The application of the brakes in the simple system was described earlier. In such a basic system, when the driver releases the foot valve, it would be necessary for the air under pressure in the brake chambers to return back to the foot valve to release the brakes. This releasing action would be slowed in long wheel base vehicles, due to longer lines between the foot valve and the rear brake chambers. To allow the brakes to release quickly and fully, by discharging the application air near the brake chambers, a quick release valve (13) may be installed.