This study numerically examines the performance of micro nozzle/diffuser pumps subject to parallel and series combinations. For a single-chamber micro nozzle/diffuser micro-pump, four stages are identified. For dual micro-pumps in a parallel combination, the flow field in each chamber is symmetrical about the center line of the arrangement. For in-phase operation, the maximum flowrate is about two times higher than that of the single-chamber. For micro-pumps in a series combination, it is found that the overall performance is strongly related to the phase angle. The effective flowrate can be significantly increased, decreased, or even reversed. This indicates that the flowrate can be controlled within a wide span by changing the phase angles. At a phase angle of 90 degrees, an eight-fold increase of effective flowrate is seen relative to that of a single-chamber operation. The significant increase of flowrate is attributed to two effects; the first effect is due to the "active valve" effect that increases the efficiency during pump mode. The second influence is attributed to the increased pressure difference that brings in more fluid during supply mode.