Example: 3rd gear (see Pl.32).

With the movement of the gear lever from one gear to another (3rd in the selected example), the pressure falls everywhere or it is established (in the circuits of the second speed) by the selector valve. There is a "hydraulic dead point" between each gear in order to obtain:

- deselection of the previous gear (comes out from engagement),

- Declutching (descent of the gear changing piston: 60 to 65kg/cm2 of pressure in the clutch cylinder).

The selector valve passes fluid under pressure to the selector fork cylinder: the cones of the synchronizer and the pinion of third come in contact: the fork stops - use of pressure. At this point, the pressure increases until it becomes high enough to overcome the 3rd gear synchronization, which goes down while compressing its spring:

- The pressure slowly increases, rapid increase at the end of the travel: movement and engagement of the pinions - use of pressure.

The pressure increase always creates a force sufficient to raise the valve of 3rd gear which actuates the gear changing piston: allowing the return of fluid from the clutch cylinder: re-engagement.

Foot-note: the flow of the engine feed pump is a function of engine speed, the automatic clutch cylinder is freed by the cluth piston which descends: the surplus fluid (fed by the pump) returns to the reservoir and the lid of the hydraulic block.

The return pipe has a load valve (see Pl.25) which maintains a residual pressure of 700gr approximately in the hydraulic block to avoid cavitation in the engine feed pump as the engine speed rises.