Medical syringe has chamber for liquid between piston on plunger and second piston that isolates liquid from needle until second piston moved to a forward position

摘要

A syringe has a chamber for a liquid between a piston on a plunger and a second piston. The second piston moves between a first position where the chamber is isolated from a needle and a forward position where the liquid can be injected via the needle. A mechanical device resists return movement of the second piston to the first position. The inner end of the needle can perforate the second piston to communicate with the chamber. Alternatively the needle communicates with the chamber via a groove in the wall of the syringe body that enables fluid to bypass the second piston. The mechanical device may be rim(s) formed on the interior of the syringe body.