940 L4-2.3L SOHC VIN 88 B230F (1992)
Brake Proportioning/Combination Valve: Description and Operation
Pressure Differential Warning Valve
The warning valve is installed only in cars without ABS. Made of aluminium alloy, the valve is incorporated in the brake pipe manifold mounted on the
inner wheel housing. Its function is to warn the driver of excessive difference in pressure between the two braking circuits (e.g. in the event of leakage).
On models from 1989 on, the warning valve was replaced by a level switch in the brake fluid reservoir, a feature already installed on cars with ABS.
The warning valve actuating pin rests on the mid-section of a movable piston in the chamber between the primary and secondary circuits of the manifold.
When the brakes are applied normally i.e. when the pressure in both circuits is approximately equal, the piston is in the position shown in figure A.
If an excessive drop in pressure (due to leakage or air in the system) occurs in one of the circuits, the piston will be displaced laterally by the higher
pressure in the other circuit (figure B).
The valve actuating pin will then ground the warning lamp on the instrument panel and the lamp will light.
