22 replies to this topic

[Lift Dinosaur]

egieszl, on Feb 5 2008, 07:38 PM, said:

I'm pretty sure Chair 21 (Yan FGT) at Mammoth Mountain has a flying return line and is a top drive.

Eric

GOT PICTURES? Which lift is Chair 21? I worked on the installation of a few of them.

Dino

[chasl]

aug, on Jan 16 2008, 02:50 PM, said:

As much as I regret in correcting the previous statment ,I must. (So whether the system is a top drive pulling the load up the hill or a bottom drive pushing the load up, should make no difference in the operation.) Regardless of where the drive sheave is on any lift using a rope, you must pull. In a bottom drive the bottom BW pulls the Haul rope up and around the top BW. One of the most compelling reasons to have a top drive is the increased tension on the top BW vs. the bottom BW. One of the dis-advantages of a top drive is the surge that is created in the slack line going down the hill to the return (bottom) terminal when the lift is slowed or stopped. In my observations over the years the surge in bottom driven lifts is less than in top driven lifts .

I will agree that with a top drive lift, there tends to be more surge than with a bottom drive. In the older lifts that is no more evident than in one of the Riblets with a top drive / bottom tension with a mass CWT.
Newer systems with hydraulic tension do not have such a dramatic line surge because of flow rates within the valve systems, also one of the reasons why ropes now come in XXIPS.
You could be correct the bottom drive system may pull from the return side. Some engineers will argue that in the initial stages of movement the bottom drive system pushes the load, hence the slack line in the loaded side. This is a lot like the hen and the egg.

Although I still believe that this causes no problems with OPERATION provided you have the correct mass or tension on the cwt. or ram.

Top drive systems have more surge on the return side, bottom drive systems more surge on the loaded side, (I agree not as much) but I feel the customer does not feel the surge in the slack line of the return side, and if one has the proper loads on their sheaves still no problem.

I was to understand we were talking about rope slippage, not line surge, which should be no problem with a proper design, unless problems arise such as super cold or incorrect oil viscosity, poorly maintained hydraulic systems (water, dirt) or someone adjusts pump parameters incorrectly. Also when I say surge I am talking about starting surge.

I may be incorrect, but one of the main reasons for a top drive is that less HP is required to operate the system (less HP lower initial cost plus less operating costs, owners love that). On this I may be corrected, not sure.

[2milehi]

chasl, on Feb 6 2008, 02:22 AM, said:

...You could be correct the bottom drive system may pull from the return side. Some engineers will argue that in the initial stages of movement the bottom drive system pushes the load, hence the slack line in the loaded side...

You can't shoot pool with a rope.