Brake Proportioning/Combination Valve: Description and Operation

The P&B valve contains two sections, each serving a different function.
The proportioning section of the P&B valve proportions outlet pressure to the rear brakes after a predetermined rear input pressure has been reached. This is done to prevent rear wheel lock up on the vehicles with light rear wheel loads. The valve has a by-pass feature which assures full system pressure to the rear brakes in the event of front brake system malfunction. Also full front pressure is retained in the event of rear brake malfunction.
The P&B valve is not repairable and must be replaced as complete assembly.