Abstract: In a hydraulic piston actuator the supply of working fluid is governed by at least one servo valve of the three-gate type, the spring-loaded valve body of which is activated by a thermowire adapted normally to hold the valve body in a position to close-off the supply of fluid. One end of the thermowire is connected to a compensating device, goverened by the movement of the actuator piston in such a manner that thermal movements are partly counteracted. The servo valve may actuate a maximum switch, and a time relay will, after a predetermined period of time put the fluid pump out of action, and connect both sides of a double acting actuator with a return flow tank.

Abstract: Valve means for governing the flow of fluid to, and possibly also from a consumer, has a housing enclosing a movable main valve member, actuable by pressure fluid operable servo means. A flow control valve in a conduit supplying pressure fluid to the flow control valve is governed by an electric resistance body, e.g. a resistance wire, included in an electric circuit. By controlling the flow of electric current through the circuit the position of the main valve member may be determined within close limits.When the main fluid to be governed is pressurized the fluid acting upon the servo means may be branched off from the main flow.