Patent ID: 8628308

Claim:
An actuator for delivering fluid through a piston channel, from a first fluid chamber above the piston channel to a second fluid chamber below the piston channel, the actuator comprising: an armature that moves between a forward position and a retracted position; and a piston coupled to the armature and moveable within the piston channel, the piston having an inlet end and an outlet end, the inlet end located in the first fluid chamber and the outlet end in fluid communication with the second fluid chamber, and the piston comprising an outer surface and at least one helical groove in the outer surface from the inlet end to the outlet end, the at least one helical groove forming a flow path between the first fluid chamber and the second fluid chamber for conducting fluid; wherein the helical groove has a number of turns, a depth, a width, and a pitch that inhibits back leakage of fluid from the second fluid chamber to the first fluid chamber during movement of the armature from the refracted position to the forward position.