Pressure regulator drop under modest flow

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by lifespeed, Oct 1, 2020.

  1. lifespeed

    lifespeed Member

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    I just replaced my Zurn-Wilkins 1-NR3XLDU 1" Pressure Reducing Valve as it was 12 years old and I wasn't happy with the pressure regulation. It would drop by as much as 10 psi from a 50psi set point depending on water flow. We're talking 2-1/2GPM from one shower, or 5GPM from two. This didn't really seem reasonable. Also, it would occasionally stick at higher pressure, so decided it was time to replace.

    I put in a new regulator, and while this one doesn't stick at the higher municipal water supply pressure (could be higher than 70psi), it still drops considerable pressure at what seems like very reasonable flow rates.

    The plumbing is a 3/4" municipal meter 20' from the house with a 1" main to the house, through a 7000SXT carbon filter, softener, and then 1" trunk all the way to the tankless water heater. Then 1" out of the tankless, branching off using 3/4" only necking down to 1/2" at the shower valves, or in the wall for small faucets, etc. The type L copper is 8 years old. The pressure drops regardless of whether the draw is inside the house (through the softener) or hose bibs (before the softener), causing me to suspect the regulator. At flows of 5GPM or greater it will drop from 50 psi down to 38-40psi. This doesn't seem reasonable to me, shouldn't the regulator maintain the set psi under benign conditions like 5GPM through a 1" pipe?
     
    Last edited: Oct 2, 2020
  2. Jeff H Young

    Jeff H Young In the Trades

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    Not nessesarily the regulator , what if that was a 1/2 inch line or the 3/4 was kinked or had a bunch of debris. pressure could still climb up but volume would be poor causing pressure loss. I cant tell you what an acceptable pressure drop would be. but it might have nothing to do with the reg.
     
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  4. lifespeed

    lifespeed Member

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    What if pigs had wings? Not sure what your point is regarding small, clogged, smashed pipes, which I made it clear is not the case. I've replaced everything all the way to the water meter.
     
  5. Reach4

    Reach4 Well-Known Member

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    You would like to have a pressure gauge, or a drain valve that can mount a garden-hose-thread pressure gauge, before the PRV. That would make identifying if the problem was at the PRV easy. If the valve before has a drain, I wonder if they make an adapter that could connect a pressure gauge to that drain.

    I would turn up the PRV to maybe 100 psi. (can you even achieve that pressure?) Watch the pressure as you draw maybe 5 gpm. If the pressure drops to about 45 or less, I would be thinking the problem is a restriction before the PRV.

    I see your pressure gauge uses a cartridge with a built-in screen. I don't know how you would clean that screen. I could guess. I am not a pro.

    You seem to think there could not be a restriction before the water meter.
     
  6. fitter30

    fitter30 Active Member

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    Check pressure at the hose bib both with and without flow (with shower on). If pressure drops more than a few pounds with flow pressure problem before prv. Between meter, prv, filters , shower head and valves could have a pressure drop of 20lbs. Check pressure at 2.5 gpm with 5 gpm shower is running compare with hose bib.
     
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  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    What kind of pipe and size runs from the house out to the supply line from the utility?
     
  8. lifespeed

    lifespeed Member

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    1" schedule K copper less than 5 years old. My plumbing is pretty new, and designed for good flow. Hence my dissatisfaction with the pressure drop.
     
  9. lifespeed

    lifespeed Member

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    I'll check the pressure drop upstream of the regulator after work.
     
  10. lifespeed

    lifespeed Member

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    Yes, that is what I think. But I will check.
     
  11. wwhitney

    wwhitney Well-Known Member

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    Best would be to simultaneously measure the pressure before and after the PRV, that would show the pressure drop attributable to the PRV, versus other components. What does the manufacturers spec sheet say is the expected pressure drop at 5 GPM?

    Cheers, Wayne
     
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  12. Reach4

    Reach4 Well-Known Member

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    Looks like about 3 psi typical, with about 5 psi at 10 gpm.
     
  13. Jeff H Young

    Jeff H Young In the Trades

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  14. lifespeed

    lifespeed Member

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    Today the municipal supply is at 68psi at the inlet to the regulator, 50psi at the gauge after the filter/softener with no flow. Flowing 7GPM from a hose before the filter/softener but after the regulator results in 64psi at the inlet to the regulator, 36psi after the softener where I have a permanent gauge mounted. So the filter/softener cascade didn't have any flow through it adding restriction and pressure drop, the gauge was just a static pressure monitor point after the regulator.

