One of the most common drives for residential elevators is the hydraulic lift system. Hydraulic elevators utilize an oil pump located in a separate machine room to provide the lifting power. It is preferred that the machine room be adjacent to the hoistway. (It can be remotely remotely located, but the closer to the hoistway, the better.) The machine room may be located on any level of the house. In flood areas, it is recommended that the machine room be located on an upper level. The hydraulic piston is located in the hoistway between the rails, next to the moving car. As hydraulic fluid is pumped into the piston, the car is forced upward. As hydraulic fluid is released back to the reservoir in the machine room, the car moves downward.
The benefits of a hydraulic elevator include a smooth, quiet operation and easy emergency lowering. A hydraulic elevator is nearly silent in the down direction because the pump is not running. In the up direction, the pump is running in the separate machine room, reducing the noise. If the elevator is stopped beteen floors for any reason, it can easily be manually lowered. All hydraulic elevators are standardly equipped with an emergency lowering valve, and by pushing and holding a button in the machine room, the elevator will slowly lower to floor level.
Negative points include hydraulic odor, and cost factor. By placing the machine room away from a common living area, such as a kitchen or living room, and locating it in a utility area or basement, the small smell factor can be avoided. A two or three floor hydraulic elevator is not much more costly than other types. But, as vertical travel distance increases, the cost of a hydraulic elevator increases more than other drive systems. If the vertical rise is more than 32 feet, a split piston is required, which adds to the cost.