Prv confusion

[RonL1]

I have an apollo prv installed and I have a question on what the pressure guage should read while water is in use and not in use,
Normal house pressure from well is 40-60. I want the outlet to be 15 psi (goes to my geothermal) when water is not flowing, the guage will read house pressure, but when flow starts, it will drop down to between 14-16 at low house pressure and slowly increase to almost 20 psi at high house pressure. Shouldn't it be stable when flowing and even when not flowing ?
And why would it go up to whatever the house pressure is when the water stops flowing ?
It seems like it should remain down in the 15 range.

 

[Reach4]

There should be a thermal expansion tank downstream of the PRV. Set the air precharge to 15 psi.

If pressure continues to rise after adding the thermal expansion tank, replace or repair the PRV.

 

[Sponsor]

 

[RonL1]

There is never an increase due to thermal expansion, I would see that in the house pressure rising. The prv has always acted this way. In order to set the pressure I want on the exit side of the prv, I have to have the water flowing, and then set it. Once I stop the flow, the pressure immediatly rises. I've always thought a prv is suppose to limit the exit pressure regardless if it's flowing or not.
In order to get the 15 psi I desire, I have to set the pvr while the water is flowing, this seems incorrect.

 

[Reach4]

I have to have the water flowing, and then set it. Once I stop the flow, the pressure immediately rises. I've always thought a prv is suppose to limit the exit pressure regardless if it's flowing or not.

That would suggest to me that the PRV has some pressure drop due to flow. I would think we could model the PRV as a perfect PRV in series with a resistance.

See https://apolloflow.com/wp-content/uploads/2023/09/ss-69ELF-PRV.pdf and see the yellow line on the graph. If I assume a 1/2 inch PRV and a 5 or 6 GPM flow, that would seem to match your observations.

Does the static pressure when there is no flow really matter, as long as there is not a relief valve opening?

 

[RonL1]

Well, what I'm trying to accomplish is a 4.5 gpm constant flow when the flow valve turns on. Any variable in incomming pressure will change that flow.
I have to turn the flow on, adjust the prv to 15, then adjust the variable flow valve to 4.5 gpm. Now, as the house pressure rises from 40 up to 60, the prv exit pressure will slowly rise from 15 to 20, thus making the flow rise from 4.5 to 5.5.
i thought the prv was defective and replaced it, but the new one was the same.
but the odd part, is when the flow stops the prv exit pressure will immediatly go up to whatever the house pressure is currently at.

 

[Reach4]

This makes sense. As the incoming pressure rises, the friction drop in the PRV does not rise much.

To accomplish a 4.5 GPM constant flow when the flow valve turns on, here are three ideas:

1. Put a flow regulator (Dole valve) in series with the flow. https://mathewsdenver.com/product/dole-valves-12-flow-regulator/ lists a 4.5 choice. I did not look a lot of places, so do more looking. These are not perfect, but should make things much more constant when after your PRV. See characteristics on https://fergusonprod.a.bigcontent.io/v1/static/295797_5055985_specification Note that page does not list a 4.5 GPM Dole valve.

2. Use a bigger PRV. You will see that the bigger PRVs will hold regulation better in the face of changing incoming pressure changes. Look at the graph. This is not my favorite at the moment; #1 and #3 seem better.

3. Put another PRV in series. Present your second PRV with say 22 PSI. So the incoming pressure to the second PRV will be much more consistent.

 

[RonL1]

Thank you for the ideas, I had a 5gpm dole valve, (before i had the prv), and it was terribly noisy. And I had thought of a second prv too. But the prv always confused me (as to setting it)
But you have helped giving me options.
Thank you.