Disabling a fluid pressurizing unit of a fluid injection system involves retracting a plunger shaft from a first position to a second position within a syringe of the unit, such that a plunger disengages from the plunger shaft and moves away therefrom within the syringe. The plunger shaft may include a groove and the plunger an internal tab that is configured for removable engagement with the groove of the plunger shaft when the shaft is fully inserted into the plunger.
