An elevated passenger ropeway, or chairlift , is a type of aerial lift, which consists of a continuously circulating steel cable loop strung between two end terminals and usually over intermediate towers, carrying a series of chairs. They are the primary onhill transport at most ski areas (in such cases referred to as 'skilifts'), but are also found at amusement parks, various tourist attractions, and increasingly, in urban transport.
Depending on carrier size and loading efficiency, a passenger ropeway can move up 4000 people per hour, and the fastest lifts achieve operating speeds of up to 12 m/s (26.8 mph; 43.2 km/h). The two-person double chair, which for many years was the workhorse of the ski industry, can move roughly 1200 people per hour at rope speeds of up to 2.5 m/s (8.2 ft/s). The four person detachable chairlift ("high-speed quad") can transport 2400 people per hour with an average rope speed of 5 m/s (16.4 ft/s). Some bi and tri cable elevated-ropeways and reversible tramways achieve much greater operating speeds. Fixed-grip lifts are usually shorter than detachable-grip lifts due to rope load; the maximum vertical rise for a fixed grip chairlift is 300–400 m (984.3–1,312 ft) and a length of about 1,200 m (3,937 ft), while detachable quads and "six-packs" can service a vertical rise of over 600 m (1,969 ft) and a line length of 2,000 m (6,562 ft).
Design and function
A chairlift consists of numerous components to provide safe efficient transport.
Terminology
Especially at ski areas, chairlifts are referred to with a ski industry vernacular. A one person lift is a "single", a two person lift is a "double", a three person lift a “triple”, four person lifts are “quads” and a six person lift is a "six pack". If the lift is a detachable chairlift, it is typically referred to as a “high-speed” lift, which results in a “high-speed quad” or “high-speed six pack”.
The capacity of a lift is constrained by the motive power (prime mover) versus the rope speed, the carrier spacing, the vertical displacement and the number of carriers on the rope (a function of the rope length). Human passengers can load only so fast before loading efficiency decreases; usually an interval of at least five seconds is needed.
Rope
The rope is the defining characteristic of an elevated passenger ropeway. The rope stretches and contracts as the tension exerted upon it increases and decreases, and it bends and flexes as it passes over sheaves and around the bullwheels. The fibre core contains a lubricant which protects the rope from corrosion and also allows for smooth flexing operation. The rope must be regularly lubricated to ensure safe operation and long life.
Various techniques are used for constructing the rope. Dozens of wires are wound into a strand . Several strands are wound around a textile core, their twist is oriented in the same or opposite direction as the individual wires; this is referred to as Lang lay and regular lay respectively.
Rope is constructed in a linear fashion, and must be spliced together before carriers are affixed. Splicing involves unwinding long sections of either end of the rope, and then winding each strand from opposing ends around the core. Sections of rope must be removed, as the strands overlap during the splicing process.
Terminals and towers
Every lift involves at least two terminals and—usually—intermediate supporting towers. A bullwheel in each terminal redirects the rope, while sheaves (pulley assemblies) on the towers support the rope well above the ground. The number of towers is engineered based on the length and strength of the rope, worst case environmental conditions, and the type of terrain traversed. The bullwheel with the prime mover is called the drive bullwheel ; the other is the return bullwheel . Chairlifts are usually electrically powered, often with diesel or gasoline engine backup, and sometimes a hand crank tertiary backup. Drive terminals can be located either at the top or the bottom of an installation; though the top-drive configuration is more efficient, practicalities of electric service might dictate bottom-drive.
Braking systems
The drive terminal is also the location of a lift's primary braking system. The service brake is located on the driveshaft beside the main drive, before the gearbox. The emergency brake acts directly on the bullwheel. While not technically a brake, an anti-rollback device (usually a cam) also acts on the bullwheel. This prevents the potentially disastrous situation of runaway reverse operation. Many chairlifts have a braking system in the sheaves.
Tensioning system
The rope must be tensioned to compensate for sag caused by wind load and passenger weight, variations in rope length due to temperature and to maintain friction between the rope and the drive bullwheel. Tension is provided either by a counterweight system or by hydraulic rams, which adjust the position of the bullwheel carriage to maintain design tension. For most chairlifts, the tension is measured in tons.
Prime mover and gearbox
Either diesel engines or electric motors can function as prime movers. The power can range from under 10 hp (7.46 kW) for the smallest of lifts, to several hundred for a long, fast detachable eight-seat up a steep slope. AC electric motors were the most common, though direct current motors are now economically competitive.
The driveshaft turns at high RPM, but with low torque. The gearbox transforms high RPM/low torque rotation into low RPM/high torque to drive the bullwheel. Higher power is able to pull heavier loads, or sustain a higher rope speed.
Secondary and auxiliary movers
In most localities, the prime mover is required to have a backup drive; this is usually provided by a diesel engine, which can operate during power outages. The purpose of the backup is to permit clearing the rope to ensure the safety of passengers; it usually has much lower power and is not used for normal operation. The secondary drive connects with the drive shaft before the gear box, usually with a chain coupling.
Some chairlifts are also equipped with an auxiliary drive, which can be used to continue regular operation in the event of a problem with the prime mover. Some lifts even have a hydrostatic coupling so the driveshaft of a snowcat can drive the chairlift.
Carriers and grips
Carriers are designed to seat 1, 2, 3, 4, 6 or 8 passengers. Each is connected to the cable with a steel cable grip that is either clamped onto or woven into the cable. Clamping systems use either a bolt system or coiled spring to provide clamping force. For maintenance or servicing, the carriers may be removed from or relocated along the rope by loosening the grip.
Restraining bar
Also called a retention bar or safety bar , these may help hold passengers in the chair in the same way as an automotive seatbelt or safety bar in an amusement park ride. If equipped, each chair has a retractable bar, sometimes with attached foot rests. In most configurations, a passenger may reach up and behind their head, grab the bar or a handle, and pull the restraint forward and down. Once the bar has rotated sufficiently, gravity assists positioning the bar to its down limit. Before disembarking, the bar must be rotated up, out of the way.
The physics of a passenger sitting properly in a chairlift do not require use of a restraining bar. If the chairlift stops suddenly (as from use of the system emergency brake), the carrier's arm connecting to the grip pivots smoothly forward—driven by the chair's inertia—and maintains friction (and seating angle) between the seat and passenger. The restraining bar is useful for children—who do not fit comfortably into adult sized chairs—as well as apprehensive passengers, and for those who are disinclined or unable to sit still. In addition, restraining bars with footrests reduce muscle fatigue from supporting the weight of a snowboard or skis, especially during long lift rides. The restraining bar is also useful in very strong wind and when the chair is coated by ice.
Some ski areas mandate the use of safety bars on dangerous or windy lifts, with forfeiture of the lift ticket as a penalty. Vermont state law also requires the use of safety bars.
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