| 摘要 |
Closed center valves include a first member movable toward and away from a vent opening in the valve for respectively closing and opening the vent opening, and a second member movable toward and away from the first member for respectively closing and opening a high pressure passage through the first member. A biasing force is applied to the first member for biasing the first member toward the vent opening. Different magnitudes of force may be applied to the second member to cause the second member to move toward the first member first to close the high pressure passage through the first member while the vent opening remains closed by the first member, and then to cause the first member to move away from the vent opening to open the vent opening while the high pressure passage in the first member remains closed by the second member. An armature will move the second member toward the first member with sufficient force to unseat the first member from the vent opening when rated current is applied to a solenoid coil surrounding the armature. A permanent magnet may be provided for moving the armature away from the second member when zero current is applied to the motor coil. Also, flat springs may be used to support the armature in coaxial alignment with the second member to prevent frictional contact between the armature and surrounding structure.
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