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Some problems on Pallivacinni Today


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#1 skierdude9450

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Posted 13 January 2008 - 09:03 PM

I was at A-Basin today. I arrived at around 9:00 to find that Pali was closed and Exhibition was only loading every other chair. I heard that Palivacinni got some ice on the cable and started to rollback around the bull wheel when it stopped. This was in the morning before they even started loading people on the chair. They were loading every other chair on Exhibition to prevent a rollback. Is this a common thing for the cable to slip due to ice on the cable? It seems that ice would accumulate often on the cable when it is stopped. Also, does load affect the possibility of a rollback? Can anyone else tell me exactly what happened?



Title edit by forum administrator – 1/15/07
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#2 aug

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Posted 14 January 2008 - 04:35 PM

First you must understand the loads on the lift line. The possibility of an unloaded lift rolling back is almost impossible. There must be some un-balance in the uphill and downhill loads for a rollback to occur. (when a lift is empty and has equally spaced chairs on the line the load is balanced on the uphill and the downhill sides of the lift)The tension load at the top of a lift is greater than at the bottom. BW's at the top of the lift have more load(traction) due to the increased loading of the BW from the force of gravity. Hence the top BW is holding the weight of the haul rope and the carriers and the haul rope tension specified in the design of the lift instalation. The bottom BW just has the specified rope tension on it. Top drive lifts have more traction than bottom drive lifts. I have worked at ski areas that have a lot of SERIOUS icing issues and have never seen the BW slip on the haul rope on an empty or loaded lift . This is not saying that it could not happen else where , but events like these I would think would be extremly rare. It is also possible that when the lift ops or lift maint. were doing their stops they noticed the haul rope slipping though the BW after the BW stopped moving. This would be from trying to stop the moving mass of the haul rope and the carriers and not having enough traction on the haul rope due to icing. This would indicate that the distinct possibility of a rollback could occur if the lift was loaded. Is this lift a detacthable lift??? What is more common on detatchables, when icing occurs is that the haul rope has less traction on it , and the detatchable terminals rely on this traction to power the conveyor assemblies and when this traction is lost (as in an icing event ) the conveyors do not run at the designated speed to keep the chairs moving around the terminals resulting in cadence or anti collision fault and even stacked up chairs in the terminal. Hope this answers a few questions.

This post has been edited by aug: 14 January 2008 - 05:05 PM

"Maybe there is no Heaven. Or maybe this is all pure gibberish—a product of the demented imagination of a lazy drunken hillbilly with a heart full of hate who has found a way to live out where the real winds blow—to sleep late, have fun, get wild, drink whisky, and drive fast on empty streets with nothing in mind except falling in love and not getting arrested . . . Res ipsa loquitur (it speaks for it self). Let the good times roll." HT

#3 coskibum

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Posted 14 January 2008 - 06:24 PM

pali is a fixed double made by YAN in the late 70's. Their website says it was scheduled to operate today?

#4 skierdude9450

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Posted 14 January 2008 - 09:21 PM

Now that I understand, I don't think that it was a full-fledged rollback, but rather the rope slipping when it stopped during the tests. The lift reopened at around 2:30. Also, if this is of any importance, there are many large spans in the downhill line where it skips three offset towers at a time that are on the uphill line. It does have a bottom drive and tension.
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#5 Peter

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Posted 14 January 2008 - 09:25 PM

View Postskierdude9450, on Jan 14 2008, 09:21 PM, said:

Now that I understand, I don't think that it was a full-fledged rollback, but rather the rope slipping when it stopped during the tests. The lift reopened at around 2:30. Also, if this is of any importance, there are many large spans in the downhill line where it skips three offset towers at a time that are on the uphill line. It does have a bottom drive and tension.


I would think this makes a difference because that means that the downhill side is shorter and has fewer chairs, and therefore less weight. It probably is not that significant of a weight difference, however.
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#6 chasl

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Posted 15 January 2008 - 12:49 AM

View PostSkier, on Jan 15 2008, 12:25 AM, said:

I would think this makes a difference because that means that the downhill side is shorter and has fewer chairs, and therefore less weight. It probably is not that significant of a weight difference, however.



WHAT!!

#7 aug

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Posted 15 January 2008 - 10:56 AM

View PostSkier, on Jan 14 2008, 10:25 PM, said:

I would think this makes a difference because that means that the downhill side is shorter and has fewer chairs, and therefore less weight. It probably is not that significant of a weight difference, however.

Unless I am missing some thing ...... both sides of a conventional lift MUST be of equal length.
"Maybe there is no Heaven. Or maybe this is all pure gibberish—a product of the demented imagination of a lazy drunken hillbilly with a heart full of hate who has found a way to live out where the real winds blow—to sleep late, have fun, get wild, drink whisky, and drive fast on empty streets with nothing in mind except falling in love and not getting arrested . . . Res ipsa loquitur (it speaks for it self). Let the good times roll." HT

#8 Kicking Horse

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Posted 15 January 2008 - 11:10 AM

View PostSkier, on Jan 14 2008, 10:25 PM, said:

I would think this makes a difference because that means that the downhill side is shorter and has fewer chairs, and therefore less weight. It probably is not that significant of a weight difference, however.



