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Thread: plumbing question - suction line reduction

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    plumbing question - suction line reduction

    Our inground pool and spa have 2.5 inch suction lines and 2 inch return lines, but the suction lines reduce down to 2 inches in two places and I'm wondering if there is any good reason for it. The pool and spa suction lines connect to a 3-way valve, which in turn connects to the pump inlet. The pipe between the 3-way valve and the pump is only 2 inch diameter. Also, there is a 2.5 inch to 2 inch reducer where the pool suction line connects to the 3-way valve, but the spa suction line connects to the 3-way valve with 2.5 inch pipe. Is there a good plumbing reason why the suction line would be reduced half an inch in diameter in these two places during the last foot before the pump? If not, would changing these two reductions to 2.5 inch pipe improve the system efficiency much?

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    Mod Squad JohnT's Avatar
    Join Date
    Apr 2007
    SW Indiana

    Re: plumbing question - suction line reduction

    The reductions are probably because they had those parts available when they built it. 2"/1.5" parts are much more widely used and available. I doubt you would benefit from changing out working parts, but you might consider going with the larger sizes if you have to replace anything.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: plumbing question - suction line reduction

    Keep in mind that using smaller pipe for very short distances makes only a tiny difference in the overall efficiency. The longer the pipe the more important it's diameter is.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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