Embodiments of the present disclosure relate to techniques, processes, devices or systems for pump devices. In one approach, a wearable drug delivery device may include a reservoir configured to store a liquid drug, the reservoir including a housing including an outer wall defining an interior chamber, a sealing member, and a slit through the housing, wherein the sealing member is configured to seal the slit. The wearable drug delivery device may further include a delivery pump device including a drive mechanism coupled to the reservoir for driving the liquid drug out of the reservoir, the drive mechanism including a piston head disposed within the interior chamber of the housing, and a lead screw coupled to a drive nut, wherein the drive nut comprises a blade adjacent the piston head, and wherein the blade is positionable through the slit of the housing.
