Brake Proportioning/Combination Valve: Description and Operation

Fig 31 Type 1 Combination Valves:

This valve assembly,is comprised of a warning switch, and a dual proportioning valve.

The warning switch detects system failure when a pressure difference occurs between the diagonally split systems. In such a case, the valve piston shuttles toward the side with the low pressure forcing the switch plunger upward over the piston's tapered shoulder. This movement closes the switch contacts causing the brake warning lamp to illuminate. Upon restoration of equalized system pressure the brake warning switch will reset.

The proportioning valve transfers full braking force to the rear brakes until a preset ratio called the split point is achieved. At this point the pressure increase is routed away from the rear brake system to prevent rear wheel lock-up.