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We have a Zurn NR3XL PRV that's less than 3 years old, but according to the plumber that was here recently it's gone bad. His reasoning was hooking up a water pressure valve to the spigot, and it read like 125psi. I had mentioned it had been turned all the way up to max allowable pressure during installation by the same company (and later the adjustment screw was turned 100% tight clockwise by a different contractor doing a bathroom remodel that forgot to adjust back and it needed backed out). The current plumber last week stated it doesn't matter; the operating max pressure is 75lbs, so even if fully adjusted to max PSI it still shouldn't read that high.

That does make sense, but I had to see myself as the PRV isn't old. I got a water pressure tester and prior to adjusting it back out, I took this reading (BTW I opened spigot to let run, then shut off, then placed valve to read as Zurn recommends to let initial pressure flow). Indeed too high: measured around 115psi. enter image description here

Next I backed it out several turns (like 10-15). Took a new reading and now I was seeing much lower as expected around 55psi.

enter image description here

I screwed it back in as that's a bit low for the house and now it's around 65psi.

enter image description here

So the adjustment seems to be working as expected. What I wonder is if the adjustment screw is fully tightened maybe the valve acts as a pass-through letting supply side sigh pressures straight through and this is normal behavior? Or was the plumber correct in that no matter how much the adjustment screw is tightened down on the PRV, it should never allow more than 75psi, indicating some sort of failure? I've already bought a replacement (figured out correct part from this post here), but it's silly to be to replace it if this is all expected behavior and the fact that the pressure is way down since I adjusted it back out, maybe I do not need to replace the PRV?

Looking at the behavior is this all normal and no need to replace the PRV, or is the fact it initially was so high a concern and I should change it out? Also as an aside the red needle would spike only initially when turning on the spigot initially but never consistently was that high, inquiring if that's normal too?

EDIT:

Here are the pressures at various times over the last 48 hours. Notice there is a bit of fluctuation. I know the PRV isn't responsible for an keeping an exact finite psi value but some of this seems kind of wide. Is this an indication of a failed PRV? Also looked into thermal expansion but the tank is practically brand new.

55psi enter image description here

90psi enter image description here

80psi enter image description here

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    If you can do without the hose for a bit, set the red needle down at the current reading and leave it in place for a day or two to see what sort of excursions you get when in use. Also look at it (since there isn't a "low saved reading" needle) while water is in use inside the house. Personally, I'm the sort of person that would have a permanently mounted gauge on both sides of the regulator ;^) But you're avoiding replumbing.
    – Ecnerwal
    May 11, 2022 at 23:04
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    Depending on your hose valve and how you're opening your hose valve, the inital spike might be essentially water hammer. The 1/4-turn sillcocks (I have them, with ceramic disc valves) will certainly promote that. You can try opening it veeeerrrry slooowwwlllyy.
    – Ecnerwal
    May 11, 2022 at 23:11
  • Yes that's what I did. If I open it slowly, it doesn't spike at all. Basically stays in step. If I turn on abruptly it will spike. So you're saying that's expected correct?
    – atconway
    May 11, 2022 at 23:41
  • Yes, that would be expected.
    – Ecnerwal
    May 12, 2022 at 2:01
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    Given you have the new valve on hand, perhaps try swapping it in to see if it behaves better. Dirt or damage on the sealing bits can cause pressure to rise - the pressure dropping with no known water use is a bit odd. It's not what I'd expect to see from a happy regulator, but I admittedly have a well system that does not actually use one of these, so my regulator expectations are based on welding gasses that may be better regulated?
    – Ecnerwal
    May 16, 2022 at 18:10

2 Answers 2

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+50

I'm inclined to await results, a bit, but I'm also very unimpressed with the plumbers you have been sent from this company, and hope you can find some more competent ones, from a different company.

If the regulator was cranked tight (by somone who should not have a plumbing license or plumbing job, and certainly was not following the instructions) then it can't regulate, which your second person posing as plumber should have known. But hey, they wanted to charge you $500 to replace a $65 thing that might not even be broken, which they misadjusted. Motive is not looking good for truth...

A regulator works by having a valve which can be closed by water (or gas, they are similar) pressure pushing on a diaphragm against a spring. If the screw is loose and the spring is extended, it doesn't take much pressure to close the valve. If the screw is tighter and the spring is more compressed, it takes more pressure to close the valve.

If the screw is cranked and the coils of the spring are touching each other, there's no "spring" in the spring and the diaphragm can't move, so the valve can't close. No close, no regulate.

So, as you suspect, the regulator does not regulate. The maximum pressure marking is for "the range of adjustment provided by the spring" and if you adjust well past the point where the spring can move, then indeed it will just pass through.

Here's a diagram from the instructions linked above that shows the screw, spring and diaphragm (in this case part of the "cartridge assembly," from reading the instructions) (from the replacement parts kit) which is as close as I can find at the moment to the cutaway view I was hoping to find for you.

Image snippet from document linked above

And as discussed in comments, if you can keep the initial pressure spike down by opening the hose valve very slowly, that's just from water hammer (the inertia of the water in the pipe suddenly moving towards the gauge as the valve is opened quickly, then suddenly slamming to a stop since the gauge is a closed end tube.) Nicer gauges may include a "snubber" (basically a tiny orifice) to prevent/reduce that. But it's of no concern if just being slow when opening the valve makes it not happen.

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    I would seriously consider making a complaint to the (usually state) licensing board for plumbers in your area...
    – Ecnerwal
    May 12, 2022 at 12:05
  • Specific to the history I updated the OP. The company that installed (and was currently diagnosing) set originally to max allowable pressure. It was another general contractor doing a bathroom remodel that adjusted fully and forgot to back out (or tell me to do it). So the original company didn't tighten fully. Regardless the situation remains the same, just the history updated on who did what. And yes... that general contractor wasn't the best plumber.
    – atconway
    May 12, 2022 at 19:43
  • I'm collecting data per your suggestion - the gauge has been on for 24 hours. I'll update soon with historic measurements. Thus far I'm actually seeing a drop in pressure from 80psi to 55psi currently yet nobody is using water. All I'm trying to isolate with this post is a faulty PRV or not. This house always had nuanced pressure and that's why I voluntarily had the PRV replaced in the 1st place 3 years ago to try and fix it.
    – atconway
    May 12, 2022 at 19:46
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I believe that the plumber who told you that the maximum output pressure from the Zurn NR3XL was wrong. I say that as a non-plumber who made that same mistake. The pressure reduction range of the NR3XL has a maximum of 75 PSI. So when you turn the adjustment screw clockwise to its maximum setting, your water pressure will match the incoming water supply pressure. As you move the adjustment screw counterclockwise the pressure will drop up to a maximum drop of 75 psi. So, for example, if the incoming pressure is 125 psi, the lowest you will be able to set your pressure is 50 psi.

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