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Which SewerGEMS solver is best for sanitary sewer model with lift station that has intermittent high points?

Which SewerGEMS solver is best for sanitary sewer model with lift station that has intermittent high points? I currently have a model set up and running the SewerCAD solver EPS, but I am not sure if this is the best solver for the job. I want to be able to check/validate the pressure at high points for the need of Air Release/Vacuum Valves. In the current SewerCAD solver, if appears that when the lift station pump stops running, all flow in the system stops and there is no check for the condition on gravity flow "away" from high points that would have the potential to create a siphon.

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  • Joshua, I would recommend that Implicit solver if you have pumps with intermediate high points. This solver will automatically account for the high points without the need for air valves, handles all other dynamic effects and it is generally more stable with pump calculations than the Explicit solver. See also: Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM)

    The GVF-Convex (SewerCAD) solver uses the EPANET solver for forecemain calculations which has the underlying assumption that pipes are flow full and under pressure. When using air valves to help it account for local high points, the results are approximated as it internally simulates them as Pressure Sustaining Valves (PSVs) with air valves. The following article has some more details on some of the situations that can arise because of this and how to deal with them, but you may want to consider the Implicit solver. Troubleshooting Air Valves at High Points with the GVF Convex (SewerCAD) Solver


    Regards,

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

  • I currently have property connections set up with a base flow and pattern. Those property connections connect to a lateral that connects to the first manhole after each building connection. From there on my model uses standard conduits that work with the implicit solver.

  • Joshua, indeed as noted in this article, taps and laterals are not supported with the Implicit solver. You will either need to remove them from the model (or make inactive) and place your inflows/loads directly on the manholes via LoadBuilder (and then reassign the patterns), or you will need to try using the Explicit (SWMM) solver.

    The Explicit solver also handles high points automatically just like the Implicit solver, but the Implicit solver tends to be more robust with force main calculations, typically providing more stable results. Perhaps if your force mains are not complex and pumps are not cycling quickly, you can try the Explicit solver with a small Routing Step like 1 second, to see if the results are stable and accurate. If not, try using the guidance in this article to achieve more stable results:

    Troubleshooting unstable SewerGEMS and CivilStorm model results using the Explicit SWMM Solver

    If that does not help, you may need to convert your taps and laterals to LoadBuilder-assigned manhole loads and use the Implicit solver. You could try converting the property connections to manholes, the laterals to conduits and the taps to transitions but this may not be easily accomplished even with tools like Batch Morph and Batch Pipe Split, and will add extra complication to the model calculations.


    Regards,

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

Reply
  • Joshua, indeed as noted in this article, taps and laterals are not supported with the Implicit solver. You will either need to remove them from the model (or make inactive) and place your inflows/loads directly on the manholes via LoadBuilder (and then reassign the patterns), or you will need to try using the Explicit (SWMM) solver.

    The Explicit solver also handles high points automatically just like the Implicit solver, but the Implicit solver tends to be more robust with force main calculations, typically providing more stable results. Perhaps if your force mains are not complex and pumps are not cycling quickly, you can try the Explicit solver with a small Routing Step like 1 second, to see if the results are stable and accurate. If not, try using the guidance in this article to achieve more stable results:

    Troubleshooting unstable SewerGEMS and CivilStorm model results using the Explicit SWMM Solver

    If that does not help, you may need to convert your taps and laterals to LoadBuilder-assigned manhole loads and use the Implicit solver. You could try converting the property connections to manholes, the laterals to conduits and the taps to transitions but this may not be easily accomplished even with tools like Batch Morph and Batch Pipe Split, and will add extra complication to the model calculations.


    Regards,

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

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