A syringe includes a retractable needle assembly comprising a needle seat, a hypodermic needle, and a barrel. A hollow plunger is slidably mounted within the barrel. A seal is provided between the plunger and barrel to prevent air from passing into or out of the barrel. A piston is slidably mounted within the plunger such that movement of the plunger into the fill position locks the piston in place. A seal between the piston and the interior of the plunger prevents air or fluid from passing into the plunger. As the plunger is depressed the plunger moves in the barrel while in the piston is stationary. The relative axial movement of the plunger in relation to the piston causes a vacuum to be created within the plunger. The plunger in the fully depressed position releases the needle carrier and the vacuum pulls the needle carrier and needle into the hollow plunger.一種可回縮之針頭皮下注射器包括一包含用於支撐一皮下注射針之針座之可回縮針頭總成,及一包含針筒且充當可注射或抽出之流體之儲集器的大致管狀體。該針筒在兩端均開口以在柱塞端接受柱塞且在相對端接受針頭。一中空柱塞可滑動地安裝於該針筒內,且自柱塞端延伸以接合於使用者。在該柱塞與該針筒之間提供一密封件用以防止空氣環繞該柱塞及經該柱塞端進入或離開該針筒。將一活塞可滑動地安裝於該柱塞內以使得該柱塞至裝料位置中之運動可將該活塞鎖定於原處。該活塞與該柱塞內部之間的密封件防止空氣或流體經該活塞進入該柱塞內。當壓下該柱塞以注射該流體時,該柱塞在該針筒內軸向運動,而該活塞係固定的。該柱塞關於該活塞之相對軸向運動引起在該柱塞內產生真空。與該針筒相比,相對較小之截面之柱塞產生一相應較大之真空力。該位於完全壓下之位置中之柱塞從該針筒端釋放持針器,且真空將該持針器及針頭拉至該中空柱塞內。1...柱塞蓋2...柱塞3...針筒止動器4...針筒4a...手指凸緣5...針頭6...活塞6a...活塞鎖6b...縱向槽7...柱塞密封件8...活塞真空密封件9...針座墊圈10...柱塞真空密封件10a...接管11...針架11a...管肩12...空腔
