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WaterCAD invalid downstream link

Hi,

In WaterCAD, after validating my network, there occurs two messages for the pump in user notifications:

1- Reference to a deleted or inactive downstream pipe.

2- Directed node has an invalid downstream link.

What do these messages mean and what can I do?

 

Regards,

Seylan

Parents
  • Negative pressure at a pump is exactly what it says. It's just a warning. If your pump is at elevation 850 and the tank it is pulling water from is at 840, you'll get negative pressure at a pump. It's probably an indication that you may run into cavitation problems. You need to either lower the pump or raise the suction HGL level.

  • Dear Bentley,

    As you know The "suction element" field is no longer used in SewerGEMS V8i SELECTseries 2 (08.11.02.46, released in July), but still in Sewercad, so what if in future if Bentley would to improve pump’s properties and would to add fields for NPSH of the pump which I like to be in pumps section, will be great if we can get NPSH calculated in the model and compare it with NPSH from manufacture. Myself and as I know many engineers using Bentley products in pump stations and lift station design and that item (NPSH) good to be in the model.

    Mohamad Azzam,

     

  • Hello Mohamad,

    With the SELECTseries 2 release of SewerGEMS and SewerCAD V8i, the pump orientation behavior actually matches. Both SewerGEMS and SewerCAD only need the "downstream link" attribute for a pump.

    Regarding NPSH - one of the great things about SELECTseries 2 is the introduction of Formula-Based User Data Extensions. With this feature, you can add your own result fields. The value in these fields will automatically update based on a formula that you enter, which can consider other calculated or user-input fields. So, in SewerCAD and SewerGEMS V8i SELECTseries 2, you can create a formula user data extension to compute the NPSH for your pumps. The next release of WaterGEMS and WaterCAD should have this feature as well.


    Regards,

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

  • Jesse,

    Thank you so much, you are as usual impressing me.

    Please may you explain more about the formual and terms of NPSH should be used in the program, as you know the formula has many terms in theory, i.e some are using vabour pressure ans so and so ..... of terms.

    what do you think is the best one to work with the product and how to create that.

    Thanks,

    Mohamad

  • Mohamad,

    You're welcome.

    Please see the screenshot in my previous post. From what I understand, NPSH is the upstream pressure head, plus atmospheric pressure, minus absolute vapor pressure. The latter two terms are different depending on your location, and the upstream pressure head can be gotten from the difference between the upstream HGL and pump physical elevation (or suction pressure field, in feet or meters). So, here's another way you might set it up, in SewerCAD:

     

     

    Our Advanced Water Distribution Modeling and Management book goes into greater detail on NPSH (see pages 324 and 325). It also has tables that show typical atmospheric pressure and vapor pressure values, for various elevations and temperatures.

    I hope this helps.


    Regards,

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

Reply
  • Mohamad,

    You're welcome.

    Please see the screenshot in my previous post. From what I understand, NPSH is the upstream pressure head, plus atmospheric pressure, minus absolute vapor pressure. The latter two terms are different depending on your location, and the upstream pressure head can be gotten from the difference between the upstream HGL and pump physical elevation (or suction pressure field, in feet or meters). So, here's another way you might set it up, in SewerCAD:

     

     

    Our Advanced Water Distribution Modeling and Management book goes into greater detail on NPSH (see pages 324 and 325). It also has tables that show typical atmospheric pressure and vapor pressure values, for various elevations and temperatures.

    I hope this helps.


    Regards,

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

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