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Negative Pressure in my Model

Dear All,

I have designed a water supply system. In this system there are four pumping stations. (Fixed location). I have assigned my desired flow and head to each pump and demand at every junctions. When I have run my model, It's giving me negative pressure in few junctions in distribution lines where elevations are higher than reservoir's elevation as there are many high and low points in whole system. Please suggest me how to solve this negative pressure. Is this problem related to boundary conditions ?

  • Hello Syed,

    Are the elevations in the system correct? The downstream reservoir has an elevation of 157 feet, but a nearby node (J-309) has an elevation of 176 feet. The pumps in your model will add enough head to help satisfy the demands and balance the hydraulic grade in the system. Because of this second item, increasing the elevation of the downstream reservoir has an impact on the pressure results. Similarly, the elevation of J-309 is quite high compared to both the nearby junctions and the reservoir. Reviewing this elevation recommended.

    Regards,

    Scott

  • Thanks a lot Scott. Yes elevation is correct. There are many high and low points in branches and also in mainline. Should I increase head of pumps in order to have positive pressure at J-309. ?  

  • Hello Syed,

    If the elevations are correct, I'm not sure if adding more pump head will help, as the head will likely decrease as it nears the low elevation of the reservoir.

    Are there air valves in the system now? If this is an existing system, do you have any details on field results to compare to the model data?

    Regards,

    Scott