A brake booster's main function is to intensify the pressure that you put on the pedal for the whole braking system to work until it stops the car. Basically, its job starts the moment you step on the brake pedal. Now, if you notice that the pedal depresses all the way to the floor with little or no resistance when you step on it, chances are you have a deteriorating brake booster. Replace it right away. Here, check out what your two main options are:
Vacuum brake booster
In essence, this type of booster uses air pressure. Inside a booster are two chambers that are divided by a diaphragm. When you're driving the car and you're stepping on the gas pedal, these chambers are clear of air because the vacuum sucks everything out. By the time you step on the brake pedal, you activate the valve that allows air outside the engine to enter the chambers. The harder you step on the pedal, the more air pressure you put to the chambers.
So, what are the pros and cons of this type? Well, the advantage of this is that in case your car stalls and engine fails, this can still work. The valve can still ensure that air only comes in when you step on the pedal. However, you have to really push the pedal harder if you want it to work.
Hydraulic brake booster
This mechanism works best in diesel-powered engines. Inside these engines, there is a steering pump that generates fluid pressure from the liquid that circulates around it. All of this air pressure is stored in the accumulator. When you step on the brake pedal, air pressure is released.
As for its advantage, it's actually more commonly used these days since modern cars use this technology. Its braking force is also stronger, and it can generate pressure ranging from 1,000 to 2,000psi. However, you have to keep in mind that this one relies so much on power steering and uses up a lot of electric energy in making the brakes work. Because the system works that way, there is a tendency for this booster to decrease horsepower.