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 disposed in the tube member , the calibration filter tube having a first end portion and a second end , and further including a bore defined in an axial direction through the calibration filter tube , 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 and which extend from the axial bore to an outer surface of the calibration filter tube ; the volume reduction member having a bore through which the calibration filter tube extends, the volume reduction member occupying a space between the outer surface of the calibration filter tube and an inner surface of the tube member , an actuator unit disposed within the fluid injector downstream of the calibration filter tube , the actuator unit engaging the second end of the calibration filter tube ; and a valve assembly operatively coupled to the actuator unit, wherein a position of the calibration filter tube 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 disposed in the tube member , the calibration filter tube having a first end portion and a second end , and further including a bore defined in an axial direction through the calibration filter tube , 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 and which extend from the axial bore to an outer surface of the calibration filter tube ; the volume reduction member having a bore through which the calibration filter tube extends, the volume reduction member occupying a space between the outer surface of the calibration filter tube and an inner surface of the tube member , an actuator unit disposed within the fluid injector downstream of the calibration filter tube , the actuator unit engaging the second end of the calibration filter tube ; and a valve assembly operatively coupled to the actuator unit, wherein a position of the calibration filter tube within the tube member sets an opposing opening force of the valve assembly. <EOS>