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Pressure at a point on a proposed Water Line that is Connecting to an existing Water Line.

Hi,

I am trying to figure out if extending a 6" line from an existing water line would be sufficient to provide service to a proposed site or not. I modelled a pump-reservoir system to mimic the flows at the water main, using fire flow data at the nearest hydrant. After calculating the 3 point curve, I basically drew 6" lines in and around the site and looped it back to the system. I have attached a proposed water line markup of the Site, which I modelled on WaterCAD. I have also attached the WaterCAD model.

Here are my questions:

1. To figure out if simply extending a 6" line to the site works or not, do I simply add demands in my junctions (J-2 and J-3) and see if the pressures at those junctions work?

2. Can someone please check if my 3 point pump definition makes sense or not. The fire flow data I was provided at the nearest hydrant was as follows:

Water Main Size - 6"

Static Pressure - 105 psi

Flow Pressure - 31 psi

GPM - 930

PDFPDFPDF7506.WaterCAD Model.zip

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  • Hello Sayan,

    Typically you require more than one hydrant to perform a flow test. One hydrant is the residual hydrant, where pressure is measured, and the other is the hydrant(s) that is flowed (opened) and where flow is measured. See the below article which discusses more on hydrant flow tests;

    Calibrating a model based on hydrant flow tests

    2. Can someone please check if my 3 point pump definition makes sense or not. The fire flow data I was provided at the nearest hydrant was as follows:

    For your pump curve you have selected the highest flow as 1002 gpm and the corresponding head as 46.2 ft. Is this the residual flow and pressure? How did you arrive at these values? See the third approach proposed in the below article to simulate connection to an existing system;

    Modeling a Connection to an Existing System

    You would however need more than one hydrant to perform the flow tests and obtain data to generate the pump curve.

    1. To figure out if simply extending a 6" line to the site works or not, do I simply add demands in my junctions (J-2 and J-3) and see if the pressures at those junctions work?

    In the model you shared, the demand at J-2 is 0 gpm and there is no demand at J-3. Once the reservoir and pump is setup you should assign the necessary demands at your demand junctions and run the simulation to check if the results are acceptable.

    Hope this helps.


    Regards,

    Yashodhan Joshi

  • Thanks Yashodhan. I calculated the GPM at 20psi using the formual "Qr=Qf*(Hr/Hf)^0.54". "Chosen design pressure" at 20psi. That's how I came up with 1002 GPM.

    Yes I will be adding the demands in J-2 and J-3. Just wanted to know if I am doing the model correctly. I think my reservoir is setup correctly? (I kept the reservoir elevation equal to the pump and the hydrant elevation. I used a 48" pipe between the reservoir, pump and hydrant).

    Thanks!

  • If possible try and get data from two hydrants as earlier suggested to generate a better pump curve. Additionally, since you are approximating an existing connection, better check the existing flow rates and generate system head curve to adjust the pump curve.


    Regards,

    Yashodhan Joshi

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