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How can I create a control whose condition is based on the sum of flow through multiple pipes? For example the total flow into a DMA from multiple entrances.
Although it is possible to use pipe flow as a condition with controls, it is not directly possible to configure a condition as the sum of flow through multiple pipes.
However, this can be accomplished by setting up a fictitious network with two reservoirs connected to two FCVs, that join at a single junction, then connect to a reservoir at a lower elevation with a single pipe. Configure a series of controls that change the setting of each FCV based on the flow in the two pipes you want to monitor. When the FCVs change their setting to match their respective pipe flow, it will effectively set the flow through their pipes, and when those pipes join together and go through a common pipe, that common pipe will have the sum of the two pipe flows, and you can use that pipe as your condition for your 'real' control.
You can download the following example model. This can be opened in version 10.00.00.55 and greater of WaterCAD or WaterGEMS:
Condition on sum of two pipe flows.wtg.zip
Note that you would need several controls to check each range. In the attached model the granularity is 10 L/s with three increments of controls for each FCV, just for illustrative purposes. In the real system, some finer granularity might be best. You would check the expected range of flow through each pipe and set up the controls based on that.
Creating a timer control to execute after a specific time period has elapsed
Controls for alternating or cycling between multiple pumps