Brakes (Copy valve): Description and operation

COPY VALVE

A copy valve, mounted inside the hydraulic modulator unit, is used to ensure balanced operation of the rear brakes when an ABS sequence is triggered. During an ABS sequence, the copy valve operates by using pressure changes in the brake circuit controlled directly by the modulator valve.

These pressure changes cause a piston in the controlled circuit (A), to operate a mechanically linked (but hydraulically separate) piston assembly in the uncontrolled circuit (B).

During normal braking, pressure from the master cylinder (C) in controlled circuit (A) flows through the solenoid valve to the RH rear caliper (A4). In the uncontrolled circuit (B) pressure passes into chamber (B2) of the copy valve, past ball valve (B3) in piston (B1) to the LH rear brake caliper (B4).