14 replies to this topic

[k2skier]

On a Riblet how is the carraige positioned? And how does this differ from line tension that the counterweight pulls?


Title edit to correct spelling and to better reflect initial posting content – Forum Admin

This post has been edited by k2skier: 26 November 2012 - 10:57 AM

[liftmech]

No, the op was correct when he said the tensioning is 'automatic'. Unless the counterweight is resting on the ground, it will hold full tension regardless. Your statement that all the loaded chairs were in one stretch does explain the line sag, however. Riblets are generally low-tension lifts. I do agree that you shouldn't have had to lift your skis up to clear the summer mid-station, though. Not sure what that was all about. It's possible the carriage was frozen up and took a bit to get moving.

[aug]

A picture of the tension carriage would be nice ..... Original bottom tension / drive was replace ten or more years ago with a drive tension terminal with Hyd.tensioning . that is as far as I will go in this forum K2

This post has been edited by aug: 14 January 2012 - 06:26 AM

[k2skier]

Pics coming soon. I thought tensioning was automatic, but wasn't sure if the carraige is positioned any other way than by the counter weight, I understand that ambient temp & line weight will cause the carraige to move accordingly.

A stuck caraige must be the explanation, beacuse on each ride we slowly rose higher. Must be a little lacking in pre guest line inspection!!!

[aug]

chair lift malfunctions should not be speculated by armchair mechanics on open forums, my 2 cents

[k2skier]

aug, on 14 January 2012 - 08:51 PM, said:

chair lift malfunctions should not be speculated by armchair mechanics on open forums, my 2 cents

So you lied huh, as far as you would go huh? Are you in charge of maintenance at Skibowl and this was your screw up?

FYI, I'm a professional mechanic for over 38 years, third generation owner of the 87 year old famiy business and I spent 3 years on a riblet in the 80's. PRETENTIOUS JERK!

[aug]

Thanks

[Kelly]

Hi I would like to add my 2 cents worth to this topic.
K2 thanks for the questions presented in post #1.
As for the pretentious comment in post # 6 - I will vouch on member Aug’s work history being very near 30 years of experience in the maintenance, construction and management of ropeways. Also I would like to mention member liftmech (see post #2 also this forums administrator) with over +20 years of experience in the maintenance, construction and management of ropeways. Heck let’s throw my experience in the pile as long as we are counting, this would be very near 40 years of experience in the maintenance, extensive engineering education, construction and management of ropeways. So we have a combined amount somewhere around 90 years of experience in the maintenance, construction and management of ropeways. I honestly don’t think anyone of us would be called pretentious.
Back to post #1 questions –
How is the carriage positioned? – I have not worked on this particular ropeway; however this type of carriage is commonly positioned manually. It has a limited range of motion. That limited range makes it visually easy to see that it is working properly – either it is placed correctly or the lift is undergoing some type of off-season maintenance procedure. The carriage position has absolutely nothing to do with tension of the haulrope. – See below.
This type of ropeway has a hydraulic rope tensioning system, there is no counterweight. This system is better described as an “active system” the description of automatic is a slight misnomer as it has a connotation of fast or speedy. Due to friction constraints combined with the length of this ropeway it may take up to one minute for any compensation of tension that would result in carriage movement…
I will post more later this evening after the playoffs -
Kelly

[vons]

I would comment but I think it’s better to let the flames die down, and Kelly will give a much more thorough answer to the original technical question far more eloquently than I.

BTW
There used to be some text book excerpts that explain tension and profile calculations on tramways.net but the site doesn't seem to exist anymore. The texts would have been a usefull explination for the curious and proffesonal.

This post has been edited by vons: 15 January 2012 - 08:52 AM

[Kicking Horse]

Attached is the file that VONS was talking about.

Attached File(s)

•  Manufacturers design formulas.pdf (308.85K)
  Number of downloads: 24
•  Physics Book.pdf (256.22K)
  Number of downloads: 14
•  US Army.pdf (1.11MB)
  Number of downloads: 12

This post has been edited by Kicking Horse: 15 January 2012 - 11:28 AM

[towertop]

k2skier, on 14 January 2012 - 10:10 PM, said:

So you lied huh, as far as you would go huh? Are you in charge of maintenance at Skibowl and this was your screw up?

FYI, I'm a professional mechanic for over 38 years, third generation owner of the 87 year old famiy business and I spent 3 years on a riblet in the 80's. PRETENTIOUS JERK!

