Braking without ABS modulation
When the brake pedal is depressed, the vacuum passage is closed and the air passage remains constantly open. The maximum possible pressure differential now acts on the diaphragm and full servo assistance is obtained.
The primary plunger closes the return passage to the brake fluid reservoir and the pressure upstream of the primary plunger increases. This pressure also acts on the secondary plunger which is pressed forward, thus closing its central valve.
The hydraulic pressure in both brake circuits rises and, since the plungers have the same diameter, the pressure will be the same in both circuits in the valve block.
The pressure is propagated throughout the brake system and acts on the brake piston in each hydraulic body. The brake pistons press the brake pads against the brake discs. When the brake pedal is released, the pistons return in the master cylinder and the return passage for the primary plunger and the central valve for the secondary plunger open. The pressure is relieved and the brake piston in each brake cylinder is returned to the rest position by the piston seal.