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Identical Pumps in Series vs. Parallel - flow rates vs. power consumption vs. longevity

tivotivo Posts: 16Member
edited January 2017 in Controls
Two identical pumps piped in series vs. parallel:

Q1: Will either piping yield double the system flow rates?
Q2: Will the power consumption be equal in both cases?
Q3: Will either piping affect the life expectancy of the pumps? Just thinking the pumps piped in parallel might be working "harder" overcoming higher head vs. pumps in series sharing the resistance. But then, when the head/resistance is shared, the pumps in series work at a higher flow rates, i.e. potentially more wear and tear so to speak... so I can't draw a conclusion... as you can already tell, I'm no engineer.

Thanks in advance.


  • Jamie HallJamie Hall Posts: 10,638Member
    Q1. No. Parallel will almost double, but not quite -- how much off will depend on the system and pump head vs. flow curves. Series will also increase flow, but not double -- again, depending on the system and pump head vs. flow curves.
    Q2. In general, no. Depends on the efficiency characteristics of the pumps. However, it may be less power -- or it might be more.
    Q3. In most cases, no. In the rare situation that the increased flow causes a sufficiently low NPSH at the pump intake, you might, just possibly, cavitate, which will reduce the life expectancy considerably. Depends on the intake conditions.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • tivotivo Posts: 16Member
    edited January 2017
    Hi Jamie, thanks for your quick response. Could you elaborate a little more on "depending on the system and pump head vs. flow curves"? I'm asking the questions assuming everything stays unchanged, same system, no other pumps other than these two within the system, and they are identical pumps hence identical pump curves. Let's assume boiler doesn't exist or simply assume this is a closed system with nothing but two pumps in it. I'm just trying to draw a simple conclusion, if there exists. :)
  • hot_rodhot_rod Posts: 11,665Member
    One way to know would be to create a system curve then overlay it on the pump curve(s)

    Some good pump basics, including how to develop a system curve in this journal.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • bob_46bob_46 Posts: 813Member
    Try this
  • hot_rodhot_rod Posts: 11,665Member
    bob said:

    Try this

    Nice! Even brings the System Syzer back to life :)

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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