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Thread: Help with System Curve

  1. #1

    Join Date
    May 2014

    Help with System Curve

    I have a new model which I am trying to verify that the system curve makes sense. Each time I ran the a system curve, the curve started at zero rather than with static head and then had a normal looking curve. To troubleshoot, I simplified the model to include just the reservoir, pump, tank and pipe in-between. Still, I see the problem of starting at zero, plus the curve just shoots off to infinity now. After much troubleshooting, I simplified yet again by creating a new stick model using approximately the same elevations and diameters, lengths, etc. This stick model appears to give me a reasonable system curve. But when I try to find what the difference is between the two models to determine why I get different results, I come up empty. What am I missing? Something obvious, probably.

    simplifiedmodel curve.jpgstickmodel curve.jpg

    Thanks for any tips of things to check!

  2. #2
    Forum Moderator

    Innovyze Employee

    Innovyze Employee

    Join Date
    May 2015

    Its hard to say without actually seeing the model, but if you are getting head values as high as shown that is usually indicative of the solver not finding an answer or not knowing what the head is. This can occur if you try running a system curve on a pumped only zone or a situation that creates a pumped only zone due to the model settings.

    I would check for the following:

    1) Is a tank initial level set at Maximum or Minimum water level? If it was then EPANET will close the pipes connected to the tank and you would likely have an imbalance of supply vs demand.

    2) With your pumps off, will the model run in the standard tab? If it does run are the results reasonable? This usually tells you enough to figure out why the system curve was acting oddly.

    3) Have you reviewed the system curve presentation in this thread: To better understand how these work as well as the curve exceptions that may require you to run a system curve manually (i.e. for closed zone pump stations) Closed zone or pumped only zones are a special case that you have to run differently.

    Feel free to reply to this thread if you need further assistance.

    Patrick Moore

  3. #3

    Join Date
    May 2014
    Thanks Patrick,

    I did review that presentation which was very helpful. I'm not sure what the issue was with my simplified model, but I started over from my original model and am now getting correct system curves. Sometimes you just have to start from the beginning again I guess.

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