Skier..... What the hell are you saying?
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#9 vt3pinandy

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Posted 15 January 2008 - 01:41 PM

The old flying return as we refer to it in the supplier side of the business. Actually Skier is correct as the straight line is definately shorter by a small amount then the bent line. Draw it out and do a little geometry and you will see that the flying return is a little shorter. Think about a comline that is hanging loose and then pull it tight and you will find the length you pull out of it is never as long as you think it is. While it seems obvious it is something I learned by others mistakes as in "my comline was to short at the bottom of the lift". So the difference is so small I doubt it makes a big deal with the loading at all. For the record in 1997 I was in Argentina and witnessed a major ice storm and to this day I saw a bullwheel slip through a rope on a bottom drive/tension fixed grip. Coulda been the water I guess. AP

#10 AlphaBet

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Posted 15 January 2008 - 02:22 PM

View PostSkier, on Jan 14 2008, 11:25 PM, said:

I would think this makes a difference because that means that the downhill side is shorter and has fewer chairs, and therefore less weight. It probably is not that significant of a weight difference, however.


It seems like that would make a perpetual motion machine :wink:

This post has been edited by AlphaBet: 15 January 2008 - 02:23 PM


#11 Lift Dinosaur

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Posted 15 January 2008 - 02:39 PM

View Postvt3pinandy, on Jan 15 2008, 02:41 PM, said:

The old flying return as we refer to it in the supplier side of the business. Actually Skier is correct as the straight line is definately shorter by a small amount then the bent line. Draw it out and do a little geometry and you will see that the flying return is a little shorter. Think about a comline that is hanging loose and then pull it tight and you will find the length you pull out of it is never as long as you think it is. While it seems obvious it is something I learned by others mistakes as in "my comline was to short at the bottom of the lift". So the difference is so small I doubt it makes a big deal with the loading at all. For the record in 1997 I was in Argentina and witnessed a major ice storm and to this day I saw a bullwheel slip through a rope on a bottom drive/tension fixed grip. Coulda been the water I guess. AP


I have only seen this "flying return line" on bottom drives - because the return line is being pulled downhill and wants to be straight. AP- have you seen one on a top drive?

I would think this makes a difference because that means that the downhill side is shorter and has fewer chairs, and therefore less weight. It probably is not that significant of a weight difference, however.

As AP has stated, because the uphill cable follows the terrain (restrained) and the downhill cable is allowed to fly (straighten), the downhill line is actually shorter. Being familiar with the Pali, I would estimate the difference on a 3500 foot long lift to be about 10 feet - not enough to effect the number of carriers on either side or an unbalanced line.

9450 - your information source?

Dino
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#12 skierdude9450

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Posted 15 January 2008 - 03:37 PM

On?? I just heard about it from some lift mechanics at A-Basin. There definately was a problem since they were running it on and off, but it was still closed. I heard from the lift mechanic that there was ice on the line, and overheard snippets of a rollback.
-Matt

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#13 Kicking Horse

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Posted 15 January 2008 - 03:57 PM

View Postskierdude9450, on Jan 15 2008, 04:37 PM, said:

On?? I just heard about it from some lift mechanics at A-Basin. There definately was a problem since they were running it on and off, but it was still closed. I heard from the lift mechanic that there was ice on the line, and overheard snippets of a rollback.


As u know you have to be able to backup what you say around here. So that is why Dino is asking for a source. If u dont want to make it public just send him a pm with the name of the techie that you were chatting with.
Jeff

#14 LiftTech

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Posted 15 January 2008 - 05:19 PM

I have never seen a lift roll back or better put slide back during icing conditions; however I have seen them lose traction and spin on the haul rope, think of it as nothing more than a rubber (mostly) surface pushing on a wet icy surface not unlike your car on the same surface (some exceptions apply, you “may” have tread, studs and maybe tire chains on your vehicle). The load must be less than the friction on the drive wheel, if it’s not the wheel will spin just like the tires on your vehicle, reduce the load and you reduce the friction needed to drive the load. A few things need to be “right” (for lack of a better term) for this to occur, first the ice needs to accumulate on the traction side of the rope, the ice must be hard enough to support the pressure of the rope entering or on the drive wheel, and lastly the ice must be soft enough to not shatter when it’s flexed or compressed as it enters or is on the drive wheel. We have two lifts that I’ve seen do this, (three times in 27 +years) both are right hand up, YAN, (I think this does not matter) face west and all the winds I’ve seen come from the south during these icing events, if they were left hand up I think it would not occur.
Dennis.

