A spray generator (10) including: a membrane (40) having a perforate portion through which, in use, a fluid is caused to flow when the membrane (40) is vibrated; an electronically-driven or a piezoelectrically driven actuator for vibrating the membrane (40); a chamber (18) for storing fluid for supply to a surface of the membrane (40); and a sealing element (13) located in and movable within the chamber (18) between a first position in which fluid flow from the chamber (18) through the membrane (40) is prevented and a second position in which fluid flow from the chamber (18) through the membrane (40) is allowed.