Patent GB-1236871-A (GB)
Title: Plunger assembly
IPC: F16B7/10
Filed: 1969-01-09
Abstract: 1,236,871. Releasable fastenings. REX CHAINBELT Inc. 9 Jan., 1969 [10 Jan., 1968], No. 1306/69. Headings E2A and E2B. [Also in Division A5] A plunger assembly comprises a housing, a plunger 12, having a recess 38 therein and mounted in the housing for movement in a certain direction from a cocked position to an extended position, spring means 20 for biasing the plunger for movement from the cocked position to the extended position, a detent ball 36 movable between a first position out of engagement with the recess so that the spring means will be free to act and a second position in engagement with the recess to retain the plunger in its cocked position with the spring means loaded, means 28 to support the ball, means 40 movable in said direction in response to a manual externally applied force from a first position in which the ball will be held in its second position when the ball is in that position to a second position in which the ball when in its second position is free to move to its first position, and spring means 48 biasing said movable means to its first position. In a first construction Fig. 2 the housing consists of a barrel 18 and a stop 24 for the plunger is secured in one end portion of the barrel, with a plate 22 secured in the other end portion of the barrel. The ball support means 28 is secured to the plate 22. The plunger passes through a bore in the stop 24 and carries a collar 14 which is secured to it by a pin 16, the spring means 20 being trapped between the collar 14 and the plate 22. The recess 38 is an annular groove and there are three said balls 36 which are carried in openings 34 in the means 28 which lead into a bore 30 in the means 28 in which an end portion of the plunger 12 can travel. The means 40 is a sleeve which is mounted on the barrel 18; the sleeve includes a ball retaining element 42 and this includes a portion 44 adapted to move in closely spaced relationship to the outer surface of the means 28; this portion 44 when in the appropriate position holding the balls in the recess 38. The element 42 also has a portion of its bore enlarged so that a space is provided between the outer surface of means 28 and the inner surface of the enlarged bore portion 46 so that when the enlarged bore portion is aligned with the balls the balls can move outwardly to free the plunger. Movement of the sleeve and element 42 in the left hand direction as shown, is necessary to release the balls and this is carried out against the pressure of spring means 48. When the plunger is released it is moved in the right hand direction by the spring means 20. The barrel carries two pins 54 and the sleeve 40 has stepped slots 52 in its end portion remote from the means 28, the slot being engageable with the pins to provide a positive lock against accidental release of the plunger. As shown, the plunger assembly is used to force a needle 56 of a cartridge assembly 58 into a patient to inject a serum into the patient. The cartridge 58 includes a wall 60 one end of which is closed by a cap 62 adapted to be pierced by a needle 56; the other end of the cartridge 58 is closed by a fluid tight sealing element 64 which is movable towards the cap 62 when urged by the plunger to force the needle 56 through plug 62 and into the patient. The element 64 also forces fluid through the needle. The plunger assembly is connected to the cartridge assembly by means of an adaptor 70 which screws on to the end portion of the barrel and which is engageable with a holder 72 for the cartridge assembly. The holder 72 has a bore for receiving the cartridge assembly and the bore has an enlarged portion 74 for receiving the end portion of the adaptor 70, a U shaped clip 76 engaging in an annular recess 77 in the holder 72 and in the groove 78 in adaptor 70 to hold the holder 72 onto the adaptor. In a modified plunger assembly the actuator is a one piece member and the housing and the plunger differ in construction but the operation is similar to the embodiment described above. In another construction however (Fig. 7, not shown) the recess in the plunger is a groove in the wall of a bore in the plunger and the balls move inwardly to releasing position instead of outwardly and they are held in the fastening position by an actuator which consists of a push button which has a stem with an annular groove which when aligned with the balls enable the balls to move inwardly to free the plunger.