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An '''elevator''' (US+) or '''lift''' (UK+) is a type of vertical transportation+ that moves people or goods between floors (levels, deck+s) of a building, vessel+, or other structure. In agriculture and manufacturing, an elevator is any type of conveyor+ device used to lift materials in a continuous stream into bins or silo+s. Because of wheelchair access laws, elevators are often a legal requirement in new multistory buildings, especially where wheelchair ramps would be impractical. The earliest known reference to an elevator is in the works of the Roman architect Vitruvius+, who reported that Archimedes+ (c.
In 1000, the ''Book of Secrets'' by al-Muradi+ in Islamic Spain+ described the use of an elevator-like lifting device, in order to raise a large battering ram to destroy a fortress. The development of elevators was led by the need for movement of raw materials including coal+ and lumber+ from hillsides. Starting in the coal mines, by the mid-19th century elevators were operated with steam power and were used for moving goods in bulk in mines and factories. Early, crude steam-driven elevators were refined in the ensuing decade; - in 1835 an innovative elevator called the "Teagle" was developed by the company Frost and Stutt in England+. The hydraulic crane was invented by Sir William Armstrong+ in 1846, primarily for use at the Tyneside+ docks for loading cargo. Henry Waterman+ of New York is credited with inventing the "standing rope control+" for an elevator in 1850. In 1845, the Neapolitan architect Gaetano Genovese+ installed in the Royal Palace of Caserta the "Flying Chair", an elevator ahead of its time, covered with chestnut wood outside and with maple wood inside. In 1852, Elisha Otis+ introduced the safety elevator, which prevented the fall of the cab if the cable broke.
The Equitable Life Building+ completed in 1870 in New York City was the first office building to have passenger elevators.
In 1882, when hydraulic power+ was a well established technology, a company later named the London Hydraulic Power Company+ was formed by Edward B. Some people argue that elevators began as simple rope+ or chain+ hoist+s (see ''Traction elevators'' below). The friction between the ropes and the pulley furnishes the traction which gives this type of elevator its name. Hydraulic elevators use the principles of hydraulics+ (in the sense of hydraulic power+) to pressurize an above ground or in-ground piston to raise and lower the car (see ''Hydraulic elevators'' below). There are economies to be made from mass production+ of the components, but each building comes with its own requirements like different number of floors, dimensions of the well and usage patterns. Machine room-less elevators are designed so that most of the components fit within the shaft containing the elevator car; and a small cabinet houses the elevator controller. CIBSE Guide D: Transportation Systems in Building Elevator Traffic Handbook, Theory and Practice.
Traditionally, these calculations have formed the basis of establishing the Handling Capacity of an elevator system. Modern Installations with more complex elevator arrangements have led to the development of more specific formula such as the General Analysis calculation.
Elevator traffic simulation software can be used to model complex traffic patterns and elevator arrangements that cannot necessarily be analysed by RTT calculations. There are four main types of elevator traffic patterns that can be observed in most modern office installations. Historically, AC motors were used for single or double speed elevator machines on the grounds of cost and lower usage applications where car speed and passenger comfort were less of an issue, but for higher speed, larger capacity elevators, the need for infinitely variable speed control over the traction machine becomes an issue. The widespread availability of variable frequency AC drives has allowed AC motors to be used universally, bringing with it the advantages of the older motor-generator, DC-based systems, without the penalties in terms of efficiency and complexity.
Gearless traction machines are low-speed (low-RPM), high-torque+ electric motors powered either by AC or DC.
In each case, cables are attached to a hitch plate on top of the cab or may be "underslung" below a cab, and then looped over the drive sheave to a counterweight+ attached to the opposite end of the cables which reduces the amount of power+ needed to move the cab. The modern generation of low cost, machine room-less traction elevators made possible by advances in miniaturization+ of the traction motor and control systems challenges the supremacy of the hydraulic elevator in their traditional market niche.
A elevator of this kind uses a vacuum on top of the cab and a valve on the top of the "shaft" to move the cab upwards and closes the valve in order to keep the cab at the same level. In the first half of the twentieth century, almost all elevators had no automatic positioning of the floor on which the cab would stop. This lever would allow some control over the energy supplied to the motor and so enabled the elevator to be accurately positioned — if the operator was sufficiently skilled.
