Pressure constrain-need help

[zho]

Hi everybody!
I am new in modelling water networks, so i am asking good people if they can help me, it would mean a lot to me.
I have to have constant pressure of 7 bar at the end of the network. At the entrance of network i have variable speed pumps, and in between junctions with demans. How can i get a required head and flow of the pumps working spot, if i have demands at the junctions changing over time, and i have to have CONSTANT pressure at the end of the network? I am working in Epanet.
Thanks everyone, and sorry for your time!