    As far as I can tell, this (brand new!) pressure regulator is garbage and doesn't meet published specs for pressure drop.

    Yeah, I can still take a shower at 36psi, but I'm kind of irritated with the poor performance that I don't think I should be experiencing based on a house plumbed with 1" main. I don't expect zero pressure drop, but 14psi below the setpoint at 7GPM seems far from reasonable.
     
  15. lifespeed

    lifespeed Member

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    Sorry about my curt response, I'm sure you encounter many people who haven't even considered the basics. In this case, the plumbing is 1" and in excellent condition as confirmed by the pressure readings at the inlet/outlet of the regulator at static and high flow conditions.
     
  16. Reach4

    Reach4 Well-Known Member

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    Check and clean the screen. https://www.zurn.com/products/repair-parts/water-safety-and-control/pressure-reducing-valve/nr3xl If that does not fix it, I would call the maker. That unit uses a cartridge, and they may just send you a new cartridge if you ask.

    On the other hand, if the city water is under 80, I would take the PRV out of the line.
     
    Last edited: Oct 2, 2020
  17. lifespeed

    lifespeed Member

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    "Flow curves are based on a 50 psi pressure differential"

    upload_2020-10-2_15-49-13.png
     
  18. lifespeed

    lifespeed Member

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    Yeah, take it apart and clean it is the standard response. Which I will do, although it has done this since I first installed it a few months back. I'm just now getting annoyed enough with it to try and do something.

    I talked to a tech at Zurn and they say it should still operate correctly with 14 - 18 psi overhead. I don't really want to allow uncontrolled water pressure into my house, as it can vary. And I have a couple automated hose bib valves that can bang pretty bad, even with 3/4" hammer arresters installed linearly opposed to the solenoid valve. My understanding is 50psi is about the max you want to run home plumbing at anyway.

    Are there better-performing regulators that can reliably operate 15psi below inlet pressure? I'm thinking this is just a design that doesn't work well under reasonable pressures available from a municipal supply.

    Edit: I ran their Excel spreadsheet calculator for the NR3XL. One of the fields is "allowable falloff (PSI)". As the allowable pressure falloff is reduced, it increases the recommendation for the valve size. The spreadsheet claims I'll get at least 10 psi falloff

    Also, they state: *Note: Falloff is typically acceptable in the range of 12-17(PSI)

    So, they're stating that 12 - 17 psi less than the setpoint is acceptable? The spreadsheet is recommending a 1-1/2" NR3XL model PRV if I want less than 5psi falloff at 12GPM, a reasonable max for my house.

    I don't think taking this apart and cleaning the screen or the cartridge is going to help, we'll see.
     
    Last edited: Oct 2, 2020
  19. lifespeed

    lifespeed Member

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    "High flow rates and low fall-off are the hallmarks of the Zurn Wilkins 500XL Series."

    Looks like I've got cheap homeowner crap with the NR3XL. A 1" 500XL series PRV is $220, while the 1-1/2" is more like $650!!
     
  20. Reach4

    Reach4 Well-Known Member

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    Turn the PRV down to 45 or 40? I understand this is not something you should have to do.

    AFAIK, nobody I know personally has a PRV.

    Some softeners have a diagnostic that tells you the max gpm through the softener since the last regen. I suspect you will find that number under 10.
     
  21. lifespeed

    lifespeed Member

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    Yes, this seems to be optional in many cases, and we know pipes can take a lot more than 50psi. But my plumbing seems to be quieter and better-behaved in the presence of solenoid valves (even with hammer arresters) if the pressure isn't too high.

    I'm not sure if mine displays max GPM, it may. But it wouldn't include irrigation. Regardless, even at a very-reasonable 7 GPM the regulator fall-off is not, in my opinion, reasonable. When two showers at 5 GPM drop from 50 to 40 psi, well, that is pretty sad. Then you flush a toilet and it drops to 36 psi. No scalding happens with my thermostatic shower valves, but that is just pitiful for the plumbing I installed. And it is all because of the PRV "fall-off".

    Zurn claims the 500XL is "high flow, low fall-off", but this difference isn't really shown in the graphs for the NR3XL vs. the 500XL. But the NR3XL doesn't come close to meeting their published specs.
     
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