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Inadequate flow through pipe

This model refers to a pump lifting water from intake well to WTP.

The pump has design head of 27.9 m & design flow of 4790 cu.m/h. But the flow though the pipe is found to be low ( approx. 519 cu.m/h) . Please guide to solve this problem. The model is attached for reference.

Regards,

Sujoy De

Model-1-May-2016.rar

  • Sujoy,

    In the model, the total length of pipe is 1,287,018 meters, which seems like an extremely long distance from a well to a treatment plant. Is this accurate?

    The reason you are not getting the flow you expect is that there is a lot of friction headloss between the pump and the tank - 1,000 km is a long way to push that much water. Here are a couple of tools that may help you:

    System Head Curve: If you right click on the pump, and select System Head Curve, you can see a graph that compares how much headloss there will be at different flow rates, as well as the pump curve. The flow rate that the pump will push is the flow at the intersection of the pump curve and the system head curve. If you put in the Maximum Flow that you are interested in (4790 cu. m/h), and press the green 'Compute' button, you'll see that you'd need a pump capable of over 3000 m of head to get your desired flow.

    Pipe Flex Table: If you find the menu button called 'FlexTables' and select the dropdown for Pipes, you will see a table of all the pipes in the model. The model currently has a large number of pipes with a length of 31,000 meters. You can right click the field column where it says 'Length (Scaled) (m)' and select Statistics, and it shows that you have 49 pipes with a total of 1,287,018 m.

    If this isn't the correct length, one easy way to simplify the model would be to delete all the pipes between the air valve and the tank and replace it with a single pipe. If you don't need the model to be referenced to a particular GIS coordinate system, you can double click on the pipe, change 'Has User Defined Length?' to True, and enter the 'Length (User Defined) (m)' to whatever the correct length of pipe is.

    Once you've got the lengths correct, you should double check that the pipe diameters, reservoir elevation, and tank elevations are correct. These will all affect the ability of the pump to achieve the desired flow rate. If you still can't get the expected flow rate, the pump may be too small.

    -Stephen

    Answer Verified By: Scott Kampa 

  • Thanks for answering this, Stephen!

    For reference, we have wiki on system head curves. You can find the link on this topic here: communities.bentley.com/.../24627.system-head-curves-in-watergems-and-watercad

    In the See Also section of the link above, there are other relevant topics to this as well.

    Regards,
    Scott