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1b. SUSPENSIONSELEVATOR LAYOUTS

Early Elevators

While lifts for carrying passengers and cargo have existed in one form or another since ancient times, the familiar modern hoist elevator system only became popular in the late 19th Century thanks to Elisha Graves Otis' creation of an automatic safety device that would engage automatically should a hoist rope fail. Over time innovations in steam and electrical motors would make the traction elevator the primary solution for architects seeking ways to efficiently move people about. Indeed one might even say that without the availability of a safe, reliable passenger elevator system, the skyscraper would have remainded nothing more than an interesting theoretical novelty found only on architectural drawing boards.

Adaptability Poses Challenges

As building owners became more accustomed to elevators they began to see the need to incorporate them into existing mid and low-rise buildings. This led to the creation of a wide range of exotic hoist rope arrangements with closely placed multiple deflector sheaves utilizing challenging groove profiles. Though some of these antique forms appear odd (indeed some shown in this manual are only rarely used today) one must remember that each design has allowed the elevator to adapt so that it could perform in a wide range of unpromising locales. Unfortunately the sheer variety of roping designs available has also created confusion among professionals trying to decide which hoist rope best suits their needs. Unfortunately a manufacturer cannot place ropes in tidy families targeted towards Gearless, Geared, Hydraulic and Machine Roomless installations. Instead one must be guided by two criteria — groove profile and rope stretch. Knowledgeable professionals understand that a sheave groove's profile affects groove pressure, rope performance and rope longevity. Rope stretch is directly influenced by the amount of rise of an installation and the car acceleration and deceleration desired. However even after addressing groove profile and rope stretch questions, one must still weigh other factors such as overall budget, maintenance needs and environmental demands prior to making any final decision on rope selection. This is the reason why we feel that the practice of certain rope manufacturers in offering generic statements concerning rope choices and specific roping arrangements is not only of limited utility to professionals, but can in fact lead to serious porblems. This is a serious subject where many varialbles must be considered. Instead we find it more valuable to assist the user so that they may understand the process behind the selection process and be better prepared to consult with the rope manufacturer themselves.

Use This Roping Suspensions Material With Brugg RLP

We recommend that you familiarize yourself with the various kinds of roping arrangments commonly available so that you may be better able to use Brugg RLP (Brugg Rope Life Predictor). This online application (at www.bruggrope.com) allows the user to enter specific key system data and determine rope longevity, rope choice suitablity for the system, and create scenarios where one can evaluate rope replacement and long-term maintenance costs. RLP is based on the works of Dr. Klaus Feyrer (author of Wire Ropes: Tension, Endurance and Reliability) and calculates with 95% confidence that a maximum of 10% of the ropes will reach maximum discard criteria. In addition to RLP, knowledge of the many different roping arrangements available will give you a greater appreciation of their vesatility and allow you to be conversant with others in the field. For more detailed information on the kinds of rope constructions available consult Rope Selection in this manual. Should you have more specific questions on rope suitability speak to a Brugg Lifting representative. Basement Machines

In some instances the main drive machine may be situated in the basement near the bottom of the hoistway, or adjacent to the hoistway at an upper floor below the top landing. This kind of traction elevator arrangement is referred to as "Basement Drive" or of "Machine Below" design. Such an arrangement can be of two basic types, Underslung or Overslung (frequently called "Direct Pick-up"). Basement Drives are more commonly found in older residential structures where the building owner has tried to fit a lift into an prexisting floorplan (sometimes called a "retrofit"). Most often of low to mid-rise nature, they are rarely found in newer structures as architects and building owners today strive to incorporate elevators in their floorplans from a building's initial conception. Basement Drives are typically more expensive than their Overhead Drive counterparts and the loads they impose on overhead pulleys at the top of the hoistway, and on the supporting building structure in general, are greater than Overhead Drive arrangements.

