82 replies to this topic

[skierdude9450]

Isn't it also better to have a top drive engine because it's pulling the loaded side?

[Lift Dinosaur]

Emax, on Sep 13 2006, 09:50 AM, said:

This is certainly not my area of expertise, but it seems to make common sense that the preferred location would be the bottom - allowing the weight of the rope to assist in creating tension. Top tensioning must first overcome the rope's weight before any additional tension can be applied - requiring a much more robust apparatus.

How about it, Lift Dinosaur?

You are correct, and as stated elsewhere, the prefered design is top drive, bottom tension. And the key to drive location is power supply, as RyanB stated. The other consideration is whether or not the lift manufacturer has a drive/tension station design available. On some older lifts, this was not possible. So if you had a fixed bottom drive, you ended up with a top return/tension. Top tensioning requires more force, which in some cases also increases rope diameter to comply with required safety factors.

[chasl]

Lift Dinosaur, on Sep 14 2006, 11:20 AM, said:

You are correct, and as stated elsewhere, the prefered design is top drive, bottom tension. And the key to drive location is power supply, as RyanB stated. The other consideration is whether or not the lift manufacturer has a drive/tension station design available. On some older lifts, this was not possible. So if you had a fixed bottom drive, you ended up with a top return/tension. Top tensioning requires more force, which in some cases also increases rope diameter to comply with required safety factors.

LD,
Let's add something else for thought.
If you remember the older top drive with bottom tension lifts (I have not seen a new one lately) the carriage movement at the bottom was a sight to see. ** would you be able to build one today with hydraulic tension**?
And if you did build a TD/BT with Hydraulic tension lift what would have to happen to the rope diameter to handle the forces from the limited carraige movement?

[floridaskier]

chasl, on Sep 14 2006, 02:15 PM, said:

If you remember the older top drive with bottom tension lifts (I have not seen a new one lately) the carriage movement at the bottom was a sight to see. ** would you be able to build one today with hydraulic tension**?

Maybe you meant something else, but aren't a lot of lifts currently built with top drive and bottom hydraulic tensioning?

[Lift Dinosaur]

chasl, on Sep 14 2006, 12:15 PM, said:

LD,
Let's add something else for thought.
If you remember the older top drive with bottom tension lifts (I have not seen a new one lately) the carriage movement at the bottom was a sight to see. ** would you be able to build one today with hydraulic tension**?

The older lifts with TD/BT that had some extreme carriage movement ("a sight to see") were generally of the a) lots of towers (125'-150' spans), b) relatively low tension (@24.000 #), and c) small rope diameter (1" - 1 1/4"). In the mid 70's an upstart Polish engineer who had formed his own company, named after himself, started using a) fewer towers (225'-275' spans), b) higher tension to keep the passengers from dragging on the ground (36,000#-56,000# using either concrete counterweights or hydraulic/pneumatic cylinders), and c) much larger rope diameters to compensate for the increased tension (1 7/16' - 1 5/8'). These were mainly on the triple chairs.

"And if you did build a TD/BT with Hydraulic tension lift what would have to happen to the rope diameter to handle the forces from the limited carraige movement?"

Modern lifts in a TD/BT arrangement routinely use hydraulic tensioning. The carriage movement is minimumized through the use of a gas-over-oil accumulator which absorbs the changes in pressure due to line-load changes and stops. Rope diameters now run in the 1 5/8'-40mm to 2'-50mm range.

[liftmech]

chasl, on Sep 14 2006, 12:15 PM, said:

LD,
Let's add something else for thought.
If you remember the older top drive with bottom tension lifts (I have not seen a new one lately) the carriage movement at the bottom was a sight to see.

I once operated an '84 CTEC that had exactly the characteristics you're describing. It was 1150' vertical, 5100' long, and when you hit a stop at full speed the carriage would rocket first forwards, then backwards. If a chair was near the load board it would knock the skiers over. The control panel was also attached to the carriage, so we ops became very adept at stepping out of its way.

The Flyer, at 9950' or so and 1910' vertical, does not have this kind of carriage movement due to the smooth tensioning of the hydraulic cylinders. I've seen the carriage move six inches over the course of the day, but that's mainly due to haul rope movement as the day warms up or cools off.

[Allan]

Our Thiokol has the same extreme carriage movement... luckily the controls aren't attached to it... I did see many people bowled over by chairs though.

[cjb]

Lift Dinosaur, on Sep 14 2006, 03:09 PM, said:

In the mid 70's an upstart Polish engineer who had formed his own company, named after himself, started using a) fewer towers (225'-275' spans), b) higher tension to keep the passengers from dragging on the ground (36,000#-56,000# using either concrete counterweights or hydraulic/pneumatic cylinders), and c) much larger rope diameters to compensate for the increased tension (1 7/16' - 1 5/8'). These were mainly on the triple chairs.

We load tested all of our lifts the last couple years (all yans) and the most carriage travel we saw was about 6 inches. Most lifts had nothing. I guess Yan had something there.

[Lift Dinosaur]

Nice find, EMAX. Thanks for sharing!

