BC Transit – Air Brake Course

The Modulator Valve (primary air loss)
Foot Valve Application (continued)
The modulator valve “senses” the foot application, and releases air from the spring
brakes, but only as much as required by the foot valve application. The modulator
valve is “modulating,” or varying the release of air from the spring brake chambers
so that the rear brakes will apply at roughly the same pressure as the front brakes.
Left click for animation
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