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Pump Curves, then and now

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hot_rod
hot_rod Member Posts: 28,010
in THE MAIN WALL

Typical single or multi speed circs had a defined curve(s).

Variable speed have a window or envelop of curves between minimum and maximum. Varying the speed can be done with after market controls, tekmar, HBX and most electronic solar differential controls, for example. Or some circulators have this function onboard.

Today's multi mode circulators have a number of curves within the envelop, depending on the selected mode.

The type of system piping helps determine the best mode selection.

Screenshot 2026-07-30 at 5.58.38 PM.png

If you analyze or define the system curve with multiple points you would lay that "system" curve over pump curve to find the actual OP, operating point.

Screenshot 2026-07-30 at 6.29.58 PM.png
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
Steve Minnich

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 27,644

    Picky picky me. I have to admit that I'm not at all keen on using the term "pump curve" for the operating characteristics of a variable controller. To me, the term "pump curve" really should be limited to describing the way the flow through the pump varies with the head or pressure (take your pick) across the pump at a specific rpm of the driver, and goes along with a set of other curves, such as efficiency and power requirement.

    As soon as a variable speed driver enters the picture, you are looking at the characteristics of the controller as much as the pump, within the range of speeds which the controller can run the driver at. "constant delta P" or "proportional delta P" or "constant delta T" or whatever really isn't a pump property at all — it is a property of what parameters are measured and where, and what (usually computer) logic is used to control the pump itself.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jumper
    jumper Member Posts: 2,593

    I agree with Jamie. There's also characteristics of electric motor to complicate this subject.

  • hot_rod
    hot_rod Member Posts: 28,010

    The pump curves define that pumps operating conditions. Run out at one end of the curve, shut off head at the other.

    It could be spun by a diesel engine , water fall, bicycle, or team of horses.

    Those pumps with those motor will work within the shaded area.

    Larger pumps will have BEP and BHP curves on the sheet also. I have never seen that info on small residential circulator pumps, which is what these graphs depict.

    Smart pump technology allows the electronics to learn the systems conditions and auto adapt. So the latest technology gives the pump some intelligence.

    The motor adjustability and control logic can do so much At some point the impeller and volute needs to be changed

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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