Vacuum servos reduce the effort required to apply brakes in cars and trucks. They work by creating a pressure differential and consist of a large vacuum reservoir divided into two compartments. Vacuum is generated by internal combustion engines, while diesel or electric engines use a vacuum pump. Vacuum brake boosters provide full braking power as soon as the pedal is depressed a certain distance. Some vehicles use air brakes or hydraulic brake boosters.
Vacuum servos are devices used in many cars and trucks to reduce the effort required to apply the brakes. This component, also known as a vacuum brake booster, consists of a large vacuum reservoir that is divided into two compartments. One end of the device is linked via a link to a brake pedal and the other end consists of a plunger that is in contact with the brake master cylinder. When the driver steps on the brake pedal, atmosphere enters one of the compartments in the tank. This pressure differential increases the force that was applied through the brake pedal, so less driver effort is required than if the vehicle lacked a vacuum servo.
Internal combustion engines generate vacuum as a natural part of the combustion process. This is generally known as a manifold vacuum, and can be used to power components like wiper motors and vacuum bake boosters. Vehicles that use diesel or electric engines can also use a vacuum servo by utilizing a component known as a vacuum pump. These devices work mechanically or electrically and work by pumping air out of a sealed container.
Early automotive braking systems used direct mechanical connections between the brake pedals and the master cylinders. This type of system uses only the available force from the driver’s foot to depress the master cylinder and activate the brakes. As a result, a great deal of force is often required and it can take some time for pressure to build up and the brakes to come on. A vacuum servo not only reduces the effort required to activate the master cylinder, but also provides full braking power as soon as the pedal is depressed a certain distance.
Vacuum brake boosters work by creating and then exploiting a pressure differential. A typical servo vacuum consists of two sealed vessels, one inside the other. Vacuum is applied to remove air from inside both vessels, and a check valve usually prevents atmosphere from accidentally re-entering.
Typical servo vacuum designs also include a diaphragm between the two sealed vessels. Air is allowed into one of the chambers as the brake pedal is moved downward, creating a pressure differential and moving the diaphragm. Additional air can be drawn into the device whenever the pedal is depressed, creating a larger pressure differential and more braking force.
Some vehicles, particularly large combination trucks, use air brakes that do not require a vacuum servo. Other vehicles use a hydraulic brake booster, regardless of whether vacuum is readily available. One particular application uses the same pressurized fluid to operate the power steering rack and provide boost force to the brakes.
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