Brakes off
In the rest position (brakes off) the vacuum servo's diaphragm and valve plunger are pressed against the rear end position of the return spring. Since an overflow valve in the diaphragm is open, the same negative pressure (vacuum) is present on both sides of the diaphragm. The master cylinder's return spring is pressed against the rear end position. In this position the primary circuit's supply hole and the secondary circuit's central valve are open and zero pressure is maintained in the brake system. A stop pin prevents rearward movement of the secondary plunger.
The master cylinder and other hydraulic components are filled with brake fluid under zero pressure.
The inlet and outlet valves in the valve block are in the rest position.