Abstract: A power brake apply system includes a master cylinder having a piston for generating fluid pressure within a braking circuit. A boost valve assembly is mounted adjacent the master cylinder and carries a slidable spool that selectively closes off a normal path of communication between a fluid reservoir and the boost chamber of the master cylinder in response to the manual actuation of the master cylinder's piston as effected through a pressurized braking circuit. After closure of communication between the reservoir and the boost chamber a power fluid supply is opened to the boost chamber to provide power assist in the actuation of the master cylinder's piston.

Abstract: A pressure control solenoid based vehicle braking system utilizes intensifiers to permit the hydraulic control components to operate at lower pressures. A method of selectively locking the intensifiers in position is provided. Unique pressure regulators provide predictable control of load pressure and are isolated in the system by a combination of enable valves and the locking method.