An integrated microvalve fabricated in a stiff polymeric (polycarbonate) device allows for formation of droplets and bubbles of arbitrary volumes and at arbitrary times of emission. Predesigned protocols of formation of sequences of volumes, intervals between the droplets and their chemical compositions can be practically and reproducibly realised and controlled from a personal computer. The design of the microvalve enables its utilization in chips made in a range of other materials, including plastics and glass and in devices operated both with positive and negative pressure providing a useful module for a range of applications of microfluidic droplet systems.