Image Number 5 for United States Patent #7789855.
The present invention provides an improved barrel type plunger for use with needle-retractable safety syringes. The plunger includes a barrel, a needle retracted trigger and a supporting member. A front portion of the barrel is fitted over a sealing rubber pad, a slotted hole is provided at a wall of the front portion of said barrel, a bearing piece is provided in the slotted hole, and one end of the bearing piece is connected to the front side wall of the slotted hole. The supporting member is releasably engaged in the barrel. After having released from the barrel, the supporting member is able to translate backwards under the action of a needle retraction force so that the bearing piece can be returned to such a position that the needle can be retracted backwards to the interior of the barrel.