Patent ID: 6015438
Filing Date: 2000-01-18
Classification: A61M

Abstract:
A full displacement syringe, comprising:an elongated housing comprising a hollow barrel having a front end portion, and an inner surface;a plunger configured to reciprocate in the barrel, the plunger having a retraction cavity within and a tubular nose in front with a leading wall having a removably sealed opening into the retraction cavity;a retraction mechanism mounted in the front end portion of the barrel, the retraction mechanism comprising a needle and needle holder having a head, a biasing element tending to drive the needle holder rearwardly and a movable holding ring mounted on the head of the needle holder, said ring holding the retraction mechanism by contact with the inner surface of the barrel, wherein the retraction mechanism forms the bottom of a variable fluid chamber in the barrel;a plunger seal forcibly slideably mounted near the front of the tubular nose of the plunger, said plunger seal being movable with the plunger in sliding contact with the inner surface of the barrel during fluid transfer operations;a plunger seal restraint located on the barrel wall to restrain the plunger seal from forward movement after it has reached the bottom of the variable chamber without said restraint preventing the plunger nose from sliding forward through the plunger seal to operate the retraction mechanism;whereby depression of the plunger to place the plunger seal at the bottom of the variable fluid chamber causes substantially full displacement of fluid from the barrel and further forward movement of the plunger causes the leading wall of the tubular nose of the plunger to operate the retraction mechanism by moving through the plunger seal to push the movable holding ring off the head of the needle holder, thereby initiating retraction.