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Why Detachable Lifts are more Susceptible to Icing Holds than Fixed Grip Lifts

Thursday, January 21, 2016

Before the snowflakes flew last weekend, we received a light mist that caused a thin layer of ice, resulting in icing holds and delays for the SuperQuad on Saturday morning. But if the whole mountain experienced the mist, why were other lifts able to run while the SuperQuad was down? Skyline has a higher top elevation than the SuperQuad, why wasn't it affected by the icing? There are a lot of factors involved with icing holds, so here's a quick breakdown of why detachable lifts (like the SuperQuad) are more susceptible to icing than fixed grip lifts (like Skyline).

For starters, there are more working parts on a detachable lift that require inspections and maintenance. As a result, when ice is added into the mix, there are more components on a detachable lift that can be affected. 

On a detachable lift, the chairs let go of the rope in the bottom and top terminals, so that the actual loading and unloading speed that riders experience meets the ANSI/State code of no greater than 450 feet per minute.  Once loaded or unloaded the chair can resume its actual line speed of 1000 feet per minute. 

In order for the chair to continue moving forward when it is not connected to the haul rope in the terminals, the chair grip has a traction plate mounted on top of it along with running wheels that guide the chair along a rail through the terminal. Inside the terminal, there are rubber tires that come into contact with the grip to propel the chair through the terminal until it is reconnected to the line. The key factors that impact this process are as follows: 

  1. Ice build-up on the traction plate
  2. The height of the rubber tires in relation to the running rail
  3. Amount of air pressure in the tires
  4. Amount of tread left on the tires
  5. Condition of the rubber belts that are linked together to turn the rubber tires 

The mist on Saturday morning caused ice to build up on the traction plates, which was causing the tires that propel the chair through the terminal to slip when they came in contact the traction plates (similar to the way your car tires slip on icy roads). The lift's built-in safety system causes the lift to stop if the chairs slip or stop. This is called an Anti-Collision Fault.

So how were we able to get the lift back up and running a few hours later? Our lift maintenance teamreplaced 14 rubber tires, where the slipping was occurring, with new tires. They also lowered the heightof the rubber tires to create more pressure on the traction plate, and eventually the ice buildup  on the traction plates decreased.

The effects of the early morning mist, only impacted mid-to-high elevations lifts; that's why Whiffletree, which is the same model lift as the SuperQuad, was able to operate without any icing issues.  

Icing also impacts detachable lifts in other ways. Detachable lifts have grip sensors that monitor the connection of the chair grip to the haul rope before the chair leaves the terminal. When the sensor detects a bad grip, it shuts down the lift until it is examined and cleared by a lift attendant. Icing events like we experienced last weekend can cause what are called "false negatives" from these grip sensors, causing the lift to stop even when the grip is not secure. Even the smallest layer of ice on the haul rope can cause the sensor to report a poor connection of the grip to the line. 

On fixed grip lifts, like Double Runner or Skyline, the chair grip is never separated from the haul rope. Therefore there are no tripped sensors that can cause the lift to stop. 

Icing on traction plates and grips sensors can also result in chair spacing issues.The chairs on a lift need to be evenly spaced in order to provide a smooth ride, and to protect the integrity of the haul rope, chair grips, and sheave assemblies. When ice build-up on traction plates prevents chairs from moving through the terminal properly, and icy grip sensors prevent chairs from reattaching to the haul rope properly, chairs get bunched together in the terminal, resulting in uneven spacing throughout the length of the line. 

As chairlifts primarily operate during the winter months, icing and its adverse effects are inevitable at a ski resort. Most ski resorts can expect to see at least a few days of icing throughout the season that result in lift delays, particularly on detachable lifts. 

Under certain conditions, when icing occurs overnight, our lift maintenance team may attempt to run lifts periodically throughout the night to help break off ice build-up. This practice comes with its own risks, however, as operating a lift with significant ice-build up can cause damage to sheaves assemblies and other components, and it is difficult for mechanics to monitor lift lines in the dark. It also is not terribly effective at preventing ice build-up on traction places and grip sensors, which are the most problematic components during icing events.