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Booster Operation

The vacuum bleed port allows only the required amount of atmospheric pressure into the booster chamber. This is determined by the force applied to the brake pedal by the driver. The harder the driver applies the brake, the more atmospheric pressure allowed into the booster chamber, and the greater the vacuum boost. Once the level of boost corresponds to the force applied to the brake pedal the bleed port on the pushrod closes, thus maintaining the level of vacuum in the chamber.

When the pedal is applied, the equalizer valve closes between the 2 sides of the diaphragm, isolating them.

As the pedal moves forward, it opens the vent port at the rear of the chamber. Air pressure then enters the rear chamber of the booster as the front is still under vacuum.

This difference in pressure adds force on the diaphragm, which assists the operator in pushing against the master cylinder piston.

When the pedal stops, both valves close, holding the last pressure differential in the booster, allowing the operator to maintain high brake pressure with little effort.

When the pedal is moved rearward, the pushrod moves back, opening the vacuum port to the rear chamber, which evacuates the air & moves the diaphragm, pushrod, pedal, & master cylinder piston back to lower the brake pressure.

When the pedal is fully released, the equalized vacuum in both chambers allows the return spring to force the pushrod away from the master cylinder piston, and the pedal to the full up position.