12 replies to this topic

[rniemi]

Hi all,

Out of curiosity, does someone here on the forum maintain the glossary on skilifts.org? Is that Bill? That's an excellent idea to illustrate everything in the new set of photos for each term, good work! My mistake if the photos were up previously, I don't remember seeing them there until my most recent visit to that page.

I noticed that the RPD photo was incorrect. In the photo is a limit switch configured as a deropement switch for the rope catcher. I may have an RPD picture around here somewhere if I dig around a bit, if no one else has one handy.

As a side-note, does this deropement switch layout appear often? It would appear that a deropement on this setup will destroy the arm on the limit switch (if not break off the switch shaft itself), possibly causing only an intermittent break in the tower circuit. I can also see a possibility that rime ice could result in the arm bending during a deropement without actuating the switch.

Cheers,
-Ryan

Image below linked to: http://www.skilifts....lossary/rpd.jpg

This post has been edited by rniemi: 12 August 2009 - 03:43 AM

[Allan]

This setup was the norm on Thiokol and maybe even early CTEC negative assemblies...

[Bogong]

Thanks for the glossary, it's an invaluable resource that makes things much easier to explain.
I frequently refer people to it myself, even if a few terms are different to those used in Australia.

However I think your item on rope tows is a bit inadequate as it doesn't differentiate them from nutcracker tows.
You still have a few operating in the USA and we have lots operating in "club fields" in Australia and New Zealand.

Here is an explanation of Nutcracker Lifts that I wrote on the Wiki Ski Australian ski lift directory Feel free to copy it or adapt it.

Nutcrackers. Some modern skiers who don't venture beyond the main resorts are unfamiliar with nutcracker tows. Most resorts in Australia and New Zealand began with them. While they have been replaced at the big resorts, nutcrackers can still be found at 'club fields'. A nutcracker is a device attached to a belt worn by a skier that clamps onto a moving rope at waist level, allowing the skier to be towed uphill. The height of the rope and the pulleys that support it is adjusted according to snow levels. While it may not be necessary to use a nutcracker on short, gently graded rope tows, it is impossible for skiers to hold onto a rope with their hands on steeper tow lines or where the rope passes over a pulley. Nutcrackers explained

A couple of pics (not cleared for copyright, but I can provide similar ones on request)
.
.

[Bogong]

I hate to be picky about such a terrific site but its says...

J-Bar
A type of surface lift created in the '40s.

My avi shows a J-Bar in operation in 1938. (Don't you love the wooden towers!)
But it was Australian, so they may not have made their way to America until the 40's.

[rniemi]

Allan, on 12 August 2009 - 05:14 AM, said:

This setup was the norm on Thiokol and maybe even early CTEC negative assemblies...

Hi Allan,

Interesting. Did deropements result in catastrophic carnage to the switch arm? Based on the geometry of the rope catcher and where the switch is placed, it seems as though damage to the switch or arm is certain.

-Ryan

[Kelly]

This is an example of a “resettable” derail switch.
Member SkiBachelor maintains the Glosary and I suspect that a change is coming soon.
The standard change recommended derail switches (none addressed before) in the early 70’s.
Mid 1980 standards and the language morphed into the Rope Position Detector (RPD) and away from the derail switch wordage but is still used as a interchangeable word.
As viewed in the year 2009 their certainly could be many improvements made to this design…as viewed in 1973 it was much better than nothing and still appears on many grandfathered or none jurisdiction ropeways.
Actual contact body “A” is protected by sheave geometry.
Rope rides over catcher “if” it lands on catcher…sometimes deropements can be rather violent.

A – water-tight body for contacts that are opened by pivot arm (or plunger)
B – Adjustable bracket that is attached to pivot
C- Trip arm that attaches to bracket
D- Cable catcher – design prevents assembly from excessive rotation, or stop bracket or bolt prevents excessive rotation. Catcher design also is slightly outdated as the rope has a high possibility of jamming in-between the sheave and sheave support arm. A slight deflector tab (seen on all new lifts) prevents this from happening.

Attached File(s)

•  ABCD.jpg (358.59K)
  Number of downloads: 50

[rniemi]

Kelly, on 12 August 2009 - 05:46 PM, said:

This is an example of a "resettable" derail switch.
Member SkiBachelor maintains the Glosary and I suspect that a change is coming soon.
The standard change recommended derail switches (none addressed before) in the early 70's.
Mid 1980 standards and the language morphed into the Rope Position Detector (RPD) and away from the derail switch wordage but is still used as a interchangeable word.
As viewed in the year 2009 their certainly could be many improvements made to this design…as viewed in 1973 it was much better than nothing and still appears on many grandfathered or none jurisdiction ropeways.
Actual contact body "A" is protected by sheave geometry.
Rope rides over catcher "if" it lands on catcher…sometimes deropements can be rather violent.

A – water-tight body for contacts that are opened by pivot arm (or plunger)
B – Adjustable bracket that is attached to pivot
C- Trip arm that attaches to bracket
D- Cable catcher – design prevents assembly from excessive rotation, or stop bracket or bolt prevents excessive rotation. Catcher design also is slightly outdated as the rope has a high possibility of jamming in-between the sheave and sheave support arm. A slight deflector tab (seen on all new lifts) prevents this from happening.

