What is Brake Booster? How Brake Booster Works?

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The techniques of driving the automobiles are totally changed and a new era comes with new technologies and inventions. With the new inventions, the old driving experience is totally changed many new mechanisms and devices has been invented to make the driving more safe and easy for example the mechanical braking system is replaced by some advanced braking systems such as hydraulic brake, air brakes and vacuum brake. For the proper functioning of the braking systems some extra devices are developed which makes the driving more convenient and safe. The brake booster is one of the safety device used in the automobiles and it is a necessary part of the braking system. The working principle and functioning of the brake booster is as follow.

Brake Booster:


Working Principle:

Brake booster is a safety device used with the brakes and it works on the principle of Pascal’s law. It helps to make the driving very comfortable because in driving the main tasks are to control speed and braking. With the help of this device the braking experience totally changed because it reduces the human effort for applying the brake. It is mounted between the brake master cylinder and brake pedal. Brake booster increases the pressure force before sending to the master cylinder so that the driver effort reduces or we can say that it multiplies the driver forces on the brake pedal with the application of vacuum caused by the piston-cylinder arrangement of the engine. It increases the brake efficiency and provides a comfortable driving experience by reducing the fatigue of driver because of very less effort required for applying brakes.



Brake Booster is the necessity device in the braking system. It has various components which are arranged in a proper sequence for proper functioning. The main parts of the Brake Booster are as follow:

Body: Body is the main part in which all the components are placed in a sequence. It is the outer casing of the brake booster which provides safety to the inner parts and prevents them from any shock and collision.

Shafts: Shafts provide the linkage between the input and the output. There are two types of shafts are used in a brake booster one is known as input or primary shaft and the second is secondary or output shaft. The input shaft makes a linkage between the input brake pedal and diaphragm. The function of this shaft is to open and close the inlet valve for the inlet and outlet of the atmospheric air. Secondary or output shaft provides a linkage between the diaphragm and the master cylinder. The function of the secondary shaft is to transmit the generated force from the diaphragm to the brake master cylinder.

Valves: Valves play important role in the functioning of the brake booster because to control and maintain the accurate pressure a proper inlet and outlet of air is required. Here two valves are used alike to the shafts. One is the atmospheric valve and the second is the vacuum valve. The function of both the valves are same but the vacuum valve is one way only because it is used to maintain the vacuum inside the brake booster and only allow exit of the air the entry of the air not permitted.

The atmospheric valve allows the entry and exit of the atmospheric air inside the brake booster when the brake pedal is pushed and released. The vacuum valve is mounted at the outlet side of the brake booster and it maintains a perfect vacuum by restricting the entry of the air inside the brake booster.

Diaphragm: It is the major component of any brake booster because it separates the primary and the secondary side of the brake booster and also transfers the motion from inlet shaft to outer shaft by the application of air pressure.

Springs: In a single brake booster two springs are used at both the sides. The size of the springs varies according to the size of the brake booster. The main function of the spring is to regulate the positions of the valves and with the help of spring, valves regain their original position after releasing the pedal.



The working of the brake booster is very simple. In the Brake Booster force is transmitted from inlet to outlet with the application of air pressure which increases the intensity of the brake force. It increases brake pedal force before implementing in the braking application. The working of the brake booster is  as follow

  • As the brake pedal is pressed for applying the brakes the atmospheric valve opens and atmospheric air starts enter into the brake booster.
  • At the same time, a proper vacuum is maintained at the secondary side with the application of engine’s piston-cylinder arrangement. The fresh atmospheric air having a pressure equal to the atmospheric pressure permits the primary shaft to push the diaphragm in the forward direction when brake pedal is pressed.
  • With the movement of the diaphragm, the secondary shaft pushes the master cylinder with the larger intensity of force.
  • The reason for the increasing the intensity of the force is the pressure difference between both the sides. At secondary side vacuum or negative pressure is present whereas at primary side atmospheric pressure exerts which is much higher than the secondary side pressure that’s why a little push of the brake pedal results in multiplication of input force which is required.
  • While releasing the brake pedal whole assembly regain their original position with the application of the springs and releasing the air which close both valves.

This is all about brake booster. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Subscribe our website for more informative articles. Thanks for reading it.

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1 thought on “What is Brake Booster? How Brake Booster Works?”

  1. i had a leak in my master cylinder and the brake fluid leaked into my booster, Will that damage the interior parts of my brake booster? I know i will have to replace the brake booster vacuum sensor but can i use the booster that had brake fluid in it at one time?
    I plan on draining the fluid and should I flush out the booster to remove all the fluid and if so how should I flush it out?

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