Vacuum servo

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.

Brake booster from a Geo Storm.

Brake vacuum servo section

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.

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.

See also

• List of auto parts

External links

• What is a brake booster?
• "How Power Brakes Work", (a 4-page basic tutorial article, with illustrations & animation) at HowStuffWorks.com