84 replies to this topic

[liftmech]

Aussierob, on Mar 10 2005, 06:35 AM, said:

The particular reason for pomas not going backward is the pressure rail is too steep where the grip is closing in forward operation. In reverse the steep angle applies too much forrce too quickly to the op roller. (pomas have a direct acting operating "arm" hence the steel roller on top.)

:D
<{POST_SNAPBACK}>

:blinksmiley: Which grip do you have on your Pomas? The Eagle and Flyer (TB-41) have compression rails which are the same ramp angle forwards and backwards. Mechanically, I don't see any reason why the grip wouldn't open in reverse as the ramps are mirror images of each other, and the departure side opens the grip up nicely prior to closing it on the rope. Hate to disagree with you, but that's what I've seen.

[highspeedquad]

I also thought that the Omega T grips also functioned like that, the opening/closing ramps had the same opening/closing angle. So I don't think that there would be a grip problem.

[Duck]

I was kinda scratchin' my head on that one, too. I seem to remember watching the Poma's at Blue and how the cam follower would get driven down, and release up at the same rate (meaning the ramp angle is the same in either direction).

-Iain

[Aussierob]

So I double checked with one one of our Lift maintenance supervisors and he said it's because af the asymmetrical pressure rail. It is steeper on the closing side. There may be other reasons we are unaware of.

[highspeedquad]

I've looked at countless Poma grips open and close, and like others have said, they seem to have the same angle either way.

[Mike]

Poma grips/terminals can be run in either direction. I've seen Poma's grip test rig setup. It runs the grip both directions through the compression rail so that tells me that it's OK to run it in reverse. The compression rails on all the Poma's I've seen are the same on the incoming and outgoing side of the lift.

[highspeedquad]

So there is no problem with the grip, it's just that Poma just doesn't want their lifts to run in reverse. If it is going to win customers, why don't they do it?

[Doppeldork]

Some Poma FG's can be run in reverse. There is also a dog on the gearbox and you pull the handle up to disengage.

And I do have to ask Who would run a chair in reverse with people on the line?

This post has been edited by Doppeldork: 12 March 2005 - 12:05 AM

[poloxskier]

Keystone has run the Montezuma in reverse when I have been on it but I dont know why they did. Maybe it was a problem they noticed with a carrier and had to take it off the line after it had passed the parking/maintenance rail. The people on the chair with me were freaking out until I told them about the sign at the bottom. They ran it very slow in reverse, probably so it wouldn't feel like a rollback

[liftmech]

highspeedquad, on Mar 11 2005, 09:03 PM, said:

So there is no problem with the grip, it's just that Poma just doesn't want their lifts to run in reverse. If it is going to win customers, why don't they do it?
<{POST_SNAPBACK}>

Who said it was a customer thing? I wouldn't want my lift to run in reverse either. There were enough rollback issues in the early days and even into the 70s to get most people thinking about how to prevent them. Correct me if I'm wrong, but reverse operation is a design and engineering item and not a customer relations issue. Most peole don't buy Doppelmayrs because they can run in reverse; they buy them because they like their product overall.

[Aussierob]

Operationally running in reverse is to be avoided if at all possible. we have a deatch quad we allow people to download on, and if we get a grip force or grip guage fault we have no option other than to reverse it back to the station. Prior to opening reverse is great for fixing spacing problems or if a chair stalls in the station at start up. Its also great for breaking out frozen sheaves. Give it a whole lot of little bumps in alternating directions. If its a poma, get out your dead blow and start climbing.

Having a reverse function in no way increases the risk of a rollback. Drives and anti rollback systems are pretty bomber these days. A number of things would have to go very bad for a rollback to occur

[Mike]

Aussierob, on Mar 12 2005, 06:41 AM, said:

...Its also great for breaking out frozen sheaves. Give it a whole lot of little bumps in alternating directions...<{POST_SNAPBACK}>

So sawing into the sheave is better???

[Aussierob]

Our sheaves tend to get rimed more than frozen with ice and bumping the lift will remove it an allow the sheave to rotate. Only in extreme conditions (maybe once per season) do we have to get out and bang sheaves. Also Dopps have smooth sides unlike the gusseted ones found on some pomas, so they tend to free themselves pretty easily. I can't remember the last time we replaced a flat spotted sheave caused by it being jammed by rime or ice.

Further discussion with our lift maintenance manager today revealed that another reason Pomas don't go in reverse is their clutching system is one way only so the carriers would need to be pushed through the turnarounds. He did say that Poma would provide a reverse function if you want it. We are currently looking into the possibility of having reverse capability put on the village gondola. He also confirmed that the asymmetrical rails are one of the reasons they don't go backward.

[highspeedquad]

Oh, so they are steeper one way. But you can get it if you ask for it, right?

[Aussierob]

I was told that you could so I guess so. It would be kind of silly to lose a sale over it.

[highspeedquad]

Has anyone ordered a Poma with the capability to operate in reverse?

[Cameron]

I have seen a mid-80s Dopp in Australia (fixed grip triple) run extremely slowly in reverse over night. I was told that it's done on nights when precipitation is expected, in order to avoid the lift freezing up.

It was really slow, though.

Cameron.

[floridaskier]

Is there a reason that they would run a lift in reverse at night like that to keep the ice off instead of forwards, besides stopping people from catching a free ride up?

[highspeedquad]

Yeah, it seems kind of weird that they run it backwards instead of forwards. Why can't they just run it normally? I would think that it would be easier.

[Mike]

highspeedquad, on Mar 14 2005, 07:05 PM, said:

Yeah, it seems kind of weird that they run it backwards instead of forwards. Why can't they just run it normally? I would think that it would be easier.
<{POST_SNAPBACK}>

I would guess it's so people don't try to load.