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Fire Flow Report comparison between scenarios

Hello,

I'm scratching my brain a little on this one, so maybe someone can help. A water system project I designed and modeled last year is undergoing construction now, and during construction a new idea came up to abandon an older line that would remove a loop in the system. Naturally, we wanted to check the effect that removing the loop would have on fire flows throughout the system. When comparing the fire flow report with and without that pipe "closed", many of the junctions experienced higher available fire flow after removing the old line from service(The line to be abandoned has a C value of 74, while the other major loop lines are over 100). At a glance this seems counter intuitive, so maybe I am thinking about this the wrong way?

Some background info:  It is a smaller system with 162 junctions, 1 tank, 3 pumps, and two pressure zones. I've ran the fire flows with the pumps on and pumps off, thinking that maybe these pumps were over powering any difference, but the issue persisted. Now I'm wondering if the PRV's are maybe part of the cause, as the junctions that have the higher flows with the loop removed are in the lower elevation pressure zone.

Any insight would be appreciated!

Thanks,

Ryan

  • Hello Ryan, 

    When you are removing loop from a system, whether the fire flow should increase of decrease will differ from model to model , as the setup and hydraulic elements are different, but with testing it appears that with removal of loop i.e. making it a branch system yields more fire flow available in the model. With the removal of loops water can travel directly to the fire flow node thus reducing the headloss and loss of water in travel. 

    Understanding Automated Fire Flow Results

    However if possible please upload your model files, for our review, to help you with your particular case. 

    Sharing model files

    Regards,

    Sushma Choure

    Bentley Technical Suppport