Elevators have residential and commercial classifications by the governing code: ASME A17.1. Elevators are vertical transports that move people or materials between the floors or levels of a structure. All elevators include a cab or platform that moves along rails located within a shaft and are powered by one or more motors. The differences between elevator systems are related to how the cab or platform is transported between levels. The two primary types of elevators used for residential and commercial buildings are hydraulic elevators and traction elevators. One key difference between hydraulic elevators and traction elevators is that hydraulic 4 Technical Bulletin 4 – July 2010 elevators push the elevator cab up using a piston and traction elevators hoist the elevator cab up with a traction motor.
A hydraulic elevator consists of a cab attached directly or indirectly to a hydraulic jack. Hydraulic elevators can be classified as direct acting or holeless. In direct acting hydraulic elevators, the hydraulic jack assembly extends below the lowest floor into the pit area (Figure 1). In contrast, for holeless hydraulic elevators, the cylinder is placed in the shaft above the pit level (Figure 2). Both types of hydraulic elevators are operated by a hydraulic pump and reservoir, both of which are usually located in a room adjacent to the elevator shaft. Hydraulic elevators are generally used in low-rise construction for residential and commercial buildings. However, in recent years, traction elevators have become more common in lowrise residential construction.
Traction elevator systems are most commonly installed in high-rise construction for residential and commercial buildings. Traditional geared traction elevator systems consist of cables connected to the top of the cab operated by an electric motor located in a penthouse above the elevator shaft, as shown in Figure 3. Traction elevators may be geared or gearless based on building height, speed requirements, and cost considerations. Geared traction elevators are typically used for small low-rise structures; while more expensive gearless traction elevators tend to be used for larger high-rise structures where speed is critical. New machine room-less (MRL) traction elevators employ a similar mechanical arrangement to geared traction elevators; however, the machinery is located within the elevator shaft at the top of the hoistway, as shown in Figure 4.
Other Conveyance Mechanisms
Pneumatic elevators are small, vacuum-like elevators typically found in residences. Pneumatic elevator cabs are controlled by a roof-mounted suction system. Although pneumatic elevators are generally less expensive than hydraulic elevators for single-family residences, they are not as widely used because the technology is relatively new and the cabs tend to be small. Pneumatic elevator systems are usually inside buildings; so they are typically located above the BFE.