What is a Reducing Tube?
In some models/sizes of Eppendorf pipettes, a reducing tube, also known as “filling tube”, is used to regulate air flow. It is used in pipettes where the ratio between the shaft orifice and the piston diameter is such that, during aspiration of the liquid, a turbulence will be created in the aspirated liquid and air bubbles will be introduced into the tip, particularly if the user lets the plunger go back too fast. The reducing tube is a proprietary design. The exact mechanical logic and the calculation of the dimensional parameters of the tubes are not shared by Eppendorf.
Replacing a Reducing Tube
If the tube gets blocked/plugged/contaminated with sample splash, it must be replaced. Though it is very easy to replace the tube – and it does not affect the calibration or any adjustment in the mechanical end – it does require tools ( i.e., the wire punch to push the old tube out and the specific wrench for the model to remove and re-install the seal [tube goes below the seal into the shaft]).
This can be done by a service person or you can buy the tools and tubes and do it yourself.
Reference Repair Kit, Including Reducing Tubes – EP 022475045
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