Abstract: Presented is a fluid-operated control device that may be operated by pressurized gas or liquid. A housing contains a double-acting piston assembly that is moveable in a longitudinal bore in the housing. A gear rack connects the two pistons. A rotor assembly in the housing includes a pinion gear meshing with the gear rack, and a second pinion gear meshes with a second gear rack attached to a slide member moveably supported on the housing. Thus, injection of fluid under pressure behind one or the other of the pistons causes axial translation of the pistons and connecting gear rack. Translation of the gear rack effects rotation of the rotor assembly, which in turn effects axial translation of the second gear rack to which is attached the slide member.