Functionally, the conveyor adopts the direction of the belts you connect to. So if you connect a belt running towards a wall....then connect a lift to it, you can go down with it. However, the animation uses different rules. It runs in the direction it was drawn. So if you have a belt that is running AWAY from a wall, and you connect the lift to that then go down to say, the belts below where your miners are, then the lift shows the animation of carrying ore downwards, even though functionally it's carrying the ore up.