Abstract: A hydraulic pressure control valve for an automobile brake mechanism which is provided with a first hydraulic pressure passage communicating with each brake units of, for instance, front wheels, and a second hydraulic pressure passage communicating with each brake units of, for example, rear wheels, and in which a plunger 5 is disposed in at least one or both of the hydraulic pressure passages and at least one hydraulic pressure regulating mechanism for converting the hydraulic pressure of a brake liquid as desire for instance, a poppet valve 14, is provided in association with the plunger in the hydraulic pressure passage having disposed therein the plunger, and in which blocking member is provided for inhibiting the plunger 5 from moving in a direction in which to cut off the brake liquid when the hydraulic pressure of either one of the hydraulic pressure passages fails.

Abstract: A free piston is reciprocally disposed within a first plunger unit associated with one of two circuits which plunger also houses a poppet valve actuatable by the free piston. A second plunger is reciprocally received in one end of the first plunger unit and also has a poppet valve actuatable by the free piston. The second plunger is biased toward the first by an actuator piston/spring arrangement subject to control by a valve responsive to vehicular deceleration. During pressure modulation the free piston reciprocates back and forth rapidly, opening and closing each of the poppet valves. Upon failure of one of the dual circuits both of the plungers shift in the same direction causing one poppet valve to remain open and prevent pressure modulation. Upon failure of the other circuit, the pressure transmitted by the arrangement markedly increases to produce the necessary deceleration to close a deceleration sensitive valve and induce modulation.