

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Old 02-20-2010, 05:45 AM   #8
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I dont see how it could pull water from the source and also through the other meter,unless you have a booster pump on one system and/or an open faucet or a leak on your other system.Two check valves (one on each system) would be a good starting point ,and that would prevent cross connection contamination caused by backflow from your irrigation or hose bibs.

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Old 10-25-2010, 04:34 PM   #9
meterman
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Default water meter running backwards

Hello i have been installing water meters for over 20 years i believe that your meter has been installed backwards by the meter installer.

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Old 10-25-2010, 06:03 PM   #10
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I wouldn't be concerned, unless you were responsible for the installation of the water meter. My water company recently told me my meter had frozen up, and they needed to replace it. I asked how they would measure the previous month when the meter was frozen, and he said they would just use the average for the last 2 years. I sure wish I would have known this earlier because I would have had the greenest lawn and fresh water in the pool. Damn!



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