Abstract: An hydraulic rotary valve is provided which permits the accurate control in an open loop system of the position of a valve plate in the rotary valve for directing the flow or pressure between multiple flow paths. Mechanical centering means are provided for returning the valve plate to a predetermined closed position whenever power is turned off or lost to a stepper motor comprising valve actuating means. A stepper motor is linked to the valve plate and machine intelligence means for controlling the operation of the stepper motor are provided, including means for registering the position of the valve plate when mechanically returned to a predetermined closed position, determining the required number of electrical pulses at the desired frequency sufficient to activate the stepper motor for a predetermined number of degrees of rotation of the output shaft to advance or return (in clockwise or counterclockwise rotation) the valve plate to a desired position.