Hi Kelly,

Roger that on RPD vs. derail switch terminology interchangeability in the past. What caught my attention is that it appears a deropement will destroy the trip arm or will bend/break the pivot shaft where it enters the IEC switch body. Since the catcher doesn't appear to extend below the sheave support arm, I would expect the top of the rope to be roughly at the same height as the bottom of the sheave support arm after a deropement. It appears that rope position is outside the range of motion of the trip arm and may rip off or bend the trip arm.

Depending on the laterial positioning of the switch body (which isn't clear without a vertical photo looking up), I would imagine one of these two scenarios would occur during a deropement:

- If the trip arm hub is set back (toward the center of the tower) from the sheave support arm, which I'm fairly sure it is, then the trip arm will swing up and impact the sheave support arm, at which point the rope will bend the trip arm upward as it continues toward the rope catcher.

- If the trip arm hub extends beyond the sheave support arm, the same thing will occur but with the added posibility of the rope striking the hub. Trip arm would swing fully upward and the rope would bend the trip arm as it continues toward the rope catcher.

Possibly the angle the photo is taken at is deceiving and I'm misjudging the range of motion of the trip arm. At the moment I'm unable to picture how the rope can reach the catcher with the trip arm remaining within the range of rotation of the switch. If this is indeed a resettable design and the trip arm survives, then it would appear likely the angle or photo is playing tricks on my interpretation of the geometry.

-Ryan

This post has been edited by rniemi: 12 August 2009 - 07:16 PM

[rniemi]

Kelly, on 12 August 2009 - 05:46 PM, said:

This is an example of a "resettable" derail switch.
Member SkiBachelor maintains the Glosary and I suspect that a change is coming soon.
The standard change recommended derail switches (none addressed before) in the early 70's.
Mid 1980 standards and the language morphed into the Rope Position Detector (RPD) and away from the derail switch wordage but is still used as a interchangeable word.
As viewed in the year 2009 their certainly could be many improvements made to this design…as viewed in 1973 it was much better than nothing and still appears on many grandfathered or none jurisdiction ropeways.
Actual contact body "A" is protected by sheave geometry.
Rope rides over catcher "if" it lands on catcher…sometimes deropements can be rather violent.

A – water-tight body for contacts that are opened by pivot arm (or plunger)
B – Adjustable bracket that is attached to pivot
C- Trip arm that attaches to bracket
D- Cable catcher – design prevents assembly from excessive rotation, or stop bracket or bolt prevents excessive rotation. Catcher design also is slightly outdated as the rope has a high possibility of jamming in-between the sheave and sheave support arm. A slight deflector tab (seen on all new lifts) prevents this from happening.

Hi Kelly,

I see a possible way I may be misinterpreting the photo, does the rope catcher actually extend *below* the sheave support arm, allowing the trip arm to swing up into the gap between the rope and the sheave support arm during a deropement? It's hard to tell with the red arrow in the photo. That could explain my misinterpretation of the geometry.

Cheers,
-Ryan

This post has been edited by rniemi: 12 August 2009 - 07:46 PM

[Allan]

The catcher does extend below the support arm. The deropement we had on our assembly just like this did result in a bent trip arm but the switch survived. Attached is a pic of an assembly with RPDs from the same type of lift. And a different angle of the negative assembly switch. We replaced the RPDs with newer CTEC brittle cards (also pictured) as the pictured RPDs can fail in the unsafe position.

Attached File(s)

•  Paradise - Tower 15 downhill.JPG (316.3K)
  Number of downloads: 94
•  Paradise - Depression Tower.JPG (299.15K)
  Number of downloads: 137
•  IMG_0805.JPG (2.12MB)
  Number of downloads: 117

[rniemi]

Allan, on 12 August 2009 - 08:01 PM, said:

The catcher does extend below the support arm. The deropement we had on our assembly just like this did result in a bent trip arm but the switch survived. Attached is a pic of an assembly with RPDs from the same type of lift. And a different angle of the negative assembly switch. We replaced the RPDs with newer CTEC brittle cards (also pictured) as the pictured RPDs can fail in the unsafe position.

Thanks Allan (and Kelly), that explains it. That confirms my suspiscion that the trip arm may suffer damage and the design is subject to a non-failsafe failure mode.

Cheers,
-Ryan

[pomafr]

Allan, on 12 August 2009 - 08:01 PM, said:

The catcher does extend below the support arm. The deropement we had on our assembly just like this did result in a bent trip arm but the switch survived. Attached is a pic of an assembly with RPDs from the same type of lift. And a different angle of the negative assembly switch. We replaced the RPDs with newer CTEC brittle cards (also pictured) as the pictured RPDs can fail in the unsafe position.

Are those brittle cards just printed circuit board?

[Allan]

pomafr, on 18 September 2009 - 08:04 AM, said:

Are those brittle cards just printed circuit board?

Yes they are!

[EagleAce]

Here's an RPD from the old Eagle (I miss that lift! ) at Badger Pass

Attached File(s)

•  Eagle_RPD.JPG (145.27K)
  Number of downloads: 36