Automatic elevators began to appear as early as the 1930s, their development being hastened by striking+ elevator operators which brought large cities dependent on skyscrapers (and therefore their elevators) such as New York and Chicago to their knees. The Otis ''Autotronic'' system of the early 1950s brought the earliest predictive systems which could anticipate traffic patterns within a building to deploy elevator movement in the most efficient manner.
Elevators are typically controlled from the outside by a call box, which has up and down buttons, at each stop. In a group of two or more elevators, the call buttons may be linked to a central dispatch computer, such that they illuminate and cancel together. Key switches may be installed on the ground floor so that the elevator can be remotely switched on or off from the outside. In destination control systems, one selects the intended destination floor (in lieu of pressing ''"up"'' or ''"down"'') and is then notified which elevator will serve their request.
The elevator algorithm has found an application in computer operating system+s as an algorithm for scheduling hard disk+ requests.
Modern elevators use more complex heuristic algorithms+ to decide which request to service next.
Some skyscraper buildings and other types of installation feature a destination operating panel where a passenger registers their floor calls before entering the car. It can also improve accessibility, as a mobility-impaired passenger can move to his or her designated car in advance. The idea of destination control was originally conceived by Leo Port+ from Sydney in 1961, but at that time elevator controllers were implemented in relays and were unable to optimise the performance of destination control allocations. However, performance enhancements cannot be generalized as the benefits and limitations of the system are dependent on many factors. To prevent this problem, in one implementation of destination control, every user gets an RFID+ card to identify himself, so the system knows every user call and can cancel the first call if the passenger decides to travel to another destination to prevent empty calls.
The same destination scheduling concept can also be applied to public transit such as in group rapid transit+. The anti-crime protection (ACP) feature will force each car to stop at a pre-defined landing and open its doors.
During up-peak mode (also called moderate incoming traffic), elevator cars in a group are recalled to the lobby to provide expeditious service to passengers arriving at the building, most typically in the morning as people arrive for work or at the conclusion of a lunch-time period.
The commencement of up-peak may be triggered by a time clock, by the departure of a certain number of fully loaded cars leaving the lobby within a given time period, or by a switch manually operated by a building attendant. During down-peak mode, elevator cars in a group are sent away from the lobby towards the highest floor served, after which they commence running down the floors in response to hall calls placed by passengers wishing to leave the building. The commencement of down-peak may be triggered by a time clock, by the arrival of a certain number of fully loaded cars at the lobby within a given time period, or by a switch manually operated by a building attendant. In areas with large populations of observant Jew+s or in facilities catering to Jews, one may find a "Sabbath elevator+". However, Sabbath mode has the side effect of using considerable amounts of energy, running the elevator car sequentially up and down every floor of a building, repeatedly servicing floors where it is not needed. Some taller buildings may have the Sabbath elevator alternate floors in order to save time and energy; for example, an elevator may stop at only even-numbered floors on the way up, and then the odd-numbered floors on the way down. Inspection service is designed to provide access to the hoistway and car top for inspection and maintenance purposes by qualified elevator mechanics. Elevators have a car top inspection station that allows the car to be operated by a mechanic in order to move it through the hoistway.
Depending on the location of the elevator, fire service code will vary state to state and country to country. Phase one mode is activated by a corresponding smoke sensor or heat sensor in the building. Phase-two mode can only be activated by a key switch located inside the elevator on the centralized control panel.
Commonly found in hospitals, code-blue service allows an elevator to be summoned to any floor for use in an emergency situation.
Once the elevator arrives at the floor, it will park with its doors open and the car buttons will be disabled to prevent a passenger from taking control of the elevator. Many elevator installations now feature emergency power systems which allow elevator use in blackout situations and prevent people from becoming trapped in elevators. When power is lost in a traction elevator system, all elevators will initially come to a halt. In hydraulic elevator systems, emergency power will lower the elevators to the lowest landing and open the doors to allow passengers to exit. A typical modernization consists of controller equipment, electrical wiring and buttons, position indicators and direction arrows, hoist machines and motors (including door operators), and sometimes door hanger tracks.
