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low velocities in the system

Hello,

i am working on design for small plan potable water network + fire using waterGems select series 5

after i have set the pipe sizing to satisfy successful fire flow results i have found very low velocities(0.01 m/s), however it is been noticed that the velocities of maximum pipe (in fire flow results flex tables) are quiet high (3.9 m/s) 

i tried to increase pressure but nothing changed. and when i try to decrease diameters it will not give me a big difference but the fire flow analysis will fail.

regards 

  • If you are working with a drinking water system, there will be times when the velocity is very low, especially for situations where the pipe is sized for fire flow and the normal demand is small.

    Just think about the pipe outside of a pump station. When the pump is off, the velocity is zero but there is nothing wrong with that.

    The place where low velocity may cause problems is that where the water age at the end of the line is so low that the disinfectant residual is lost.

    What size pipes are you using and what are the fire flow requirements? How large is the system in terms of distance from source to farthest user?

    To increase velocities, you can always reduce pie diameter, but there is a tradeoff in reduced fire flows and peaking capacity.

    In general, I would not worry about low velocities.

    Answer Verified By: ahmed hassan