I agree with Mohamad.
The problem is that you are pumping into a dead end system with fixed demands. If the flow is fixed, you can't get a curve. In order to get this to work, you need to have storage on both sides of the pump or model the demands as emitters or pressure dependent.
I've attached a journal paper we did a few years ago explaining this.
Good Evening, I tried to model the demands as emitters or pressure dependent, but i could not and the problem for the system head curve still. so please if you can explain on the attached model how to model the demands emitters or pressure dependent.
Thanks in Advance
Eng Sayed Ali
Here is good topics will help you:
Thanks for this information. i tried to model the demand at juctions using pressure dependent demand function but this results as not as expected. i attached again the watergems model and excel spreadsheet for the expected system head curve. so please if you specify what to de exactly in the model to get the same result as per attached excel sheet, this will be so kind of you. please not that the minimum required residual pressure 3 bar at least.
Is this your entire system that you have modelled here? I'm guessing that it probably isn't and perhaps that is part of your issue. Is that system head curve you included with the project files based on the entire system? Is the power function for your pressure dependent demands that you are using in this model the same thing that is being used in your system? Do the demands in the model seem correct based on the pressure at the locations you've specified in this model? I'm really looking for you to provide me with as much information as you have on this issue so that I can try to help you out more.
Is this your entire system that you have modelled here?
Yes it is the entire system.
Is that system head curve you included with the project files based on the entire system?
It is based on entire system and the following steps explain how i developed the attached system head curve.
Cloumn B in Excel File it represents the range of expected flow.
Cloumn C in Excel File It represents the static head Difference between elevation of highest juction elevation (8.0 m) and suction tank elevation (5.1m) = 2.90 m.
Cloumn D in Excel File It is the friction loesses based on the expected flow. i divided the expected fow equally on the three juctions and run the waterjems model and see what are the headloss at each flow.
Cloumn E in Excel File it is the desired residual pressure.
Is the power function for your pressure dependent demands that you are using in this model the same thing that is being used in your system?
Acually i tried to make setting up for pressure dependent demand fuction to get the system head curve for my project but i could not. so all i need to know what is suitable pressure dependent demand fuction to be used to develop the correct system head curve for attached project. so if you can can develop the system head curve for the attached project and explain how you develop it this will be great help
Regards Sayed Ali
The model looks ok - I think the problem is with the Excel sheet. Normally a system head curve doesn't include a a 'desired residual pressure' component.
If you remove that column from the spreadsheet, then the system head curve in the model matches the spreadsheet pretty well.