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Thread: developing pump curve

  1. #1
    Member
    Join Date
    Dec 2016
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    37

    developing pump curve

    I am developing a pump curve. I follow the standard procedure. Remove the pump, to the suction node apply a water demand, and to the discharge node apply the same demand as inflow. Then, Discharge Head - Suction head

    After a given demand, the suction head is higher than the discharge head.
    What is the meaning of such negative value?

  2. #2
    Forum Moderator

    Innovyze Employee



    Join Date
    May 2015
    Posts
    295
    Vladimir,

    Without seeing your system it is difficult to tell, but here are a few things you can check for your system curve calculation which is what it sounds like you are actually generating, rather than a pump curve.

    1) What does the system look like?
    2) What is controlling the HGL on the suction side and on the discharge side. Is it a tank or is it something else.
    3) In certain circumstances (like low flow or low demand) there can be times where the suction head is sufficient to serve customers and water does not need to be pumped. As the flow increases headloss would drop the suction pressure and cause pumping to be needed during high demand periods to maintain the desired HGL for all customers. Since in your system this happens when the demand increases, I suspect something unexpected is controlling the suction HGL like perhaps another pump came on?) It would be best to investigate what is controlling the HGL on the suction side as something is changing the conditions of the run. You need to make sure you run the system with as close to constant boundary conditions as possible.
    4) if this was your pump with the tank system in another thread, make sure the fill line is closed when running the analysis. Otherwise the tank could be filling and increasing the suction HGL.
    5) Check your running a full status report with warning messages and check the run report for warnings and errors as well. Make sure each run is actually converging.


    Essentially the only way for this to occur as the demand increases is that something else not on at low demands must be coming on as the demand increases or that some unexpected pipe or zone break got accidentally opened which changed the suction conditions form those used in low demands. Investigate your model runs and I suspect you will find something changed in the boundary conditions. Look at all pump controls and what else is controlling the suction HGL. Verify by lowering the demand, does the suction HGL drop? Find out why.

    Patrick

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