23 replies to this topic

[Snowy Ferries]

So, I know almost everything about the inner workings of a skilift, but one thing that has always baffled me is how PTO belts work, so I'm just going to suck up my pride and ask you experts. I know their purpose is to accurately moderate the speed of each tire on the accelerator/decelerator rails, but I just can't figure out how...

[SkiLiftsRock]

Snowy Ferries, on 11 June 2014 - 07:19 PM, said:

So, I know almost everything about the inner workings of a skilift, but one thing that has always baffled me is how PTO belts work, so I'm just going to suck up my pride and ask you experts. I know their purpose is to accurately moderate the speed of each tire on the accelerator/decelerator rails, but I just can't figure out how...

On Doppelmayr there is different shaft sizes from the pulley to the tires.

On Leitner Poma there is different gear sizes all the way around the terminal.

Correct me if I am wrong.

Hope this helps!

[liftmech]

Well, skiliftsrock, you're (partially) wrong

Poma, Doppelmayr, CTEC (Garaventa), Leitner, and so forth all use the same principle to move carriers through the terminal. Each tire is connected to its neighbours by a belt or two. The pulleys are different sizes depending on whether the tire needs to be going slower or faster than the next one.

Where the manufacturers differ is how the tires in the contour are powered. This is where Poma uses the beveled gears you're referring to. CTEC and Doppelmayr use belts with angled pulleys, and I've seen Garaventa use tiny little drive shafts with u-joints and individual gearboxes (not sure if they put that setup into the export CTEC hybrids at all).

Technically when you refer to PTO belts you're talking about the big belts that transfer power from the PTO sheaves to the tire banks.

There you go.
(photo credits to remontees-mecaniques.net, except the last one which is mine)

[Yooper Skier]

First one shows the different pulley ratios in the accelerator ('08 Doppelmayr). Second one is a Doppelmayr drawing of a PTO. My '92 Poma uses cog belts to achieve the same thing.

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•  chondola acceljpeg.jpg (27.76K)
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•  conveyer drawing.png (252.91K)
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[Lift Dinosaur]

 mechanism pto assembly MARK UP.jpg (1.64MB)
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So here's how it works. The Haul Rope drives the PTO Sheaves which in turn drive the PTO Belts which turn the 2 input sheaves (not marked) which turn the V Belt Pulleys which are connected to the Traction Tires that act on the Traction Plate on top of each carriers grip. As you can see the V Belt Pulleys are different diameters.
If the carrier is arriving from the right of the photo the first few traction tires will be running at "line speed" (say 1000 fpm). Once the grip opens and is no longer on the cable the traction tires will decelerate the carrier at a designed rate through the use of ratios (different diameters) to "station speed" (usually @ 200 fpm). After the carrier passes through the contour or turn around it will be accelerated back to "line speed" where it will be coupled onto the cable.
You can see from this arrangement that everything is synchronous with the speed of the haul rope.
Hope this answers your question.

Dino

[SkiDaBird]

You learn something every day...

[Snowy Ferries]

Thanks guys.

[snowmaster]

Why are PTO sheaves used instead of transferring power from the gearbox or bullwheel? Is seems that transferring power via the cable would be prone to slippage. Are there any detachable lifts where this is done?

[vons]

snowmaster, on 15 June 2014 - 12:54 PM, said:

Why are PTO sheaves used instead of transferring power from the gearbox or bullwheel? Is seems that transferring power via the cable would be prone to slippage. Are there any detachable lifts where this is done?

On older lifts it was done as you has described in the early 90s almost all the lift manufacturers switched to a PTO sheave belt arrangement to power the conveyor systems on detachable lifts. Slippage can be an issue that is why the tension on the belts is checked by maintenance and operations personnel regularly.

[mikest2]

snowmaster, on 15 June 2014 - 12:54 PM, said:

Why are PTO sheaves used instead of transferring power from the gearbox or bullwheel? Is seems that transferring power via the cable would be prone to slippage. Are there any detachable lifts where this is done?

One terminal (return) has no drive, it only has the haul rope driving the pto sheaves, that drive the pto belts, that drive the tire conveyor. This is much less expensive, less clumsy, and way faster to repair than gearboxes and shafts. There's no point in driving the drive station any differently.

