Combination Valve Description. Chevrolet Chevy P32 RV/Van Chassis 1998


(1)	Metering Valve
(2)	Warning Switch
(3)	Proportioner

The combination valve has three sections. Each section serves a different function.

•	The metering, or hold off, section limits front disc brake pressure, allowing just enough pressure to overcome the rear brake shoe springs. When the inlet pressure is below 200 kPa (30 psi), there is no restriction. This allows for pressure equalization when the brakes are not applied.

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The pressure differential warning switch constantly compares front and rear brake pressures from the master cylinder. The switch closes if the front or rear brake systems lose pressure, completing the circuit to ground. This illuminates the BRAKE lamp on the instrument panel. The switch latches in the WARNING position after a malfunction occurs. To turn off the BRAKE lamp you must repair the malfunction and apply enough pedal pressure in order to develop about 3100 kPa (450 psi) brake line pressure.

•	The proportioning section limits brake line pressure to the rear brakes after the rear brakes reach a predetermined rear input brake line pressure. This minimizes rear wheel lockup on vehicles with light rear wheel loads.

The combination valve has a bypass feature. The bypass feature ensures full system pressure to the rear brakes when there is a malfunction in the front brake system. The bypass feature ensures full system pressure to the front brakes when there is a malfunction in the rear brake system.