#15 Allan

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Posted 15 January 2008 - 05:46 PM

If we get just the right conditions this happens on our right hand up YAN that also faces directly west; and a with a rimy southerly wind we've observed the rope slipping under a full load but never roll back. Scares the hell out of the passengers on the line so we either scrape the ice off the BW or we go to loading doubles until the conditions improve. We're going to try and come up with some sort of built in scraper that we can activate when needed.
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#16 chasl

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Posted 16 January 2008 - 12:43 AM

I will agree, ice on the liner is a problem and can cause slippage. This is not a Northwest problem only, it happens in the East also.
As all lifts are designed to a tensioning force taking into account the coefficient of friction of the bullwheel liner to the rope,(as well as other variables) on lifts that are close to this design value, you can get slippage in certain situations. (some people have adjusted the plus and minus % values on the tension panel) this has also caused problems. I also know of a rope that was lubed, too late and too much in the fall, that had slippage and the rope and liner had to be cleaned.

So whether the system is a top drive pulling the load up the hill or a bottom drive pushing the load up, should make no difference in the operation. By the way look at your tensiong system, from empty to having a full load, pulling or pushing the load (newer drive tension systems) you will not have an unbalanced line, at the most you might see 1 meter of difference x 2 so approximatly 6 feet of sag (not much) over the complete side, not enough to unbalance your line and cause slippage even if design tolerances are close, and yes most of the sag will be near the bottom of the lift.

So the friction between the bullwheel liner and the rope is the driving force, (no pun intended) anything we do to change this value will effect the system including, allowing ice to build up between the rope and bullwheel liner.

#17 ccslider

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Posted 16 January 2008 - 06:35 AM

I've observed a similiar slippage problem at the drive sheave due to the late (in the off-season) and excessive application of rope lube - very disconcerting to see the drivetrain and sheave operating at full speed while the actual rope is barely moving. A rather low-tech application of kitty litter between the rope and sheave liner saved the day.

#18 aug

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Posted 16 January 2008 - 11:50 AM

View Postchasl, on Jan 16 2008, 01:43 AM, said:

I will agree, ice on the liner is a problem and can cause slippage. This is not a Northwest problem only, it happens in the East also.
As all lifts are designed to a tensioning force taking into account the coefficient of friction of the bullwheel liner to the rope,(as well as other variables) on lifts that are close to this design value, you can get slippage in certain situations. (some people have adjusted the plus and minus % values on the tension panel) this has also caused problems. I also know of a rope that was lubed, too late and too much in the fall, that had slippage and the rope and liner had to be cleaned.

So whether the system is a top drive pulling the load up the hill or a bottom drive pushing the load up, should make no difference in the operation. By the way look at your tensiong system, from empty to having a full load, pulling or pushing the load (newer drive tension systems) you will not have an unbalanced line, at the most you might see 1 meter of difference x 2 so approximatly 6 feet of sag (not much) over the complete side, not enough to unbalance your line and cause slippage even if design tolerances are close, and yes most of the sag will be near the bottom of the lift.

So the friction between the bullwheel liner and the rope is the driving force, (no pun intended) anything we do to change this value will effect the system including, allowing ice to build up between the rope and bullwheel liner.

As much as I regret in correcting the previous statment ,I must. (So whether the system is a top drive pulling the load up the hill or a bottom drive pushing the load up, should make no difference in the operation.) Regardless of where the drive sheave is on any lift using a rope, you must pull. In a bottom drive the bottom BW pulls the Haul rope up and around the top BW. One of the most compelling reasons to have a top drive is the increased tension on the top BW vs. the bottom BW. One of the dis-advantages of a top drive is the surge that is created in the slack line going down the hill to the return (bottom) terminal when the lift is slowed or stopped. In my observations over the years the surge in bottom driven lifts is less than in top driven lifts .
"Maybe there is no Heaven. Or maybe this is all pure gibberish—a product of the demented imagination of a lazy drunken hillbilly with a heart full of hate who has found a way to live out where the real winds blow—to sleep late, have fun, get wild, drink whisky, and drive fast on empty streets with nothing in mind except falling in love and not getting arrested . . . Res ipsa loquitur (it speaks for it self). Let the good times roll." HT

#19 Lift Dinosaur

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Posted 16 January 2008 - 12:28 PM

I talked with the Lift Manager at A-Basin. There was NO ROLLBACK. Temperature -13 F and rime ice (more than hoar frost) on the rope. After a full loaded stop, on restart the rope was popping on the drive (bottom) bullwheel. Heat Guns were used to warm the liner, the slow speed pot was turned down, and the fully loaded line was successfully evacuated. The remainder of their lifts were then loaded at every other chair as a precautionary measure to avoid similar issues.

Dino
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#20 egieszl

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Posted 05 February 2008 - 06:38 PM

View PostLift Dinosaur, on Jan 15 2008, 02:39 PM, said:

I have only seen this "flying return line" on bottom drives - because the return line is being pulled downhill and wants to be straight. AP- have you seen one on a top drive?


I'm pretty sure Chair 21 (Yan FGT) at Mammoth Mountain has a flying return line and is a top drive.

Eric





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