What is air-displacement pipetting?

Air-displacement pipetting is driven by a piston moving vertically within an airtight sleeve. To aspirate, the piston travels up vertically, generating a vacuum within the sleeve. This causes the air in the pipette tip to move up and fill that space and the tip air is then replaced by the sample/liquid which is drawn up into the tip. To dispense, the piston moves down, pushing the air in the sleeve into the pipette tip, which then pushes the sample/liquid out into the well.