Abstract: A metering pump for a medical injector includes a housing, a sleeve at least partially received within the housing, a piston at least partially received within the sleeve, and an interlock. The piston has a first position where the chamber has a first volume and a second position where the chamber has a second volume, with the first volume larger than the second volume. The sleeve has a first rotational position where an inlet is in fluid communication with the chamber, a second rotational position where an outlet is in fluid communication with the chamber, and a third rotational position where the inlet and outlet are isolated from the chamber. The interlock includes an elastomeric member and a protrusion, where engagement between the elastomeric member and the protrusion is configured to restrict movement of the sleeve until the sleeve overcomes a predetermined torque value.