Disclosed herein is a double reservoir configuration for a pumping mechanism for a drug delivery device wherein one reservoir is rigidly fixed to a housing of the device and the other reservoir moves linearly translates with respect to the fixed reservoir. To avoid having either the input fluid port or the output fluid port moves as the second reservoir linearly translates, one port is in fluid communication with the fixed reservoir and a second fluid port is in communication with the moving reservoir via a hollow tube supporting a static plunger disposed within the moving reservoir. This arrangement provides for the added benefit of allowing air trapped within either of the reservoirs to be almost completely removed as the pump mechanism is filled with the fluid.

Disclosed herein is a double reservoir configuration for a pumping mechanism for a drug delivery device wherein one reservoir is rigidly fixed to a housing of the device and the other reservoir moves linearly translates with respect to the fixed reservoir. To avoid having either the input fluid port or the output fluid port moves as the second reservoir linearly translates, one port is in fluid communication with the fixed reservoir and a second fluid port is in communication with the moving reservoir via a hollow tube supporting a static plunger disposed within the moving reservoir. This arrangement provides for the added benefit of allowing air trapped within either of the reservoirs to be almost completely removed as the pump mechanism is filled with the fluid.