Patent ID: 7932647

Claim:
An electromagnetic reciprocating fluid apparatus comprising: a piston having a piston rod and a magnetic armature secured to the piston rod, the piston being reciprocatable along a longitudinal axis of the piston rod; and a magnetic circuit device having a pair of magnetic pole members spaced apart from each other in a direction normal to the axis and disposed on opposite sides of the axis, the magnetic circuit device being intermittently excited to induce magnetic force between the magnetic pole members, thereby magnetically attracting the magnetic armature to drive the piston in the direction of the axis; wherein the magnetic circuit device further comprises: an annular magnetic circuit member having opposite side surfaces in the direction of the axis, wherein the magnetic pole members are integrally formed with the annular magnetic circuit member so that the magnetic pole members project from mutually opposing portions of an inner peripheral surface of the annular magnetic circuit member, the magnetic pole members and the annular magnetic circuit member having a uniform thickness in the direction of the axis, further wherein the annular magnet circuit member is configured to surround the axis of the piston rod; and a first additional annular magnetic circuit member superimposed on one of the opposite side surfaces of the annular magnetic circuit member and configured to reduce a magnetic flux concentration near an intersection of the inner peripheral surface of the annular magnetic circuit member and the outer peripheral surface of the pole members.