Message ID 40005 "Network Unbalanced".

Question

I have a looped system, with 2 points of connection to an existing water main that are modeled as reservoirs. Each reservoir has a GPV. 
 When I run the model I receive an error (Message ID 40005) and flow is showing through the reservoir at 500gpm even though there is no demand proposed for any of the junctions. 
 I don't receive this error when I only have 1 reservoir. 
 Why is the network considered "unbalanced" when there are 2 reservoirs?

MPachlhofer · Accepted Answer

Jaclyn, 
 
I wanted to add some other information that I found while working with the model. The reason that network unbalanced notification is being generated is because the difference between the hydraulic grades in the reservoir is so minimal the computation engine is going to have a problem solving the equation. On top of that the GPV's are trying to induce a 15 foot headloss at 0 flow with no demands in the model, so the difference between the reservoir hydraulic grades would have to be at least 15 feet in order to solve the equation. For example, I've found that if you make the elevation of R-2 316 ft. the network equation is able to be solved. This difference provides the 15 feet of head difference at the second GPV (GPV-1) to allow the model to balance, while satisfying all the other losses in the system. 
 
I also noticed that if you provide a fire flow demand of 500 gpm at one of the junctions or hydrants in the system, while the reservoirs are maintained at their original elevations the model will solve. This is because with a 250 gpm demand there is enough flow to be able to induce a 15 ft. of headloss at both GPV's. With flows closer to 0 it makes it difficult to solve the network hydraulics. 
 
I would still suggest modeling a connection to an existing system using the information in the wiki for getting the best results from this model. 
 
Regards,

Scott Kampa · Answer

Hello Jaclyn,

Try increasing the number of trials in the calculation options. To do this, open the calculation options from the Analysis menu. Double-click the active calculation option to view the properties. Find the Trials property and increase the value. For instance, if this is set to 40, change it too 100. Sometimes a few more trials are needed for some models.

If that doesn't help, check the properties of the GPV. Make sure the curve is accurate and make sure that the orientation is correct (basically that the correct pipe is the downstream pipe).

The following link has other steps that you can try as well: communities.bentley.com/.../8769.troubleshooting-network-unbalanced-or-cannot-solve-network-hydraulic-equations.

If none of this helps, we will need to see a copy of the model files. The following link has information on sending the model to us: communities.bentley.com/.../32255.sharing-hydraulic-model-files-on-the-haestad-forum. If you upload the model to Sharefile, please post here with the name of the file so that we know it is available.

Regards,
Scott