How do pumps work in the hydraulics and hydrology products?
Pumps add enough head and the corresponding flow rate, which is defined on your pump definition curve, to overcome the losses and elevation differences between your upstream and downstream boundary conditions. Boundary conditions are tanks, pumps, reservoirs, and valves in the Water products and manholes, catch basins, outfalls, and wet wells, headwalls/endwalls in the SewerCAD.
The pump operating point is where the pump curve intersects the system head curve. For more details on this please refer to this wiki.
In the case of a closed system with only downstream fixed demands in WaterCAD and WaterGEMS, the operating point will be based on the demands. Essentially, it operates at the point where the pump characteristic curve intersects with the system head curve. You can read more about this in the book Advanced Water Distribution Modeling and Management
For the initial conditions calculations in HAMMER, pumps are treated in the same manner described above since it uses the same numerical solver as WaterCAD and WaterGEMS.
For a transient simulation, a pump is treated as a hydraulic boundary based on it's settings (such as the transient pump type, pump valve type and operating rule) along with the four quadrant characteristic curve based upon the selection of Specific Speed (in the Transient tab of the pump definition).
For example if the pump should remain on during the transient simulation, it can be treated as either the original pump curve, or a four quadrant curve (see this article). If an emergency shut down should occur, you can select "shut after time delay" and it will model the applied torque dropping to zero at the time specified (see more here).
As transient conditions change such as a transient wave reaching the pump, it will use the built in four quadrant characteristics to simulate the resulting change in the model, which can then propagate past the pump. See more: Specific Speed and Pump Flow Calculations for a Transient Simulation
In SewerGEMS with the Implicit numerical solver, the downstream boundary is considered to be the crown of the pressure pipe where it meets the receiving gravity node, or any intermediate high point. System Head Curves can only be generated with the GVF-Convex solver: Generating a System Head Curve in SewerGEMS
When using StormCAD or the GVF-Rational solver pumps are supported as of Select Series 3 [08.11.03.77]) and are treated as ideal flow pumps, meaning that flow in will equal flow out and the pump curve is not used in the calculations. This means that the pump flow will be equal to the flow into the upstream wetwell or pond. This solver does not support parallel pumping or pump controls.
When using the GVF Convex solver pumps will work the same as the pressure solver for pressure situations and will work the same as the implicit solver for gravity situations. When running a steady state the solver doesn't support pump controls.
A pump exceeds the maximum operating point user notification
System Head Curves in WaterGEMS and WaterCAD