The theory behind system head curves is that there is a tank or reservoir on both the suction and discharge side of the pump for which the curve is developed. In the case of closed (dead end) systems, there is no reservoir or tank downstream of the pump. The demands must always be exactly met. In order to develop a system head curve for such a pipe network, it is necessary to account for the relationship between usage and pressure. Therefore the network demands must be represented by pressure dependent demands.

To develop a system head cure for such a network, the demands must be set to pressure dependent demands (PDD) and there must be no threshold pressure set for demands. This is done by:

1. Defining a PDD function in Components > Pressure Dependent Demand.
2. Setting up a PDD alternative assigning the PDD functions and making certain that "Reference Pressure Equals Threshold?" is unchecked.
3. Setting the Calculation Option "Use Pressure Dependent Demand" to True.

Check the model to make sure it runs correctly before creating the System Head Curve.