Pressure Differential Valve (Warning Switch)

The pressure differential switch is used to operate a warning light that alerts the driver if the pressure in a system is lost or low. The brake warning switch has been standard equipment since 1970, and is connected to the front and rear brake lines. It alerts the driver if either set of brakes is not working properly. There are two types of pressure differential switches; mechanical or hydraulic. Mechanical switches are activated by excessive brake travel. Hydraulic switches are activated by a difference in pressure between the front and rear system. When pressure in one of the lines is sharply reduced, pressure from the other side forces a piston to move. A plunger pin then drops into a groove in the piston, activating a switch that turns on a dashboard warning light.