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Huge pressure drop at the downstream of TCV

Dear Sir,

The pump has design head of 38.3 m & discharge of 2570 cu.m/h. The pump startup condition is modeled in this file. The transient result viewer shows a pressure drop of 10 m at the downstream of TCV. Please ascertain the reason behind such high head loss near the TCV in this model.

Also severe negative pressure is observed along the pipeline. Please recommend the solution without using surge vessel & without increasing the inertia of the pump & motor.

One thing that requires attention is the flow through the pipe. The flow is shown as 2690 cu.m/h although the pump is delivering 2570 cu.m/h. Why such disparity is occurring in the model?

The model is attached at the end of this message for reference.

Regards,

Sujoy De7762.model.rar

Parents
  • In the pump properties under Initial status the pump is off; change it to On since you do not have any control.

    Regards....Mohamad.
  • We want to model the startup event of the pump. Hence, the initial status of the pump is set to "Of".
  • Hello Sujoy,

    In the latest version of HAMMER, there doesn't appear to be any negative pressures in the model that you sent.

    If you are not already using it, you may want to download and install the latest version of HAMMER. Otherwise, make sure that you provided the correct model.

    Regards,

    Scott

  • The transient result viewer shows a pressure drop of 10 m at the downstream of TCV. Please ascertain the reason behind such high head loss near the TCV in this model.
  • Hello Sujoy,

    Could you please send a screenshot of what you are seeing? Thank you.

    Regards,
    Scott
  • I'm seeing the same results as Scott - in the scenario "With Air Valve 120 mm dia", when the pump first starts up, there's a drop in head across the TCV, but that it due to the valve starting in the closed position per its "15 s opening" Operating Rule, which quickly starts opening from a relative closure of 100% at time 8 seconds to 0% at 17 seconds. So, after the valve opens and the flow form the pump passes downstream, the system eventually settles on a final steady state where I see no noticeable headloss through the valve.

    I tested this model in both the latest version (08.11.06.113) as well as the version you appear to be using (08.11.06.58) and had the same result.

    The only thing that stood out to me was the initial status of the valve - it's set to active with a headloss coefficient of 0.4, whereas the operating rule suggests that the valve is initially fully closed. If 0.4 represents the fully open conditions, you may want to enter that as the Minor Loss Coefficient (fully open coefficient) and set the initial status of the valve to Closed. In this particular case (and in my version) this should not make a difference though.

    It would indeed help to have additional information such as the scenario name and exactly where you're looking. Screenshots can help.


    Regards,

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

Reply
  • I'm seeing the same results as Scott - in the scenario "With Air Valve 120 mm dia", when the pump first starts up, there's a drop in head across the TCV, but that it due to the valve starting in the closed position per its "15 s opening" Operating Rule, which quickly starts opening from a relative closure of 100% at time 8 seconds to 0% at 17 seconds. So, after the valve opens and the flow form the pump passes downstream, the system eventually settles on a final steady state where I see no noticeable headloss through the valve.

    I tested this model in both the latest version (08.11.06.113) as well as the version you appear to be using (08.11.06.58) and had the same result.

    The only thing that stood out to me was the initial status of the valve - it's set to active with a headloss coefficient of 0.4, whereas the operating rule suggests that the valve is initially fully closed. If 0.4 represents the fully open conditions, you may want to enter that as the Minor Loss Coefficient (fully open coefficient) and set the initial status of the valve to Closed. In this particular case (and in my version) this should not make a difference though.

    It would indeed help to have additional information such as the scenario name and exactly where you're looking. Screenshots can help.


    Regards,

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

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