Pump Curve Behavior

I am new to trying to model VFD Pumps. I have a single pump running on a single type 3 curve without controls besides on-off levels. Looking at the pump operation curve, the purple diamond indicates that the pump is operating on the curve most of the time but at various time steps the red line of the curve changes so that the purple indicator is no longer riding along it. It looks like the pump is operating at the same flowrate but the curve changes. Is this a graphical error or is there something going on? I've attached screenshots fr reference.

Also, what is the best way to ensure that the pump and forcemain are operating correctly according to the system curve?

Thanks for any insight.

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  • You can also send me your model if you want and I can take a look at it.

  • Hi Ross,

    A small time step, make sure that the force main nodes have a surcharged depth, more iterations and a lower tolerance will help.  If you get reverse flow then use a flap gate.  Sometimes also adding a break node will help.


    Bob Dickinson

    • Thanks Bob,

      I've been using a 1 second routing time step but still see issues. Surcharge depths are used for every node in the forcemain. I will try using flap gates though, since I do see reverse flow. Is a break node simply used to break up a FM into smaller lengths?

      It is indeed a strange setup for a FM which isn't ideal for modeling. The FM starts as a single pipe then splits into parallel FMs before reconnecting. There is also a gravity line that enters the forcemain at a high point and another pump station that pumps into the FM.

      This is in Moon Township by the way.

      Thanks for the tips!


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