Dino

[spark's]

Well what iv'e seen as a electrician is the fact of you can not get the power you need half the time and nor where u want it the other half. Meaning its up 2 the MT. how much they want 2 shell out 2 your local power comp 4 the power where u want and etc. cost's 4 transformer's and dissconnect's and so on (copper is not cheap). On a smaller mt. it's not so much of a prob, bottom drive is the way. On the older (i haven't seen a new fixed in a while) poma's fixed say quad say 80's the hydrolic tension and drive are both at the top or bottom not separate. The reasoning behind (from what i've seen and it's only my reasoning) the whole lorry move's. With tension on a detach it is just a bullwheel that travel's. So if you put 2 of the same lifts (fixed) and on the same slope 1 top drive, 1 bottom there really isn't much of a difference maybe a extra compresion tower on a bottom drive why i dont know i'm not a engineer. But there would not be a diff in the Hp of the moter, cap 2'3'4 whatever, the load is the same. There is not a size diff in the cable (this is only what i've seen and i'm very involved with or in house NDTing, 2 guy's cert) . Here is my point that is why we have tension system's( and 4 rope stretch and the difference in a load a lift see's all day) it is so that a 400 Hp moter or 500 Hp moter or 900 Hp moter can drive that rope around and it's load whatever the length maybe. A counter weight system is a whole different animal from a Yan 2 a Borvic etc. It is a set weight that is your tension, it is a whole different animal than a hydrolic it may only take a hydrolic lift say 1,540 pound's of pressure 4 a hydrolic system 2 tension a lift and a 30,678 pound counter weight 2 tension a true counter weight system, (same load. weight of the the true counter weight is also depending on the the load). From again what i've seen there is not enough room nor is it practical 4 a detach 2 have that much "stuff" in 1 lorry. The drive and tension system on 1 end top or bottom would be just 2 much and again from what i've seen ur average poma, ctec, dopp, u will find the tension oppesite of the drive. Why i'm not sure but there is no diff top or bottom drive on a detach ctec, garaven poma, etc. U will find the tension oppasite (a detach is a Lot more complicated than any other a true 1 of a kind). Then again i'm no engineer but i've been in the bis for 12 yr's and some of my co hort's 22 too 37 yr's(now that's time served) any ? i'd love 2 answer exserpt where i learned how 2 spell LOL. PLs just ask....

[skiersage]

As far as I am concerned, pretty much any fixed grip lift is capable of using a bottom drive. I may be wrong but look at the burfield quad at sun peaks. it is the longest fixed grip in North America and it has a bottom drive. This leads to my conclusion. As for detachable lifts go, I have no idea but I know there are long ones that use a bottom drive out there.

[garthd]

OK, I'd like to ask a different question about tension. What would happen if a tension system failed? Would the chairs hit the ground?

I have heard a story about an old gondola in NH that went something like this. The guy I know who told me this story was working in the rental shop, which was located at the bottom terminal of this gondola. Two skiers came in, rather flustered, and demanded to know where the mountain manager was. The skiers then told my friend that they were minding their business, riding the gondola when all of a sudden the cabin was falling towards the ground. It then sprang back up. The lift kept moving, and then the cabin fell again and hit the ground. It then sprang up again. These guys got off at the top, skied down and found the manager to complain. My friend said later that day he was talking to the gondola attendant, and he told him that story. The attendant proceeded to say that he did see the concrete counterweight rocket up and then go back down into its hole, only to do the same thing again.

I was skeptical about this story, but I wanted to know if this is possible. And by the way, this lift is no longer in service.

[LiftTech]

Definitely “possible”. If the counter weight or carriage is frozen in or otherwise hung up on something, and after the lift is loaded it released... Very, very important to look very close at these things on the morning preoperational inspection. If you do not you have built the world’s largest slingshot.

[liftmech]

To Garth's question about what would happen if a tension system failed:
On a hydraulic lift, it would depend upon which part failed. If a hose bursts, the rams have 'parachute valves' (flow-activated safety valves) on the pressure inlet. These are designed to close upon rapid depressurisation of the ram and keep the carriage from moving forward. If a component of the pump and piping system fails, most likely the carriage would bleed forward slowly until either the low-pressure cutoff stops the lift or the carriage contacts the carriage stops. Not too spectacular.
If a counterweight system failed, however, you would quite possibly have what LiftTech calls the world's largest slingshot. There are few parts to a counterweighted system; there is the weight, the tensioning rope, the assorted blocks to bend the rope(s), and the fist grips/Crosby clips to tie back the live and dead ends of the rope. Off all of those, the fist grips are most likely to fail, either from overtightening or undertightening.

There is one special case of a counterweight with different parts. This would be the Yan setup utilising RC-240 roller chain to connect the carriage and the weight. It's still quite simple, though; instead of cable clamps/clips there are bolts of high-grade steel connecting the various parts.

[garthd]

Thanks alot for the information. Lifts are not my area of employment, but I have always been fascinated by them. I'm still trying to learn as much as I can about their different aspects...and what a great place I've come to for just such an education!

[liftmech]

Most definitely. The last such test I know of was the old Eskimo double over at WP in 1990; some of our forum members weren't even born then.

[lastchair_44]

I was 7!!!

[liftmech]

14...

[Jonni]

One of the young ones at 4 years of age