Injection device

An injection device designed to receive therein a two-compartment syringe having a front end quipped with a septum that can be pierced by a double-ended needle, a cylindrical side wall, a slidable front wall and a slidable rear wall that are liquid-tightly and slidably fitted inside the side wall, and a bypass which is defined in the internal surface of the side wall between the front end and the slidable front wall and has a longitudinal length sufficient to stride the thickness of the slidable front wall, the two-compartment syringe containing a first pharmaceutical component in the front space defined between the front end and the slidable front wall and a second, liquid pharmaceutical component in the rear space defined between the slidable front wall and the slidable rear wall, and to be used to mix, in the two-compartment syringe, the first pharmaceutical component and the second pharmaceutical component and then conduct injection of thus prepared injectable liquid, the injection device comprising,

• a generally cylindrical barrel portion so configured that the two-compartment syringe can be inserted therein in a rear-end first manner to a predetermined depth,
• a piston rod for pushing the slidable rear wall from behind to advance the same, the piston rod being placed slidably in the longitudinal direction in the barrel portion, so that it may be pushed forwardly from behind the barrel portion,
• a front spring provided in the region between the front end of the piston rod and a position which is in the rear of the front end of the piston rod and in intermediate part of the barrel portion, so that, when the two-compartment syringe is inserted into the barrel portion and the front end of the piston rod is thus moved backward by the pressure from the slidable rear wall of the two compartment syringe, the first spring may be compressed and then push back the piston rod in the forward direction, and
• a sleeve provided at rear part of the barrel portion by screw engagement with the outer surface of the barrel portion, so that the distance of backward extension of the sleeve from the rear end of the barrel portion may be varied by rotating and shifting the same back and forth relative to the barrel portion,
• wherein the piston rod and the sleeve are so configured and arranged that rear part of the piston rod may abut on the sleeve and be thus prevented from advancing further in the forward direction from the position where it abuts on the sleeve.