Abstract: A brake cylinder fluid pressure distributor having a control valve device of the pressure proportioning type that includes a main and auxiliary reaction piston, each subject on a corresponding face to pressure delivered by the control valve device to the brake cylinders in order to provide an actuating force on the piston valve assembly in a counteracting direction to the control force thereon, thereby automatically regulating the brake cylinder pressure. The auxiliary reacting piston is arranged on the piston valve assembly so as to be either engaged therewith or disengaged therefrom according to the effective load condition, speed range, deceleration rate or other parameter of a vehicle to be braked, thereby adjusting the effective brake cylinder pressure by adjusting the point in time when the delivery of pressure to the brake cylinders is terminated by the regulating action of the control valve device.