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Thread: Pipe size selection for a new/small pool

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    Join Date
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    Pipe size selection for a new/small pool

    I am undertaking a DIY pool project and have been reading quitea bit about the plumbing – trying to make it perfect and save me money and hasslein a long run. Still, tubes seem little undersized after the calculation andwanted to make sure I am not missing anything before putting the piping down.Here are the details and thanks for your help:
    Pool is in-ground relatively small: 12x18x5 with total of 8,000gallons. Two turnovers of 16,000 over 16 hours (8 hour for eachturnover) comes out to about 1,000 GPH = 17GPM.
    I was looking at the Steve Gutai’s article (http://watershapes.com/pools/spas/water-under-pressure-2.html)about water flow speed and pressure considerations that recommends the averagewater speed at 6fps and according to the chart in the article, I need:
    · 1 ¼ pipe for main feed (4.29fps at 20GPM) (thechart says 7.29 but it seems a typo comparing to numbers before and after).
    · Then, ¾ pipe for secondary feed (6.02fps at10GPM)
    · I do not even have a size for a tertiary feed (that will loop around the pool) orthe outlets (should I use ½” for tertiary and then ¼” for outlets?)
    Questions:
    1) Should I simplify the layout by getting rid of secondary feed and use 1 ¼” as the primary feed that connects to the 3/4" loop that goes around the pooland use ¼ for outlets?


    2) Irrespective of the two proposed layouts, these tubesizes seem too small but, at the same time, wanted to make sure the flow was ata recommended level. Are my size calculations correct? Should I be so concerned about keeping the flow rate around 6fps or can it tolerate much slower speeds?


    Thank you so much,
    Mike

    pool.jpg

    pool2.jpg

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    Re: Pipe size selection for a new/small pool

    Use 1.5" pipe until you have to adapt down to connect the fittings. Use it on both suction and returns.

    The increased cost is VERY minuscule and 1.5 inch pipe is better in every respect.

    I do not understand the purpose of the "tertiary" piping.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Pipe size selection for a new/small pool

    Hi Dave, thanks for your response. Yes, the cost had zero consideration for me, like you said, it is a trivial difference. I was more concerned about the velocity: not getting enough speed in outlets to promote healthy circulation needed for skimmers, etc. also, I was reading that velocity should be kept relatively consistent from pump to discharge for efficiency, etc.

    The attached article by Zodiac pools stated that 6fps is a target velocity for pool return plumbing and this is what I was aiming for.

    I was not sure how important it is to stay closer to that range (6fps) or whether having a slower velocity (3.1fps for 1.5" pipe at 20GPS) is going to make a noticeable difference in efficiency.

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    Re: Pipe size selection for a new/small pool

    Control the velocity with the diameter of your eyeball fittings...probably 4-8 different sizes. You'll still decrease your head loss with the larger pipe but get the velocity you say you want at the pool.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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