Anti-lock control apparatus for air over hydraulic brake system

An anti-lock control apparatus for an air over hydraulic brake system wherein a brake valve is connected to an air pressure source, said brake valve is connected to a pneumatic chamber of an air master cylinder through a first air pressure line, a hydraulic chamber of said air master cylinder is connected to a liquid input port of a modulator, a valve device is interposed in a passage between said liquid input port of the modulator and a liquid output port thereof, said valve device is arranged such as to be capable of being opened by a hydraulic piston fitted in the modulator, a pneumatic piston is connected to said hydraulic piston, and said liquid output port of said modulator is communicated with a hydraulic chamber of said modulator and is connected to a wheel cylinder, a pneumatic chamber of said modulator is connected to the brake valve via a second air pressure line, and air pressure in said modulator pneumatic chamber is controlled by a first valve apparatus, said anti-lock control apparatus for an air over hydraulic brake system comprising:

• a second valve apparatus provided to leave a prescribed amount of residual pressure in said modulator pneumatic chamber at the time of the release of braking.