Non-reusable syringe

Claim 1

In a non-reusable syringe element having a syringe body with a lower barrel portion of uniform diameter inner walls and closed by a base pierced with a channel, an opened upper barrel portion, a piston disposed in and tightly slidable in the lower barrel portion, a shaft disposed in said barrel portions with a shaft lower extremity attached to said piston and a shaft upper extremity projecting beyond said upper barrel portion, wherein said piston is displaceable by said shaft along said lower barrel portion, and a friction means for imposing a friction such that a weak frictional force results when the piston is displaced in said lower barrel portion in one direction and a strong frictional force results when the piston is displaced in said lower barrel portion in the other direction, the improvement wherein the friction means comprises: (1) at least one flexible and resilient plate operably disposed on said shaft with outward peripheral edges of said plate being in contact with the inner walls of said lower barrel portion, said plate having on each side thereof a collar which has a configuration such that said plate is positioned and held between said collars but wherein the peripheral edges of said plate are free to move from a generally concave configuration to a convex configuration; (2) a portion of said plate disposed at least at said peripheral edges thereof such that when the plate is disposed within said lower barrel portion at least the peripheral edges of the plate can assume said generally concave or convex configuration wherein the piston may be displaced inwardly or outwardly in said lower barrel portion and such that said weak frictional force is generated when the piston is displaced in said lower barrel portion in a direction tending to increase the curvature of the plate and strong frictional force is generated when the piston is displaced in said lower barrel portion in a direction tending to decrease the curvature of the plate; and (3) a portion of weak traction resistance on said shaft such that the traction force on said shaft necessary to separate the shaft at said portion of weak traction resistance is between the said weak frictional force and the said strong frictional force.