To increase safety, most modern car brake systems are broken into two
circuits, with two wheels on each circuit. If a fluid leak occurs in
one circuit, only two of the wheels will lose their brakes and your car
will still be able to stop when you press the brake pedal.
The master cylinder supplies pressure to both circuits of the
car. It is a remarkable device that uses two pistons in the same
cylinder in a way that makes the cylinder relatively failsafe. The
combination valve warns the driver if there is a problem with the
brake system, and also does a few more things to make your car safer to
In this article, we will learn how the master cylinder and
combination valve work.