Master cylinder, which is used to create fluid pressure in the brake system, consists of a housing, inside which is the brake fluid reservoir and cylinder. There is a hole in the front of the cylinder for the brake hoses. This opening is closed by a non-return valve. There is a piston at the rear of the cylinder, On which the piston rod connected to the brake pedal works. There are two holes in the top of the cylinder, connecting it to the brake fluid reservoir. Piston, most often aluminum, it is sealed in the cylinder with rubber gaskets. There is a recess at the rear of the piston, which enters the piston rod connected to the brake pedal, forming a steel bar. Connector, which connects the piston rod to the brake pedal, serves to adjust the clearance between the end of the piston rod and the bottom of the cavity in the piston. One end of a coil spring in the cylinder presses the rubber seal against the piston crown, and the other end, a check valve to the bottom of the cylinder. Non-return valve, in the center of which there is a by-pass valve, serves to maintain constant overpressure (Ok. 0,5 at) brake fluid, which protects against air in the system. When you press the brake pedal, the piston moves and compresses the spring, and the pressure created in the cylinder opens the bypass valve and the fluid passes through the lines to the hydraulic rams, which in turn press the brake shoes against the brake drum. When braking is stopped, the bypass valve closes, the spring moves the piston to the starting position, and the fluid flows back into the cylinder. When the fluid pressure in the brake lines drops to a certain value, the non-return valve closes, so that the fluid in the lines and in the hydraulic rams is constantly under a slight pressure, which prevents air pockets in the brake system. Hydraulic spreaders are used to press the jaws against the drum. Each spreader consists of a cylinder, in which two metal plungers are placed, sealed from the inside with rubber pistons (gaskets), and from the outside, they are also protected with a rubber cover. The pistons, via short metal pushers, rest against the upper ends of the jaws. The constant pressure of the pistons with papychaezes to the jaws is ensured by a helical spring embedded in the cylinder between the pistons. There is a vent valve in the upper part of the cylinder housing, and immediately below it an opening for connecting the brake fluid supply line to the inside of the cylinder. In some cars, you can find a single-acting hydraulic expander. Its construction is the same with this, that it is, as it were, half of the double-acting spreader and can press only one jaw against the drum.