Pressure control device for a vehicle brake

A pressure control device for a dual type vehicle brake system having a pair of first and second circuits mutually independent for delivering the braking fluid pressure produced in a master cylinder, which is provided with a pair of pressure chambers, to each wheel cylinder disposed respectively on a pair of right and left rear wheels, said pressure control device for controlling the pressure rising in each of said rear wheel cylinders, when the deceleration rate of the vehicle exceeds a predetermined value, comprising:

• an inertia valve, installed in said first circuit, provided with an inertia body which is allowed to shift, resisting the biasing force, to close a passage for the braking fluid when the deceleration rate of the vehicle exceeds a predetermined value;
• a shut-off valve installed in said second circuit for closing a passage for the braking fluid in said second circuit;
• a housing accommodating said shut-off valve;
• a balance piston, slidably accommodated in said housing, provided with a pair of first and second pressure-receiving faces, on opposite ends thereof, of identical area, said first pressure-receiving face being affected by the pressure coming through said inertia valve in said first circuit, said second pressure-receiving face being affected by the pressure coming through said shut-off valve in said second circuit, said balance piston being operated by the pressure difference between the pressure acting on said first and second pressure-receiving faces, for opening said shut-off valve when the pressure in said first circuit is higher, and for closing said shut-off valve when the pressure is said second circuit is higher.