Modernization can greatly improve operational reliability by replacing mechanical relays and contacts with solid-state electronics. Past problems with hydraulic elevators include underground electrolytic destruction of the cylinder and bulkhead, pipe failures, and control failures. In addition to the safety concerns for older hydraulic elevators, there is risk of leaking hydraulic oil+ into the aquifer+ and causing potential environmental contamination. In the past decade, recent innovations in inverted hydraulic jack+s have eliminated the costly process of drilling the ground to install a borehole jack. Passenger elevators may be specialized for the service they perform, including: hospital emergency (code blue+), front and rear entrances, a television in high-rise buildings, double-decker+, and other uses.
Residential elevators may be small enough to only accommodate one person while some are large enough for more than a dozen. A freight elevator, or goods lift, is an elevator designed to carry goods, rather than passengers.
Vehicular elevators are used within buildings or areas with limited space (in place of ramps), generally to move car+s into the parking garage or manufacturer's storage. Rare examples of extra-heavy elevators for 20-ton lorries+, and even for railcar+s (like one that was used at Dnipro Station+ of the Kiev Metro+) also occur. In some smaller canals, boats and small ships can pass between different levels of a canal with a boat elevator rather than through a canal lock+.
On aircraft carrier+s, elevators carry aircraft between the flight deck and the hangar deck for operations or repairs. On some passenger double-deck aircraft+ such as the Boeing 747+ or other widebody aircraft+, elevators transport flight attendants and food and beverage trolleys from lower deck galleys+ to upper passenger carrying decks. A residential elevator is often permitted to be of lower cost and complexity than full commercial elevators. Elevators are generally powered by electric motors that either drive traction cables or counterweight systems like a hoist+, or pump hydraulic fluid to raise a cylindrical piston like a jack+. Several types exist, such as the chain and bucket bucket elevator+, grain auger screw conveyor+ using the principle of Archimedes' screw+, or the chain and paddles or forks of hay elevator+s. In the 17th century the prototypes of elevators were located in the palace buildings of England and France.
The invention of a system based on the screw drive+ was perhaps the most important step in elevator technology since ancient times, leading to the creation of modern passenger elevators. The technology developed by these industries and the introduction of steel beam construction worked together to provide the passenger and freight elevators in use today.
These steam driven devices were soon being applied to a diverse set of purposes - in 1823, two architect+s working in London+, Burton and Hormer, built and operated a novel tourist attraction, which they called the "ascending room". These quickly supplanted the earlier steam driven elevators: exploiting Pascal's law+, they provided a much greater force.


It included a light, two benches and a hand operated signal, and could be activated from the outside, without any effort on the part of the occupants. Construction for Peter Cooper+'s Cooper Union+ Foundation building in New York+ began in 1853. The inventor Anton Freissler+ developed the ideas of von Siemens and built up a successful enterprise in Austria-Hungary. An elevator is essentially a platform that is either pulled or pushed up by a mechanical means.
Roped hydraulics use a combination of both ropes and hydraulic power to raise and lower cars. Hydraulic elevators are cheaper, but installing cylinders greater than a certain length becomes impractical for very-high lift hoistways.
The most common configuration is to have two panels that meet in the middle, and slide open laterally. Other than the machinery being in the hoistway, the equipment is similar to a normal traction or hole-less hydraulic elevator. They are up peak traffic, down peak traffic, lunch time (two way) traffic and interfloor traffic. Geared machines use worm gear+s 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. The older MG-based installations are gradually being replaced in older buildings due to their poor energy efficiency. The counterweight is located in the hoist-way and rides a separate railway system; as the car goes up, the counterweight goes down, and vice versa. This is a separate set of cables or a chain attached to the bottom of the counterweight and the bottom of the elevator cab. A diaphragm or a piston is used as a "brake", if there's a sudden increase in pressure above the cab. Some of the older freight elevators were controlled by switches operated by pulling on adjacent ropes. More typically, the operator would have to "jog" the control, moving the cab in small increments until the elevator was reasonably close to the landing point. These electromechanical systems used relay logic+ circuits of increasing complexity to control the speed, position and door operation of an elevator or bank of elevators. Relay-controlled elevator systems remained common until the 1980s and their gradual replacement with solid-state, microprocessor+-based controls are now the industry standard.
The operation of the door close button is less transparent, and it often appears to do nothing, leading to frequent but incorrect reports that the door close button is a placebo button+: either not wired up at all, or inactive in normal service.
