Single Vacuum Unit

In a normal operating mode, with the service brakes in the released position, the single vacuum booster operates with vacuum on one side of the diaphragm. When the brakes are applied, air at atmospheric pressure is admitted to one side of the diaphragm to provide the power assist. When the service brake is released, the atmospheric pressure is cut off from the one side of the diaphragm. The air is then drawn from the booster through the vacuum check valve to the vacuum source.