main water pressure question

Discussion in 'General Plumbing Help' started by pmn, Nov 20, 2018.

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  1. Nov 20, 2018 #1

    pmn

    pmn

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    I have an problem with ver low flow at a bathroom most distant from my hot water heater. The hot water is barely flowing in the shower and the sink. In fact, I feel like most of my facility is suffering from low flow except possibly the urinal. I put a gauge on the shower head, it reads 38 psi. I also put a gauge in the 3/4" supply line to the (new) hot water heater - it too reads 38-40 psi. I then put a gauge on line right after the water meter which is as close as I can get to the street. With no water flowing, it reads a static 58psi. If I flush the toilet which is closest to the water meter, it drops to 48-50psi and stays there until the toilet stops running. Is 40 psi at the shower head normal? Is the 10 psi drop on the main from one toilet flush indicative of a FLOW problem rather than a PRESSURE problem? I'm going to call the city and ask them to take a look at their valve but wonder what others think about this. The state code information I can find says that 40 psi should be OK but it sure seems low to me.

    Thanks!
     
    Last edited: Dec 4, 2018
  2. Nov 20, 2018 #2

    havasu

    havasu

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    It seems low to me as well. Can you go to a spigot outside, preferably as far from the PRV as possible and measure this?
     
  3. Nov 20, 2018 #3

    pmn

    pmn

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    Thanks for the reply! The only outside spigot is on the same wall as the meter - about 2 feet away :-(
     
  4. Nov 20, 2018 #4

    havasu

    havasu

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    Is this a house or mobile home? What type of plumbing do you have (Galvanized, CPVC, copper?) Many cities offer free replacement of the PRV's, so that would be your first call.
     
  5. Nov 20, 2018 #5

    pmn

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    It's a small commercial office, has copper pipe. 3/4" copper supply to the water meter, 1" copper going to center of building where it then branches off to various places including the water heater which is a 3/4" copper line.
     
  6. Nov 20, 2018 #6

    havasu

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    With what you have just typed, I'd call the water department who may either adjust or replace the PRV.
     
  7. Nov 20, 2018 #7

    Diehard

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    I retracted my comments once I saw the additional comments.
    You have a pressure reducing valve(PRV)?

    Static pressure readings at the shower or water heater don't help. It's the flowing pressures(residual pressure) that should be evaluated. The only thing that static pressure readings at different locations within the bldg tell you, are the difference in elevation.

    With a 10 psi pressure drop while flushing a toilet, I assumed no PRV.
     
    Last edited: Nov 20, 2018
  8. Nov 20, 2018 #8

    pmn

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    There is no pressure reducing valve that I know of unless it is out at the street. Definitely not one inside the building.

    There is a backflow valve, it just recently passed inspection by Koorsen. I have called the water company to schedule a visit by one of their techs.
     
  9. Nov 20, 2018 #9

    Diehard

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    You may not get this far but for your info, I would record the pressure loss at the meter when flowing the maximum gpm possible from a nearest spigot or faucet from the meter. Once we know that, we can calculate what should be available at different fixtures.
     
  10. Nov 22, 2018 #10

    ExtraMilePlumbing

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    I believe 40psi is the minimum citys are required to provide.i would start taking off aerators
     
  11. Nov 22, 2018 #11

    Diehard

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    "The City of Dallas provides water to all services with a minimum pressure at the water meter of 25 pounds per square inch (psi). The State of Oregon has set a minimum pressure standard of 20 psi for public water systems. Most homes receive water at a pressure between 35 and 85 psi."
    No aerators on showers.;)
     
  12. Nov 23, 2018 #12

    FishScreener

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    Those sound more like fire flow pressures, and not normal delivery pressure at the service. Which is normally 35 to 85-psi.
     
  13. Nov 23, 2018 #13

    Diehard

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    Totally agree with you!
    Of course, I just found that info on a web search. It was probably quoted out of context.
    I know 20 psi is typical minimum for fire flow under all conditions.
    I have been at isolated cases here in Mass. where due to various and/or unusual conditions town pressure was so low at the house we had to install a pressure booster system. Definitely not common.
     
  14. Nov 23, 2018 #14

    pmn

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    I pulled aerators and also removed the showerhead completely. Same.... Hoping I don't have to put a pressure booster system on it. :(
     
  15. Nov 23, 2018 #15

    Diehard

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    A static pressure of 58 psi isn't that bad if the fall off pressure isn't too bad.
    In order to get an idea if the city supply has a problem once it gets flowing or whether your piping is restricting the flow vs pressure, you should check the pressure at the meter again with a flow rate that is measured(called the residual pressure). That is, a GPM reading. Get a 5 gallon pail or equivalent and time how long it takes to flow a specific amount of water. Record the pressure while flowing as wide open as convenient. Same idea as what you did with flushing of the toilet except you should get a flow rate, in GPM(gallons per minute).
    Once we have that info, we can extrapolate what types of flow and pressure you should expect at various locations by looking at the the elevation differences and what the friction losses SHOULD be. Hopefully we can closely estimate if the problem is in your piping and/or with the city's supply.

    EDIT: BTW...You had mention calling the water company to schedule a visit by one of their techs. Did that happen yet?
     
    Last edited: Nov 23, 2018
  16. Nov 24, 2018 #16

    pmn

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    The water company can't get a tech out until next week. :(
     
  17. Nov 24, 2018 #17

    Diehard

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    Chances are he likely wouldn't have been able to help.
     
  18. Nov 24, 2018 #18

    ExtraMilePlumbing

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    booster pumps require lots of maintenance especially if running 24/7
    I would recommend upsizing water main 2 sizes minimum to see if that helps
     
  19. Nov 24, 2018 #19

    Diehard

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    I believe finding where the problem is should come before arbitrarily replacing pieces of the system. But that's just me.
     
    Last edited: Nov 24, 2018
  20. Nov 24, 2018 #20

    mike fiore

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    depending on bacfklow preventer youll automatically loose anywhere from 5 to 10 psi. even in working order.
     

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