Hypodermic syringe

Claim 1

A medicinal syringe, comprising: a generally cylindrical syringe body formed with a first end having a needle-receiving fitting, a second and opposite said first end and a bypass intermediate said ends; a first piston slidable in said body proximal to said second end; a second piston slidable in said body between said first piston and said first end, said pistons defining a liquid compartment between them adapted to communicate with a downstream compartment between said second piston and said first end through said bypass upon displacement of said second piston so that opposite sides thereof are bridges by said bypass; a piston-actuating stem axially engaged by said first piston, extending out of said second end and axially displaceable to drive said pistons toward said first end of said body; and velocity damping means formed at said second end or said body for restricting a velocity of displacement of said first piston substantially until said first piston reaches said bypass, thereby limiting a velocity with which liquid from said liquid compartment enters said downstream compartment, and thereafter disengaging to permit less-braked axial displacement of said pistons by said stem, said damping means including a cap fitted onto said second end and formed with a central bore having an internal screwthread, said stem having over part of its length an axially extend in shank having an external screwthread threadedly engaging said internal screwthread, and shank having a length such that said external screwthread passes out of said internal screwthread upon rotation of said stem to advance said first piston as said first piston reaches said bypass.