How to create Multi Pumps Model?

Question

Dear All, 
 I'm trying to model a system in WaterCAD it consists of 7 Pumps each pump should left certain flow . Each pump has a pressurized pipe then these pipes are connection together to the final location where I want to deliver the total flow. 
 
 What I did is creating a junction before the pump with negative demand equal to the flow which is needed to be lifted by the pump. But at the connecting junction the pressure is very high than the pressure of the pump although the ground level is flat in the served area. 
 
 So How waterCAD calculate the pressure at this Junction? 
 
 AYA

Tom Walski · Accepted Answer

In answer to your specific question, the HGL, and hence pressure, is calculated by starting at a know HGL (e.g. reservoir) and adding or subtracting head loss depending on the direction of flow. 
 
It is usually advisable to have a reservoir on the suction side of the pumps. Using a negative demand will force that amount of water through the pumps regardless of whether it makes sense or not.

Jesse Dringoli · Answer

To add to Tom's response - when using a reservoir on the upstream side, the pumps will operate on the defined pump curve, at the point of intersection with the system head curve . So, if the rest of the model is configured appropriately to match the real system, the pumps will operate as expected. 
 If the pumps in question are variable speed pumps that vary their speed to meet a fixed flow setpoint, set "Is variable speed?" to "True", then configure the fixed flow amount. 
 Other wiki resources that may help: 
 How do pumps work in the hydraulics and hydrology products? 
 General Pump Selection Process