Abstract: The metering device of the present invention is characterized by controlling the simultaneous relative positions of two sliding valve elements so that the degree of opening between fuel inlet and outlet orifices always corresponds to the setpoint of the fuel flow. If the position of either of the two sliding elements in the metering device of the present invention can no longer be controlled for whatever reason, such as being jammed, the other element may always be controlled to move relative to the jammed element such that the fuel flow may be controlled by the other element to correspond to that of the fuel flow setpoint. Thus, the metering device according to the present invention will continue to operate effectively even if the position of either of its slide elements can no longer be properly controlled, either because the element has jammed or because there has been a malfunction in its control system.

Abstract: A control system for a fluid actuated control member is disclosed which uizes a pair of electrically controlled servo valves to control the supply of servo pressure fluid to a control valve piston. The pair of servo valves are electrically controlled such that, under normal conditions, one of the servo valves is operative to supply the servo pressure signal, while the other servo valve remains in an inert, open position. Upon the detection of a malfunction in the operative servo valve, electrical switches render the malfunctioning valve inert and transfer the operative capabilities to the second servo valve. The hydraulic control system does retain 100% of its performance capabilities following a malfunction of the initial servo valve.