Abstract: A rotary-to-linear motion actuator having helical bevel gear and methods of use thereof are described. The actuator may be utilized with an apparatus for managing a fluid flow passage between one or more input ports and output ports. A pinion gear engages, and during operation turns, a bevel ring gear arranged on a helical path along an external periphery of a sleeve retaining a seat, which forms a fixed orifice. The teeth of the bevel gear are arranged on the helical path at the same pitch as external threads on the sleeve, which in turn, engage internal threads in a thrust tube. The trust tube is engaged with a thrust tube jam nut that locks the thrust tube into position within the valve body. The area of the flow passage is changed by movement of the fixed seat orifice axially with respect to a contoured plug assembly. The threads of the sleeve and the thrust tube resist axial load imparted by the pressure drop across at the fixed orifice.