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.
Hi Mal Sharkey;
Based on my undertanding that in order to develop the system head curve the static head (Differnce in water elevation between suction tank and disharge tank) shall be add. since we do not have discharge tank on our project and we have juction so the static head should be the difference between HGL in Suction Tank and HGL at the juction that is whey residul pressure should be add on the calculating the system head curve, so please if correct what i am saying if it is wrong. again please i need to know how to setting up for pressure dependent demands for the attached model in order to develop the system head curve. please if anybody can open the model and give me exact values and steps for doing the system head curve this will be great help for me. thanks in advance for every one.
Regards Sayed Ali
As I said before this is dead end system and I interested in the duty point in such models.... I agree with Mal input about the residual pressure. also I disagree with the way the spreadsheet developed.
It seems your goal from this model is to develop the system head curve curve only and that could be by excel for that simple system (but hard in big and loops network), I think you can play around to develop the loss curve only by adding reservoir at the end with the same elevation in J-3, but your duty point will not true, the only benefit is to copy the curve data into your excel and insert your pump curve in the excel sheet. again the most important in such models is to determine the duty point and that you can get it from the pump properties .