hydraulic
Elevators raised by a fluid-powered cylinder-and-piston mechanism and lowered by controlled release of fluid.
Hydraulic elevators are vertical transportation cabs driven by a fluid-filled cylinder and piston: pumping oil or water into the cylinder raises the cab, and releasing the liquid allows it to descend.
Because the cylinder must push the full dead weight of the cab and its load, and because this energy is not recovered on the trip down, conventional hydraulic systems generally use more energy than traction systems. There is also a high power demand when the pump is started up.
Hydraulic elevators are most common in low-rise buildings and other short structures, as there are practical limits to the length of a hydraulic cylinder. One main advantage of hydraulic elevators is that they place lower demands on the structural framework of the building housing it. The cylinder is supported by the ground below instead of the building skeleton which supports the lift mechanism of other elevator types.