Vacuum Brake Booster: Description and Operation

The vacuum booster is a single diaphragm vacuum suspended unit. Engine vacuum is provided to the vacuum booster through a hose and a vacuum check valve. The one-way check valve is provided between the engine and the booster to prevent a loss of booster vacuum when engine vacuum falls below that stored in the booster. When the brakes are not applied, internal valves within the booster provide vacuum to both sides of the diaphragm. When the brakes are applied, air at atmospheric pressure is applied to one side of the diaphragm. Since a higher pressure now exists on one side of the diaphragm than the other, a force is created, assisting the brake application.