GB1189894A - Hypodermic Syringes - Google Patents

Abstract

1,189,894. Hypodermic syringes. S. GRANT. 5 April, 1968 [5 April, 1967], No. 16611/68. Addition to 1,159,958. Heading A5R. A hypodermic syringe allowing for prior aspiration of body fluid (e.g. blood) comprises a syringe body 36, means for mounting an ampoule 41 and a needle 39 on the syringe body, a plunger 40 for driving the contents of the ampoule out through the needle, a spring 44 biassing the plunger towards the needle holder, a cylinder within the body, a piston 42 attached to the plunger and fitted for axial movement within the cylinder 43, the piston and cylinder defining a first compartment in front of the piston which when filled with damping fluid prevents movement of the plunger by the spring and a second compartment behind the piston, a conduit 46 connecting the first and second compartments, a manually operable valve 50, 52 in the conduit to control the flow of damping fluid between the compartments to allow controlled advance of the plunger under the action of the spring, and a manually operable ram movable within a chamber, 55 connected to the first compartment to force damping fluid into the first compartment (via 56, 47, 46) and thereby partially withdraw the plunger against the biassing spring. The plunger preferably has a hook on the outer end for engagement in the body of the stopper closing the end of the ampoule. The specification also discloses an improved form of valve for controlling the flow of damping fluid between the compartments for controlling the rate of injection. The valve is described with reference to Fig. 3 which illustrates a syringe wherein the valve 76 comprises a metering slide 84 movable axially through a sleeve 86 and having a recess 89 in its surface of greater axial length than the sleeve, the recess forming with the sleeve a flow passage of increasing cross-section whereby the slide progressively changes the flow through the valve.