WaterGEMS Disconnected Demand Nodes Due to Booster Pump Shuts Off

I have a water model with multiple pressure zones.  There is one main low pressure zone that is fed by reservoirs and a couple storage tanks and there are 4 other parasitic higher pressure zones that feed off the low pressure zone.  3 of the 4 pressure zones have their own storage tanks.  The 4th pressure zone has just a booster pump that kicks on and off depending on the system pressures seen at the station on the discharge side of the pump.  This booster station feeds a couple dead end water mains that go up a steep hill.  I am getting a "disconnected demand nodes detected; hydraulic results are likely to be compromised" error when the pump is off which isolates that zone from the low pressure zone which has the water sources.  How is a situation like this modeled?

  • Usually when a pump to a dead end zone with no storage turns off, the customers are without water.

    What may be happening in your system is that there could be a bypass check valve around the pump station that enables water to flow around the station at times when the pumps are off. This will result in lower pressures in that zone, but depending on the elevations, the customers will still have some water.

  • To add to Dr. Walski's reply - the reason you get the "disconnected demands" message is because when you enter a demand in WaterGEMS, the model will always try to satisfy that demand. When that is not physically possible (because the only path supplying them it closed), then you get the message in question and flow will be forced through the pump to satisfy the "known in the equation". If the demands really do get cut off and those customers are without service, you could model this using Pressure Dependent Demands (PDD), where the demand drops as the pressure drops. See more here: Disconnected Demand Nodes user notification when computing model


    Jesse Dringoli

    Technical Support Manager, Haestad Products
    Bentley Communities Site Administrator
    Bentley Systems, Inc.