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Transition from Gravity to Pressurized Flow

Erin Daugherty
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I am trying to model a situation where I have suction lift pumps that pump up to a high point approximately 2 feet above the pump. After this initial high point, there are several peaks and valleys along the force main all of which are at a lower elevation than the high point resulting in what people are calling gravity assisted flow. All I am trying to do is develop a system curve for the pump, but I'm not sure how SewerCAD can indicate when flow in this situation will be completely pressurized.

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    Hello Erin,

    Typically, SewerCAD will be looking at what is happening in the upstream wet well and the elevation of the downstream manhole do create the system head curve. You mention high points in the system. Do you have air valves at this high points? If so, the presence of the air valve will impact the system head curve as well. This is because the head from the pump will be higher in order to reach the air valve, if the air valve property "Treat air valve as a junction" is set to False.

    So the system head curve will be dependent on the elevation at the end of the pressure system, the wet well, the status of other pumps in the pressure subnetwork, and the status of any air valves that may be in between the wet well and the end of the pressure system.

    For more general information on system head curves, see the following link: communities.bentley.com/.../24627.system-head-curves-in-watergems-and-watercad

    For information on modeling air valves in SewerCAD, see the following link: communities.bentley.com/.../modeling-force-mains-with-air-valves

    In addition, there are upcoming presentations on modeling air valves in SewerCAD planned for November 18 on modeling air valves in SewerCAD. You can find more information and sign up for the presentation at the following link: pages.info.bentley.com/sigs

    Regards,
    Scott
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  • 0 Offline
    Hello Erin,

    Typically, SewerCAD will be looking at what is happening in the upstream wet well and the elevation of the downstream manhole do create the system head curve. You mention high points in the system. Do you have air valves at this high points? If so, the presence of the air valve will impact the system head curve as well. This is because the head from the pump will be higher in order to reach the air valve, if the air valve property "Treat air valve as a junction" is set to False.

    So the system head curve will be dependent on the elevation at the end of the pressure system, the wet well, the status of other pumps in the pressure subnetwork, and the status of any air valves that may be in between the wet well and the end of the pressure system.

    For more general information on system head curves, see the following link: communities.bentley.com/.../24627.system-head-curves-in-watergems-and-watercad

    For information on modeling air valves in SewerCAD, see the following link: communities.bentley.com/.../modeling-force-mains-with-air-valves

    In addition, there are upcoming presentations on modeling air valves in SewerCAD planned for November 18 on modeling air valves in SewerCAD. You can find more information and sign up for the presentation at the following link: pages.info.bentley.com/sigs

    Regards,
    Scott
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