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WaterGEMS for Autodesk Latest Version

I have run Scenario EPS and Pump 16276 (supplies Western Standpipe) is running. Lag pump 16277 and lag 2 16278 are not.

I then ran Scenario "with Loop" which has same demand and an added loop (P-1722 - P-1726. Now all 3 pumps are running.

What is causing this if there is no increase in demand?

Note: I have sent previous uploads and failed to post question.

  • Hello Dick, 

    The lag pumps will not turn on until the lead pump in the VSPB has a relative speed factor of 1.0. If the flow required is high enough that the maximum relative speed factor is reached and more flow is required, the lag pumps will turn on then. 

    There must be some change in hydraulics in "with loop scenario" that triggered lag pumps to turn on, need to look into it. 

    If possible please upload model files for our review, in that case. 

    Sharing model files.

    Meanwhile here is detailed information on VSPB, if you haven't gone through it yet. 

    Benefits of using variable speed pump batteries (VSPB) element and how it works

    Modeling variable speed pumps (VSP’s) in parallel

    Regards,

    Sushma Choure

    Bentley Technical Suppport

  • Hello Dick,

    Even if the demand stays the same, if the pump is a VSP with a hydraulic grade target, or if the pump has HGL/pressure-based controls, your change to the network may cause a change to the HGL (for example due to changes in headloss), which can shift the pump operating point or the number of required lag pumps (or change when controls trigger).

    I see that you uploaded a model called "Water System EPS" so I took a look. In the scenario named "EPS", both the "lead pmp" and the "lag pmp" pumps turn on at times during the EPS (seen via a graph). The "loop" scenario would not compute for me, due to an issue with junction J-1002 which is set as inactive (is active = false). If I make that junction active I am able to compute and I do see that all three pumps turn on at times during the EPS, but as mentioned above, the addition of extra pipes (to make a loop) change the network hydraulics, causing the pump behavior to change due to the change in pressure.

    I see that you are not using VSPs ("is variable speed pump" is set to false) but rather you have controls set on fixed-speed pumps to turn them on and off based on the HGL of a tank on the other side of the network. If you graph the flow in the loop (the new pipes) and the tank HGL for both scenario (select both in the graph series options) you will see that the addition of the loop changes the network hydraulics in such a way that the tank drains faster at times due to the new pipe, causing the tank-based pump controls to trigger at times when they otherwise would not have.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

    Answer Verified By: Dick Schneider