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Mmajner
August 29, 2016, 04:14 PM
My mode contains several in ground storage tanks with pumps. The existing ground elevation in my area is at sea level which means my elevations for tank levels and pump elevation levels would be a negative value. The model seems to be functioning oddly when I use the negative values. Is InfoWater not set up to handle negative values?

Patrick Moore
August 29, 2016, 10:45 PM
Martin,

Negative elevations should not be a problem. Elevations are simply used to calculate pressures from the Head values calculated when the software solves the network equations.

Recall Pressure = (Head (ft) - Elevation (ft))/ 2.31 ft/psi so that negative elevations would simply be added to the head values rather than being subtracted as subtracting a negative number would result in adding the value.

If you get negative pressures this means that the hydraulic grade line falls below the elevation value. This is more of a mathematical construct within the modeling software though indicating if the demands as noted were fully supplied that it would result in negative pipeline pressures. In reality, the demands would generally be less when the pressures drop below 20 psi and any vacuum relief valves in the system would let in air before negative pressures could occur in the real system.

If you are not sure of results when using negative elevations please drop us a line at support@innovyze.com and we can look at your model in further detail to investigate further.

Patrick Moore