Double Flow Pipe

Question

Hi, 
 
 I uploaded 2 files using Benetly Sharefile the first one is called ONE VFD where the system is running smoothly and the pipe PP11 is having a flow of 15,583 GPM and 7.07 ft/s velocity which is our design parameter. After defining the second pump to be a VSP in the second uploaded file called TWO VFD, the same pipe (PP11) is having 31,162 GPM and 14.14 ft/s velocity. Apparently, the pump-2-VFD is directing flow into that pipe for some reason, and that is only happening when it's defined as VSP. Even when I defined all the pumps as VSPs, I got 62,000 GPM and approx. 41 ft/s for the same pipe (PP11). 
 I couldn't find out what is happening and why this pipe is getting these results, I even added check valve on it, but still the same problem. 
 
 Please review the models and reply as soon as possible. 
 
 Regards,

Scott Kampa · Accepted Answer

Hello Pedro, 
 
This is related to the setup of the model. Technically, this is not a valid setup for the VSPs in the model. The VSP have too many nodes between the pump and the connecting nodes. Because of these, the program does not treat them as parallel VSPs. Since they are not parallel VSPs, they cannot use the same control node. 
 
The next release of WaterCAD and WaterGEMS will have a validation message related to this. In the meantime, you can resolve the issue by reconnecting the pipe PP6 to be connected to J-21. With this setup, the pumps will be considered parallel VSPs and the flow downstream will be accurate. 
 
You can find more information on parallel VSPs in the Help documentation under the topic "Parallel VSPs". 
 
Regards, 
Scott

Scott Kampa · Answer

Hello Pedro, 
 
Yes, that setup makes the most sense if you will be using the same control node for all of the pumps. 
 
Regards, 
Scott