The service brake valve (1) has a pressure piece (10) with a blind hole-like tappet receptacle (8) to incorporate a tappet operated by a brake pedal. The pressure piece is guided on a radially inner guide surface of the piston wall of a piston (18). A combined guiding unit is provided between the radially inner guide surface of the piston and a radially outer guide section (14) of the pressure piece. The guiding unit contains an O-ring held radially outside the ring groove of the guiding section.
