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Thread: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

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    uxbridgechris's Avatar
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    small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    So my pump only has a 1.5” input. Return line from skimmer is 60’ to pump dead straight. I would like to use 1.5” line from skimmer to pump and 1.5 to both return jets. Are there any issues here? Thanks guys, and gals.
    Blue Hawaiian “Wellington” FG pool 6500 Gal. Raypak 266 NG Nickle plated, 3/4hp Hayward super pump, Heater Reader wifi / app controller. Pentair 420 sq' cartridge filter. Hayward 25k SWG
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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    Anyone? Bueler? lol
    Blue Hawaiian “Wellington” FG pool 6500 Gal. Raypak 266 NG Nickle plated, 3/4hp Hayward super pump, Heater Reader wifi / app controller. Pentair 420 sq' cartridge filter. Hayward 25k SWG
    Pal LED pool lighting. Jandy K-1100 Electronic Autofiller Build thread here: 2018: Fiberglass install uxbridge ointario

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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    I would use 2" pipe.
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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    Quote Originally Posted by JamesW View Post
    I would use 2" pipe.
    please explain why
    Blue Hawaiian “Wellington” FG pool 6500 Gal. Raypak 266 NG Nickle plated, 3/4hp Hayward super pump, Heater Reader wifi / app controller. Pentair 420 sq' cartridge filter. Hayward 25k SWG
    Pal LED pool lighting. Jandy K-1100 Electronic Autofiller Build thread here: 2018: Fiberglass install uxbridge ointario

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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    2" pipe gives you better flow due to less resistance. 2" pipe has a negligible cost increase. So, it's all benefit for almost no cost.

    Will you have a main drain?
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    uxbridgechris's Avatar
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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    I'm having trouble grasping this. I know the accumative effect of elbows adds head. completely understandable. But does a 6" pipe that is reduced to 1.5" have less resistance than a 1.5" pipe? hard to wrap my head around it.
    Blue Hawaiian “Wellington” FG pool 6500 Gal. Raypak 266 NG Nickle plated, 3/4hp Hayward super pump, Heater Reader wifi / app controller. Pentair 420 sq' cartridge filter. Hayward 25k SWG
    Pal LED pool lighting. Jandy K-1100 Electronic Autofiller Build thread here: 2018: Fiberglass install uxbridge ointario

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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    The resistance of a pipe depends on the flow rate, pipe diameter and pipe length.

    For example, 100' of 1.5" pvc pipe at 50 gpm results in a water velocity of about 7.88 ft/sec and a head loss of about 15.4 ft.

    However, 99 ft of 2" pvc at 50 gpm has a head loss of about 4.8 ft and 1 foot of 1.5" has a head loss of about 0.154 ft for a total head loss of about 4.954 ft or about 1/3.

    So, you get more flow.

    To get a better idea of the dynamics, you can graph various system curves on the pump curve chart to see where various system curves intersect with the pump curves and choose a good pump and pipe size based on the desired flow rate.

    The 2" pipe will have a lower, flatter curve vs a 1.5" pipe, which would have a steeper system curve.
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    uxbridgechris's Avatar
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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    wow. Thanks james
    Blue Hawaiian “Wellington” FG pool 6500 Gal. Raypak 266 NG Nickle plated, 3/4hp Hayward super pump, Heater Reader wifi / app controller. Pentair 420 sq' cartridge filter. Hayward 25k SWG
    Pal LED pool lighting. Jandy K-1100 Electronic Autofiller Build thread here: 2018: Fiberglass install uxbridge ointario

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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    I would say that 1 1/2 inch pipe would be fine for a 7000 gallon pool. The flow rate needed for good circulation and overturn on that size pool will not be impaired, especially with your large filter.

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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    Pool gallons do not matter when sizing pipes, neither does turnovers.

    To really answer the question, what kind of pump do you have, need a head count.

    Either will work, I'll edge on the 2" due to the long run.
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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    You get better flow with 2" pipe. So, you can use a smaller pump or less run time or a lower rpm if it's a variable speed pump.

    Good hydraulic design is to keep the suction line water velocity to less than 6 ft/sec.

    At 1.5", the velocity will exceed 6 ft/sec and at 2", the velocity will be less than 6 ft/sec.

    Since the cost for 2" vs 1.5" is insignificant, I don't see any benefit to using 1.5" pipe.
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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    Ok, so part the reason I even asked the question was because I was having a real hard time sourcing 2" locally. I have found it so it's a no brainer.

    2" from skimmer to pump.
    All 2" between pump, filter, Heater and SWG. 2", 3 way valve with outputs reduced to 1.5", then 1.5" lines to both returns.

    Thanks guys
    Blue Hawaiian “Wellington” FG pool 6500 Gal. Raypak 266 NG Nickle plated, 3/4hp Hayward super pump, Heater Reader wifi / app controller. Pentair 420 sq' cartridge filter. Hayward 25k SWG
    Pal LED pool lighting. Jandy K-1100 Electronic Autofiller Build thread here: 2018: Fiberglass install uxbridge ointario

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    Re: small pool, 3/4hp pump 1 skimmer and 2 returns. Suction line size?

    Quote Originally Posted by cfherrman View Post
    Pool gallons do not matter when sizing pipes, neither does turnovers.

    ...
    Well, that would certainly surprise engineers who deal with such matters.

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