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Available Fire Flow In Model vs Field Tests

Hello,

I put a model together that is giving me wildly large available fire flows from the hydrants in the system. The city we are providing services for have provided us with a spread sheet showing significantly lower flows from those hydrants. 

Here is an example:

NW_115 in model is giving an available flow of 4,000 gpm (upper limit for the model is 4,000 gpm).

NW_115 in the field is giving an available flow of 2,255 gpm.

All hydrants are discharging from 2 inch orifices'

Is there something in my model that is set incorrectly?

Please help. How do I upload a file that is 9.5 MB?

Thanks,

Clint Taylor, EIT

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  • Hello Clint,

    The automated fire flow run will add available fire flow until either the upper limit is reached or if the zone pressure constraint. I would review the pressures that you are seeing for the node in the Fire Flow report compared to the field test. More information on automated fire flow results: Understanding Automated Fire Flow Results.

    If that doesn't help, you can use this link to send the model files: Sharing Hydraulic Model Files.

    Regards,

    Scott

  • Hello Scott,

    Thank you for sending me those links. I have spent some time looking through both of the links, as well as some additional videos, but I am still unsure if my results make sense in comparison to the field data.

    Can you take a look at my model and let me know if I have something set up wrong? There are a row of hydrants (SW_1 through NW_116) that I am trying to get the numbers to be close to the field measurements.

    Even when I apply the peak weekly demand to the system, I still get no change in flow or pressures.

    Thank you,

    ModelForBently.wtgpkg.zip

  • Hello Clinton,

    I checked your model and all your nodes are passing and the fire flow constraints are getting satisfied except for hydrant NW_166 where the residual pressure constraint (20 psi) is getting violated. Is there a different value of fire flow needed for this hydrant? i.e. as per the field data you have?

    What values does the spreadsheet of field data represent? Are they hydrant flows at residual head? Or flowed hydrants at a particular time?

    As suggested, automated fire flow provides the capability of a hydrant. So if the fire flow needed = 2000 gpm and the fire flow available  = 3500 gpm this means that the hydrant can provide the required fire flow when needed and satisfying the pressure constraints too.

    See the articles Scott shared for more information on this.


    Regards,

    Yashodhan Joshi

Reply
  • Hello Clinton,

    I checked your model and all your nodes are passing and the fire flow constraints are getting satisfied except for hydrant NW_166 where the residual pressure constraint (20 psi) is getting violated. Is there a different value of fire flow needed for this hydrant? i.e. as per the field data you have?

    What values does the spreadsheet of field data represent? Are they hydrant flows at residual head? Or flowed hydrants at a particular time?

    As suggested, automated fire flow provides the capability of a hydrant. So if the fire flow needed = 2000 gpm and the fire flow available  = 3500 gpm this means that the hydrant can provide the required fire flow when needed and satisfying the pressure constraints too.

    See the articles Scott shared for more information on this.


    Regards,

    Yashodhan Joshi

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