PURPOSE: To secure braking effect when a failure is caused in a brake system of X type pipe arrangement, by a method wherein the hydraulic press of dual circuit can be controlled by providing a free piston to a hydraulic press control valve which responds to deceleration of a car.

CONSTITUTION: The G ball 1 and a valve seat 2 compose an inertia valve, which controls the tension of a spring 7 by means of an actuator piston 3. On the other hand, both ends of a free piston 20 act to poppet valves 16 and 19, which perform proportional control by the tension of springs 6 and 7, which is received by a plunger 14. The free piston 20 is supported by guide rings 22, between which a seal 21 is installed to separate both circuits. Since hydraulic press control can be performed for dual circuit, said structure can be also used for a brake system of X type pipe arrangement.