17 replies to this topic

[SkiBachelor]

Well, when Bill and I were hiking Mt. Hood this past summer, we came across this type of sheave train on all the Poma HSQs at Meadows and never really knew what it does. Does anyone know the reason behind this and why Poma is the only company to do something like this? I guess John is the only lift mechanic that works on Poma HSQ's so I thought you might be able to help Bill and I solve this question. Anyone else can take a stab at it too if they know or think what it does.

It just seems kind of weird to have a sheave train set up this way rather than how we normally see it. B)

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[KZ]

The only thing i could guess would be to help keep the rope tensioned

[SkiBachelor]

Yea, I guess they probably want to the grip enter perfectly rather than be off by a little. Doppelmayr has that funnel for the grip so that straightens out the chair while Poma doesn't and this is probably their answer.

[Kicking Horse]

here is a another pic. i seems to be that most of the poma lifts @ WP has this.

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[Kelly]

Assembly and tower design shown in the picture is a package that works as a complete terminal design.

It often used with large profile changes: 1 degree per sheave = 12 degree profile change.
It saves on engineering and manufacturing costs by putting a large (walking beam) assembly that carries primary hold down assemblies, this eliminates 1 tower (x-arm, ladder etc).

The distance from the haul rope to the adjustment axel requires careful alignment and constant inspection of this design. The grips passing under the sheave can and usually do impart out of plane or "side flex loads" on the assembly and tower.

Notice that the assemblies are a support "style". The axels holding the secondary sheave assemblies have a high degree of rotation which will cause considerable wear if not lubricated frequently.

For the lift mechanic this style of tower can be a pain-in-the-ass to change sheaves or assemblies, because of non-intuitive load changes due to offset axels.

Ryan B

[Kicking Horse]

if i remember right the Timberline HSQ @ copper uses this also. And I think that is a Dopp Lift.

[floridaskier]

The Flight of the Canyons 1997 gondola has it too. And it's got like 18 sheaves on it. I think Tombstone Express at The Canyons has it to, but I can't quite remember exactly

[SkiBachelor]

Well, I wasn't talking about the integrated tower that is built into the terminal, but rather on how the haul rope comes out of the terminal going down and then going up. If you look at the sheaves, you will know what I'm talking about. Sorry for confusing you, it's kind of hard to describe.

[Allan]

Maybe so there's a bit more friction between the haul rope and the Power Take Off Sheaves (The sheaves that drive the tires).

[liftmech]

That is exactly the reason. I actually took a class this spring on aligning Poma terminals, and Jim told us that on the Omega terminals, you want to have at least a -4 degree angle on the rope as it leaves the terminal to maintain pressure on those PTO sheaves. That also ensures that there is no 'wandering' of the rope happening as it does on the older lifts. The Flyer was redesigned a few years ago to have this same feature, although it still has Tower 1 instead of the reaction arm.

What Ryan says about the reaction arms being difficult to work with is quite true, unfortunately...

[Kelly]

SkiBachelor:
Sorry about the first post.

What we are looking at is a negative cord angle of the haul rope.
As a lift gets designed, each tower cord angle has a critical relationship with the tower below and above it.
For a full load condition on the up-line side of this tower, the haul rope will want to sag away from the tower towards the ground; the tower is lowered so the minimum design sheave weight is maintained to prevent the haul rope from moving out of its groove, (quite common on some lifts). In effect this tower is preloaded so it can produce the proper sheave load in all loaded conditions.
It's possible this design could also be accomplished by putting a compression style assembly at this tower; however this would complicate the tower design as it would have to be built to accept both positive and negative loads.
This style of tower is an elegant engineering solution – the negative load that the haul rope imparts on the tower is canceled out by the weight of the assemblies and tower components. No support to the ground is needed.
The negative cord angle also preloads the assembly that is in the terminal, this sheave load can become negative when a large load passes the center pivot line of the tower in the image. Again remember each tower has a close relationship with the towers next to it.

Top drive, bottom tension lifts will induce extreme dynamic negative loads on down line terminal assemblies. The drive system will also lift the counterweight at it tries to pull the load uphill.

YAN has many towers that were similar to image but the tower is hinged at the terminal cross arm. The tower just floats on the haul rope! This provides a constant weight on the haul rope regardless of loaded condition.

Definitions-
Cord Angle: the change of angle between the slope of the haul rope and horizontal; measured at the tower cross arm.
Breakover cord angle: difference in cord angles between towers. Also called breakover.
Up-line: the haul rope that goes up the hill.
Down-line: the haul rope that come down the hill. Also written as Dn-line.

Up hill: an object that is up-the-hill from you.
Down hill: an object that is down-the-hill from you.

Dead load: weight from all of the components of the structure and or object. For a lift the haul rope is under tension but no loads are in the carriers. Also written as D.L. or DL
Live load: weight that is added to the structure. Due to the dynamics of a lift it can be negative and positive. Also written as L.L. or LL
Total load: DL+LL

Profile: a side view of lift showing towers, cord angles, loads and ground.

Example of a tower load "call out" from profile of Ski Bach image.
T-1 Up-line 6+6 hold down DL= -6000 lbs LL= +4800 lbs TL=-1200 lbs <10
T-1 Dn-line 6+6 hold down DL= -6000 lbs LL= -6600 lbs TL= -12600 lbs* <10

*Note to construction crew and lift mechanics: STRUCTURAL DAMAGE will occur if haul rope derails and misses cable catchers on up-line assemblies when lift is in a loaded condition. This will impart an unbalanced load that will exceed tower design. FAILURE WILL OCCUR if lift is started. We recommend a counter weight with lifting eye under each side of this tower to facilitate re-railing.

T-2 Up-line 4support DL=+1000 lbs LL=+4000 lbs TL=+5000 lbs <2
T-2 Dn-line 4 support DL=+1000 lbs LL=+4000 lbs TL=+5000 lbs* <2

*Note to construction crew and lift mechanics: down line TL will only occur if carriers are loaded in both spans.

Ryan B

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[SkiBachelor]

Thanks Ryan B. :)

[KZ]

very very good info ryan

[coskibum]

Ryan B, do you use LRFD or ASD when the live and dead loads are calculated?

[floridaskier]

Skibachelor: Poma doesn't have the same type of entry funnel as Doppelmayr, but they still have one. It's not solid and it's not bright orange like of a Doppelmayr, but it's just two arms that positionthe grip the right way. all HSQs have them

[SkiBachelor]

Well the top terminal isn't set up this way, only the base terminal and I was just wondering why. It's kind of like the Yan HSQ. The bottom end went up while the top end was flat. Although not all Poma HSQ's have this though. I think only with the new Omega terminal design and up. I don't ride a lot of Poma HSQ's because the only resort here in Oregon that has them in Meadows.

[floridaskier]

I've only ridden 1 in my life ,and a gondola. Soon to be more this spring break :D

If I remember correctly, the Yan at DV went down at the top terminal a little bit just like the top terminal went up.

[Kelly]

coskibum:
Good question! I will reply by starting new topic.

Ryan B