The door is unlocked and opened by a machine sitting on the roof of the car, which also drives the doors that travel with the car. This is primarily used to serve different floor plans: on each floor only one set of doors opens. An introduction to these algorithms can be found in the "Elevator traffic handbook: theory and practice" given in the references below.
The system lets them know which car to wait for, instead of everyone boarding the next car.
Manufacturers of such systems claim that average traveling time can be reduced by up to 30%.
The newest invention knows even where people are located and how many on which floor because of their identification, either for the purposes of evacuating the building or for security reasons. This allows a security guard or a receptionist at the landing to visually inspect the passengers.
Elevators are dispatched one-by-one when they reach a pre-determined passenger load, or when they have had their doors opened for a certain period of time. This allows the elevator system to provide maximum passenger handling capacity for people leaving the building. In this mode, an elevator will stop automatically at every floor, allowing people to step on and off without having to press any buttons. For a tall building with many floors, the car must move on a frequent enough basis so as to not cause undue delay for potential users that will not touch the controls as it opens the doors on every floor up the building.
It is activated by a key switch either inside the elevator itself or on a centralized control panel in the lobby. It is first activated by a key switch on the car operating panel usually labeled 'Inspection', 'Car Top', 'Access Enable' or 'HWENAB'.
This mode was created for firefighters so that they may rescue people from a burning building.
Each floor will have a code-blue recall key switch, and when activated, the elevator system will immediately select the elevator car that can respond the fastest, regardless of direction of travel and passenger load. Medical personnel must then activate the code-blue key switch inside the car, select their floor and close the doors with the door close button. One by one, each car in the group will return to the lobby floor, open its doors and shut down. The doors then close after an adjustable time period and the car remains unusable until reset, usually by cycling the elevator main power switch. As the elevator ages and equipment become increasingly difficult to find or replace, along with code changes and deteriorating ride performance, a complete overhaul of the elevator may be suggested to the building owners. Ride quality can be improved by replacing motor-generator-based drive designs with Variable-Voltage, Variable Frequency (V3F) drives+, providing near-seamless acceleration and deceleration. Single bulkhead cylinders, typically built prior to a 1972 ASME A17.1 Elevator Safety Code change requiring a second dished bulkhead, were subject to possible catastrophic failure+. This has led to the introduction of PVC+ liners (casings) around hydraulic cylinders which can be monitored for integrity.
For example, there is a 3-station underground public elevator in Yalta+, Ukraine+, which takes passengers from the top of a hill above the Black Sea on which hotels are perched, to a tunnel located on the beach below. Cars may be ornate in their interior appearance, may have audio visual advertising, and may be provided with specialized recorded voice announcements. For example, it moves between the ground floor and a skylobby+, or it moves from the ground floor or a skylobby to a range of floors, skipping floors in between. Wheelchair, or platform elevators, a specialized type of elevator designed to move a wheelchair+ or less, can often accommodate just one person in a wheelchair at a time with a load of . Freight elevators are generally required to display a written notice in the car that the use by passengers is prohibited (though not necessarily illegal), though certain freight elevators allow dual use through the use of an inconspicuous riser. Sidewalk elevators are used to move materials between a basement and a ground-level area, often the sidewalk+ just outside the building. Geared hydraulic chains (not unlike bicycle chains) generate lift for the platform and there are no counterweights.
These elevators are designed for much greater capacity than other elevators, up to of aircraft and equipment. They may have unique design characteristics suited for home furnishings, such as hinged wooden shaft-access doors rather than the typical metal sliding doors of commercial elevators. Louis XV of France+ had a so-called 'flying chair' built for one of his mistresses at the Chateau de Versailles+ in 1743. The first screw drive elevator was built by Ivan Kulibin+ and installed in Winter Palace+ in 1793. It elevated paying customers to a considerable height in the center of London, allowing them a magnificent panoramic view of downtown. A water pump supplied a variable level of water pressure+ to a plunger encased inside a vertical cylinder, allowing the level of the platform (carrying a heavy load) to be raised and lowered. A governor device engages knurled roller(s), locking the elevator to its guides should the elevator descend at excessive speed. An elevator shaft was included in the design, because Cooper was confident that a safe passenger elevator would soon be invented. The safety and speed of electric elevators were significantly enhanced by Frank Sprague+ who added floor control, automatic elevators, acceleration control of cars, and safeties. It constructed a network of high-pressure mains on both sides of the Thames which, ultimately, extended to 184 miles and powered some 8,000 machines, predominantly elevators (lifts) and cranes. In 1887, American Inventor Alexander Miles+ of Duluth, Minnesota patented an elevator with automatic doors that would close off the elevator shaft. A modern-day elevator consists of a cab (also called a "cage", "carriage" or "car") mounted on a platform within an enclosed space called a shaft or sometimes a "hoistway". Recent innovations include permanent magnet motors, machine room-less rail mounted gearless machines, and microprocessor controls.
