Step pipette

Claim 1

A step pipette, comprising: a frame; a cylinder provided on said frame; a piston provided within said cylinder and movable in a direction between a lower and an upper position within said cylinder; a dosing rack supported by said frame which is parallel to said direction and which is fixed to said piston, said dosing rack being provided with a dosing toothing; a striker supported by the frame and movable between an upper and a lower position, a portion of said striker capable of meshing with the dosing toothing for transferring the dosing rack and the piston downwards by predetermined strokes; said dosing rack also including a longitudinal transmission toothing, a gear in mesh with said longitudinal transmission toothing and supported by said frame, a filling rack supported by said frame parallel with the dosing rack, a second longitudinal transmission toothing provided on said filling rack, which is in mesh with the gear from the opposite side relative to the transmission toothing of the dosing rack; a striker spring means for pressing the striker against the dosing toothing; a release element means on the filling rack for releasing the tension of the striker spring after a last full-length stroke thereby disengaging said striker form said dosing toothing; a loosening spring for moving the striker from the dosing toothing to an upper disengaged position after the last full-length stroke to thereby allow filling of the cylinder by retraction of the piston; means for reengaging said striker with the dosing rack.