Servo-valve responsive to small control pressure

Claim 1

In a servo-valve providing an output pressure having a predetermined relationship to a control force, said servo-valve comprising a distributor memBer mounted in a valve body having an input port, an output port and an exhaust port, said distributor member being mounted for sliding movement between a first position in which said output port is connected to said input port and a second position in which said output port is connected to said exhaust port, means for applying to said distributor member a control force urging it to slide in one direction between said positions and means for applying to said distributor member a feedback force dependent on the pressure in said output port which urges said distributor member in the opposite direction, the improvement according to which said last-mentioned means comprises a movable member slidable toward and away from said distributor member, subjected at one end to the pressure in said outlet port and constantly urging said distributor member in said opposite direction in response to the difference between the pressures in said output and exhaust ports, a first spring mounted between said movable member and a stationary abutment in said body to partially counteract the force exerted on said movable member by said pressure difference and thereby decrease the force with which said movable member urges said distributor member in said opposite direction, and an additional spring positioned between one end of said distributor member and said movable member to transmit movement from said movable member to said distributor member, both of said springs being located in a single chamber.