GB993309A - Improved hypodermic injector - Google Patents

Abstract

993,309. Hypodermic injectors. EXPRESS INJECTOR CO. Ltd. April 6, 1962 [April 11, 1961], No. 13038/61. Heading A5R. A hypodermic injector comprises a housing 10 surrounding the nearly uniform thin walls of an ampoule 11 to support it against any expansion when means 15 impart to its rear end first a percussive force to produce a transient high pressure which discharges medicament from the ampoule followed by a compressive force capable of introverting the ampoule as in Fig. 2 and discharging the remaining medicament from it at a reduced pressure. The front end of the ampoule may be closed by a plug 12 with a minute orifice 13 enabling the medicament to pierce the skin without use of a hypodermic needle or the plug 43 as in Fig. 7 may be of plastic formed with a thin walled nozzle 43 of large bore to cooperate with an orifice 44 formed in the cap 44 which holds the ampoule in the housing of the injector. The rear, thin wall of the ampoule may be flat, stepped annularly as in Fig. 3, or annularly bevelled (Fig. 5, not shown). The plug 43 is assembled to the ampoule shell 42 with a gap 49 which is taken up when the ampoule is screwed home in the housing by the cap 44, thereby ejecting any air bubbles present in the ampoule. The plunger 15 which applies the load to the ampoule is driven by a guide 18 which compresses springs 21 and 22 between a flange on its lower end and a flange on a guide member 17 which is held on the injector casing 16 by a screwed cap 29 which can be turned to adjust the tension of the springs. The guide 18 is mounted telescopically on the member 17 and the springs are held in compression by balls 26 located in holes 25 in the guide member 17 which are locked in a groove 18a around the inside of the member 18 by the conical end 23a of a plunger 23 on a button 28 which is movable with respect to the member 17 against a spring 24. When the button 28 is depressed the plunger head 23a frees the balls 26 from the groove 18a allowing the guide 18 to fly forward and strike the plunger 15 a blow which is followed by a steady pressure, due to the residual compression on the springs. A loading device (not shown) is provided for putting the initial compression on the springs 21 and 22. The members 17 and 18 can be locked together by rotation of a ring 34 on the member 17. Specifications 964,584 and 964,585 are referred to.