I have a stupid question about flow rate

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Giovannip, Feb 11, 2021.

  1. Giovannip

    Giovannip In the Trades

    Joined:
    Jul 9, 2019
    Location:
    Orange county, CA
    Hey everyone,

    I have a small plumbing shop in southern CA.

    Regarding single family detached residence . Municipal city water supply, no well water involved.

    I keep noticing inch and a quarter pressure regulators installed from the builder, BUT the water meter is only 1 inch.

    I have also seen 1" regulators and main shut off valves attached to the home with 3/4 water meters.

    Isn't the total overall available flow rate dictated by the source ?
    Seems simple to me.

    If the flow from a 1" meter is X at X psi then upsizing the pipe from the meter to the home can't produce additional volume. ?

    It may reduce working volume at a fixture, but static pressure would still build to capacity and be whatever the city pressure is at the regulator and whatever the set pressure is after the pressure regulator.

    I'm thinking that the Municipal water department installs the meters sometimes well before the developer builds the tract, but it doesn't seem to make sense to use larger more expensive material than the meter supply itself.

    What started this ponderance is why go purchase an 1 1/4 regulator when I can get a Wilkins 1" 70 for half the price if the meter is only one inch?

    I look forward to the opinions and education if I am missing something.

    Thanks
    Giovanni
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Look at the pressure drop graphs vs flow rate.

    https://www.zurn.com/media-library/web_documents/pdfs/specsheets/reg-70xl-pdf
    Looks like the 70 only loses about 4 psi with a 10 gpm flow rate, however.

    If you compare the 3/4 on that graph to the 1 inch, you might see a similar relationship between a 1 inch and a 1.25.

    One inch water meters are a premium many places. 3/4 and even 5/8 inch meters often drive 1 inch pipe.
     
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  4. kreemoweet

    kreemoweet In the Trades

    Joined:
    Sep 7, 2009
    Location:
    Seattle. WA
    No, every part of the pipe system will influence total flow rate. When you say "the flow rate from a 1" meter is X at
    X psi", you fail to consider that the "X psi" is determined by BOTH the upstream piping and static pressure, and
    the downstream piping (which will in turn influence the pressure at the meter discharge). In other words, the "X psi"
    is a pressure difference, not just the upstream static pressure.

    The regulator specs should indicate pressure drop at various flow rates. Undoubtedly, the 1 1/4 device will show lower
    pressure drops.
     
    skoronesa likes this.
  5. skoronesa

    skoronesa Member

    Joined:
    Feb 7, 2021
    Location:
    East Bumfuk, Mississippi
    My understanding, something heard long ago, was that meters were always "undersized" to increase the velocity of the water through the meter for accuracy purposes. The meters being the "least accurate" at lower flow rates aka they could under count your usage. I have also had a water company employee tell me that they weren't allowed to upsize specifically for accuracy reasons although he didn't understand why.

    In my area, for standard residences, the meters are almost always 5/8" even if the line is 3/4" or 1".
     
  6. skoronesa

    skoronesa Member

    Joined:
    Feb 7, 2021
    Location:
    East Bumfuk, Mississippi
    My understanding, from something heard long ago, was that meters were always "undersized" to increase the velocity of the water moving through them for accuracy purposes. Meaning they were "least accurate" at low velocities aka flow rates. I have even had a water company employee tell me they weren't allowed to upsize meters for accuracy reasons, although he didn't know the reasoning behind it.

    The technical term for the mechanism that measures the flow is "Nutating Disk". They are extremely hard, ceramic discs which are caused to "nutate", not rotate, when water flows through/past them.

    In my area, standard residences always have 5/8" meters even if the line is 3/4" or 1". At the 80-120psi which is common this is more than sufficient even when paired with a prv that matches the line size(3/4" prv on 3/4" line).

     
  7. fitter30

    fitter30 Well-Known Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    I you look at that zurn link that Reach4 posted. Fall off pressure is the difference between shut off pressure and flow pressure. Between the 3/4 and 1" @ 5 gpm theres only .75# difference and at 10 gpm 1.25#. Unless your using 20 gpm most houses couldn't tell the difference.
     
    skoronesa likes this.
  8. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    pretty normal to have a smaller meter. I dont know about accuracy . but flow is good

    Beside putting small meter they put a small service to meter so upsizing meter dosent help a lot either with out coughing up big bucks to get that up sized as well. they dont run an 1 1/2 line to a curbstop just incase customer needs are greater.
    I think its about meeting the basic needs of most and costs of material and labor if some one needs bigger they can pay for it .
     
    Last edited: Feb 11, 2021
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