In a cascading telescopic configuration (potentially allowing wider entryways within limited space), the doors roll on independent tracks so that while open, they are tucked behind one another, and while closed, they form cascading layers on one side. The world's first machine room less elevator, the Kone MonoSpace was introduced in 1996, by Kone+. These machines are generally the best option for basement or overhead traction use for speeds up to . Gearless traction elevators can reach speeds of up to , A brake is mounted between the motor and gearbox or between the motor and drive sheave or at the end of the drive sheave to hold the elevator stationary at a floor. This action is powered by the traction machine which is directed by the controller, typically a relay logic or computerized device that directs starting, acceleration+, deceleration+ and stopping of the elevator cab. This makes it easier to control the elevator, as it compensates for the differing weight of cable between the hoist and the cab. Climbing 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. To go down, it opens the valve so that the air can pressurize the top of the "shaft", allowing the cab to go down by its own weight.
In general, most elevators before WWII were manually controlled by elevator operator+s using a rheostat+ connected to the motor. Most older, manually-operated elevators have been retrofitted with automatic or semi-automatic controls. This may also trigger a "full car" indicator, indicating the car's inability to accept more passengers until some are unloaded.
In some elevators, certain floors are inaccessible unless one swipes a security card or enters a passcode (or both). Working door open and door close buttons are required by code in many jurisdictions, including the United States, specifically for emergency operation: in independent mode, the door open and door close buttons are used to manually open or close the door. Door controls are provided to close immediately or reopen the doors, although the button to close them immediately is often disabled during normal operations, especially on more recent elevators. For example, in an elevated crosswalk setup, the front doors may open on the street level, and the rear doors open on the crosswalk level. If the particular elevator is currently serving traffic in a certain direction, it will only answer calls in the same direction unless there are no more calls beyond that floor.
In this way, travel time is reduced as the elevator makes fewer stops for individual passengers, and the computer distributes adjacent stops to different cars in the bank. Sometimes, one person enters the destination for a large group of people going to the same floor.
Another way to prevent this issue is to treat everyone travelling from one floor to another as one group and to allocate only one car for that group. The next elevator to be dispatched usually has its hall lantern or a "this car leaving next" sign illuminated to encourage passengers to make maximum use of the available elevator system capacity. This prevents violation of the Sabbath+ prohibition against operating electrical devices when Sabbath is in effect for those who observe this ritual.
When an elevator is placed on independent service, it will no longer respond to hall calls. When this switch is activated the elevator will come to a stop if moving, car calls will be canceled (and the buttons disabled), and hall calls will be assigned to other elevator cars in the group (or canceled in a single elevator configuration). Both the RUN and a direction button must be held to move the car in that direction, and the elevator will stop moving as soon as the buttons are released.


The elevator will wait an amount of time, then proceed to go into nudging mode to tell everyone the elevator is leaving the floor. Passengers inside the elevator will be notified with an alarm and indicator light to exit the elevator when the doors open. The elevator will then travel non-stop to the selected floor, and will remain in code-blue service until switched off in the car.
People in the remaining elevators may see an indicator light or hear a voice announcement informing them that the elevator will return to the lobby shortly. Typically, due to the high current draw when starting the pump motor, hydraulic elevators are not run using standard emergency power systems. The cost of an elevator modernization can range greatly depending on which type of equipment is to be installed.
