Patent ID: 8273058

Claim:
An implantable infusion apparatus, comprising: an infusate reservoir; a metering assembly comprising: an accumulator having an inlet, an outlet, a first mechanical stop and a second mechanical stop; an inlet valve in communication with said infusate reservoir and with said accumulator inlet, and an outlet valve in communication with said accumulator outlet; a metal diaphragm disposed in said accumulator such that said diaphragm has a resting state position, deflects in a first direction and deflects in a second direction, wherein said first direction and said second direction are different; and a valve accumulator pump programmed to selectively actuate said inlet valve to cause infusate to flow into said accumulator and deflect the diaphragm in said first direction and against said first mechanical stop, and selectively actuate said outlet valve to cause infusate to flow out of said accumulator and deflect the diaphragm in said second direction and against said second mechanical stop, wherein said accumulator further comprises a spacer, said spacer having a concave surface defining said second mechanical stop, said concave surface comprising an annular groove and a trough in fluid communication with said annular groove and with said inlet and said outlet of said accumulator, wherein said annular groove is the only annular groove in said spacer, and the total volume of the space within the annular groove and the trough provides a dead volume in the accumulator that is equal to or less than 5% of the total volume of infusate discharged by the accumulator.