Abstract: A power-assist hydraulic system for use in connection with a linkage extending through a housing and mechanically coupled to an actuated member. The power-assisted hydraulic system includes a double-acting hydraulic cylinder having a rod configured for interconnection to the actuated member, an accumulator for storing pressurized hydraulic fluid and a rotary valve. The rotary valve has a valve interface for selectively connecting the hydraulic cylinder to the accumulator. The rotary valve has at least one valve piston for receiving pressurized hydraulic fluid to maintain a hydraulic balance at the valve interface. A sleeve having a bore through which the linkage can extend is mechanically coupled and movably mounted with respect to the rotary valve for moving the rotary valve between a neutral position and first and second rotated positions in response to forces between the linkage and housing.