Sprinkler supply line, 3/4 vs 1"

Discussion in 'Irrigation / Sprinkler Forum' started by John May, Jun 30, 2020.

  1. John May

    John May New Member

    Feb 12, 2018
    New Mexico
    So right now my sprinkler supply line is 3/4" and travels 200' from a well to my furthest zones.
    Sprinklers also use 3/4" PVC. My water pressure is not that great. There is an unused 1" pipe coming from the same well that never got used for anything so I could tap into it to give me a larger supply line, but this pipe would add another 100' to my total supply line on the furthest zone, less on others though. Would I gain anything by going with a larger pipe and a longer distance or would they cancel each other out?
    Last edited by a moderator: Jun 30, 2020
  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    The chart below shows friction loss over distance for PVC can copper sizing.


    This chart is for PEX which is smaller ID

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  4. wwhitney

    wwhitney Well-Known Member

    Mar 17, 2019
    Berkeley, CA
    Each 1' of 3/4" Schedule 40 PVC pipe (inner diameter of 0.804") is equivalent to about 3.3' of 1" Schedule 40 PVC pipe (inner diameter of 1.029") in terms of pressure drop. This comes from the empirical Hazen-Williams formula, which says the pressure drop varies as the the inside diameter d^(-4.8655). And (1.029/0.804)^4.8655 = 3.3.

    So you can compare your two options with different sizes by converting one size of pipe to the equivalent length of the other size of pipe, and then comparing the total lengths after conversion. Be sure to include the equivalent lengths of fittings.

    Cheers, Wayne
  5. WorthFlorida

    WorthFlorida The wife is still training me.

    Oct 28, 2009
    Orlando, Florida
    Your piping arrangement may be part of the problem. If you feed a zone with 3/4" pipe, you tee off with 1/2" pipe. If it is 1" you tee off with 3/4" or 1/2". Short runs with plenty of pressure and flow would not be noticable. Long runs and a lower flow you want to step down in pipe. Someone may have changed with 3/4" all around with 3/4" sprinklers trying to get more water to the sprinklers. To make sense of it you have a 3/4" pipe and then teeing off to the sprinkler and continuing to the next sprinkler. One 3/4" pipe cannot supply enough water to two 3/4" pipes.

    For the zones with the furthest sprinklers, the sprinklers closest to the zone valve, change a few of them to 1/2 inlet sprinklers. This will allow more water to the one further down the line that might improve the performance of the furthest sprinklers and still get coverage that you want.
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