When defining the pump capacity/performance curve for a pump in the database, the recommendation is to define the curve across the full quadrant. The image below shows two example approaches to defining a pump curve.

The blue colored curve is incomplete and depending on the number of data-points defined by the user, this type of curve-fit is possible. When solving a model, FluidFlow interprets flow rates past the inflection point of the curve which can then produce erroneous results in a model as well as lead to non-convergence. 

The recommendation is therefore to define the capacity/performance curve for a pump across the full quadrant. This can also speed-up model calculation, particularly in models with multiple pumps. 

The orange colored curve below therefore represents good practice and the approach which should be taken when adding any new pump curve to the database.

When adding your pump curve to the database, you can also set the Min and Max Limits (flow limits) to the values which relate to the vendor curve data. For instance, lets consider the curve data shown below. Let's say a vendor has provided a capacity curve between 5 m3/h and 40 m3/h. When defining the curve-data in FluidFlow, you can enter a data-point for 0 m3/h and 60 m3/h to complete the curve but in doing so, set the Min and Max Limits to 5 m3/h and 40 m3/h respectively.

This means that, if you were to model this pump in a system and the solved flow rate was below 5 m3/h, you would receive a warning message advising that the pump flow rate was below the minimum limit. Equally, if you were to model this pump in a system and the solved flow rate was above 40 m3/h, you would receive a warning message advising that the pump flow rate was greater than the maximum limit.

This therefore prompt us to review the pump performance more closely.