Shame on you "MY 2ct"...YOU ASK? Are you in charge of maintenance at Skibowl and this was your screw up? Well I know for a fact that Aug workes with me... I am the lift maintenance supervisor at_______ I worked on my first lift in 1982, spent many years working for Doppelmayr, mechaniced at some of the worlds finest areas, and would like to think that in 30 years I have spent a few days in the trenches and know somthing about ski lifts. Since I am the tramway athuority at this area, also the inspector, and responable for 1500 passengers in the air at one time (since we have no agency that oversees what we do) Aug is the best right hand I have had the pleasure of working with. What did you call him, OH yea a PRETENTIOUS JERK, you don't even know this man... how about I call you a douchebag since I don't know you! You should probly stick to what you know and that is not ski lifts! Just my 2 ct. and you can call me whatever you want since I am an asshole, but stay away from my friends!

[Kicking Horse]

k2skier, on 14 January 2012 - 10:10 PM, said:

So you lied huh, as far as you would go huh? Are you in charge of maintenance at Skibowl and this was your screw up?

FYI, I'm a professional mechanic for over 38 years, third generation owner of the 87 year old famiy business and I spent 3 years on a riblet in the 80's. PRETENTIOUS JERK!

K2,

Why in the world would you pick a fight over nothing? You need to check your ducks and get them relined. Calling Aug what you did should get you banned from this place. Have you been wrenching on skilifts for those 38 years, or wrenching on other things?

Aug is a very well respected member here. Why in the world did you say what you said?

You made yourself look really bad here!

[Peter]

Let's steer this discussion back to the facts, please. Here are a few pictures of the summer setup for anyone who's still interested.

Attached File(s)

•  IMG_7851.JPG (358.11K)
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•  IMG_8029.JPG (367.91K)
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•  IMG_8041.JPG (333.39K)
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•  IMG_7546.JPG (246.51K)
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[Peter Pitcher]

I like the spirited discussion myself, I can understand why a lift that only has one tower span loaded, particularly a bottom drive lift and particulaly a Riblet would have a lot more sag on that section than usual. If the rope os removed from tower 10b for winter operations and the chairs are expected to clear the sheaves on 10b then they should clear by at least 5 feet under the most adverse loading condition which apparently is what is being described. I have certainly been called a pretentious jerk and alot worse and I have generally not been offended, I think the speaker of the insult is most ofen the true recipient.
My two cents?

[Kelly]

A continuation from post #8
Tension and carriage position are not related.
Tension and carriage movement can be related but are not instantaneous.
Understanding ropeway spans Part 2
Sag=Low tension…well maybe.
It’s helpful to remember that tension may not be the primary controlling factor for sag investigation – see below.
Some ropeway history
The formula for the sag in rope between supports was solved many centuries ago. For all practical purposes* it resembles a parabolic shaped curve so for this topic’s explanation I will reference that formula.
 Early-ropeway.jpg (237.74K)
Number of downloads: 41
 Sag calc 4 for excel.jpg (140.51K)
Number of downloads: 36
Sag in feet = (Weight per foot X Length between supports X Length between supports) / (8 X Tension) …S=(WLL)/8T…use feet and lbs for this equation**
Sag can also be controlled by tower spacing…notice the span length is squared in the equation above. Tower spacing most case relates better to the load at each tower.

Ropeway oversight by outside agencies
In Oregon the US Forest Service mandates a load test every 7 years or sooner for major modifications - any questions regarding incorrect tensioning or haulrope sag would have been seen and addressed at that time.

The perception the sag was “improving” each time you rode the lift.
Yes this perception is quite correct; implying it is related to a change in tension might be premature. Any load at any other point on the lift will always raise the longest span first – easy to do after the first group of powder hounds thins out over the next few runs and gets distributed along the lift at different spans.

Did someone drop the ball on setting up the lift for winter operation??!!
Nope – it’s either on the lower towers with the correct carriage position and tension or off of the lower towers and again with the correct carriage position and tension. Also see ropeway oversight above.

*Parabola or parabolic curves work quite well with flat spans under 1000’. For ropeways a catenary curve formula is used along with a slope correction formula, break-over angle, upline or downline, and more specific weight per foot formula as this gives more precise results. The parabolic formula is presented here because it is easier to understand for the lay person.
** You can play around with this formula and get some astonishing results if your input figures are not well understood.
Typical ropeway tension varies between 20,000 and 40,000 lbs…changing this value even by 1000 lbs has little meaning.
As a reminder tension for sag calculations is one-half the total tension of the system. Tower spacing varies between 100 and 400 ft with a 250 ft a well used average.
The weight per foot is the rope weight plus the carrier weight plus the rider weight.