Patent GB-843520-A (GB)
Title: Multi-dose hypodermic injector
IPC: A61M5/30
Filed: 1958-03-28
Abstract: 843,520. Hypodermic injection appliances. SCHERER CORPORATION, R. P. March 28, 1958 [July 15, 1957], No. 10147/58. Class 81(2). In a multiple dose hypodermic injection appliance the power springs are compressed by hydraulic means, the operation of which is associated with a valve controlling the passage of medicament into and out of the medicament chamber. In the embodiment described this valve 35, Fig. 1, is of the sliding type under the control of a cam ring 31, moved by a handle 33, and connects the medicament chamber 25 either directly with the outlet orifice 26 or with a tube 43 leading from the medicament container 44, which also has a vent tube 46. The medicament chamber 25 is closed by a plunger 22 fitted in the end of a carrier 61 and, mounted at the further end of this, is an anvil member 70, which drives the plunger carrier forward through force multiplying wedges 67. The hammer 80 is normally held retracted by a latch 112 but, when this is withdrawn, it is driven forward by power springs 98 which have been previously compressed by a piston 100 actuated by fluid under pressure, admitted to the cylinder 93 through a pipe 92. Hydraulic pressure for compressing the springs is derived from an electrically driven pump assembly comprising a mains driven motor 154, fig. 6, and a pump 152. Oil from a reservoir 150 is normally circulated continuously through pipes 162, 166, 158 via a solenoid actuated stop valve 156, and, under these conditions, a pressureactuated two-way valve 169 connects the injector conduit 94 with the intake of the pump 152, so that there is no pressure in the injector cylinder 93, fig. 1. These conditions arise when a switch 53, actuated through a plunger 51, Fig. 1, is opened by moving the cam ring 31 to the position in which the valve 35 connects the medicament chamber 25 with the reservoir 44. Thus the whole piston and its actuating assembly is driven back by a retracting spring 79, the medicament is. drawn into the chamber 25 and the hammer 80 is held by the latch 112. The handle 33 is now returned to the position in which the valve 35 connects the chamber 25 with the outlet 26 and, as a consequence of movement of the cam ring 31, the switch 53 is opened and the valve 156, Fig. 6, closes, so that the pressure builds up in the tube 158 until valve 169 changes over and pressure is communicated to the injection cylinder 93, fig. 1. The piston 100 consequently compresses the springs 98 and maintains them in this condition until the latch 112 is withdrawn by the trigger 122. The resultant movement of the hammer 80 causes it to strike the anvil 70 and drive the plunger 22 forward, so ejecting the medicament. In order to provide for adjustment of dosage the entire plunger assembly is carried in a rear cylindrical portion 13 of the body which is screwed at 18 into the forward part, so that the effective capacity of the chamber 25 may be varied. A spring-loaded locating detent 125, protruding through an aperture in the body wall, ensures that, after adjustment, the assembly is correctly adjusted for the latch 112 to be aligned with the trigger mechanism. For cleaning the medicament chamber and associated parts, the head 24, together with the plunger 22, may be withdrawn after a ring nut 29 has been unscrewed. This nut is normally prevented from turning by engagement, with recesses in its periphery, of a tongue on the end of the pivoted frame 45, which holds the container in position. Specification 707,515 is referred to.