Hello,
I have a water model where two of my tanks that 'float' on the distribution system (both have same base and overflow elevations) that will gradually empty in my EPS scenario. Neither has a separate inlet. There is a 3rd tank some distance away that is about 20' taller than the other two, thus, it should fill the two lower tanks. However, there is a PRV in between the higher and lower tanks that drops the hydraulic grade to below the lower tanks. Downstream of the PRV some distance away is a booster pump that is controlled to fill one of the lower tanks (turns ON when tank is < 80% full, and OFF when tank is > 98% full). During the EPS scenario, the two lower tanks gradually empty over time (see graph below). Furthermore, a graph of the pump shows Zero flow throughout the 72-hour simulation, although it seems to be providing sufficient head on the downstream side. There are no error/warning notifications for the pump at all. When I create a profile of the higher tank to the lower tank, the hydraulic grade shows that it is higher than the lower tanks, so i would expect the lower tanks to eventually fill up again. Demands in the system are fairly low and should not stop the tanks from filling.
Any Insight would be appreciated. Thanks.
I am using WaterCAD CONNECT. Engine compatibility is WaterGEMS 2.00.12
Have you checked the orientation of the pump and valves? The hydraulic grade in the second screenshot appears to be flat, suggesting zero or very low flow. If you believe the controls are not operating correctly, check to make sure they are added to the control set used in the current scenario. See: Troubleshooting Controls in WaterCAD and WaterGEMS
For further investigation, we would need to see a copy of the model: Sharing Hydraulic Model Files on the OpenFlows Forum If you need to send the model, please be sure to respond here with the file name and detailed steps to reproduce/observe.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Thanks, Jesse. I uploaded the model files to the Bentley secure file upload page, " Cutter Lateral Regional Water System"
Steps to reproduce troublesome results:
- Open file and run the 'EPS Run' scenario.
- The pump in question is label: WHL-PMP-NEW-WHL-NE
-the lower tanks in question: WHL-T-NEW-WHL-NE and WHL-T-WHL-1&2
- the higher tank is COP-T-PUEBLO_PINTADO
-when graphing the two lower tanks, you will see the gradual emptying of both tanks. Graphing the pump shows zero flow through the pump. The controls for this pump are intended to fill Tank: WHL-1&2 when it reaches 80% full, and shut off when it reaches 0.5' below max level.
Thanks for sending the model. It appears that there is a very high headloss through PRV "COP-PRV-4" causing the HGL to be very low on the upstream side of your pump, which causes it to be unable to turn on (pass any flow) because the downstream HGL ends up being 182 ft higher than the upstream HGL. Since the pump shutoff head is 106 ft, it cannot turn on. Since it cannot turn on, the flow is zero and those two lower tanks do not get filled. The profile appears to show a higher HGL near the lower tanks, but that is just the tank's hydraulic grade. If you graph the flow for the pipes adjacent to the lower tanks you will see that they have a small outflow, not enough to cause a significant hydraulic gradient to appear in profile view.
The reason for the the very high headloss through the PRV appears to be due to the setting of 50 psi. This would at first glance appear to be a reasonable pressure, but the elevation of the PRV is very low (6,665 ft), so the PRV is actually trying to reduce the hydraulic grade to 6665+(50 psi * 2.31)=6780.5 ft, whereas the upstream tank is at nearly 7000 ft. In general it is best to use HGL instead of pressure for valve settings.
There also appears to be a problem with the pump controls. Both the on and off control are using the less than operator (see below screenshot which uses the new control UI, upgrade to the latest version to see this) See related article here: Troubleshooting Controls in WaterCAD and WaterGEMS
If for example I change "COP-PRV-4" to use a hydraulic grade setting of 6970 ft and change the second pump control above to use the greater than operator, the two lower tanks no longer drain:
Thanks for your review of the model! The pump control was a silly error on my part, thanks for catching that. I also modified the pump curve design point to have a higher shutoff head, and that allowed the pump to run as expected. I kept the same pressure setting for COP-PRV-4 because that was a field-verified setting for that valve.