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Static Head in WaterCAD

WaterCAD generates nice system head curve if the model has (reservoir -pump - reservoir) configuration. I have other case which common force main; two pumps joining one force main as shown in the screenshot below, the question is: why when one pump is operating (PMP-1) I have correct static head (25 m) but when two pumps operating the static head of (PMP-1) does change?

I trust the result but the presentation needs elaboration because if I attach the system head curve resulted from the model to the design report; it could be somebody will ask about the static head, in theory the static head should be fixed even other pump contributed with the force main.

I had this situation many times and was hard to convince others by the output in terms of how the static head change to satisfy the pump and operation and always they expect the static head reflect the real life.

I am looking to understand why that is happening? and how to explain that to others? 

PS: Why I am not able to see my post at the Home tab??, I have to go to Forum tab to follow up, previously when add new post it does appear in the Home tab, Please support.

  

Regards........Mohamad

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  • Thank you Mal, that is perfect answer and it is really; exactly what I am looking for.

    One more thing, I know that you estimated the HGL(@J-1) = 45m when PMP-2 is one and PMP-1 is off because I provided the system head curve and the elevation at the R-1, how to calculate the HGL at J-1 when PMP-2 is on and PMP-1 is off? how is the calculation would be (J-1 is not in the flow path)

    Thanks..............Mohamad

  • I would probably just use WaterGEMS to compute the HGL at J-1 when PMP-2 is on and PMP-1 is off...

    But you should also find that the HGL at J-3 is the same as the HGL at J-1. That's because there is no flow from J-1 to J-3 (so no headloss)...but they are still connected hydraulically so J-1 'sees' the HGL from J-3.

          

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  • I would probably just use WaterGEMS to compute the HGL at J-1 when PMP-2 is on and PMP-1 is off...

    But you should also find that the HGL at J-3 is the same as the HGL at J-1. That's because there is no flow from J-1 to J-3 (so no headloss)...but they are still connected hydraulically so J-1 'sees' the HGL from J-3.

          

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