Brake Proportioning Valve

A proportional valve is a valve that relies on the law of fluid pressure to distribute input force to one or more output lines. Proportional valves can increase or decrease the force of each output, depending on the cross-sectional area of those output lines.
Proportional valves are often used in automobiles to reduce brake fluid pressure on the rear brakes. In a car with front disc brakes and rear drum brakes, the front disc brake requires more pressure. The proportional valve prevents the rear brakes from engaging before the front brakes during emergency stops.