Elevator drive systems
Geared traction elevators
Geared traction machines are driven by AC or DC electric motors. Geared machines use worm gears to control mechanical movement of elevator cars by "rolling" steel hoist ropes over a drive sheave which is attached to a gearbox driven by a high speed motor. These machines are generally the best option for basement or overhead traction use for speeds up to 500 ft/min (2.5 m/s). In order to allow accurate speed control of the motor, to allow accurate levelling and for passenger comfort, a DC hoist motor powered by an AC/DC motor-generator (MG) set was the preferred solution in high-traffic elevator installations for many decades. The MG set also typically powered the relay controller of the elevator, which has the added advantage of electrically isolating the elevators from the rest of a building's electrical system, thus eliminating the transient power spikes in the building's electrical supply caused by the motors starting and stopping (causing lighting to dim every time the elevators are used for example), as well as interference to other electrical equipment caused by the arcing of the relay contactors in the control system.
Gearless traction elevators
Gearless traction machines are low speed (low RPM), high torque electric motors powered either by AC or DC. In this case, the drive sheave is directly attached to the end of the motor. Gearless traction elevators can reach speeds of up to 2,000 ft/min (10 m/s), or even higher. A brake is mounted between the motor and drive sheave to hold the elevator stationary at a floor. This brake is usually an external drum type and is actuated by spring force and held open electrically; a power failure will cause the brake to engage and prevent the elevator from falling (see inherent safety and safety engineering).
There are three types of hydraulic elevators:
Conventional hydraulic elevators. They use an underground cylinder, are quite common for low level buildings with 2–5 floors (sometimes but seldom up to 6–8 floors), and have speeds of up to 200 feet/minute (1 meter/second).
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 2, 3, or 4 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 traction-hydraulic elevator has overhead traction cables and counterweight, but is driven by hydraulic power instead of an overhead traction motor. The weight of the car and its passengers, plus an advantageous roping ratio, reduces the demand from the pump to raise the counterweight, thereby reducing the size of the required machinery.
Rack & pinion elevator
A rack & pinion elevator is a self-ascending elevator with its own propulsion.
The "Bailong Elevator" (Pai long elevator) is an example of a rack & pinion elevator.
The propulsion can be done by an electric motor, or possibly also a combustion engine.
The motor is mounted to the elevator car top. Connected to the motor is a gear. Next to the gear, there is a rack of gear teeth. When the gear turns, the elevator moves up or down.
Rack & pinion elevators are used in guyed masts or towers, in order to make easy access to parts of these constructions, such as flight safety lamps for maintenance.
An example would be the Moonlight tower in Austin, Texas, where the elevator holds only one person and equipment for maintenance. The Glasgow Tower — an observation tower in Glasgow, Scotland — also makes use of two rack & pinion elevators.
Pneumatic vacuum elevator
A pneumatic vacuum elevator is an elevator driven by air pressure. This type of elevator is machine room less, and does not require a pit. At the top of the shaft is a vacuum pump. There is a vent at the bottom of the elevator shaft, but not at the top of the shaft, so the part of the shaft under the elevator car is not air tight, but the part of the shaft above the elevator car is air tight. When the elevator goes up, most likely, the vacuum pump pulls air out of the shaft above the elevator car, causing the elevator car to go up because of suction. When the elevator goes down, a small hole likely opens up, letting air in, causing the elevator to go down via gravity at a safe speed. Pneumatic vacuum elevators have circular shafts. There is also a safety mechanism (possibly similar to a parachute) in case the elevator starts to free fall. There is an air tight seal on the elevator car top, so the area above the elevator car is air tight. The hoistway doors are manual, and create an air tight seal when closed. This type of elevator has no car door. This type of elevator is usually used as a residential elevator.