Pressure independent droplet generation

The invention relates to an apparatus for ejecting droplets of a fluid material, comprising: a reservoir for storing the material, a channel connected with the reservoir, which is provided with at least one outflow opening from which, in use, flows a jet of the material breaking up into droplets, a pump for pressurizing the fluid material in the reservoir, so as to pass the material under pressure through the channel in the direction of the outflow opening, and a movable member provided in the reservoir, the member formed by a plurality of surfaces shaped to induce a pressure variation in the fluid material upstream of the outflow opening, for the purpose of obtaining the jet breaking up into droplets; the movable member mounted to have each opposed surface receiving identical hydrostatic pressure, to generate a net resulting zero force exerted on the movable member by the hydrostatic pressure. Accordingly, a simple mechanism is provided for providing multiple printing nozzles.