GB1206340A - Improvements in or relating to hypodermic injection apparatus - Google Patents

Abstract

1,206,340. Hypodermic injection apparatus. DEFENCE, SECRETARY OF. 13 Sept., 1967 [13 June, 1966], No. 27814/70. Divided out of 1, 205, 551. Addition to 1, 149, 042. Heading A5R. A hypodermic syringe comprises a syringe casing having a forward end for contacting a patient in the body of whom an injection is to be made, a chamber for containing a liquid to be injected and housed in a forward end portion of the casing, which chamber has a puncturable forward end, a side wall and a piston constituting a rear end of the chamber and being capable of movement within and in sliding contact with the side wall of the chamber thereby to reduce the volume of the chamber, a hypodermic needle through which liquid can pass and which prior to use of the syringe is disposed through almost the full length of the interior of the chamber with its pointed end directed to the forward end of the chamber; main spring means located in the casing behind the chamber to act on the rear end of the piston, a release mechanism located in the casing and retaining the main spring means until it is released, and a secondary spring positioned between the casing and the side wall of the chamber in a manner such that it is capable of urging the forward end of the chamber in a rearward direction; the main spring means has sufficient power and throw, when released, both to drive the piston forward relative to the side wall of the chamber, thereby to inject the needle and at least some of the liquid in the chamber therethrough into the body of the patient, and to drive the chamber forward against the reaction of the secondary spring, the secondary spring being sufficiently powerful thereupon to drive the forward end of the chamber rearward to complete the injection of the desired dose of liquid. The piston may be formed with a tubular well which opens into the chamber and in the entrance to which well is located a hollow deformable plunger which bears on the rear end of the needle to hold the needle away from the piston and which is displaceable into the well by the rear end of the needle if the needle is subjected to a predetermined axial force, for example as a result of contacting gristle or bone during an injection operation; the plunger may be cup-shaped and have a side wall with a plurality of projections such that the maximum outside diameter of the plunger is just greater than the bore of the well in the piston whereby, when the plunger is subjected to the aforesaid force, the side wall of the plunger buckles inwards to allow the plunger to be driven into the well. As illustrated in Figure 1, the syringe comprises a casing which consists of a forward housing 1 and a rear housing 2, the forward housing having located therein a tubular sleeve 50 which is made of stainless steel or of inert plastics material and within which is housed in slidable manner a piston assembly 51 which comprises a rubber piston 52, a non-collapsible portion constituting a well 13 and a hollow deformable plunger 30 which is located in the entrance to the well to support the rear end of a hollow needle 33. The forward end of the tubular sleeve is formed with an internal flange 41 which locates a puncturable bung 53 formed with a recess to accommodate the pointed end of the needle; the bung, piston assembly and tubular sleeve define the chamber for containing liquid to be injected. Located in an annular space between the tubular sleeve and the forward housing is a secondary spring 55 the rear end of which seats against an external flange 56 provided on the tubular sleeve and the front end of which seats against an internal shoulder 57 provided in the forward end portion of the forward housing. Seated against the rear end of the piston assembly is a tubular carriage 14 within which is situated main spring means in the form of a compression spring 19 one end of which rests against the sealed forward end of the carriage and the other end of which rests against a hollow detent body 20 fixed to the rear end of the rear housing and provided with an axial bore 21 in which is located a shaft comprising a spindle portion 24 and a recessed portion 25 to which is integrally attached a push button 23. Situated within the compression spring is a release spring 27 one end of which rests against the sealed forward end of the carriage and the other end of which rests against a flange 26 provided on the spindle portion of the shaft. An external flange 16 of the carriage is provided with detent recesses 1 and the detent body is provided with detent holes 22; situated in the detent recesses and detent holes are balls 28 which are retained in position prior to operation of the syringe by the spindle portion of the shaft thereby to prevent axial movement of the carriage under the influence of the compression spring. Depression of the push button against the action of the release spring brings the recessed portion of the shaft into alignment with the aligned detent recesses and detent holes thereby to allow the balls to move radially out of the detent recesses and into the recessed portion of the shaft whence the carriage may move axially under the influence of the compression spring to initiate the movement both of the piston assembly relative to the side wall of the chamber and of the chamber relative to the casing. Prior to operation of the syringe, a protective cap 29 is located about the push button to prevent accidental operation of the syringe. The forward housing advantageously is separable from the rear housing in order that the syringe may be reloaded; the reloading procedure entails rearward movement of the piston assembly and carriage to re-tension the compression spring, refilling of the chamber with liquid to be injected and the provision of a fresh plunger, needle and bung. Reference is made to Specification 1, 205, 551.