Clutch master cylinder is a hydraulic control device that converts physical pressure into hydraulic pressure. It is used in brake and clutch systems. The operated device in the clutch system is called the slave cylinder. It is made up of a reservoir of fluid, two pistons and two or more circuits. When the brake pedal is depressed, the pistons move to create pressure in the cylinder. This pressure compresses the fluid through each circuit and into the brake calipers. The engine vacuum is used to assist in applying pressure to the system. In case of failure of a brake line, the master cylinder will redirect hydraulic pressure to the remaining lines.