proportioning vavle?

[JeepJeepster]

What is this and what does it do. I know where its at, but have no clue what it does? I know it has something to do with the brakes?

 

[Bonehead]

It controls how much brake pressure goes to the front and rear brakes to keep the car/truck brakes working evenly front to rear, its also where the sensor is mounted that turns on the brake warning light on if pressure is lost.