A rotary multi-port valve has a valve body having a primary flow port and a plurality of secondary flow ports. A rotary diverter is rotatable within the valve body and has an internal piston receptacle. A port selector piston is linearly moveable by hydraulic pressure from a de-energized position within the piston receptacle to an energized position for sealing with a selected flow port and accomplishes development of a spring force during hydraulically energized piston movement. Upon reduction of the hydraulic pressure the stored spring force returns the port selector piston to its de-energized position freeing the rotary diverter member for selective rotation to another selected flow port.