Pipette which may be calibrated

Claim 1

Pipette having a fixed volume which can be calibrated, of the type comprising: a casing of oblong shape defining internally and essentially cylindrical cavity intended to receive, at its center, the rod of a piston-rod arrangement urged permanently upwards in a resilient manner, said rod being capped at its upper end by a push-button member able to be actuated from outside said casing and an outer tube, fixed to said casing coaxially with respect to said cavity, inside which the lower part of the piston-rod arrangement of straight circular section is able, due to actuation of the push-button member, to slide in a sealed manner and along a certain predetermined path limited in both directions, in order to define a variable volume chamber intended to cause filling or discharge of the sample to be taken, characterised by the fact that it comprises, inside said cavity in the casing, a calibration member arranged coaxially to the latter and whereof at least the upper part is in the shape of a sleeve, to which is imparted a rotary movement about its axis; by the fact that the calibration member comprises, on at least part of its outer surface, a screwthread intended to co-operate with a corresponding screwthread provided on the inner surface of said cavity; by the fact that said pipette also comprises a tubular abutment member coaxial with respect to the calibration member and adjacent the lower end of the latter, said abutment member being intended to co-operate with a locking bush integral with said rod of the piston-rod arrangement, in order to limit the useful upwards travel of said piston-rod arrangement in an adjustable manner and by the fact that the outer surface of the calibration member comprises an annular groove able to receive a braking ring compressed between the inner surface of the cavity in the casing and the outer surface of said calibration member in order to prevent the latter from rotating.