Passenger safety is also improved by updating systems and equipment to conform to current codes. In 1998, it was estimated that approximately eight millionths of one percent (1 in 12 million) of elevator rides result in an anomaly, and the vast majority of these were minor things such as the doors failing to open. At Casco Viejo station in the Bilbao Metro+, the elevator that provides access to the station from a hilltop neighborhood doubles as city transportation: the station's ticket barriers are set up in such a way that passengers can pay to reach the elevator from the entrance in the lower city, or vice versa. In order for an elevator to be legal to carry passengers in some jurisdictions it must have a solid inner door. They are controlled via an exterior switch and emerge from a metal trap door at ground level. To accommodate building designs and improve accessibility, the platform may rotate so that the driver only has to drive forward. Some sources from later historical periods mention elevators as cabs on a hemp+ rope powered by hand or by animals. Several years later another of Kulibin's elevators was installed in Arkhangelskoye+ near Moscow+. He demonstrated it at the New York exposition in the Crystal Palace+ in a dramatic, death-defying presentation in 1854, and the first such passenger elevator was installed at 488 Broadway+ in New York City+ on March 23, 1857. His elevator ran faster and with larger loads than hydraulic or steam elevators, and 584 electric elevators were installed before Sprague sold his company to the Otis Elevator Company in 1895.
In the past, elevator drive mechanisms were powered by steam and water hydraulic pistons or by hand. This can be configured so that two sets of such cascading doors operate like the center opening doors described above, allowing for a very wide elevator cab. 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+). The weight of the counterweight is typically equal to the weight of the elevator cab plus 40-50% of the capacity of the elevator. If the elevator cab is at the top of the hoist-way, there is a short length of hoist cable above the car and a long length of compensating cable below the car and vice versa for the counterweight.
An example would be the Moonlight tower+s in Austin, Texas, where the elevator holds only one person and equipment for maintenance. This rheostat (see picture) was enclosed within a cylindrical container about the size and shape of a cake. The handle also served as a dead man switch+: if the operator let go of the handle, it would return to its upright position, causing the elevator cab to stop.
Beyond this, programming varies significantly, with some door close buttons immediately closing the door, but in other cases being delayed by an overall timeout, so the door cannot be closed until a few seconds after opening. Objects in the path of the moving doors will either be detected by sensors or physically activate a switch that reopens the doors.
Although travel time is reduced, passenger waiting times may be longer as they will not necessarily be allocated the next car to depart. The dispatching algorithm+ is usually unable to completely cater for the variation, and latecomers may find the elevator they are assigned to is already full. The elevator can now only be moved by the corresponding 'Access' key switches, usually located at the highest (to access the top of the car) and lowest (to access the elevator pit) landings.
Once the elevator has left the floor, depending on where the alarm was set off, the elevator will go to the fire-recall floor.
Some hospital elevators will feature a 'hold' position on the code-blue key switch (similar to fire service) which allows the elevator to remain at a floor locked out of service until code blue is deactivated. Once all cars have successfully returned, the system will then automatically select one or more cars to be used for normal operations and these cars will return to service.
Buildings like hospitals and nursing homes usually size their emergency generators to accommodate this draw. In the event of a cylinder breach, the fluid loss results in uncontrolled down movement of the elevator. Freight elevators are typically larger and capable of carrying heavier loads than a passenger elevator, generally from 2,300 to 4,500 kg. Sidewalk elevator cars feature a uniquely shaped top that allows this door to open and close automatically. In a "traction" elevator, cars are pulled up by means of rolling steel ropes over a deeply grooved pulley+, commonly called a sheave in the industry.
In less expensive installations the elevator can also use one large "slab" door: a single panel door the width of the doorway that opens to the left or right laterally. But it can also be some form of disc type+ like 1 or more calipers over a disc in one end of the motor shaft or drive sheave which is used in high speed, high rise and large capacity elevators with machine rooms(an exception is the Kone MonoSpace's EcoDisc which is not high speed, high rise and large capacity and is machine room less but it uses the same design as is a thinner version of a conventional gearless traction machine) for breaking power, compactness and redundancy+(assuming there's at least 2 calipers on the disc), or 1 or more disc brakes with a single caliper at one end of the motor shaft or drive sheave which is used in machine room less elevators for compactness, breaking power, and redundancy+(assuming there's 2 brakes or more). The grooves in the drive sheave are specially designed to prevent the cables from slipping. If the compensation system uses cables, there will be an additional sheave in the pit below the elevator, to guide the cables. The "shaft" is made of acylic, is always round due to the shape of the vacuum pump turbine. This was mounted upright or sideways on the cab wall and operated via a projecting handle, which was able to slide around the top half of the cylinder. In time, safety interlocks would ensure that the inner and outer doors were closed before the elevator was allowed to move.
