Dual differential displacement fluid metering

An apparatus for accurately and reliably metering of liquid volumes comprising:

• a cylinder holding a seal at each end that defines a chamber and takes into the chamber a piston from above and a tube from below, the diameter of the piston being less than the diameter of the tube, and the cylinder, piston and tube being concentric and coaxial to each other,
• the cylinder configured and arranged to slidably move up over said piston and tube to release a portion of the tube from the cylinder while taking in an additional similar portion of the piston, thereby increasing a volume of air in the chamber and to create a negative pressure or vacuum therein,
• the cylinder further configured and arranged to slidably move down over the piston and tube to release a portion of the piston from the cylinder while taking in an additional similar portion of the tube, thereby reducing the volume of air in the chamber and to create a positive pressure therein,
• said piston configured and arranged to move with the cylinder by a same distance as the cylinder moves, so that the tube moves alone within the cylinder with no offsetting movement of the piston in the cylinder, thereby causing a change in the volume of air in the chamber,
• a probe or mandrel that can hold a disposable tip, that is part of or attachable to the tube, extending downward with an inner channel that is one with or continuous with that of the tube and which can sample from a liquid,
• each of the foregoing parts being supported within a frame or sleeve, the frame or sleeve having a top end, so as to comprise a handheld pipettor, which supporting sleeve may itself nest within a molded handle or be absent if its support functions are provided by the molded handle,
• wherein a lower end of the frame or sleeve holds a tube or tube mandrel concentric thereto,
• and wherein a top end of the frame or sleeve holds a knob with a stalk that threads down into a movable pusher that holds the cylinder below, such that by moving the knob an operator can move the cylinder up and down to aspirate or dispense liquid,
• and wherein the knob is configured and arranged to be turned to adjust a distance to a top of the piston to define an aspiration volume,
• said apparatus further comprising a viewing window in the knob that shows a vernier label corresponding to an aspiration value that has been selected,
• said apparatus further comprising a hole in the sleeve and molded handle that permits ambient air temperature regulation as well as viewing of an interior of said apparatus, and
• a disposable tip-stripper ejection switch coupled to said disposable tip so as to disengage said tip from other parts of said apparatus.