Two valve micropump with improved outlet

A micropump comprising a first wafer, at least one second wafer adhered face to face to said first wafer to form a pump chamber, and actuator means for causing a periodic variation in the volume of said pump chamber, wherein said first wafer is made of a material capable of being machined using photolithographic technology and is machined in such a way as to define said pump chamber, a first valve of the check-valve type through which said pump chamber can selectively communicate with an inlet of the pump and a second valve of the membrane type through which said pump chamber can selectively communicate with an outlet of the pump, wherein said outlet communicates directly with an isolated volume of said pump chamber defined by an annular rib of said second valve in its closed position, wherein said annular rib of said second valve, said outlet of the pump and a channel through which said second valve communicates with the pump chamber are situated on the same side of said first wafer in such a way that the pressures prevailing respectively in said pump chamber and in said outlet act in the direction of opening said second valve, wherein said pump is without a valve of the check-valve type between said first and second valves such that said second valve is in continuous communication with said first valve via said pump chamber during the input phase of the pump and said pump chamber communicates directly with said outlet via said second valve in its open position during the output phase of the pump, and wherein said second valve is pretensioned to be normally closed such that pump output is substantially independent of outlet pressure over a predetermined pressure range.