This paper deals with a specific aspect of nonmiscible liquid?liquid systems in microfluidic. For Chemical Engineering applications, the main constraints of functioning lie in the droplets velocity and frequency. Furthermore, the material used and the composition of the fluids is often imposed by the chemistry of the system (material resistance and fluids composition) and there is no possibility of adding other compounds (e.g., surfactants). A technique under evaluation is presented: by using secondary channels and pumps, it is possible to increase or decrease, at will, the droplets velocity after they have been generated. Some experimental results are presented and discussed, including the possible limits of such an approach.