Aerosol metering valve provided with pumping effect

In an aerosol valve assembly, a hollow cylinder adapted to be fixed to an upper portion of a container the contents of which are to be dispensed, said cylinder having an inner open end adapted to communicate permanently with the interior of the container, an outer piston slidable fluid-tightly in said cylinder and having an elongated piston rod portion extending fluid-tightly through and beyond an outer end of said cylinder, said piston rod portion being formed with an axial bore passing therethrough and forming part of a dispensing path of travel for the contents of the container while said contents travel through said axial bore from an inner end toward an outer end thereof, an inner piston situated in said cylinder between said outer piston and said inner end of said cylinder, and spring means in said cylinder urging said inner piston toward said outer piston, said inner piston having an elongated solid piston rod portion normally pressed by said spring means against said inner end of said axial bore for normally closing the latter to prevent dispensing of the contents of said container, said inner piston having between said outer piston and said inner end of said cylinder an outer portion in slidable fluid-tight contact with said cylinder, and said inner piston having between said outer portion thereof and said outer piston an outer surface spaced from said outer piston and an inner surface of said cylinder to define a pressure chamber with said inner surface of said cylinder and said outer piston, said spring means urging both of said pistons to a rest position where said outer piston is distant from said inner end of said cylinder while said inner piston is maintained by said spring means in a closed position closing said axial bore, said inner piston having a passage means placing an interior portion of said cylinder at the region of said inner end thereof, and thus the interior of said container, in communication with said pressure chamber when said pistons are in said rest position thereof but preventing communication between said interior portion of said cylinder and said pressure chamber when said pistons are both manually displaced toward said inner end of said cylinder in opposition to said spring means during a pressure stroke applied to said outer piston and through the latter to said inner piston for dispensing the contents of the container through said axial bore, said inner piston having in said pressure chamber in a plane normal to the axis of said bore a cross-sectional area at the outer surface of said inner piston great enough to provide from the incresing pressure of the fluid in said pressure chamber during the pressure stroke of said pistons a force sufficient to advance said inner piston automatically in opposition to said spring means inwardly beyond said outer piston for opening said axial bore to provide for automatic dispensing of the contents of the container when the pressure in said pressure chamber has increased sufficiently, whereby the contents of the container will be dispensed at a pressure greater than that prevailing in the interior of the container.