No matter what I do I can't get the design run to be within the minimum or maximum velocity constraint that I have set. Why is this?
The automated design feature attempts to minimize excavation, so constraints like the minimum and maximum velocity are at the bottom in terms of priority (see article in "See Also" section below.) For example in order to meet a minimum velocity constraint, it may be necessary to bury at least one end of the pipe deeper to increase the slope, which increases excavation costs.
If a design priority is violated a user notification alert for the element that violates it will be generated and you might need to make a need an engineering decision on whether this is going to be ok for your project or not. The automated design tool can give you a good starting design but you will still need to use your engineering judgment to refine further.
What is the order of the design Priorities used in StormCAD and SewerCAD?