A brake booster has two chambers, which are separated by a moving membrane. To amplify the driver's pedal force, a pressure difference is created between both chambers of the brake booster. To do this, the brake booster is evacuated in a non-activated state. When the driver actuates the brake pedal, ambient air flows into the rear chamber, creating higher pressure in front of the membrane. Such a pressure difference is created between both of the chambers that the diaphragm plate presses in the direction of the tandem master cylinder and thus supports the force of the driver's foot.
For larger vehicles, tandem vacuum brake boosters with four chambers are used. In addition to the standard variant, Bosch also offers Tie Rod variants of the vacuum brake booster. In these, the stiffness is increased by so-called tie rods and the thickness of the shells is reduced at the same time. The Tie Rod variants are available in steel or aluminum.