The master cylinder consists of a reservoir and one or two cylinders complete with pistons. Dual circuit type master cylinders are designed to hydraulically separate the front and rear brake systems in the event of a brake fluid leak. The master cylinder converts the mechanical pedal pressure into hydraulic pressure inside the pipeline. This pressure is converted back into mechanical or wheel cylinders (drum brakes), or calipers (disc brakes). Since the pressure to them comes from the master cylinder, they are classified as slave cylinders.
Brake fluid is supplied to the appropriate places on the vehicle frame near the wheels through steel pipelines, and then to the executive cylinders - through flexible tubes, which allows the suspension and steering elements to move freely.
Each wheel cylinder contains two pistons, one at each end, which act in opposite directions to bring the brake shoe into contact with the drum. In systems with disc brakes, the slave cylinders are part of the calipers. This uses one, two or four cylinders, but they all contain only one piston. All pistons use some kind of sealant (usually rubber), to reduce fluid leakage around the piston. The rubber dust cover protects the cylinder from dust and dirt. The cover is put on the protruding end of the piston or the brake lever.
At rest, the entire hydraulic system, from the pistons in the master cylinder to the pistons in the wheel cylinders or calipers, is filled with brake fluid. Under the influence of the brake pedal, the fluid entrained by the pistons (piston) master cylinder, is routed through pipelines to the slave cylinders, in which it sets the pistons in motion - outward, in the case of drum brakes, or inward (to disk) in the case of disc brakes. Piston movement is balanced by return springs mounted on the outside of the cylinders (drum brakes), and internal springs or spring seals (disc brakes).
When the brake pedal is released, the spring inside the master cylinder immediately returns the piston (And) master cylinder to its original position. The pistons contain control valves and the master cylinder has compensation channels drilled inside it. They open when the pistons return to their original position. Piston check valves allow fluid to enter the wheel cylinders or calipers when the pistons return. Then, as soon as the return springs bring the brake pads to the main position, the excess fluid in the pipelines leads to the filling of the replenishment tank through the compensation channels.
Diagonal brake master cylinders use two pistons arranged coaxially one behind the other in one cylinder. The primary piston is actuated directly by a mechanical linkage from the brake pedal. The secondary piston is driven by a fluid trapped between the pistons. If a brake fluid leak occurs in front of the secondary piston, then it moves forward until it reaches the front wall of the master cylinder, and the fluid between the pistons actuates the rear brakes. If the leak occurs in the rear brakes, the primary piston will move forward until it makes direct contact with the secondary piston, which will actuate the front brakes. In any case, the brake pedal has the ability to move farther and usually a little braking force is sufficient.
All dual circuit brake systems have an alarm that is sensitive to either line pressure or fluid level. Such a system will alert the driver if half of the braking system fails.
Some disc brake systems also have a metering valve and, in some cases, a control valve. A metering valve keeps the pressure in the front disc brakes at a constant level until the brake pads on the rear wheels come into contact with the drum, ensuring that the front brakes are never used separately.
The control valve controls the pressure in the rear brakes, preventing the rear wheels from locking in the event of emergency braking.
WARNING: Brake pads contain asbestos, which is a carcinogen. Never clean brake surfaces with compressed air. Avoid inhaling any dust from the surface of the brakes. When cleaning brakes, use special brake cleaning fluids.