During the down peak period the benefit of destination control will be limited as passengers have a common destination. The elevator will remain parked on a floor with its doors open until a floor is selected and the door close button is held until the elevator starts to travel. The access key switches will allow the car to move at reduced inspection speed with the hoistway door open.
However, if the alarm was activated on the fire-recall floor, the elevator will have an alternate floor to recall to.
However, like independent-service mode, the car will not respond to a car call unless the firefighter manually pushes and holds the door close button.
The car(s) selected to run under emergency power can be manually overridden by a key or strip switch in the lobby. However, the increasing use of current-limiting motor starters, commonly known as "soft-start" contactors, avoid much of this problem, and the current draw of the pump motor is less of a limiting concern. In fact, prior to the September 11th terrorist attacks+, the only known free-fall incident in a modern cable-borne elevator happened in 1945 when a B-25 bomber struck the Empire State Building+ in fog, severing the cables of an elevator cab, which fell from the 75th floor all the way to the bottom of the building, seriously injuring (though not killing) the sole occupant — the elevator operator. This creates two significant hazards: being subject to an impact at the bottom when the elevator stops suddenly and being in the entrance for a potential shear if the rider is partly in the elevator. Freight elevators may have manually operated doors, and often have rugged interior finishes to prevent damage while loading and unloading. Today the Otis Elevator Company+, now a subsidiary of United Technologies Corporation+, is the world's largest manufacturer of vertical transport systems. Some buildings have elevators with the single door on the shaft way, and double cascading doors on the cab.
If the compensation system uses chains, the chain is guided by a bar mounted between the counterweight railway lines. The ThyssenKrupp MULTI elevator system is based on this principle and it uses a linear motor, like the ones used in maglev trains.
However, the door close button will cause a hall call to be ignored (so the door won't reopen), and once the timeout has expired, the door close will immediately close the door, for example to cancel a door open push.
Independent service is useful when transporting large goods or moving groups of people between certain floors.
This speed can range from anywhere up to 60% of normal operating speed on most controllers, and is usually defined by local safety codes. When the elevator is recalled, it proceeds to the recall floor and stops with its doors open. Once the elevator gets to the desired floor it will not open its doors unless the firefighter holds the door open button. In order to help prevent entrapment, when the system detects that it is running low on power, it will bring the running cars to the lobby or nearest floor, open the doors and shut down.
Because it is impossible to verify the system at all times, the code requires periodic testing of the pressure capability.
Although hydraulic freight elevators exist, electric elevators are more energy efficient for the work of freight lifting. Sometimes two elevators are built so that their cars always move synchronously in opposite directions, and are each other's counterweight. As the ropes age and the traction grooves wear, some traction is lost and the ropes must be replaced and the sheave repaired or replaced.
Due to technical limitations, these elevators have a low capacity, they usually allow 1-3 passengers and up to 525 lbs. The minimum timeout for automatic door closing in the US is 5 seconds, which is a noticeable delay if not overridden. This is particularly useful when passengers have luggage or carts, as at an airport, due to reduced maneuverability.
However, this will make the computer think multiple people are waiting and will allocate empty cars to serve this one person. This is in case the floor is burning and the firefighter can feel the heat and knows not to open the door. Another solution to protect against a cylinder blowout is to install a plunger gripping device.
Sheave and rope wear may be significantly reduced by ensuring that all ropes have equal tension, thus sharing the load evenly. Rope tension equalization may be achieved using a rope tension gauge, and is a simple way to extend the lifetime of the sheaves and ropes.
The fire-service key switch has the ability to turn fire service off, turn fire service on or to bypass fire service.
If for any reason the firefighter wishes to leave the elevator, they will use the hold position on the key switch to make sure the elevator remains at that floor. This is a device which, in the event of an uncontrolled downward acceleration, nondestructively grips the plunger and stops the car.
The only way to return the elevator to normal service is to switch it to bypass after the alarms have reset. If the firefighter wishes to return to the recall floor, they simply turn the key off and close the doors. If a pipe or hose were to break (rupture), the flow rate of the rupture valve will surpass a set limit and mechanically stop the outlet flow of hydraulic fluid+, thus stopping the plunger and the car in the down direction.



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