Open System acting like a Closed System

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Adam August

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The water system for my home is an open system; i.e. no backflow directly after city main connection. I bought the house ~1.5yrs ago; built in the 70's in Oregon.

We had no issues with pressure fluctuation over the first year of ownership.

This summer I installed a sprinkler system and tied in to my water line in my crawlspace. I tied in to the supply line running to my water heater, about 10ft away from the water heater. I tied in to the 3/4" copper line with a sharkbite 3/4" copper to 1" PVC Tee (my sprinkler line is 1" PVC).

I get the obvious pressure drop when my 1" sprinkler line is opened up, but I have had another unexpected occurrence.

My system is building up pressure after sufficient depletion of my water heater tank (i.e. clothes washer, dishwasher, or shower); enough to make my water heater pressure relief valve go off (I replaced the pressure relief valve just to make sure it wasn't bad, didn't help.)

You can also notice the system pressure when running the kitchen faucet, shower, etc.. immediately after the tank has filled and heated up. High pressure for a brief moment, then back to normal again after the excess pressure is released.

I have no idea what could be causing this... I thought maybe my backflow for my sprinkler system wasn't working properly and somehow pressure was building up back in to the home system, but I've had a shutoff valve to the sprinkler system closed for a couple months now and still have the same issue (I also had the sprinkler backflow inspected).

The only thing that is different is there is a Tee running off the copper supply line to a 1"PVC for about 10ft then it hits a (currently) closed shut off valve...

Any help/ideas would be appreciated!
 

Reach4

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You said city. Many places are putting in water meters that have a check valve, and that makes the house a closed system. Find a thermal expansion tank calculator or table to make sure you get a tank that is big enough. Set the air precharge at, or 1 or 2 psi higher than the city water pressure.

I tied in to the 3/4" copper line with a sharkbite 3/4" copper to 1" PVC Tee
I tried to find a reference to that part on Sharkbite.com, but I did not succeed.
 
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MACPLUMB

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What Reach4 posted the City's are required to install these backflow by the EPA and Clear Water Act,
a lot of homeowners are adding sprinklers or other water devices Without Installing the proper Backflow,
so the city probably added this about the same time as you added your sprinkler, So you need a
thermal expansion tank you can always Google thermal expansion, also this voids your water heater warranty if
not installed,
 

Jadnashua

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The utility can put a check valve in more than one place...it may not be in the house, but it sure sounds like you have one. FWIW, it doesn't hurt to have an ET in the system, regardless, as eventually, if you don't have one now, you're likely to get one in the future.

Depending exactly how your backflow preventer device is plumbed...that would make at least that branch, closed.
 
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