Dispensing device having improved plunger assemblies

Claim 1

A plunger assembly for a fluid dispenser having a frame, a cartridge containing fluids to be dispensed, and a nozzle from which said fluids to be dispensed are dispensed, said plunger assembly comprising: an end cap disposed within said cartridge adjacent to said fluid to be dispensed, and including a generally cylindrical body portion and a dome portion projecting forwardly from said body portion, and further including an annular sealing lip disposed near the juncture of said body and dome portions of said end cap for sealingly engaging the inner wall of said cartridge; and a piston assembly slideably mounted upon said dispenser frame for coaction with said end cap, and including a piston having a front face of a predetermined diametrical extent to which is integrally secured a compressible pad of elastomeric material having a diametrical extent, under non-compressed conditions, which is substantially equal to said diametrical extent of said piston face so as to permit said piston and said compressible pad to be inserted within said body portion of said end cap, said pad being positioned so as to engage said end cap proximate to said juncture of said body and dome portions of said end cap whereby an air chamber is sealingly defined between a front face of said pad and said dome portion of said end cap such that movement of said plunger assembly against said fluid to be dispensed transmits forces against said dome portion of said end cap and through said air chamber onto said front face of said elastomeric compressible pad causing said elastomeric compressible pad to be axially compressed and radially expanded beyond said predetermined diameter of said piston so as to prevent the escape of air out of said air chamber between said body portion of said end cap and said piston and to force said sealing lip into sealing engagement with said cartridge wall.