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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 ?

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  • You mentioned that you will be serving a hilly area. If the range of elevations is large (difference between highest and lowest customer > about 50 m), it may be necessary to divide the system into multiple pressure zones. There would be a high zone for the highest elevation customers' a low zone for the lowest and possibly multiple intermediate zones. Depending on the elevation of the source, there will be pump stations to feed uphill, and PRV stations to feed downhill.

    See the help for pressure zone manager.

    Answer Verified By: Syed 

  • Thanks a lot for your suggestions. I have also uploaded in my model files in Bentley Secure File Upload. I will really appreciate if you see my model.

    Thanks 

  • Thanks a lot Jesse. If I assign air release valve at high point and treat this air valve as junction "False" then it gives me error "disconnected from reservoir or tank". I have uploaded my model as well. 

  • 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. ?