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Water flow through pipe

LarryC_4
LarryC_4 Member Posts: 3
What is the discharge pressure?

I'll give you one flow rate, at 95 psi discharge, flow rate equals 0 gpm.

Larry C

Comments

  • Edward A. (Ed) Carey_3
    Edward A. (Ed) Carey_3 Member Posts: 236
    Need help with a water flow question

    I need a chart or formula to estimate the approximate flow of water in GPM through a 3/4" copper pipe that is 30 feet long, at a 95 psi water supply pressure. There are only a few fittings. I can calculate them in as is needed.


    Thanks

    Ed
  • RJ_4
    RJ_4 Member Posts: 484


    Bell & Gosset System sizer wheel. Check there Web SIte. Remember water flows when there is a differential. You stated 95 psig this would be your static pressure.

    There was an error rendering this rich post.

  • Edward A. (Ed) Carey_3
    Edward A. (Ed) Carey_3 Member Posts: 236
    Flow from pipe

    Thanks for your replies. I think that I did not provide enough information in my original question.

    I am looking to calculate the estimated GPM flow of water out of the end of an open 3/4" copper pipe that is approximately 40 feet long, and connected to a water main that is operating at approximately 90 to 100 lbs pressure.

    I am looking for a chart or a formula to calculate the estimated (expected) GPM flow out of the end of the pipe, and be able to know the estimated change in that GPM flow if the other known factors would change.


    Thanks,

    Ed
  • Carl_20
    Carl_20 Member Posts: 4
    Flow rate

  • Carl_20
    Carl_20 Member Posts: 4
    Flow rate

    The formula no one seems to want to help you with is:
    Cv = GPM divided by the square root of the pressure differential. Meaning, your 3/4" pipe has a Cv (flow coefficient) of about 24 to 28. Therefore, to get your gpm or gallons per minute of flow, you multiply say 24 times the sq. root of your pressure diff. What's that? You have 95 psig coming in but how much are you losing or how much pressure is being dropped due to friction, bends, coils, faucet flow restrictors etc. You'll have to guess at that number. So let's say you drop 50 psi. You would subtract this from 95 and get 45. Take the sq. root of that and you get 6.708. Multiply this by 24 and you get 160 gpm. Seems like a lot and it is. That's because you would drop a lot more across a faucet at this input pressure. My guess is that your faucet manufacture will suggest putting on a water pressure regulator to get that pressure down to around 50 to 55 psi at most otherwise you'll damage the faucet and also over pressure your hot water tank etc. etc. Hope this helps
  • Not into

    sq. roots and all that, but here`s a "Fred Flintstone" way sometimes used for well pumps.

    Dave
  • zeke
    zeke Member Posts: 223
    Basic drop equation

    It's little bit more complicated than indicated since you aren't designing this pipe.

    First off you need to write the basic pressure drop formula"
    f*l/d*V^2/64 where

    f is the friction factor (that is complexly determinsd from the diameter, roughness, viscosity and density of the fluid)
    l= equivalent length of pipe in inches

    d= diameter of pipe in inches

    V= fluid velocity

    Since we know the pressure drop-95psi,95*144/62.4= 219 feet of head we can write the equation

    219=f*40*12/.75*V^2/64 +V^2/64 (note the additional term is the loss at the output)

    I first assumed a friction factor of .02, getting

    V=35 feet/sec and
    flowrate =60 gpm

    I then checked the assumed f=.02 by getting a Reynolds Number*, RE, and determined a more accurate f= .017 which, after plugging it in would increase the V slightly, so .02 is a fair estimate.

    * RE=VD/mu

    V ft/sec

    D dia in feet

    mu = kinematic viscosity, FT^2/sec
  • RJ_4
    RJ_4 Member Posts: 484


    Is this line a city water line piped into a water meter?

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  • hot_rod
    hot_rod Member Posts: 23,251
    How long would the copper last at

    35 feet per second flow rates, I wonder? Seems like the erosion corrosion would be a big factor. If the water had any deposits the life expectancy would be fairly short.

    A 90 ell may turn into a heel outlet fitting within minutes.

    I've seen somne big flow rate numbers like that in fire sprinkler design. But it may be only a one time use :)

    The CDA has some flow rate tables but they limit to 10 FPS and a 30 gpm flow rate at that velocity.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Weezbo
    Weezbo Member Posts: 6,232
    it might be best to add a few more ideas to the mix...

    with a well that produces 8 gallons a min.....you can meet codes using 3/4" within 30 ->50 psi.....for small homes with less than 19 fixture units under 2 stories in height and less than 200 ' of developed length....most likely.

    i have owned a hydraulic pump that you could likely run the pipe to destruction...

    at 95 psi.... the faucets and valves might not like you much for sending 95 psi at them even at 8 gallons a min. many residential shallow wells produce around 5 -> 8 gallons a min.
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