A fluid injector, comprising: a fluid inlet disposed at a first end and configured to receive a fluid, and a fluid outlet disposed at a second end of the fluid injector for discharging the fluid, the fluid injector defining a fluid path for the fluid from the fluid inlet to the fluid outlet; a tube member having an end disposed at or near the fluid inlet of the fluid injector, the tube member configured to pass fluid along the fluid path; a calibration filter tube (402,502) disposed in the tube member, the calibration filter tube (402,502) having a first end portion (402B,502B) and a second end (402D,502D), and further including a bore (402A,502A) defined in an axial direction through the calibration filter tube (402,502), the bore defining at least a portion of the fluid path through the fluid injector, the calibration filter tube including a plurality of holes which are disposed at least along an upstream portion of the calibration filter tube adjacent a volume reduction member (408,508) and which extend from the axial bore (402A,502A) to an outer surface of the calibration filter tube; the volume reduction member (408,508) having a bore (402A,502A) through which the calibration filter tube (402,502) extends, the volume reduction member (408,508) occupying a space between the outer surface of the calibration filter tube (402,502) and an inner surface of the tube member, an actuator unit disposed within the fluid injector downstream of the calibration filter tube (402,502), the actuator unit engaging the second end (402D,502D) of the calibration filter tube (402,502); and a valve assembly operatively coupled to the actuator unit, wherein a position of the calibration filter tube (402,502) within the tube member sets an opposing opening force of the valve assembly. a fluid inlet disposed at a first end and configured to receive a fluid, and a fluid outlet disposed at a second end of the fluid injector for discharging the fluid, the fluid injector defining a fluid path for the fluid from the fluid inlet to the fluid outlet; a tube member having an end disposed at or near the fluid inlet of the fluid injector, the tube member configured to pass fluid along the fluid path; a calibration filter tube (402,502) disposed in the tube member, the calibration filter tube (402,502) having a first end portion (402B,502B) and a second end (402D,502D), and further including a bore (402A,502A) defined in an axial direction through the calibration filter tube (402,502), the bore defining at least a portion of the fluid path through the fluid injector, the calibration filter tube including a plurality of holes which are disposed at least along an upstream portion of the calibration filter tube adjacent a volume reduction member (408,508) and which extend from the axial bore (402A,502A) to an outer surface of the calibration filter tube; the volume reduction member (408,508) having a bore (402A,502A) through which the calibration filter tube (402,502) extends, the volume reduction member (408,508) occupying a space between the outer surface of the calibration filter tube (402,502) and an inner surface of the tube member, an actuator unit disposed within the fluid injector downstream of the calibration filter tube (402,502), the actuator unit engaging the second end (402D,502D) of the calibration filter tube (402,502); and a valve assembly operatively coupled to the actuator unit, wherein a position of the calibration filter tube (402,502) within the tube member sets an opposing opening force of the valve assembly.