Abstract: A reaction type control valve, primarily intended for controlling a power assisted steering system, comprising a hydraulic interface having variable effective reaction areas, the extent of which is determined by selected functions of values of torque applied thereto. Differential hydraulic fluid pressure is generated by the valve, which differential hydraulic fluid pressure is proportional to the applied torque and inversely proportional to any particular effective reaction area. Hydraulic fluid is induced to flow through a hydraulic interface between first and second valve members wherein primary and secondary sets of input and return orifices are selectively utilized to define the effective reaction areas as a function of the input torque. The primary and secondary sets of input and return orifices are located at selected radii.