부산대학교 도서관

Two stage spool valves having, in a single assembly, a first stage spool and a second stage spool. The first stage spool may have a solenoid actuator with a return spring, with the second stage spool having either a hydraulic return or a spring return, or both. The solenoid actuator may be comprised of a stationary structure defining a magnetic flux path, including a stationary structure pole face, that together with a moveable structure, including a moveable structure pole face, define a substantially zero air gap magnetic circuit when the solenoid actuator is actuated, the pole faces of the stationary structure and the moveable structure each being defined in part by soft magnetic iron and in part by hardened steel, the hardened steel of the moveable structure contacting the hardened steel of the stationary structure and the soft magnetic iron of the moveable structure being face to face with the soft magnetic iron of the stationary structure when the solenoid actuator is actuated.