Is this normal pressure behavior for this Zurn NR3XL PRV?

Question

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.

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.

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

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

90psi

80psi

Answer 1

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.

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.

Answer 2

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.