When the relative pump speed reaches maximum speed (usually 1.0), the model treats the pump essentially as a constant speed pump. In the case of pumps controlled by a junction node, when the conditions warrant, the pump will once again behave as a VSP.

However, for pumps controlled by tanks, the pump will run at a maximum speed for the remainder of the EPS run, once they reach maximum speed. To get the pump to switch back to variable speed operation, you need to insert a control statement that switches the pump back to variable speed. Consider the example below:

PMP-1 tries to maintain 280 ft. discharge at node T-1 on the discharge side of the pump, but pump (PMP-1) switches to full speed when the flow is so great that it cannot maintain 280 ft. In that case, the water level drops below 280 ft. As demand decreases, the level increases until it reaches 280 ft., at which time variable speed operation begins again. To make this occur in the model, you must use a logical control to restore variable speed operation:

IF (HGL T-1 >= 280 ft) THEN (PMP-1 = ON)