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Is it possible to have a pump curve in the pump definitions use linear interpolation (go from point to point) instead of follow a curve?
By default, the pump curves for WaterGEMS, WaterCAD, SewerCAD, and SewerGEMS follow a quadratic interpolation, giving the pump curve a smooth shape, as shown in the screnshot below.
At times, a user might want a multipoint pump curve to follow a linear interpolation. This could be because the values in the pump curve may work better with a linear interpolation. For instance, there may be a large different in flow for a small change in head. A user may also have pump data from a manufacturer that follows a linear interpolated pump curve and want the data in the model to match exactly.
In such cases, there is a setting in the calculation options where a user can set a multipoint pump curve to use linear interpolation. To use this, open the calculation option properties by going to Analysis > Calculation Options, then double-clicking the active calculation option. In WaterGEMS and WaterCAD, find the section called Hydraulics and change the setting for the attribute Use Linear Interpolation for Multipoint Pump Curves to "True". In SewerCAD, the same attribute can be found in the section called Pressure Hydraulics.
Note: This only works for multipoint curves and not for three-point or one-point curves.
If the user is using SewerGEMS, quadratic interpolation is also used as a default, and there is no direct way to change this. However, for SewerGEMS SELECTseries 3 and later, there is an indirect way to use linear interpolation for pumps. To do this, first change the Active Numerical Solver in the calculation options from "Implicit" or "Explicit" to "GVF-Convex (SewerCAD)". The SewerCAD calculation option properties will then be available, including the attribute Use Linear Interpolation for Multipoint Pump Curves. Change the setting of this property to "True", then change the Active Numerical Solver back to "Implicit" or "Explicit". The multipoint pump curve will not follow linear interpolation.
With linear interpolation set, the pump curve will look like the screenshot below: