Fire flow available greater than field measurements

Hi,

I recently received a model from someone else and noticed that the fire flow available for select hydrants was greater than the field measurements for hydrant testing.

i.e. the fire flow alternative has an upper limit of 3,500 gpm. For the hydrants we opened in the field, each of them report an upper limit of 3,500 gpm:

However, in the field these hydrants (fully open) were only able to produce anywhere from 914-1085 gpm. What is this an indication of? An inappropriately calibrated model? Hazen Williams coefficients that are too large? Incorrect tank levels?

Thank you!

Parents
  • Let me throw in my 2-cents worth.

    The key sentence in the link that Mr. Walksi referred to is:  "In a Fire Flow Analysis, the results are based on distribution system capacity."

    There are two types of fire flow tests:  One which measures the amount of flow a hydrant is capable of providing (a "single hydrant test").  The other, a "two-hydrant test", measures the amount of flow the system itself is capable of providing.  They are two very different tests and can yield very different results.

    If you want to replicate a single-hydrant flow test, try setting the hydrant status to "open", then run your model and see what happens. I'm guessing that the results will show a flow of significantly less than 3500 gpm.

    I would suggest that you not blindly use the Fire Flow Analysis option unless and until you are confident that you fully understand what it is telling you.

Reply
  • Let me throw in my 2-cents worth.

    The key sentence in the link that Mr. Walksi referred to is:  "In a Fire Flow Analysis, the results are based on distribution system capacity."

    There are two types of fire flow tests:  One which measures the amount of flow a hydrant is capable of providing (a "single hydrant test").  The other, a "two-hydrant test", measures the amount of flow the system itself is capable of providing.  They are two very different tests and can yield very different results.

    If you want to replicate a single-hydrant flow test, try setting the hydrant status to "open", then run your model and see what happens. I'm guessing that the results will show a flow of significantly less than 3500 gpm.

    I would suggest that you not blindly use the Fire Flow Analysis option unless and until you are confident that you fully understand what it is telling you.

Children