Abstract: An in-line valve is employed in a droplet generator for sharply cutting off the flow of liquid and preventing drips from forming at the outlet of the generator. In order to effect valve action, the interior surface of a droplet-forming orifice plate is machined optically flat. A movable valve plate having openings therein, corresponding to the pattern of orifices in the orifice plate, is positioned in abutting relationship to the interior surface of the orifice plate; and its interface surface is likewise machined optically flat so that the interface forms a liquid seal. When the valve plate is moved to a position where openings therein are in registry with the orifices, a droplet stream is generated. However, when the valve plate is moved in shear translation, registration between the openings therein and the orifices no longer exists and the flow of fluid therebetween is quickly stopped.