Buzz
If you’ve ever popped open the hood of your car, you’ve likely noticed the brake booster—a round, black canister tucked away at the back of the engine compartment on the driver's side.
Back in the days of drum brakes, power brakes weren't as critical—drum brakes naturally offered some power assistance. However, with most modern cars using disc brakes on at least the front wheels, power brakes are a necessity. Without them, drivers would quickly tire their legs.
The brake booster taps into the vacuum from the engine to amplify the force you apply to the master cylinder. In this article, we’ll explore the inner workings of the black canister that enables power braking.
- How Brakes Function
- How Master Cylinders and Combination Valves Operate
- How Drum Brakes Operate
- How Disc Brakes Operate
- How Anti-Lock Brakes Function
- Complete Braking Guide
The Vacuum Boosting Mechanism
The vacuum booster is a metal canister containing an innovative valve and diaphragm. A rod passing through the center of the canister links to the master cylinder's piston on one end and to the pedal linkage on the other.
A crucial element in the power braking system is the check valve.
The image above illustrates the check valve, which is a one-way valve that permits air to exit the vacuum booster. If the engine shuts off or a leak occurs in the vacuum hose, the check valve ensures no air can enter the vacuum booster. This is vital because the vacuum booster must be capable of providing sufficient boost to allow the driver to make multiple stops if the engine stalls. You definitely don’t want to lose braking ability if you run out of fuel on the highway. In the upcoming section, we’ll explore how the booster operates (and check out a cool animation!).
The Booster in Action
The vacuum booster is a brilliantly simple design. It requires a vacuum source to function. In gasoline-powered vehicles, the engine provides the necessary vacuum for the booster. In fact, if you attach a hose to a specific part of the engine, you can extract some air from the container, creating a partial vacuum. Since diesel engines don’t generate a vacuum, diesel vehicles must rely on a separate vacuum pump.
On vehicles with a vacuum booster, the brake pedal pushes a rod through the booster into the master cylinder, activating the master-cylinder piston. The engine generates a partial vacuum within the vacuum booster, acting on both sides of the diaphragm. When you press the brake pedal, the rod opens a valve, allowing air to enter the booster on one side of the diaphragm while sealing off the vacuum. This increases pressure on that side of the diaphragm, helping to push the rod, which in turn pushes the piston in the master cylinder.
As the brake pedal is released, the valve closes off the external air supply and reopens the vacuum valve. This restores the vacuum on both sides of the diaphragm, allowing the system to return to its original position.
Power Brake Diagram
MytourNow, let’s assemble the components to understand how power brakes function as a complete system. This diagram offers a detailed close-up view and shows where the brakes are situated in your vehicle.
