Abstract: A valve assembly for regulating the amount or pressure of hydraulic fluid supplied to a hydraulically operated machine system comprises a progressively movable valve member, especially a rectilinearly-moving valve spool controlling ports in a ported valve sleeve, a motive power unit, such as an electric stepper motor, disengageable speed-reducing coupling means, including a worm and worm wheel, to convert the rotary output motion of the motor into valve motion, a valve member position feedback transducer, and an electrical controller controlling the motor in response to input command signals and the feedback signal. A manual override control lever is provided for moving the valve member when the power drive is disengaged.

Abstract: A valve assembly for regulating the amount or pressure of hydraulic fluid supplied to a hydraulically operated machine system comprises a progressively movable valve member, especially a rectilinearly-moving valve spool controlling ports in a ported valve sleeve, a motive power unit, such as an electric stepper motor, speed reducing coupling means such as a leadscrew or worm and worm wheel driving a rack and pinion, to convert the rotary output motion of the motor into valve motion, a valve member position feedback transducer, and an electrical controller controlling the motor in response to input command signals and the feedback signal. A manual override control lever, and a centering unit for centering the valve in the absence of hydraulic pressure, can also be provided.