Patent ID: 8357337

Claim:
A pipette with an adjustable volume of an aspirated liquid built of a handle ( 1 ) and of a nozzle ( 3 ) and of coupled with them an exchangeable pipette tip ejection mechanism comprising an ejector push button ( 7 ) seated in the upper part of said handle ( 1 ) and an ejector ( 9 ) seated with its lower end onto said nozzle ( 3 ), a drawing up and discharging mechanism comprising a pipetting push button ( 5 ) connected via a pipetting rod ( 6 ) with a piston assembly ( 11 ) of which a plunger ( 12 ) is placed in said nozzle ( 3 ), a plunger working stroke adjustment mechanism provided with a drive assembly of an adjustment screw of a plunger working stroke with at least one driving member ( 16 ), a manually actuated lock mechanism locking said plunger working stroke adjustment mechanism, an engaging mechanism engaging said plunger working stroke adjustment mechanism with a counter ( 14 ) for indicating a volume of a liquid aspirated by said pipette depending on the set plunger working stroke, a calibration mechanism for a change of a pipette calibration coefficient determining a relationship between a plunger movement length which is set by said plunger working stroke adjustment mechanism and the liquid volume indicated in said counter, whereas said driving member ( 16 ) of said drive assembly of said adjustment screw of the plunger working stroke is accessible from outside through at least one window ( 38 ) in a wall of said handle ( 1 ), characterised in that said lock mechanism locking said plunger working stroke adjustment mechanism comprises a lock member which is non-rotatably mounted relative to said pipette handle ( 1 ) and is axially slidable along an axis defined by the pipetting rod ( 6 ) between LOCKED POSITION and UNLOCKED POSITION of said plunger working stroke adjustment mechanism, whereas said driving member ( 16 ) of said drive assembly of said adjustment screw of the plunger working stroke is axially fixedly and rotatably mounted relative to said pipette handle ( 1 ), and said lock mechanism locking said plunger working stroke adjustment mechanism constitutes a friction brake between said lock member and said driving member ( 16 ), whereas said lock member has a frictional surface ( 31 ) on an inner cone and said driving member ( 16 ) has a frictional surface ( 32 ) on an outer cone.