This is the first version. It has 3 gears.
When you turn the crank the pneumatic pump makes a pressure.
The valve is there to make a tiny leak in the system.
If you stop turning the pressure gets lower.
If the valve is closed it shifts only upwards.
This pressure controls the cylinder that shifts the gears.
So the faster you turn the crank the faster gear is connected
and the axle on the other end is turning even faster.
This is the second version. It also has 3 gears.