How Car Brakes are Suppose to Work
Source: http://news.carjunky.com/how_stuff_works/how-anti-lock-car-brakes-work-abc275.shtml
An anti lock braking system (ABS) is a system on motor vehicles that prevents the wheels from locking while you are braking. It is a very safe and effective system and the purpose of this is twofold: it allows the driver to maintain steering control under heavy braking and, in most situations, it shortens the braking distance (by allowing the driver to hit the brakes really hard without losing control of the vehicle).
If you have a vehicle that does not have an anti lock braking system, you can manually pump the brakes to prevent the wheels from locking up. Whereas, in vehicles that are equipped with an anti locking brake system, the drivers foot needs to remain firmly on the brake pedal, and this will allow the system to automatically pump the brakes.
A typical anti locking braking system (ABS) is composed of a central electronic unit, which has four speed sensors (one for each wheel), and two or more hydraulic valves on the brake circuit. The electronic unit will constantly monitor the rotation speed of each of the wheels. When it senses that any number of the wheels might be rotating slower than the others, which will bring it to lock, it will move the valves to decrease the pressure on the braking circuit. This will reduce the braking force on that wheel and it will cause a pulsing feeling through the brake pedal.
If the sensors become contaminated with any metallic dust, it is not always picked up by the internal ABS controller therefore they will fail to detect any wheel slip.
On high traction surfaces, wet or dry, ABS equipped vehicles are able to attain braking distance better than those vehicles without. In most conditions, in typical states of alertness, ABS will reduce the majority of drivers chances of crashing. With an alert skilled driver who isn’t using ABS, with the use of techniques like cadence braking (technique used to stop the vehicle more quickly on a slippery surface) or threshold braking (the driver adjusts the control of the brake system in an attempt to maximize the braking force of the vehicle), the driver should be able to match or even improve on the performance of a typical driver that has an ABS equipped vehicle.
If you are a non-expert driver and using an ABS equipped vehicle, if you are in a full braking emergency, you would need to press the brake pedal as firmly as possible and then, where necessary, to steer around any obstructions. In these kind of situations, the ABS will reduce the chances of a skid and any loss of control.