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.
Thanks A lot for your responses i figured out the problem as both of you said it is due to dead end system. and i should use pressure dependent demand functions.
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