Conventional hydraulic elevators. They use an underground hydraulic cylinder, are quite common for low level buildings with two to five floors (sometimes but seldom up to six to eight floors), and have speeds of up to 1 m/s (200 ft/min). For higher rise applications, a telescopic hydraulic cylinder can be used.
Holeless hydraulic elevators were developed in the 1970s, and use a pair of above ground cylinders, which makes it practical for environmentally or cost sensitive buildings with two, three, or four floors.
Roped hydraulic elevators use both above ground cylinders and a rope system, allowing the elevator to travel further than the piston has to move.
The low mechanical complexity of hydraulic elevators in comparison to traction elevators makes them ideal for low rise, low traffic installations. They are less energy efficient as the pump works against gravity to push the car and its passengers upwards; this energy is lost when the car descends on its own weight. The high current draw of the pump when starting up also places higher demands on a building’s electrical system. There are also environmental concerns should the lifting cylinder leak fluid into the ground.
The modern generation of low cost, machine room-less traction elevators made possible by advances in miniaturization of the traction motor and control systems challenges the supremacy of the hydraulic elevator in their traditional market niche.