Microfluidic device comprising a tank (6) supplying a microchannel (2) with a first fluid (S), and a circuit (8) in which a flow of a second fluid can be established without contact with the microchannel (2). The circuit (8) passes through the tank (6) or is connected to the tank (6) by a pipe (30). The circuit (8) comprises a first on/off valve (12) mounted in parallel with a first proportional valve (11), these first valves (11, 12) being controllable so as to modify the pressure applied in the tank (6) to the first fluid (S) by the second fluid.