Method and apparatus for controlling the movement of fluid to and from a syringe

摘要

A syringe for injecting fluid into a body or for removing body fluids is coupled to move together with the piston of a double acting hydraulic actuator having two chambers. For the purpose of aspirating fluid into the syringe, the second chamber of the actuator has within it a liquifiable gas which exerts a constant pressure on the piston. The expulsion of fluid from the syringe is accomplished by the admission of a hydraulic medium under pressure to the first chamber of the actuator. The apparatus also includes a calibrating mechanism which preselects a quantity of hydraulic medium proportional to the quantity of fluid to be expelled from the syringe.