PRV, Expansion Tank, pressure gauge question

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Reach4

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Did I do it right? Why would a new ET go down to 29 PSI so soon?
  • Defective tank.
  • Leaky Schrader valve, and no good tire stem cap on the Schrader valve.
  • You set the pressure while the water pressure was non-zero.
Always measure and change the air precharge with the water pressure zero. The right precharge is the same as the PRV setting. Put the valve cap cap on after filling.


I would consider upgrading to a Therm-X-Trol expansion tank if this new tank is actually failing.
 

JoeSD

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  • Defective tank.
  • Leaky Schrader valve, and no good tire stem cap on the Schrader valve.
  • You set the pressure while the water pressure was non-zero.
Always measure and change the air precharge with the water pressure zero. The right precharge is the same as the PRV setting. Put the valve cap cap on after filling.


I would consider upgrading to a Therm-X-Trol expansion tank if this new tank is actually failing.

It was #3 on your list I believe that did it. The tank seems to be working properly again. After showering the WH runs for a good while (I have it set to hot) and the PSI rises from 67.5 to 77.5 on the gauge. Is that acceptable?
 

jadnashua

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There are calculators you can find on the web that will calculate the pressure changes based on the volume of the tank, and the amount of water that tries to move into the ET. That last part you can get from an ET sizer program. Or, you can look up and run the calculations yourself! Easier to use someone's calculator! As long as it stays below 80-psi, to me, it's okay. I expect the system to keep the pressure within the design parameters, and code say no more than 80. Yes, plumbing devices are tested to a higher pressure than 80 (a WH is tested to 150psi), but the more pressure you exert on things, the more stress you're applying. Some hoses don't like it nor do most gaskets, seals, O-rings.

60psi is what many things like showerheads are designed for, but they will work at different pressures, but the volume they pass and how the showerhead feels will change. Some places would be thrilled with even 30-psi. When I lived in the middle east for awhile, we had an open, atmospheric tank on the roof, and it was all gravity fed at 0.43#/foot of elevation change...you got used to it. A water tanker came by periodically and refilled the tank for us.
 
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Reach4

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The tank seems to be working properly again. After showering the WH runs for a good while (I have it set to hot) and the PSI rises from 67.5 to 77.5 on the gauge. Is that acceptable?
Quite acceptable! 110 would have been acceptable, but there would have been one objection to that. ;)
 

JoeSD

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Quite acceptable! 110 would have been acceptable, but there would have been one objection to that. ;)

Thank you! Is 67.5 PSI an ok setting for 24/7 on the PRV? I would set it lower but our sprinkler systems are behind the PRV and the heads don't like to pop up and work properly if the PSI is set too low.
 

Reach4

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Yes.
My point was that if the thermal expansion tank doesn't keep the max pressure down under 100, no problem. That is how they are normally sized.

But no problem setting your PRV to 67.5 or 70 psi.

Some of the thermal expansion tank sizing programs take the PRV setting into account when choosing the minimum thermal expansion tank size. https://tools.watts.com/ETP/ is one of them. It calculates to keep the max thermal expansion pressure below 130 psi (IIRC), which is plenty low enough to keep the T&P valve on the WH from weeping.
 
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