[2milehi]

snowmaster, on 15 June 2014 - 12:54 PM, said:

Why are PTO sheaves used instead of transferring power from the gearbox or bullwheel? Is seems that transferring power via the cable would be prone to slippage. Are there any detachable lifts where this is done?

If you ever get to Vail, take a good look at some of the older Doppelmayr lifts on the front side. There are driveshafts, gearboxes, pulleys, belts and cogs. The PTO system greatly simplifies how a terminal is powered.

If you worked on both types you would see what we are talking about.

This post has been edited by 2milehi: 16 June 2014 - 10:18 AM

[snoloco]

I have two videos that show both systems. This video taken by someone else shows an view inside the terminal of the Stratton Gondola. It has the terminal powered off the bullwheel.

https://www.youtube....h?v=_YXzFH9l8EU

This video that I took myself shows the inside of the terminal of the Kaatskill Flyer at Hunter Mountain. It has the terminal powered by PTO sheaves.

https://www.youtube....h?v=XT9rQRD0QrQ

Both videos are taken at the drive end which is the bottom on both lifts. The Stratton Gondola is a vault drive while the Kaatskill Flyer is obviously an overhead drive.

This post has been edited by snoloco: 16 June 2014 - 04:20 PM

[liftmech]

Another view of the bullwheel PTO system, on a 1993 Poma gondola. This is the same setup I have on the Flyer, as well as on the aforementioned Stratton Gondola.


You can see how many moving parts and subsystems there are to take care of. While this eliminates the slippage some of you have mentioned, there is much more to maintain and inspect. I'm actually doing this service now, and it takes me on average two days longer than the guys with PTO-belt-driven lifts.
photo credit to remontees-mecaniques.net

[Keymech]

Love the guy doing the drive shaft limbo in the background

[snoloco]

On lifts with the drive shaft system, how is it worked at the return. The Stratton Gondola video was taken at the drive end. How would it be set up at the tension/return end which is the top on the Stratton Gondola. With a PTO system, it doesn't matter where the bullwheel is.

[Peter]

Here's a picture of Killington's Skyeship Gondola which uses chains.

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[Yooper Skier]

Peter, on 17 June 2014 - 12:46 PM, said:

Here's a picture of Killington's Skyeship Gondola which uses chains.

Those are cog belts. My '92 Poma quad has them...VERY temperamental and usually good for snapping one a season. How they work (at least on mine) is the #1 incoming PTO powers tires 1-8, #2 incoming PTO powers tires 9-33, #1 outgoing PTO runs 34-58, and #2 outgoing does 59-66. The picture of the Skyship one has the Emergency Belt in place, which ties one entire sides conveyor together. It's the belt between the two that makes an upside down "V" and is easily installed if one of the two PTO belts snaps and can run the remainder of the day.

[snoloco]

I was told that the South and Bear Peak Express at Mountain Creek both have had some issues with slippage. I was told that the reason they are turned down to 800 fpm so frequently during the night hours is because when it gets cold, the PTO is in danger of slipping which messes up chair spacing and shuts the lift down. I was told this by a mechanic, so no one come after me for speculating, because I actually know what was going on here. What is weird is that there were at least two days when the South Peak Express was closed for ice, while the Bear Peak Express was still running when they are on adjacent peaks. Sometimes, ice is bad enough to close both of them. These are both 1998 Doppelmayr HSQ's. It might be that I ski there so often that I see any and all operational issues, but I think I have seen these closed for ice more than most other lifts I have ridden.

[liftmech]

snoloco, on 17 June 2014 - 12:00 PM, said:

On lifts with the drive shaft system, how is it worked at the return. The Stratton Gondola video was taken at the drive end. How would it be set up at the tension/return end which is the top on the Stratton Gondola. With a PTO system, it doesn't matter where the bullwheel is.

The photos I posted are at the return end. The bullwheel provides the driving power. You can see a shaft between the fixed column and a gearbox on the carriage. Because of the sliding coupling on the square shaft, it doesn't matter where the bullwheel is there either.

[SuperRat]

Whats the drive train with all the U-joints with the needle bearing that seize and grind?
SHAFTS!
Ya damn right!

Whats the tension carriage systems that galls and binds?
SHAFTS!
Can you dig it?