Pressure fluctuation in PEX?

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DTAZ

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How much daytime to nighttime pressure fluctuation can I expect in a PEX system? I've got about 130 ft of 3/4" under 100 psi test and don't have a sense of how much variation I will see. I'm in Tucson so there's about a 30º swing from day to night...

Thanks!
 
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CountryBumkin

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I doubt anyone can tell you without you providing "specific pipe or water temperatures", the temperature change over time (constant change or variable), etc. Perhaps you take a temp reading of the water at the coldest and hottest times of the day.
Is the PEX sitting out in direct sunlight now, or installed in your house?
 

DTAZ

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I doubt anyone can tell you without you providing "specific pipe or water temperatures", the temperature change over time (constant change or variable), etc. Perhaps you take a temp reading of the water at the coldest and hottest times of the day.
Is the PEX sitting out in direct sunlight now, or installed in your house?

Thanks for the reply. I think it answered my question. The PEX is installed in the house and pressurized with air to 100 psi. It's a hybrid system with PEX and copper. Everything is covered and indoors. I'm getting about a 1 psi fluctuation day to night but the system holds steady pressure between the day and night readings. That's with about 130 ft of material (PEX only not including copper) installed. Daytime highs 105º and nighttime lows around 78º.
 

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Jadnashua

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Is the Zurn stuff pex-A? Type -A is more flexible and could stretch a slight bit more than types -B or -C.
 

DTAZ

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Zurn PEX is PEX B.

Got it. Thanks. Six days out and holding a pressure test with a +- 1 psi bounce from day to night - depending on the temperature swing. The pressure fluctuation seemed a bit more pronounced at the beginning but has now settled down to the barely perceptible range.
 

Reach4

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You certainly have gone above and beyond normal pressure testing.

Is there a thermal expansion tank in your system? If so, that would have a big effect in damping down the pressure excursions.
 

DTAZ

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You certainly have gone above and beyond normal pressure testing.

Is there a thermal expansion tank in your system? If so, that would have a big effect in damping down the pressure excursions.
No expansion tank. It's not a closed system. Just potable water. As for normal pressure testing, I don't want leaks. My grandfather was a cabinet maker and welder of the highest order. He drilled the "do it once" mode of work into me. Hence, I frequently cannot afford people who will do work the way I want it done. It's sort of a curse.
 
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