An injection device for injecting into a medical tubing a medical liquid from a medical liquid container, said injection device comprising: - a body defining an inner space extending in a longitudinal direction between an upper end of the body and a lower end of the body, the lower end of the body comprising a medical tubing interface through which the medical liquid can penetrate the inner space from the medical liquid container and can exit said inner space to be injected into the medical tubing, - a piston arranged within the inner space and configured for travelling within the inner space along the longitudinal direction, said piston delimiting an upper space and a lower space of the inner space, said lower space configured to receive the medical liquid, - an evacuation path, said evacuation path traversing the piston in the longitudinal direction from the lower space to the upper space of the inner space, characterized in that the injection device further comprises: - a selector (24, 50, 60) arranged within the evacuation path between a lower portion of the evacuation path and an intermediate portion of the evacuation path, said lower portion of the evacuation path being connected to the lower space, wherein the selector (24, 50, 60) is configured for selectively allowing gas to go through said selector and to travel along the evacuation path from the lower portion to the intermediate portion of the evacuation path, said selector (24, 50, 60) configured for selectively preventing the medical liquid from going through said selector (24, 50, 60) and from travelling along the evacuation path from the lower space to the upper space of the inner space, - a purge valve arranged in the evacuation path between the intermediate portion of the evacuation path and an upper portion of the evacuation path and configured for moving between a blocking configuration in which the purge valve closes the evacuation path and a passing configuration in which the purge valve keeps open said evacuation path, wherein the passing configuration of the purge valve requires an overpressure in the intermediate portion of the evacuation path caused by the piston travelling towards the lower end of the body. - a body defining an inner space extending in a longitudinal direction between an upper end of the body and a lower end of the body, the lower end of the body comprising a medical tubing interface through which the medical liquid can penetrate the inner space from the medical liquid container and can exit said inner space to be injected into the medical tubing, - a piston arranged within the inner space and configured for travelling within the inner space along the longitudinal direction, said piston delimiting an upper space and a lower space of the inner space, said lower space configured to receive the medical liquid, - an evacuation path, said evacuation path traversing the piston in the longitudinal direction from the lower space to the upper space of the inner space, - a selector (24, 50, 60) arranged within the evacuation path between a lower portion of the evacuation path and an intermediate portion of the evacuation path, said lower portion of the evacuation path being connected to the lower space, wherein the selector (24, 50, 60) is configured for selectively allowing gas to go through said selector and to travel along the evacuation path from the lower portion to the intermediate portion of the evacuation path, said selector (24, 50, 60) configured for selectively preventing the medical liquid from going through said selector (24, 50, 60) and from travelling along the evacuation path from the lower space to the upper space of the inner space, - a purge valve arranged in the evacuation path between the intermediate portion of the evacuation path and an upper portion of the evacuation path and configured for moving between a blocking configuration in which the purge valve closes the evacuation path and a passing configuration in which the purge valve keeps open said evacuation path, wherein the passing configuration of the purge valve requires an overpressure in the intermediate portion of the evacuation path caused by the piston travelling towards the lower end of the body.