Patent ID: 7306123

Claim:
A piston adapted to be engaged inside a cylindrical container, constituted by an elastic member comprising: a sliding member having an upper fluidtight portion and a lower fluidtight portion, both of which fluidtightly and slidably contact an inner wall of the cylindrical container, wherein the upper and lower fluidtight portions each have at least one annular convex bump portion; and a support member having an upper concentric flexion and a lower concentric flexion to urge the sliding member against the inner wall of the cylindrical container, said lower concentric flexion being disposed between the upper fluidtight portion and the lower fluidtight portion with respect to an axis of the piston and being disposed closer to the axis of the piston than is the upper concentric flexion, wherein the lower concentric flexion is disposed on a plane perpendicular to the axis of the piston, which is positioned nearly half way between the upper fluidtight portion and the lower fluidtight portion.