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Max Flow Through Water Main

NYplumber Member Posts: 503
Hi there wallies,

As with heating there are max flow rates for hot and cold water pipes in homes. Honestly I went off of feel and rules of thumb from years in the field when piping domestic water lines, haven't had an issue yet. I have a client with a specific sized water main and he wants a filter (most likely sand media filter) for all incoming water. With the size of this home and the MANY bathrooms its impossible to say lets take a worst case load (gpm) and use that. His fixtures can surely out draw his piping.

The water main is 1 1/4 in copper. With 60 psi street pressure, and max flow, what flow will this pipe support? I came up with a conservative number of 25gpm. Is there a size and gpm table somewhere on engineering toolbox? While I dont want to over engineer his filtration, I also dont want to under design.

Thanks in advance.


  • SWEI
    SWEI Member Posts: 7,356
    Do you have a Cv (or pressure drop versus flow curve) for the filter? How much pressure drop is he willing to tolerate? That plus the equivalent pipe length should get you close.
  • uge
    uge Member Posts: 6
    A 1-1/4" line can flow 20 gpm with minimal pressure drop. With 60 psi street pressure you should have no problem installing the filter.
  • NYplumber
    NYplumber Member Posts: 503
    Have 3m working on it for him. Seems like three filters in reverse return piping will suffice.