Modeling fixed head parallel VSPs that have different head values

  Applies To 
  Product(s): WaterCAD, WaterGEMS, HAMMER
  Version(s): 08.11.XX.XX, 10.XX.XX.XX
  Area:  Layout and Data Input
  Original Author: Mark Pachlhofer, Bentley Technical Support Group

Problem

When trying to model fixed head parallel Variable Speed Pumps (VSPs) that have different head values, the following user notification is seen:

"Parallel VSPs are not allowed to be controlled by different nodes."   

Solution

1) Make sure both pumps have their own unique pump curves. One just has to be slightly different than the other one, so perhaps if they are the same or close you can just make the head and flow values on one of the pumps 0.01 feet or 0.01 meters large or smaller than the other one. 

2) Make sure that both pumps reference unique control nodes. 

3) Add in one or two additional junctions just upstream of each pump and add in one or two additional junctions just downstream of each pump. 

4) Set up controls that turn the pumps on or off, so only 1 pump is on a time. These controls can be based on Clock Time or System Time. Something similar to the example below should work. 

IF Clock Time  > 8:00 AM  THEN UWTP1 Pump Status = On  ELSE UWTP1 Pump Status = Off 

IF Clock Time  <= 8:00 AM  THEN UWTP2 Pump Status = On  ELSE UWTP2 Pump Status = Off 

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