How do I develop a pump curve if the only known information is the required flow that the pump should supply?Area: Modeling, Problem ID#: 46730
To estimate the head the pump would need to add, add two junctions to the drawing, one before and one after where that pump will be, without connecting them (see screenshot).
Then add the required flow on the first junction as a positive demand (J-2), and add the same flow as negative demand (inflow) on the other junction (J-1). For example, on J-2 you might have a demand of 1,000 L/s, so on J-1 you would input -1,000 L/s for the demand. The head that a pump would need to add is the difference in hydraulic grade between those two nodes, after running the model.
After going through the steps above add a pump element in place of those two junctions (J-1 and J2), then add a one point design pump curve (with the head estimated from above steps). Run the model, then generate a system head curve (by right-clicking on the pump) to size the pump based on it.
Note: For a closed system (only demands downstream, no storage) this process will not work since all elements must be connected to a reservoir or tank. Consider using pressure dependent demands in this case, so flow on the system head curve is allowed to vary or simply size the pump based on the sum of the downstream demands.
System Head Curves in WaterGEMS and WaterCAD
Efficiency Curve vs. Wire-to-Water Efficiency Curve