6 replies to this topic

[Kelly]

One of my old posts on counterweights.

Counterweights:
YAN mini chairs (late 70s) have a grip hoist on the counterweight ropes that is attached to a hydraulic ram. The hoist was used to remove most of the slack from the haul rope with the ram doing the rest of the work. This was a static system.

YAN was one of the first to use a pneumatic (bottled nitrogen) tension system. Also one of the first to use "side plate roller chain" in place of counterweight ropes. The dynamic movement of the larger lifts is taken up in the space of a double tower span. The tension system is used to adjust for haul rope changes.

Seals of the large tensioning rams have proven to be very troublesome.

Side plate chains are extremely hard to inspect for cracks and are no longer being used in new installations.

Minor Denver had the great idea to save on costs by making a floating bullwheel just like you see on the platter lifts. Needless to say the bolts holding the axel to the bullwheel frame broke, the bullwheel took a flying saucer type trajectory into the unloading ramp.

Riblet engineers had a great idea of a side pull counterweight system - ala old KT-22 at Squaw Valley. This reduced the size and I might add the cost of the tension system. The load of the lift was supposed to counteract the side-pull of the counterweight system. This system usually worked except when the lift was rollback tested and wanted to rotate with this force, or when the side loads broke the tension carriage wheels and or bent the I-beam rails that they rode on, then bent the columns that supported the rails, then displaced the base foundations that the columns were imbedded into.

Poma's first hydraulic tension systems used pressure against a constant opening relief valve. This heated the oil past its breakdown temperature. Early lifts were run with there counterweight/tension stops bypassed until Poma engineers came up with the idea of a cooling fan for the oil.

Poma's later pressuring systems had a fan that was always on. This made the oil very cold on cold days, which tricks the system into thinking it has normal pressure. This makes the drive bullwheel slip on the haul rope usually under full load. This makes the lift mechanics crap there pants in seeing the possibilities for a uncontrolled rollback. Poma "fixed" this by putting a thermostat on the fan. This kinda worked unless it was to hot or cold in the motor room, again lift mechanics bypassed this system. Finally somebody got the bright idea that the thermostat should be actually in the oil that the fan was supposed to cool that the system worked.

Doppelmayr counterweight system always worked, regardless if the lift mechanics said the tension of the lift was wrong. To give lift mechanics credit they had the experience of changing grossly overloaded sheave wheels every other day or trying to talk the lift inspector into viewing the haul rope not touching a sheave wheel on a under loaded tower as a labor saving device. Some jurisdictions fixed this pesky problem by requiring "as built" surveys/load analysis of all new or modified lifts.

Garaventa counterweight systems copied the best of the other manufactures. Also they like to adjust there counterweights by adding or subtracting concrete as needed. See the counterweights on Squaws or Snowbirds trams for this crafty engineering fix.
Ryan B

[KZ]

Ryan, that is some more really cool information

With all the experience you had, can you say what resorts you worked at? It sounds like you know a lot about squaw.

[floridaskier]

Thats really interesting

[poloxskier]

I have noticed in a similar fassion to garaventa many of the older riblets in colorado I have noticed have had cinder blocks added to the top of the counterweight. Im guessing this is to account for the strech that has increaced in the cable.

[liftmech]

No, rope stretch and tension weight are not related. Ropes stretch as they get older and have more hours on them, but the tension needed to operate them stays the same. Tension is the force needed to 1) keep the rope from slipping in the drive sheave and 2) keep the rope securely in the sheaves on the towers.
The Summit daily profiles people around the county about their jobs periodically. Last fall they did Brad Henning over at Breck, and the picture they showed was of him raising the counterweight on 5-chair. The caption read, and I'm not kidding here, ' Henning explains that raising the counterweight increases the tension on the (haul rope).' So does that mean that gravity increases the further away from the ground you get? I'm pretty sure the reporter misquoted Brad or didn't understand his explanation, but it made for a good laugh in the shop the day it was published.

[liftmech]

I didn't answer your guess about the cinderblocks. Have you noticed if the underside of those counterweights has started chipping away? We will add blocks to the top to make up for that loss sometimes. Also, if an area adds more carriers to the line that will increase the amount of tension needed, and adding the blocks is easier than casting a new counterweight.

[poloxskier]

That makes sense. I didn't think through the physics of pulling tension on a streched rope before I posted.