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User notification is generated after computing a model with parallel variable speed pumps (VSPs) about the pumps or "Network Unbalanced" or "Cannot compute network hydraulics"
Variable speed pumps have special rules because of the way they operate which make user notifications with them common. Please be assured we work on improving there functionality with future versions of the software whenever possible.
These are the VSPs rules that must be followed, which are outlined in the help document that comes with the WaterCAD, WaterGEMs, and HAMMER software titled "Parallel VSPs":
-- Parallel VSPs need to be modeled with the same pump curve and the same control node. If this cannot be done in a model, there are two workarounds you can try:
a. Instead of modeling them as parallel VSPs, model one VSP at one station and then set the relative speed factor of other pumps by using logical controls.
b. Set the relative speed factor of all the pumps by using the logical controls.
This setup in a model may cause problems because the pumps are not all connected to the same upstream and downstream node. I this case you might get a "Network Unbalanced", "Cannot compute network hydraulics", or "Variable speed pumps not in parallel cannot be controlled by the same control node." user notification.
The setup for the VSPs that will compute looks like this:
How do I model parallel fixed head (target head) variable speed pumps that are controlled by flow in a downstream pipe?