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Surge vessel is completely draining

Surge vessel is keep draining even after increasing & down surge is also not controlling at all, kindly check the attached model For_Surge_PS_Variation_UDC_10.8_TB _IRR_Primary_IFC_07_11_2022.zip

  • Nagesh,

    Looking at your profile, this is a system where you are pumping over a high point with no downstream storage. Once the pumps shut down, there is nothing to prevent the hydropneumatic tank from continuing to drain, until the pumps turn back on. 

    This is a common situation which is documented in its own article here: Negative pressures occur during a transient simulation no matter what protection is used

    You may need to consider how long the pumps will remain off, and model a pump stop + restart per this article: Modeling a pump startup and shutdown transient event in the same simulation

    Some other comments/observations:

    • Your timestep is a bit too large at 0.1 seconds. I suggest using a slightly smaller timestep in order to accurately capture fast changes. For example 0.01-0.05 seconds.
    • You have significant resistance through the hydropneumatic tank inlet. Your main pipeline is 700 mm, which goes down to 400 mm in the lateral tee pipe connecting to the tank, and then the tank inlet orifice diameter is set to 200 mm. As a quick example you will see better controlling of the initial downsurge if you change the pipe and inlet diameter to 500 mm and the minor loss coefficient to 1.0. If you then change the gas preset pressure to 10 m, it will no longer become empty during the simulation (but again you will need to determine the balance here, and restart the pumps.
    • Similarly your air valve lateral pipes are very small compares to the main line and may significantly reduce their effectiveness due to headloss. For example pipe P-89(2) is 700 mm and the lateral P-57 connected to the air valve is only 80 mm.
    • Some air valves are not configured correctly, such as AV-37 which has zero for both the inflow and outflow diameter.
    • You may also want to double check the pump check valves (which can often "slam" when using with a downstream hydropneumatic tank) and the pump inertia and specific speed, as they will influence the transient response during shutdown. You appear to have modeled your check valves twice; once in the pipe properties downstream of the pumps, and again in the pump properties.


    Regards,

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

  • Thank you so much Jesse for your detailed observations & suggestions, will check the model considering your observations & will update as per your suggestion