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A refresher please

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2 in series dbls head, 2 in parallel dbls flow (approximately in both cases)

ME

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  • Bob Sweet
    Bob Sweet Member Posts: 540
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    2 pumps in series

    increases gpm?? 2 pumps in parrallel increases head??
    Thanks.


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  • mtfallsmikey
    mtfallsmikey Member Posts: 765
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    I'll try a dumb question on this thread too

    If 2 pumps double flow, how would you go about sizing the pipe for the increased flow?
  • Joe Billow_6
    Joe Billow_6 Member Posts: 69
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    I did this one time for a flash tank. Sized the piping for 85% of the total flow of both pumps. I didn't do anything different than normal, calculated head then figured total flow for one pump, added both flows together and sized pipe to 85% of that flow. The pumps were staged up to half tank one pump and over half both pumps. I did it to try and reduce energy use and because I was told by a Maint. MGR that it would not work "we need one really big GF100"
  • Jim Pompetti
    Jim Pompetti Member Posts: 552
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    Pumps

    Keep them 18" apart
  • Brad White
    Brad White Member Posts: 2,398
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    Mike-

    If you have two pumps in parallel to support a doubling of flow, size the piping for the desired (doubled) flow.

    Say you have two pumps at 10 GPM (1.25-inch pipe each). Combined the 20 GPM would require a 1.5-inch pipe for example.

    It would be expected that when only one of the circulators operates that the resistance of all of that 1.5-inch pipe with only 10 GPM flowing through it, will be about 1/4 of the original head. Thus that single pump will "run out on it's curve" and may deliver 15 GPM depending on the pump characteristics. When the second pump is brought on, both will settle to their 10 GPM versus the design resistance.

    A little bargain in that low load periods gets you higher flow per Watt for much of the year.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Brad White
    Brad White Member Posts: 2,398
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    Or else

    they breed, right Jim?

    :)
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • jp_2
    jp_2 Member Posts: 1,935
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    that depends!!!

    in an existng system:
    2 series pump can increase head, which in turn will increase gpm, 2 parallel can increase gpm if the pipe resistance is low enough.

    not straight forward......

    if a existing system needs more flow, 2 parallel pumps won't work.
  • mtfallsmikey
    mtfallsmikey Member Posts: 765
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    I see the point

    I'd just like to see the original design specs for my condenser water system...2/ B&G 30 hp pumps in parallel, no L/L, but 2nd pump comes on if CW temp. rises 10 deg. above setpoint; 2nd pump starts. Pumps are on the roof, suction direct from 2-cell tower sumps,8" suction, 8" supply, discharge pumps down all 6 floors, then back up to the hot decks of the towers...never understood that concept, but it is faily common with most office buildings in this area with self-contained water-cooled units.
  • Joe Billow_6
    Joe Billow_6 Member Posts: 69
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    I thought I was spot on. Good thing it worked. Would have looked like an idiot if all I needed was the extra 15%.
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