I am having some trouble with model.
At first, I was getting an unbalanced system. I did the walkthrough on how to check and fix an unbalanced system. We updated the controls, elevations, and pump curves.
Right now the Model is getting three errors.
I am getting reverse flow through PRV-5. I have been trying to fix this but I think there is something going on with the pump near it that I can't figure out how to fix. The other issue is that I am getting negative pressure in my system. The wells should be producing more than enough water to have descent pressure. I have already checked with the engineer and the client to make sure the set up is correct at this specific Tank.
I am working with the newest Watergems version and Engine used was WaterGEMS 2.00.12.
Hello Mark,
First, double-check that the downstream pipe for the PRV is correct.
Otherwise, the issue may be related to the disconnected demand nodes message you are also getting. WaterGEMS is a demand-driven system, so all demands must be satisfied to have valid results. If there are demands not able to be satisfied (because a tank is empty, a pump is off, a valve is closed, etc.) this will lead to errors in the calculation, including the possibility that WaterGEMS will try to force flow the wrong way through the valve. Resolving the disconnected demand nodes message will hopefully resolve the issue.
Regards,
Scott
I took the check valve off the pipe going from the system into the Tank-3E1. This corrected the problem disconnected demand nodes and the reverse flow at the PRV-5. Now it is saying another PRV-11 has reverse flow but I don't have a check valve set up in there.
See if you are getting a Network Unbalanced user notification. If so, you can try making some adjustments to the calculation options to see if that helps with the issue.
Otherwise, we would need to see a copy of the model.
Some practical tips.
Make sure the tank is at a very low level (tank essentially empty), if the PRV opens. Put the PRV target HGL near the bottom of the tank. The PRV should only open when, e.g. there is a large fire in the lower zone that has drained the tank.
Make sure the pump does not run when there is flow through the PRV. Otherwise, you'll be just pumping in a circle.
I am not getting network unbalanced user notification. The notification I am getting is "unexpected reverse flows calculated." and Pressure below the lowest physically possible in system at one or more time steps.I have already uploaded the model to the secure link.
Hi Mark,
The first thing that I could notice in your model when running the calculation were the error messages that appear, when going through the messages I found the message that your network is unbalanced so the first step to make your model work would be to get the network balanced:
A big problem that appears repeatedly in the error messages are tanks getting empty or full which ends up causing the network unbalanced, to visualize this situation you can right-click on your Tank element in the Element Symbology tab and then Select All > Right-Click on a blank space and in the window that will open, in the Fields section you should leave checked only the check-box for Percent Full and then you will receive the following chart, that demonstrates several tanks getting completely full and / or empty at different times of the simulation:
With this situation in mind I went to check your defined controls and I could notice that some of the controls only activate or deactivate your pump if they are higher or lower than the maximum or minimum tank elevation respectively, which is a situation that does not occur, so they end up never being activated, as is the case of tank T-3E1 where in the current configuration the pump is configured to turn on if the Hydraulic Grade goes below the minimum tank elevation which will never occur:
So, a first check that you should do in your network is about these controls and conditions so that the pumps turn on and off at the right points not leaving tanks full or empty, we have a very extensive article explaining the use of command and how to perform its correct use:
Using Controls, Conditions, Actions and Control Sets in WaterGEMS and WaterCAD
I also recommend the following that deals specifically with troubleshooting controls:
Troubleshooting Controls in WaterCAD and WaterGEMS
Another point that concerns me as mentioned by Tom is the way that some of his regions are configured, such as this section of the PRV-11 with the downstream pipe set to pipe P-263, because this way the valve is configured and with the pump On, the section ends up looping and returning to the reservoir, and this configuration is repeated in several section by the model, I find it interesting to go through the following article because it can take some doubts about the use of the PRV valve and help you to make the correct use for your model:
How does the Pressure Reducing Valve (PRV) work in WaterGEMS and WaterCAD?
Luca BillisTechnical Support Engineer, OpenFlowsBentley Systems, Inc.