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An apparatus for delivering a fluid includes a housing, an inlet in the housing for receiving the fluid, and an outlet in the housing for discharging the fluid. A piston channel is provided within the housing through which the fluid flows from the inlet to the outlet. An actuator is positioned withi

An apparatus for delivering a fluid includes a housing, an inlet in the housing for receiving the fluid, and an outlet in the housing for discharging the fluid. A piston channel is provided within the housing through which the fluid flows from the inlet to the outlet. An actuator is positioned within the housing and is moveable between a retracted position and a forward position, the actuator defining a piston chamber for storing fluid received through the inlet when the actuator is in the retracted position and for driving the fluid stored in the piston chamber toward the outlet when the actuator transitions from the retracted position to the forward position. The actuator includes an armature and a piston coupled to the armature and moveable within the piston channel. The piston is provided with a groove in an outer surface for conducting fluid from the inlet to the outlet.

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What is claimed is: 1. An infusion device apparatus for delivering a medication fluid, the apparatus comprising: a housing; an inlet in the housing for receiving the fluid; an outlet in the housing for discharging the fluid; a piston channel within the housing through which the fluid flows from the

What is claimed is: 1. An infusion device apparatus for delivering a medication fluid, the apparatus comprising: a housing; an inlet in the housing for receiving the fluid; an outlet in the housing for discharging the fluid; a piston channel within the housing through which the fluid flows from the inlet to the outlet; and an actuator positioned within the housing and moveable between a retracted position and a forward position, the actuator defining a piston chamber for storing fluid received through the inlet when the actuator is in the retracted position, the actuator driving the fluid stored in the piston chamber toward the outlet when the actuator transitions from the retracted position to the forward position, the actuator comprising: an armature; and a piston having an overall length along an axial direction and having an inlet end and an outlet end, the piston coupled to the armature and axially moveable within the piston channel with the armature, the housing having defined therein a first fluid chamber above the piston channel, and the housing having defined therein a second fluid chamber below the piston channel, the first fluid chamber in fluid communication with the inlet and the inlet end of the piston located in the first fluid chamber, the second fluid chamber in fluid communication with the outlet and the outlet end of the piston being in fluid communication with the second fluid chamber, and the piston having a groove in an outer surface from its inlet end to its outlet end to form a flow path between the first fluid chamber and the second fluid chamber for conducting fluid from the inlet to the outlet, wherein the groove is a helical groove around the piston. 2. The apparatus of claim 1, wherein the helical groove has between 1 and 7, inclusive, turns around the piston. 3. The apparatus of claim 2, wherein the helical groove includes 2-5 turns around the piston. 4. The apparatus of claim 1, wherein the groove has a hemispherical cross-section. 5. The apparatus of claim 4, wherein the groove has rounded edges. 6. The apparatus of claim 1, wherein the groove has a depth between 0.001 inch and 0.004 inch, inclusive. 7. The apparatus of claim 1, wherein the groove has a width of between 0.002 inch and 0.006 inch, inclusive. 8. The apparatus of claim 1, wherein the groove has a pitch of between 0.006 inch and 0.050 inch, inclusive. 9. The apparatus of claim 1, wherein the groove has a cross-sectional area of between 0.00001 square inches and 0.00003 square inches, inclusive. 10. The apparatus of claim 1, wherein the groove has a depth that is between 1.5-6% of the diameter of the piston, inclusive. 11. The apparatus of claim 1, wherein the groove has a width that is between 3-30% of the diameter of the piston, inclusive. 12. The apparatus of claim 1, wherein the groove has a pitch that is between 8-70% of the diameter of the piston, inclusive. 13. The apparatus of claim 1, wherein the groove has a cross-sectional area of between 0.2-0.6% of the area of the piston, inclusive. 14. The apparatus of claim 1, wherein the groove is configured to convert laminar flow to turbulent flow when the actuator is transitioning from the retracted position. 15. The apparatus of claim 1, wherein the groove is one of a plurality of helical grooves around the piston. 16. The apparatus of claim 15, wherein the plurality of helical grooves includes first and second oppositely wound helical grooves. 17. The apparatus of claim 1, further comprising a coil located within the housing and in a position relative to the armature to generate an electromagnetic field upon energization sufficient to cause the armature and piston to move from a quiescent position to the forward position. 18. The apparatus of claim 17, further comprising a valve member located on the opposite end of the piston channel relative to the armature, wherein the piston chamber is located between the piston and the valve member. 