Hydraulic elevators are used extensively in buildings up to five or six stories high. These elevators—which can operate at speeds up to 46 meters (150 ft) per minute—do not use the large overhead hoisting machinery the way geared and gearless systems do. Instead, a typical hydraulic elevator is powered by a piston that travels inside a cylinder. An electric motor pumps oil into the cylinder to move the piston. The piston smoothly lifts the elevator cab. Electrical valves control the release of the oil for a gentle descent.