A chairlift is basically a looping steel cable with a large pulley at each end (the bullwheels). Carriers (the chairs) are hung from the cable and held in place with a mechanical grip. The grip functions similarly to a vice and is tightened around the cable to keep the chair from sliding back. A chair gradually slides back a bit each season, which is why lines are often painted on the cable. The paint mark provides the lift mechanic with a visual indicator of how far the chair has moved. Don't worry if the paint mark is far away, chairs are often moved every few seasons to ensure even wear on the cable.
A series of towers form the line and keep the cable from dropping to the ground below. Towers are installed with either a crane or a helicopter depending on the budget, terrain, and weather. The towers are topped with cross-arms that hold sets of wheels called sheaves. The cable can go either above or below the sheave assemblies. On the vast majority of towers the cable travels over the sheaves, exceptions are when the lift is about to climb a steeper section, traveling under adds tension to the cable allowing it to achieve a more drastic angle.
So what makes the big wheel turn? Today, most lifts are powered by electric motors, but have an auxiliary diesel backup drive. The Single Chair used to run exclusively on diesel until it was completely refurbished in 2007. Today's electric motors are cleaner and cheaper than their diesel counterparts. If you hear an engine running, then the lift is most likely running on a backup diesel for some reason. The engine can be located at the top or bottom of the lift, depending on the engineer's advice.
What keeps the cable from going too slack? On older lifts, a large counterweight provides tension to one of the big wheels, ensuring the cable stays taut. Newer lifts use hydraulic tensioning (giant shock absorbers) to allow for easier adjustment and improved ride quality.
We all know that high-speed detachable chairs are much faster, and as the name implies, the chair "detaches" from the cable. In fact, high-speed chairs are 2.4 times faster than fixed-grip chairs. These detachable chairs typically travel at 1,200 ft/min (14 mph, 22 km/h, 6 m/s), while fixed grip chairs typically travel at 500 ft/min (6 mph, 9 km/h, 2.5 m/s). In theory, a fixed grip chair can move just as fast. However, getting on and off at 14 mph can be extremely painful and awkward.
High-speed detachable chairs work much like fixed grip chairs, with one key exception. High-speed detachables feature a grip mechanism that allows the chair to be released from the cable at the loading and unloading station. The cable continues to run at a faster speed while passengers are loaded and unloaded at an easy, slow speed, reducing the number of times the lift must stop.
To detach or not to detach? There are many reasons why traditionalists favor fixed grips. Fixed grip lifts are ideal for servicing rough terrain that doesn't require the capabilities of a high-speed lift. They provide more recovery time and plenty of time to chat with neighbors, enjoy a beverage, or anything else that suits your fancy. Most importantly, the powder was not traced that quickly.
In the West, detachables are a treat because there is more acreage available for skiers to use. Resort designers in the East must carefully consider where detachables are placed and how they affect skier traffic. Detachables also help get new skiers onto the lifts faster because loading and unloading is at a near standstill.