Dispenser for flowable materials having a piston with a flexible sealing rim

In a dispenser for flowable materials comprising a barrel having an upper end and an open lower end, a dispensing spout at said upper end of said barrel, a plunger telescoped into said barrel, the upper end of said plunger having a piston head spaced from the inner surfaces of said barrel, a chamber formed between said upper end of said barrel and said upper end of said plunger whereby the flowable material may be inserted in and fill said chamber, and said barrel and said plunger being slidably mounted with respect to each other to vary the size of said chamber whereby the flowable material is caused to be discharged from said dispensing spout when said chamber is made smaller by said upper end of said barrel and said upper end of said plunger being moved toward each other, the improvement being in an annular peripheral sealing rim extending around said plunger below said piston head, said sealing rim having an outer longitudinal surface terminating in a corner at its upper edge, said sealing rim having an upper surface, said sealing rim having a thin portion which comprises hinge means, said corner being on a longitudinal extension of said outer longitudinal surface and positioned upwardly beyond said hinge means, said hinge means being disposed inwardly of said outer longitudinal surface for causing said outer longitudinal surface to pivot downwardly in response to pressure from the flowable material when said chamber is made smaller to thereby create sealing surface contact of said corner and a portion of said outer longitudinal surface with said inner surfaces of said barrel, and the degree of contact of said outer longitudinal surface increasing as materials continue to be dispensed from said spout.