Fixed head control is achieved by selecting Fixed Head from the VSP Type? menu. Once Fixed Head is selected, you must describe how the control is implemented.

You must identify a node that controls the pump. This is the node where some type of pressure or water level sensor is located. This can be done by:

• Using the menu and picking the node from the list
• Clicking the Ellipsis (...) button and using the Select Element dialog box
• Clicking the Select From Drawing button and picking the node from the drawing

In selecting the control node, you must choose a node that is actually controlled by the VSP. For example, the selected node must be in the same pressure zone (i.e., one that is not separated from the pump by another pump or PRV) and should not have a tank directly between the node and the pump.

You must then select the head to be maintained at that node. If the node selected for control is a tank, then the Target Head is set as the initial head in the tank. If a junction node is selected, the head must be a feasible head. If a physically infeasible head is given, the problem may not be solved or some unrealistic flow may be forced to meet this head (e.g., backward flow through pump).

You also have the option of setting the maximum relative speed of the pump, which would usually correspond to the rated speed of the motor. The default value for this is 1.0. You can have the model ignore this limit by placing a large value in the field for maximum speed.