Automatic injection devices

摘要

An injection device has a needle (22) which, when the device is operated, is first caused to project, then liquid is forced out through it, and finally the needle is automatically retracted. The needle (22) extends forwardly from a capsule (18) that can slide longitudinally within a barrel-like body (1), a relatively weak spring (19) normally maintaining the capsule and needle retracted. A more powerful spring (14) acts oppositely on a plunger (26) which, when released, shoots the capsule forward by acting on the liquid therein, and then forces the liquid out through the projecting needle (22). At the end of the forward stroke the plunger (26) and capsule (18) are decoupled and the weak spring (14) returns the exhausted capsule and its needle to the retracted position.