Background:

I am modeling our storm water collection system using InfoWater. We pump excess storm water from ponds (tanks with negative demand nodes) around the county to a ground storage tank (GST) before treating it and distributing it for irrigation. The modeled system ends at the GST.

Issue:

The GST has a free surface intake at an elevation of 26 feet modeled using a PSV set to zero as suggested in the FAQs. Many of the pumps and ponds are at elevations well above 26 feet (as high as 90+ feet). The result is a negative pressure at any node above 26 feet suggesting a siphoning of all contents above that elevation. This causes the pumps to operate outside of their curve or at pressures well below their actual operating condition. This siphoning effect is also seen in lines and at pumps where there is an intermediate maximum elevation. I have tried experimenting with Vacuum Breaker Valves and Pressure Sustaining Valves with no success in overcoming the siphoning effect.

Has anyone been able to overcome such a scenario and how? Any suggestions would be appreciated.