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Pumps performance

Good evening

i have problem with the results of the network's pressure and flow when the pumps in the shutdown in the EPS mode

the graphs of the junction's pressure shows unreasonable results

so i need to know the correct way of modeling a water network consist of two tanks and one pump station ( 4 pumps ) in EPS mode at the time of pump's sutdown

thank you

 

  • Hello Bushra,

    It appears that the issue is related to the pumps pumping against a tank that is full. The pump status is still on, but this the pump is full (and there is no demand in the system), that this is causing the system to be unbalanced. I would recommend one of two things here.

    First, if the concern is with the EPS run, I would include controls for the pump. The pumps would turn on and off based on the level in the downstream tank. You can find more information on controls in the Help documentation or the following link: communities.bentley.com/.../2567.creating-controls-conditions-actions-and-control-sets-tn. Including controls may help in this as the pumps will turn off and no longer supply flow to the tank when it is full. That said, with no demands in the system, I don't see how the tank will be expected to drain. If there are demands in the system they should be included as well. If not, controls on the pumps will likely turn the pumps off and they will remain off for the rest of the EPS run.

    Given that this appears to be a HAMMER model, another option would be to replace the tanks on the upstream and downstream side of the pump station with reservoirs. There are a couple of reasons for this. First of all, the system balances during the EPS run since the reservoir element will not become full like the tank. Second, during a transient simulation the level in the tanks one either side of the pumps will not fill or drain much during the time frame generally used in a transient run. This makes replacing the existing tanks T-3 and T-4 with reservoirs a viable option.

    Regards,
    Scott

    Answer Verified By: Sushma Choure 

  • good morning

    regards to my yesterday question i have updated the model (WATERGEMS)  communities.bentley.com/.../130050

    from that model i would like to see the pressure curve for junction 1 during 24 hrs from the time of pumps shutdown 

    also i would like to see the flow reduction  and curves for all the discharge pipes during 24 hrs from the time of pumps shutdown

    or at lest the few seconds from the time of shutdown

    by now the results shown for both pressure and flow seem unreasonable,i would like to know what is the problem

    thank you

    Best regards,

    Bushra Alnaamani

  • Hello Bushra,

    Could you provide information on what the results are? What sort of pressure are you seeing?

    It is possible that this is related to either a "network unbalanced" user notification or to disconnected demand nodes in the system. If you are getting a "network unbalanced" user notification, you will want to resolve any issues indicated in the user notifications before you will see viable results. The following link has information on this user notification: communities.bentley.com/.../8769.troubleshooting-network-unbalanced-or-cannot-solve-network-hydraulic-equations

    Another issue may be that there are disconnected demand nodes in the model. If there are demands downstream of the pump when the pump turns off and no other source to feed the demand, you will see strange results. This is because demands are always assumed to be satisfied in WaterGEMS and WaterCAD. You would see a user notification about disconnected demand nodes if this issue was occurring. You can find more information on that here: communities.bentley.com/.../10506.disconnected-demand-nodes-user-notification-when-computing-model.

    If that doesn't help, we will likely need to see a copy of the model, as well as an explanation of where the issue is occurring. The following link has information on sending model files to us: communities.bentley.com/.../32255.sharing-hydraulic-model-files-on-the-haestad-forum.


    Regards,
    Scott