Answer:
it is used because
- It occupies less space
- heavy loads are easily moved
- minimum of effort is used
- it is a bit lighter than screw jacks.
They are also less likely to jam due to rust in the screw thread.
Hydraulic jacks are often used to lift elevators in low and medium rise buildings.
A hydraulic jack uses a liquid that is forced into a cylinder by a pump plunger.