How much expansion should I see when my HW heater is running?

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TCP

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So I installed a PRV today and bumped the pressure down to 50psi. I also precharged the expansion tank to 50psi before filling the system. When the HW heater is running the pressure climbed to 60psi. Now my PRV has a 10psi backflow feature, meaning if the pressure is 10 psi greater than what it is set to it will back flow. So now I dont know if the expansion tank is doing its job. How much climb in pressure should there be with a properly set expansion tank?
 

Jadnashua

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If the ET is properly sized and functioning, you don't normally see a pressure rise when heating water.
 

Reach4

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The rise can be considerable. I would not be alarmed to see 100 PSI. It depends on how big the WH and how much temperature rise there is between cold and hot. It also depends on the size of the expansion tank. I would not be surprised to hear that you see a lot more rise when you use more hot water, and then stop using water.

If you use a little water, such as flush a toilet or get a glass of water, that could remove enough water to make the rise much smaller.

http://www.engineeringtoolbox.com/expansion-tanks-d_885.html is the non-simple version.

Now my PRV has a 10psi backflow feature, meaning if the pressure is 10 psi greater than what it is set to it will back flow.
Are you saying that it pushes the water back to the city water pipe? In that case, that would require the pressure to be higher than the city water pressure. If you are saying there is a port to release water to a drain, then it could work as you described.
 

TCP

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Yes its properly sized (I'm in the middle of the table/chart on the box so I'm not maxed out) and the air pressure is the same as the line pressure after the PRV. Watts Det-5 50 psi, 50gal tank and hotwater tank on lowest setting. I'll see what else I could be missing.
 

Reach4

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Yes its properly sized (I'm in the middle of the table/chart on the box so I'm not maxed out) and the air pressure is the same as the line pressure after the PRV. Watts Det-5 50 psi, 50gal tank and hotwater tank on lowest setting. I'll see what else I could be missing.
You are missing being pleased with your install, which you should be congratulating yourself on -- not fretting.
 

TCP

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You are missing being pleased with your install, which you should be congratulating yourself on -- not fretting.

Actually after rereading it, you are right it only backflows if its 10 psi higher than SUPPLY pressure not set pressure! Now I just have to figure out how to stop the water hammer on the high side when my sprinklers go on and off. It spikes and pins the gauge.


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