Patent ID: 7291126

Claim:
A drug delivery device for metered delivery of a liquid medicament to an outlet, the device comprising: (a) a pressurized reservoir configured for storing and supplying the liquid medicament at a pressure above atmospheric pressure; (b) a flow path in fluid communication with said pressurized reservoir and the outlet, said flow path including: (i) a first valve assuming a normally-closed flow-blocking state and selectively actuatable to an open state which permits fluid flow through said first valve, (ii) a flow restriction configured to limit fluid flow along said flow path, and (iii) a second valve assuming a normally-closed flow-blocking state and selectively actuatable to an open state which permits fluid flow through said second valve, said first and second valves and said flow restriction being deployed such that, when both said first valve and second valve are in said open state, the liquid medicament flows from the pressurized reservoir along said flow path to the outlet at a rate limited primarily by said flow restriction, and such that, when any one of said first and second valves is in said flow-blocking state, flow through said flow restriction is blocked; (c) a pressure measurement arrangement deployed in pressure-sensing engagement with a first point and a second point along said flow path, at least part of said flow restriction being between said first and second points, one of said first and second points being intermediate to said first and second valves; and (d) a controller electronically associated with said pressure measurement arrangement and said first and second valves, and configured to selectively open said first and second valves to deliver a defined quantity of the liquid medicament to the outlet, said controller being further configured to: (i) actuate said first and second valves such that said first and second valves close sequentially, thereby trapping a quantity of the liquid medicament between said first and second valves with a pressure differential across at least one of said first and second valves; (ii) while said first and second valves are closed, monitor measurements of said pressure measurement arrangement; and (iii) if said measurements vary so as to indicate a reduction in said pressure differential across said at least one valve, generate a malfunction indication.