Underslung and Overslung Elevators

The Underslung arrangement (see Drawing 1) consists of lifting sheaves located under the car platform and requires more pit depth and hoistway space than an overslung arrangement. An Overslung (Drawing 2) is lifted at the car crosshead like any conventional traction elevator. Both require adequate overhead space for rope sheaves

and a machine room located either to the rear or the side of the hoistway.

Winding-Drum Elevators

Winding-Drum machines (Drawings 4 and 5) were widely used in the early days of elevators but have become outmoded as alternative overhead traction designs have surpassed them in high rise, load and speed capabilities. In this arrangement a sole suspension rope (though some may also use multiple rope arrangements) is wrapped around the drum and is used to lift and lower the elevator car. In such suspensions one commonly uses EHS ropes in order to be able to handle load requirements. Many Drum machines are used in dumbwaiter, material and platform lift applications (both indoors and outdoors). The number of ropes that can be used in such an installation is limited by the drum's size. All Winding-Drum machines are required to include a safety device that will stop the motor should any rope become slack.

Hydraulic Elevators

Hydraulic elevators (Drawings 6 and 7) require only sufficient hoistway space for the car, pump, control equipment, and the pipes that convey liquid both to and from the elevator shaft to a machine room (which may be remotely situated). However adequate pit space for the plunger and cylinder supports are necessary, and impacts on the buffers must be considered. Hydraulic machines are common for up to four-stop elevators, but are deemed less efficient due to power needs for more than five floors. A hydraulic elevator is termed a "direct hydraulic driving machine" if the hydraulic jack is directly attached to the car frame or platform. Hydraulic drives come as either Direct Plunger (Image 7), which require a hole in the ground to house the hydraulic jack, or Holeless designs (Image 6), which utilize a cylinder in the hoistway attached to both sides of the frame. The most common Holeless design features two jacks placed on each side of the car platform. Should the presence of groundwater be a concern when a Direct Plunger design is planned, provisions must be taken to secure both the cylinder and well casing to protect them against corrosion by electrolytic action, and also to keep them from floating upwards. The Hydraulic elevator has become the popular choice for low-rise structures (and heavy-duty freight and truck elevators) due to the system's relative cheapness when compared to other traction elevator types and the fact that the vertical loads imposed on the building structure that contains it are minimum.

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Overhead Traction Designs

The vast majority of elevators in the world are roped in either 1:1 or 2:1 arrangements. On higher speed gearless traction machines of 800 fpm (4.0 mps) or more, the Double-Wrap principle is generally applied to obtain greater traction and minimize rope wear. Traction in both designs is the result of pressure generated by the ropes on the sheave groove surface. Traction may be increased through the use of more demanding (less round) groove designs such as U-or V-Grooves; undercutting the groove surface interior so that the rope may settle more deeply within the

sheave groove inner surface (which increases the friction between the groove and ropes, but can result in mutually damaging sheave groove and rope surface interaction), or increasing the weight of the car and in the counterweights used. In Double-Wrap arrangements traction is increased by wrapping the rope from the car around a main drive sheave, to a secondary (or idler) sheave, and around the main sheave again before it proceeds downwards to the counterweight. Gearless and Geared Machine elevators are also roped with Single-Wrap arrangements. The single

wrap arrangement derives the major part of its traction through the use of grooves that pinch the ropes with varrying amounts of preasure depending upon the shape of the groove and its degree of undercut. The most effective Single-Wrap design provides a 180° arc of contact for the rope around the sheave without the use of a deflector sheave (for further details concerning "Arc of Contact" review: "Sheaves and Groove/Background" online). Though both 1:1 and 2:1 roping may appear similar at first glance to a novice, one simple distinction defines each. In 1:1 roping the car sling and counterweight

1. 2. 3. 4.

