> hydraulic cardboard compactor that pushes down on a bale of cardboard somehow uses gravity?
If the compactor is only pushing down, and it is not secured to the ground, then yes, it needs gravity to hold it in place. But most compactors are secured to a frame, so the force is produced between the hydraulic ram and that frame.
Most (all?) road equipment is held down by gravity: if it weighs 10 tons, then it can't apply more than 10 tons of downward force. However, if you need to apply more downward force, the easy answer is to secure your compactor to the ground.
If the compactor is only pushing down, and it is not secured to the ground, then yes, it needs gravity to hold it in place. But most compactors are secured to a frame, so the force is produced between the hydraulic ram and that frame.
Most (all?) road equipment is held down by gravity: if it weighs 10 tons, then it can't apply more than 10 tons of downward force. However, if you need to apply more downward force, the easy answer is to secure your compactor to the ground.