Detachable Grip Compression/Hold Down

TomWhite

This YouTube on Liftblog is entitled “…heating”, which I presume are the two yellow strips to the right. What I couldn’t see is how the grip is being held in the compression position. I’m used to seeing a continuous bar holding down the white top right roller down. What does this system use? Is there latch, or similar, that locks it down then releases at the other end?
https://liftblog.com/swift-current-6-big-sky-mt/comment-page-1/#comment-192627

Jonni

It has to do with how the grip is setup and what direction the springs are pushing against the fulcrum in the grip itself. On Leitner-Poma grips (and Doppelmayr Agamatic grips for that matter), typically the springs are acting on the grip in an up and down position perpendicular to the fulcrum (or slightly diagonal to the fulcrum) which is right next to where the haul rope is. Meaning that when the springs are compressed via the compression roller on top of the grip it momentarily opens the grip, the haul rope is moved out of the way, and then compression is released thereby closing the grip. If you were to draw the setup on an x/y axis, the fulcrum would be at 0,0 and the compression roller on top of the springs would travel up and down on the y-axis without going lower then 0. The springs are always wanting to push the lever that acts on the grip up (positively) in order to keep it closed and to never allow the compression roller to have a 0 or negative position on the y-axis.

The Doppelmayr D-Line grip on the other hand works with the idea that there’s an open and closed position based on the location of the fulcrum in the grip. The main compression springs are diagonally positioned like many other grips but the fulcrum is positioned slightly higher up in the grip so that the springs can be compressed and pivoted down past the fulcrum point. This allows the grip to have an “open” position while in the terminal and makes the grip act almost like a switch that will either snap open or snap closed depending on what position it’s closest to. Going off of my example of the x/y axis above the fulcrum would still be at 0,0 but the compression roller on top of the springs can be pushed on the y-axis below the 0 mark such that the springs now are in a position to want to pull down on that lever and keep it open (toward the negative y-axis).

This video from Doppelmayr shows pretty well how it works. The actual part of the video showing the movement starts around 0:30 seconds or so.

Edited for some clarity.

TomWhite

Thanks for the detailed explanation. But my little brain isn’t getting it. The video shows the springs moving from up/gripped position to down/compressed/not gripping the haul rope. But I don’t see the force doing that. I’m obviously missing something.

ceo

It’s the same sort of over-center mechanism as a pair of Vise-Grips. When you squeeze the handles, if you have it adjusted right, the jaws lock onto the bolt you’re about to strip so you don’t need to keep squeezing.

Jonni

Here’s another video that shows the compression rail (I’ve also heard it be called the compression plate) pushing down on the compression roller on top of the grip as the chair/grip passes under it. This is how a fair amount of detachable lifts work - there are definitely variations. In this video the compression rail is red.

In the case of the D-Line grip in the first video I shared, it’s a little bit different in that the compression roller on top of the grip eventually has to be forced back up. This video shows that on Doppelmayr D-Line lifts, there’s a lower piece on the compression rail that can direct the compression roller back into the up position. In this video it’s the little bit of steel hanging down from the blue compression rail in the following video from the “Heating” post you shared.

Hope that helps make it make more sense. I realize I do tend to get a bit wordy in my explanations sometimes. 🙂

TomWhite

Thanks for the 2nd video, that did it for me. I had presumed that the depression bar (red) had to continue all the way around the terminal. But no, of course, it’s only necessary to release the grip from the haul rope. Since the carrier is riding on the rollers, it doesn’t matter what the grip is doing. Thanks.