19. The apparatus of claim 1, further including means for urging the piston and armature toward the retracted position. 20. The apparatus of claim 19, wherein the urging means includes a spring. 21. The apparatus of claim 20, further including an adjuster for enabling adjustment of the piston chamber volume. 22. An infusion device for delivering a fluid, the infusion device comprising: a housing; an inlet chamber, formed in the housing, for receiving the fluid; an outlet chamber, formed in the housing, for discharging the fluid; a piston channel formed within the housing and extending from the inlet chamber to the outlet chamber, the inlet chamber located above the piston channel and the outlet chamber located below the piston channel; an actuator positioned within the housing and moveable between a retracted position and a forward position, the actuator comprising an armature located within the inlet chamber and further comprising a grooved piston coupled to the armature and axially moveable within the piston channel, the grooved piston having an inlet end, an outlet end, an outer surface, and a groove in the outer surface that forms a flow path for the fluid between the inlet end and the outlet end; and a valve assembly having a valve that seals the piston channel from the outlet chamber when the actuator is in the retracted position; wherein the valve, the grooved piston, and the piston channel together define a piston chamber when the actuator is in the retracted position, the piston chamber being configured to store the fluid received from the inlet chamber via the groove; wherein movement of the actuator from the retracted position to the forward position reduces volume of the piston chamber, and increases pressure within the piston chamber to open the valve such that the fluid stored in the piston chamber is discharged into the outlet chamber, the groove having a number of turns, a depth, a width, and a pitch that inhibits back leakage of the fluid from the piston chamber during the movement of the actuator from the retracted position to the forward position; and wherein movement of the actuator from the forward position to the retracted position causes the valve to close, and creates negative pressure which draws the fluid from the inlet chamber, through the groove, and into the piston chamber for a next discharging operation. 23. The infusion device of claim 22, wherein the fluid is a protein drug, and wherein the groove is configured and dimensioned to provide the first flow path in the presence of heavy protein deposits on surfaces of the piston channel, the heavy protein deposits being caused by the protein drug. 24. An implantable infusion device for delivering a fluid protein drug to the body of a patient, the implantable infusion device comprising: a hermetically sealed and biocompatible housing; an inlet chamber, formed in the housing, for receiving the fluid protein drug; an outlet chamber, formed in the housing, for discharging the fluid protein drug; a piston channel formed within the housing and extending from the inlet chamber to the outlet chamber, the inlet chamber located above the piston channel and the outlet chamber located below the piston channel; an actuator positioned within the housing and moveable between a retracted position and a forward position, the actuator comprising an armature located within the inlet chamber and further comprising a grooved piston coupled to the armature and axially moveable within the piston channel, the grooved piston having an inlet end, an outlet end, an outer surface, and a groove in the outer surface that forms a first flow path for the fluid protein drug between the inlet end and the outlet end; an annulus between the grooved piston and the piston channel, the annulus forming a second flow path for the fluid protein drug between the inlet chamber and the outlet chamber; and a valve assembly located within the housing, the valve assembly having a valve that seals the piston channel, the first flow path, and the second flow path from the outlet chamber when the actuator is in the retracted position; wherein the valve, the grooved piston, and the piston channel together define a piston chamber when the actuator is in the retracted position, the piston chamber being configured to store fluid received from the inlet chamber via the groove and the annulus; wherein movement of the actuator from the retracted position to the forward position reduces volume of the piston chamber, and increases pressure within the piston chamber to open the valve such that the fluid stored in the piston chamber is discharged into the outlet chamber; and wherein movement of the actuator from the forward position to the retracted position causes the valve to close, and creates negative pressure which draws the fluid protein drug from the inlet chamber, through the groove, and into the piston chamber for a next discharging operation, the groove being configured and dimensioned to provide the first flow path in the presence of heavy protein deposits in the second flow path, the heavy protein deposits being caused by the fluid protein drug. 25. The implantable infusion device of claim 24, wherein the groove has a number of turns, a depth, a width, and a pitch that inhibits back leakage of the fluid from the piston chamber during the movement of the actuator from the retracted position to the forward position.