Basement Drive 2:1 MachineUnderslung

Basement Drive Winding-Drum Machine

Basement Drive 1:1 MachineSingle WrapOverslung

Basement Drive 2:1 Machine Along SideSingle WrapOverslung

sling are directly coupled to and suspended by the hoist ropes. In a 2:1 suspension the ropes pass through sheaves mounted on the car crosshead and counterweight crosshead and are then terminated in hitch plates at the top of the hoistway (this sort of termination is called "dead ending"). Neither roping method is intrinsically better than the other. Both simply provide an engineer with multiple options to address system design problems, and offer design alternatives that allow the engineer to improve sytem performance capabilities. Over the years the elevator industry has utilized

various roping arrangements, rope constructions, component designs, implemented new materials and incorporated the close placement of multiple deflector sheaves in an effort to increase system performance. In addition system designers are using smaller, faster machine drives and taking strides to reduce the amount of floor area occupied by elevator systems (which has led to the popularity of MRL designs).

Compensation Ropes

You will note that certain methods of traction elevator

roping use compensation chains and ropes while another (Image 8) does not. Compensating rope, or chain cables, are used to equalize (or compensate) for the change in balance of the car and counterweight due to the weight of the suspension ropes, and to minimize out-of-balance rope tensions on the drive sheave. If this force were not compensated for the traction force may become eitehr deficient or excessive and a dangerous situation could be created. In addition, Compensating cables allow the torque on the elevator motor to be reduced, which greatly reduces motor power requirements, and assists


Counterweighted Hydraulic Direct Plunger

Overhead Type 1:1Single-Wrap Traction Low-Rise

Roped Hydraulic Horizontal PlungerHoleless Hydraulic

6. 7.5.

Overhead Drive Winding-Drum Machine

8.

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Overhead Type 1:1 Double-Wrap Traction High-Risewith Compensation Ropes

Overhead Type 2:1 Double-Wrap TractionHigh-Risewith Compensation Ropes

Overhead Type 2:1 Single-Wrap TractionHigh-Risewith Compensation Ropes

Overhead Type 1:1 Single-Wrap Traction Mid-Risewith Compensation Chain

somewhat with system speed and leveling control. Compensation is usually necessary for travels of over 100 ft (35 m) and for 2:1 roped systems with more than 75 ft (25 m) of travel. Compensating chains are normally used for rated speeds of 350 ft/min (1.75 m/s) or less. Geared machines with more than 100 ft (35 m) of travel utilize compensating chains. Compensation chains normally feature simple chain, or metal shot cores submerged in PVC casings. Compensation ropes cables may use various traction ropes depending upon on system requirements.

Governor Ropes

The Governor Rope passes from a governor pulley in the machine room to a tensioning pulley in the pit, connects to the car, and then returns to the governor pulley again. The Governor rope trips a safety gear should a car's speed exceed recommended limits. We recommend the use of Governor ropes featuring a Mixed polypropylene core to prevent the accumulation of lubricant that is squeezed from the central core during service. The use of Mixed Core ropes prevents the layering of environmental debris on

the Governor rope surface (preventing dirty ropes) and greatly minimizes the potential for variations in rope length and rope diameter over time.

11.10. 12.9.

Schematic Diagrams ForCommon Roping Arrangements


Roping system for overhead position,double wrap drive, roping factor 1

1.

4.

2. 3.

5.

Roping system for overhead position,single wrap drive, roping factor 2

Roping system for overhead position, double wrap drive,

roping factor 2


(installation with deflector sheave on right)


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Roping system for basement position,double wrap drive,

roping factor 1

Roping system for basement position,single wrap drive, roping factor 1

6. 8.7.

11.10.9.

Roping system for basement position,2:1 (Underslung)

Roping system for basement position,singlewrap drive, roping factor 2

Schematic Diagrams OfCommon Roping Arrangements


Roping system for overhead position,

single wrap drive, roping factor 2,

with Deflector sheave

Roping system for basement position, single wrap drive with 2 deflector sheaves,

roping factor 1

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