Automatic self-protecting hypodermic needle assembly

DETAILED DESCRIPTION These and other objects of the invention are achieved by a mechanism that uses gas pressure produced by the combining of two chemicals to propel a protective cap along the needle shaft and over the needle tip.
The two chemicals are combined when the attendant pushes the syringe to inject medication into the patient, and, in a first embodiment, simultaneously squeezes a small bellows located under the plunger.
The bellows pumps a liquid chemical through a tube and into contact with another chemical located in a chamber at the hub of the needle.
In a second embodiment, the attendant depresses a circular disc and push rod assembly simultaneously with the syringe plunger to cause communication between the two chemicals in the chamber.
The chamber in both embodiments is connected to a flexible sheath that is in an initially collapsed configuration.
A plastic cap with a small aperture through which the needle protrudes is connected to the other end of the flexible sheath.
A slow progressive gas pressure results from the chemical reaction in the chamber causing the flexible sheath to elongate and push the protective cap down the needle shaft and over into contact with the tip.
The protective cap contains a plastic wafer with a small moveable tab member in its center that is elastically biased toward the center, but held aside by the needle.
When the needle tip is withdrawn from the aperture in the cap, the moveable tab member returns to center, blocks the aperture, and prohibits the needle from reemerging from the protective cap.
Other objects and features of the invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the drawings wherein reference to specific parts is made.