Plunger stroke pipette

A plunger stroke pipette for replaceable pipette points comprising:

• a seat for the detachable mounting of a pipette point, the seat having a first end including an opening;
• a cylinder;
• a connecting channel abutting the cylinder and connecting the cylinder to the opening in the seat;
• a driving equipment;
• the driving equipment comprising a lifting rod;
• a plunger for providing a volumetric stroke, the plunger having proximal and distal ends;
• the driving equipment coupled to the plunger for displacing the plunger in the cylinder;
• an upper stopper;
• a lower stopper;
• the lifting rod comprising at least one counter-stopper for limiting the stroke of the plunger;
• a holder, supporting the lower stopper wherein an overstroke spring is sandwiched between the holder and the upper stopper;
• an adjustment equipment for adjusting the position of the holder with respect to the cylinder;
• an indicating equipment for indicating the position of the holder;
• a spindle;
• a spindle nut;
• the spindle connected in the spindle nut;
• wherein a lower front side of the spindle forms the upper stopper, that is stationary with respect to the cylinder;
• wherein the spindle has a passage channel through which the lifting rod is guided through;
• a volume adjustment equipment;
• wherein the spindle is rotationally coupled with the volume adjustment equipment;
• the volume adjustment equipment comprises an adjustment sleeve accommodating coaxially the spindle, the adjustment sleeve having a gearwheel (23);
• a driving tenon which is connected with the spindle;
• the volume adjustment sleeve has axial grooves in an inside into which the driving tenon engages;
• a numerator, the numerator having a gearwheel;
• a set of gearwheels comprising two gearwheels;
• a gear comprising the gearwheel of the numerator, the two gearwheels of the set of gearwheels and the gearwheel of the adjustment sleeve;
• the adjustment sleeve is coupled with the numerator for indicating the volume adjustment via the set of gearwheels (29);
• an equipment for uncoupling at least two of the gearwheels comprising the gear, between the adjustment sleeve and the numerator;
• wherein one of the gearwheels of the set of gearwheels engages with the gearwheel of the adjustment sleeve and the other of the gearwheels of the set of gearwheels engages with the gearwheel of the numerator;
• wherein each gearwheel of the set of gearwheels are mounted on an axis and are shiftable along their axis by means of the equipment for uncoupling, whereby at least one of the gearwheels of the adjustment sleeve and the numerator being uncoupled from one the gearwheels of the set of gearwheels.