A partially closed valve would not restrict the water flow, when running or on plane, enough to harm the pump, even if the pump is on, I think! If I can adjust the valve enough to equal the capacity of the out flow tube, then this would be the same amount of water the pump would ordinarly pump anyway.
The question is, when I stop, the pump is going to be pumping with a restriction (partially closed valve), is this going to harm the pump? Do I need to fully open the valve once I stop?
I think you answered the question, if the pump is getting any water, the impeller will not be harmed????