■ 4.9.10, Suspension Ropes and Their Connections: All elevators, except freight elevators that do not carry passengers or freight handlers and have no means of operation in the car, are to conform to the following requirements:
(a) Suspension ropes are to conform to the requirements of 3.12.1 through 3.12.3, 3.12.5, 3.12.8, and 3.12.9.
(b) The minimum number of hoisting or counterweight ropes used for roped hydraulic elevators is not to be less than two.
(c) The minimum diameter is to be 0.375 inches and the outer wires of the rope are to be not less than 0.024 inches in diameter. The term “diameter” where used in this section refers to the nominal diameter as given by the rope manufacturer.
The most common hydraulic elevator has a conventional configuration with a single below-grade cylinder directly below the car. Because of required excavation depth, height is generally restricted to four or five stories. A telescoping piston permits higher rises, at the cost of greater complexity. Combination roped-hydraulic systems allow the car to move farther than piston travel.
Hole-less hydraulic elevators, with two above-ground cylinders, are an option where high water table or bedrock preclude a conventional design. Where the site permits, the less complex conventional hydraulic elevator has been well-suited for low-rise, low-traffic installation. A downside is that they are less energy efficient than purely traction designs. High current draw when the pump starts under load places a greater demand on facility electrical resources, so for a new installation, alternatives should be weighed. The latest low-cost machine room-less traction elevators (see below) are strongly competitive in areas where previously hydraulic elevators were the clear choice.
Because of high startup current draw, in an outage emergency power may not be used to operate a hydraulic elevator, unless it is designed to do so. Typically, emergency power is used to lower the car to the next landing, and to open the doors. There the car rests until normal power is restored. In a low-rise building, occupants can use the stairs. In healthcare facilities, the emergency power system must be sized out to run the elevators throughout an outage.
Traditional elevator configurations include a machine room located at or below the lowest landing or above the top of the hoist. The machine room typically includes, for a traction elevator, separate electrical feeders for the motor (via VFD) and motion controller and for lighting, receptacles, and outlets in the machine room. For the motor, a dedicated disconnect must be located within sight in the machine room. Also in the machine room are the motion controller, VFD, motor with gearbox and related mechanism, and the drive sheave with pulleys and wire ropes. There may be a telephone, work table, and file cabinet for documentation. For a hydraulic elevator, the machine room consists of many of the same components. The difference is that rather than the type of motor and drive mechanism unique in a traction elevator machine room, the hydraulic elevator machine room houses an oil reservoir with submersible pump/motor and associated wiring and piping.
The machine room brings together many elevator components so they can be readily accessed for maintenance and servicing. The only downside is that valuable space within the building is not available for other essential services. To confront this problem, manufacturers developed the machine room-less (MRL) elevator, shown in Figure 2-4.
The MRL design was made possible by a new generation of smaller, lighter permanent magnet motors that permit installations consisting of the motor and associated components to be located in the hoistway without benefit of a machine room.
MRL hoisting methods allow a reduced sheave-to-rope ratio of 16:1 as opposed to the 40:1 ratio in the conventional traction elevator configuration. At the smaller ratio, a more flexible, higher-strength wire rope is used.
The MRL design incorporates motor, drive sheave, counterweight, and wire ropes as in both the geared and gearless traction elevators. In MRL elevators, the gear-less drive is preferred although either is possible. The MRL components are located in a space above the hoistway except for the motion controller, which may be located in a locked cabinet in the top floor hallway adjacent to the shaft door. MRL elevators may be either traction or hydraulic. MRL elevators do not have a fixed machine room at the top of the hoistway. Instead, the traction hoisting machine is installed either on the top side wall of the hoistway or on the bottom of the hoistway. The permanent magnet motor works in conjunction with a VFD. This design eliminates the need for a machine room and saves space. While the hoisting motor is installed on the hoistway side wall, the main controller is installed on the top floor next to the landing doors. Most elevators have their controller installed on the top floor, but some are installed on the bottom floor. Some elevators have the hoisting motor located at the bottom of the elevator shaft pit. This is called a bottom drive MRL elevator. The controller cabinet may be installed in the door frame. MRL elevators sometimes use flat steel belts instead of wire ropes, permitting a smaller hoisting sheave. Machine room-less elevators in mid-rise buildings usually serve less than 20 floors. The traction mechanism may be located under the elevator cab as in some Schindler designs. Like the traction version, machine room-less hydraulic elevators do not have a fixed room to house the hydraulic machinery. In the MRL design, hydraulic machinery is located in the elevator pit. The controller is located on a wall near the elevator on the bottom floor. MRL hydraulic elevators like the traction models require less space.
FIGURE 2-4 The machine room-less motor is located on top of the car or elsewhere in the hoistway. (Wikipedia)
Rather than in a machine room, most components in MRL designs are in the shaft. The motor and drive mechanism may be on top of the car, under the car, at the top of the shaft, or at the bottom of the shaft. The motion controller is frequently located in a locked cabinet in the top-floor hallway adjacent to the hoistway door. Except for their compact size and unusual locations, components are similar to those in conventional traction or hole-less hydraulic elevators. Kone introduced the MRL design in 1996 and it is currently offered by many manufacturers.
In addition to freeing up valuable space, the MRL design uses less energy and initial cost is significantly lower. A significant disadvantage is that maintenance and servicing are more difficult, and workers have been injured. (Imagine doing dynamic vibration testing on the motor on top of a moving car!)
In a double-deck elevator, there are two attached cars, one on top of the other. They move together in the same shaft. The great advantage in a many-story building is that two adjacent floors can be served simultaneously, with half as many stops. The capacity of each shaft is doubled, cutting down on dedicated floor space on each story.
In some designs, one of the cabs serves as a freight elevator. During peak traffic periods, it becomes a second passenger car.
Worldwide, many double-deck elevators have been built, as many in Asia as in Europe and North America combined.
In densely populated areas where space is limited, multi-level parking lots have inclined ramps so that users can drive to the desired level. Some of these facilities have automotive elevators that carry cars and passengers to their destinations. Most of these are hydraulic elevators, and they must be rated for large loads to safely accommodate a heavy vehicle loaded with passengers and luggage.
Closely related are aeronautic elevators on aircraft carriers. Here considerable space is needed on deck for the runway plus nautical equipment, and that leaves room for only a few aircraft. Most of the 100 or so jets are stored in below-deck hangars, which is convenient for servicing and general maintenance. But how are they moved back and forth? Early aircraft carriers experimented with various methods such as