Mechanical hydro servo valve

Abstract From the Canadian patent

A hydro mechanical condition-responsive servo control valve for controlling a variable condition, such as position or rate of change of position, of a remote element, comprises a rotary fluid valve controlled by a differential gear train arranged to register differential movement between two input shafts, one of which is connected for movement according to a desired input condition and the other of which is alternatively connected either to register the actual element condition or a reference datum condition; the rotary valve including mating stationary and rotary valve plates each incorporating fluid flow ports cooperatively arranged on the mating plate surfaces thereby to control fluid …