The built-in piston uses the air pressure difference to replace the same volume of air with the target liquid through the movement of the piston inside the pipette. In this way, there is a long air column between the piston and the liquid, and there is a filter element in the middle, so the piston of the pipette is not polluted, and it is convenient to replace the suction head.

The external piston directly contacts the piston with the target liquid. When the piston is pulled up, the atmospheric pressure will squeeze the liquid into the suction head. In this way, there is no air gap between the piston and the liquid, and the air pressure is 0, which can avoid the internal and external pressure imbalance caused by liquid gas/vaporization, and can better deal with the liquid with poor liquidity. Such as stepper continuous liquid separator.