Vacuum servo

{{Short description|Car part}}

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Image:2008-05-05 1990 Geo Storm GSi vacuum servo.jpg.]]

Image:Servofreno seccionado.jpg

A vacuum servo is a component used on motor vehicles in their braking system, to provide assistance to the driver by decreasing the braking effort. In the US it is commonly called a brake booster.

A vacuum servo, also known as a power booster or power brake unit, uses a vacuum, usually supplied by the engine, to multiply the driver's pedal effort and apply that effort to the master cylinder. {{Cite web|url=http://www.edumech.co.uk/brakes-hydraulic/4591385319|title=Brakes - Hydraulic - EduMech|website=www.edumech.co.uk|access-date=2016-04-25 |url-status=dead |archive-url=https://web.archive.org/web/20160425204917/http://www.edumech.co.uk/brakes-hydraulic/4591385319 |archive-date=2016-04-25}}

Because the servo depends on the vacuum supplied by a running engine, a check valve is typically used in the vacuum line to maintain residual vacuum without engine support, allowing limited use even after parking.