A braking pressure control unit comprises a valve assembly with a valve seat (25) formed fast with the housing and a closure member (26) which latter, with the brake circuits (I, II) intact, when performing its relative movement to the valve seat (25), is kept in abutment on an extension (II) of a stepped piston (6) by a closure spring (28) supported on a malfunction piston (7). The valve (25, 26) is prevented from closing by the extension (11) at the stepped piston (6) and by a stop (29) for the closure member (26) at the malfunction piston (7). Because of the closure member (26) being in constant abutment on the extension (11) of the stepped piston (6) during its relative movement, there results a smaller stroke of the malfunction piston (7) and thus less fluid input of the braking pressure control unit and less wear of the sealing elements (22, 23) at the malfunction piston (7).
A flow regulating valve having an opening valve, which opens or closes a first passage 5m, 25, 5k, 5j and 5h and this opening valve is provided with a second passage 8 and includes a housing 5a accommodating an orifice 9 and a cylindrical member 24 concentrically engaged on this housing 5a. By relative movement of the housing 5a and the cylindrical member 24, the first passage is opened or closed. Further, in normal case, the flow regulating valve 6 opens the opening valve and communicates the master cylinder 1 with the passage selector valve 5 through the first passage. When the pressure difference on both ends of the cylindrical member 24 exceeds the preset value, the cylindrical member 24 is slid and the opening valve closes the first passage, and the discharge side of the pump 12 is communicated with the passage selector valve 5 only through the second passage 8.
