Abstract: A needle covering mechanism for a hypodermic syringe includes a protective cover sleeve which is movable between a retracted position in which a needle is exposed and an extended position in which the needle is covered. A retainer includes first detents which by means of a spacer is forced to engage indentations in the cover sleeve to prevent a movement of the cover sleeve towards the extended position. The spacer is made from a material which after some time in contact with an injectant loses its mechanical strength, and some time after filling the syringe with an injectant, the spacer deforms, the first detents slip out of the indentations in the cover sleeve, and a spring forces the cover sleeve to the extended position.

Abstract: An automatic needle retracting mechanism (1) for a hypodermic syringe (2) comprises a body (3) which slidingly supports a needle (27). A retainer (9) for an actuator (8) and the needle (27) is kept in a retaining position by a spacer (11), which after some time in contact with an injectant loses its mechanical strength. A filing of the needle with an injectant causes a deformation of the spacer (11), a release of the actuator (8) and a retracting of the retainer (9) and needle (27) into a needle retraction chamber (4). The needle retracting mechanism may also include an inner sleeve (20) which is manually movable towards the retainer (9) for a manual release of the actuator (8). The needle retracting mechanism may be included in a needle holder (33) or integrated in a syringe (2′).