prevent eccentric loadings on the rod.
■ 4.9.6, Car Safety Devices, states that car safety devices conforming to the requirements of Section 3.5, except 3.5.2 are to be provided. Counterweight safeties are not to be provided.
■ 4.9.7, Car Speed Governors, states that car speed governors conforming to the requirements of Section 3.6 are to be provided.
■ 4.9.8, Sheaves, states that sheaves are to be cast iron or steel and are to have finished grooves for ropes.
The traveling sheaves are to be guided by means of metal guides and guide shoes. The guide shoes are permitted to be equipped with nonmetallic inserts. Sheave frames, where used, are to be constructed of structural or forged steel and are to be designed and constructed with a factor of safety not less than eight for the material used. Single continuous straps (known as U-strap connection) are not to be used for frames or as connections between piston rods and traveling sheaves.
■ 4.9.9, Slack-Rope Device: Roped-hydraulic elevators are to be provided with a slack-rope device and switch of the enclosed, manually reset type that will cause the electric power to be removed from the pump motor and the valves if the hoisting ropes become slack or are broken.
■ 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!)
