Grounded27- I agree that extension can be done by gravity alone as well and is done during non-normal conditions.
But that doesnt give us any control over the movement of the gear and might lead to its free fall, suddenly increasing drag and even damaging the mechanical structure. To avoid this risk every time we extend the gear, the actuators we use are dual acting hydraulic actuators, which move the gear by hydraulic pressure during both, extention and retraction.
This is evident from the drawings and schematics provided in AMM. I would have inserted the picture here but I am not authorised to do that yet. In the version that I have, it is in chapter 32-32. Might be someplace else in your AMM. But please do have a look yourself.