Elevators, Escalators, and Moving Walkways Information
Elevators, escalators, and moving walkways are used to raise or move people or goods from one location to another within a building. Elevators are transport devices that are used to lift people and goods vertically up and down, from one floor to another. Because of handicap air access laws, elevators are often legally required in multi-story buildings. Elevators are platforms that are pulled or pushed by mechanical means. Most often, elevators are enclosed in a cab mounted on a platform that travels in an enclosed shaft. There is more than one type of elevator; traction elevators and hydraulic elevators are two examples. Elevators can open in a few different ways, but most often two sliding panels meet in the middle to close the door.
Elevators, or lifts, have been around for centuries in one form or another. The early ones used simple winches to hoist a platform and cage with miners and ores out of vertical mine shafts or moving items up to the top of towers like in a castle. Later, steam power was used to hoist primitive elevator cabs. These were usually found in coal mines or mills that already had steam engines. The first modern elevator, the Otis Safety Elevator, was developed in the 1850s. It had automatic emergency safety brakes. Electric motors replaced the steam engines in the 1880s. Between these two modern innovations, the elevator as we know it was born. Over the next 140 years, various aspects were improved such as the doors, controls, and motors. Early elevators used either single speed AC motors or variable speed DC motors. The trouble with the older DC motors is that they needed an AC motor-generator pair to power it. That caused higher initial costs and increased energy consumption. Modern elevators employ variable voltage and frequency AC motors and controllers that have eliminated the need for DC motors. These efficient AC motors provide lower initial machinery and energy costs compared to DC motors. Today’s elevators can have variable lifting speeds depending on demand and traffic patterns.
Most elevators are cable hoist types, or traction powered. This style is used in very tall buildings. Smaller buildings can utilize a hydraulic style elevator, where pressurizing a piston ram pushes the elevator’s cab up and bleeding the pressure off lowers the cab. These elevators are like the old-fashioned center piston automobile lifts. The limit for hydraulic elevators is usually eight stories, using telescoping pistons. They use more energy than a traction elevator, since they can’t exploit conventional counterweights of traction elevators. But hydraulic elevators are simpler, easier to install and maintain, and are less expensive to purchase. Newer elevators can come with no machine rooms to save space. The controls and motors are small enough to fit into the elevator shaft way. Some state and local regulations still require an elevator machine room. Also, for really tall buildings, the elevators need a penthouse on top to house the extra-large winches and cable drums it needs to hoist the elevator up hundreds of feet.
There is a third style of elevator, the climbing ones, or self-powered elevators. These are used in industrial, maritime, or other applications where it is impossible to get external power, limited or no space for a shaft way, or any way to hook up cables, winches, or rams. In climbing elevators, the motors are attached to the cab. They can be gas powered or electrically powered running off a vertical conductor rail. They can run off tracks attached to the side of a stable column. Usually, these elevators have a low load limit with just two people or one person and his or her tools, at the most. The elevator’s built-in motors power a pinion drive that works on a vertical rack, like a vertical cog railway, to move the cab up and down. These are usually used on tall masts or radio towers, mainly for worker access. Of course, these elevators have safety brakes but lack all the amenities like today’s average building elevators.
Parallel with the development of the lifting machinery of the elevators, are the evolution of elevator controls and doors. The first elevators had simple controls and usually featured a full-time operator. Later on, in parallel with the time and way the dial telephone superseded the switchboard controlled telephone, elevators featured user operated controls. These are the controls one takes for granted today such as pushing a button for the floor that one wants. In order to satisfy safety codes in eliminating the dedicated human elevator operator, items such as user activated alarms and emergency telephones in the cabs became part of various legal codes. With the development of computer and micro-processor controls, internal elevator operational controls went from simple mechanical relays and switches to digital logic. That meant building elevator operations, especially in tall, heavily trafficked buildings, could be refined and optimized for traffic flow and/or economy in real time.
One of the most important developments in elevator technology is the modern double sliding safety doors. This way, both the riders in the cab and people near the shafts are protected from any chance of falling into or getting hung up in the elevator. The older manual operated doors, slide-up doors, and open cabs are now illegal in most places. Elevator doors also have various ways to prevent from shutting on obstructions, like a rider’s leg. Usually that is accomplished with a pressure sensitive rubberized switch that runs the full height of both sets of doors. When the rubber bumper switches senses an obstruction, the doors open up. The doors also have interlocks to prevent the elevator from moving if the door switches sense that any door is still open.
Escalators are conveying devices that are used to move people vertically on individual, linked stairways. In installing escalators in a building, many things must be taken into consideration. The most important factors are the height to be climbed and the distance available to run the unit; since they determine the pitch and length of the escalator. Other design factors include:
- physical requirements
- traffic pattern
- safety precautions
Components of escalators include top and bottom landings, trusses, tracks, handrails, and steps. Unlike an elevator, a disabled or powered down escalator can still be used as a conventional flight of stairs. So building managers can shut them down without adversely inconveniencing the users in the building, unlike an elevator.
The average speed of an escalator falls between 1 ft. to 2 ft. per second, or .3 m to .6 m per second. The angle of ascent of an elevator is usually around 30 degrees to the horizontal. The max vertical ascent is usually around 60 ft., or 18 m. At a 30% incline, that means the elevator truss length would be 120 in., or 36 m, long. Step width can vary from 16 in. to 40 in., or 40 cm to 1 m. The standard step width is 32 in. or 80 cm. Escalators are usually powered by AC induction motors and usually run at one speed.
Like elevators and escalators, moving walkways are used to move people. They are also known as moving sidewalks and are called “travelators” in the United Kingdom. Much like escalators, moving walkways use a conveyor belt to transport people. However, moving walkways move people and goods horizontally, or on a lower angle of incline to the horizontal than an escalator. They are often found in large airports where people have luggage and have to walk a long distance between various sub terminal buildings. Moving walkways are often installed in pairs, for movement in each direction. They usually run about half of walking speed, around 1.4 mph or 2.2 kmph and can be from 27 in. to 56 in., or 67.5 cm to 140 cm wide. They are usually powered by AC induction motors. Moving handrails, like those found on escalators for code and safety reasons, are optional on horizontal moving walkways.
Moving walkways come in one of two basic styles: pallet type or moving belt. Pallet type moving walkways are built from a series of connected metal plates that are joined together to form a walkway. Pallet type moving walkways are essentially flat elevators. This type of moving walkway has a metal surface, although they are available with a rubberized tread bonded on top of the metal plates. Moving belt walkways are essentially human conveyor belts. Moving belt walkways are typically built with mesh metal balls, which is a rubber surface over metal rollers.
All three types of these people movers require extensive architectural and structural engineering support since they are heavy and need a stable base. Elevator shaft ways have to be strong and straight and are usually framed with girders or at least reinforced concrete. Elevator shafts can be the most problematic part of a building’s construction process. There are modular elevator units that come enclosed in their own shaft and everything else one needs for an elevator. But these are usually limited to 100 ft., or 30 m, tall and still require a stable base pad to stand on. When adding an elevator to an older structure, especially a wood-framed structure, a separate steel and concrete combination elevator shaft and fire stairwell addition is usually built on to the side of that building. These refit jobs are a good place to install a modular elevator and do away with the extra expense and engineering effort that a custom built shaft requires. Horizontal people movers need a good solid, usually reinforced concrete base. All of these types of movers require high voltage, high current power feeds, at least 440 VAC 3 phase power.