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Mmajner
February 4, 2016, 12:38 PM
Ran a scenario and received the following message

WARNING: Negative pressures at demand node(s) at 0:00:00 hrs.
WARNING: Pump U7060 open but exceeds maximum flow at 0:00:00 hrs.
WARNING: Pump U7062 open but exceeds maximum flow at 0:00:00 hrs.
WARNING: Pump U7094 open but exceeds maximum flow at 0:00:00 hrs.
WARNING: Pump U7096 open but exceeds maximum flow at 0:00:00 hrs.
WARNING: System unbalanced at 0:00:00 hrs. EXECUTION HALTED.

** Run failed **

** Error: hydraulic simulation failed due to unbalanced error **
Analysis ended Thu Feb 04 09:50:15 2016

How can I tell which nodes have the negative pressure so I know where to look for a problem.

Patrick Moore
February 5, 2016, 10:04 AM
Martin,

Unfortunately, if the model fails to complete the simulation at hour zero of the analysis, there are no results to display to check for negative pressures, which can make troubleshooting a bit more challenging. In these cases you have to look at things that could cause low pressures like perhaps not having enough water supply pushing pumps to run way out on the right of their curves which would lower the system discharge pressure.

You might want to check your settings for supply to make sure that your expected supply is close to what the expected demand at hour zero is reasonably balanced. With four pumps exceeding maximum flow it may be that you don't have enough supply to meet the model demand which is a possible cause for the "unbalanced" condition.

You could use the design flow of the pumps as a first guess on supply based on which pumps are running. Compare that to the base demand times the first pattern values to get demand at hour zero. If you use multiple categories for demand and this is too difficult, consider placing a reservoir at the discharge head of the pump station set to the discharge HGL of the pump station as a temporary measure which will allow enough supply for hour zero. Once you can verify there is enough supply for the demand you can remove this reservoir.