Hydraulic master apparatus for a hydraulic brake or clutch of handlebar-guided vehicles and hydraulic brake of a handlebar-guided vehicle

A hydraulic master apparatus, in particular, for a hydraulic brake or clutch of handlebar-guided vehicles with a lever, which is pivotally mounted in a support, and a hydraulic cylinder, which can be disposed in a handlebar tube of the handlebar-guided vehicle and has a piston movably disposed therein, wherein a central valve is disposed in the piston.